Download The chemical composition of subducting sediment and its

Chemical Geology 145 Ž1998. 325–394
The chemical composition of subducting sediment and its
consequences for the crust and mantle
Terry Plank
a
a,)
, Charles H. Langmuir
b
Department of Geology, 120 Lindley Hall, UniÕersity of Kansas, Lawrence, KS 66045, USA
Lamont-Doherty Earth ObserÕatory and Columbia UniÕersity, Palisades, NY 10964, USA
b
Received 25 September 1996; revised 29 August 1997; accepted 4 September 1997
Abstract
Subducted sediments play an important role in arc magmatism and crust–mantle recycling. Models of continental growth,
continental composition, convergent margin magmatism and mantle heterogeneity all require a better understanding of the
mass and chemical fluxes associated with subducting sediments. We have evaluated subducting sediments on a global basis
in order to better define their chemical systematics and to determine both regional and global average compositions. We then
use these compositions to assess the importance of sediments to arc volcanism and crust–mantle recycling, and to
re-evaluate the chemical composition of the continental crust. The large variations in the chemical composition of marine
sediments are for the most part linked to the main lithological constituents. The alkali elements ŽK, Rb and Cs. and high
field strength elements ŽTi, Nb, Hf, Zr. are closely linked to the detrital phase in marine sediments; Th is largely detrital but
may be enriched in the hydrogenous Fe–Mn component of sediments; REE patterns are largely continental, but abundances
are closely linked to fish debris phosphate; U is mostly detrital, but also dependent on the supply and burial rate of organic
matter; Ba is linked to both biogenic barite and hydrothermal components; Sr is linked to carbonate phases. Thus, the
important geochemical tracers follow the lithology of the sediments. Sediment lithologies are controlled in turn by a small
number of factors: proximity of detrital sources Žvolcanic and continental.; biological productivity and preservation of
carbonate and opal; and sedimentation rate. Because of the link with lithology and the wealth of lithological data routinely
collected for ODP and DSDP drill cores, bulk geochemical averages can be calculated to better than 30% for most elements
from fewer than ten chemical analyses for a typical drill core Ž100–1000 m.. Combining the geochemical systematics with
convergence rate and other parameters permits calculation of regional compositional fluxes for subducting sediment. These
regional fluxes can be compared to the compositions of arc volcanics to asses the importance of sediment subduction to arc
volcanism. For the 70% of the trenches worldwide where estimates can be made, the regional fluxes also provide the basis
for a global subducting sediment ŽGLOSS. composition and flux. GLOSS is dominated by terrigenous material Ž76 wt%
terrigenous, 7 wt% calcium carbonate, 10 wt% opal, 7 wt% mineral-bound H 2 Oq., and therefore similar to upper
continental crust ŽUCC. in composition. Exceptions include enrichment in Ba, Mn and the middle and heavy REE, and
depletions in detrital elements diluted by biogenic material Žalkalis, Th, Zr, Hf.. Sr and Pb are identical in GLOSS and UCC
as a result of a balance between dilution and enrichment by marine phases. GLOSS and the systematics of marine sediments
provide an independent approach to the composition of the upper continental crust for detrital elements. Significant
discrepancies of up to a factor of two exist between the marine sediment data and current upper crustal estimates for Cs, Nb,
Ta and Ti. Suggested revisions to UCC include Cs Ž7.3 ppm., Nb Ž13.7 ppm., Ta Ž0.96 ppm. and TiO 2 Ž0.76 wt%.. These
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Corresponding author.
0009-2541r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.
PII S 0 0 0 9 - 2 5 4 1 Ž 9 7 . 0 0 1 5 0 - 2
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T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
revisions affect recent bulk continental crust estimates for LarNb and UrNb, and lead to an even greater contrast between
the continents and mantle for these important trace element ratios. GLOSS and the regional sediment data also provide new
insights into the mantle sources of oceanic basalts. The classical geochemical distinction between ‘pelagic’ and ‘terrigenous’
sediment sources is not valid and needs to be replaced by a more comprehensive understanding of the compositional
variations in complete sedimentary columns. In addition, isotopic arguments based on surface sediments alone can lead to
erroneous conclusions. Specifically, the NdrHf ratio of GLOSS relaxes considerably the severe constraints on the amount of
sediment recycling into the mantle based on earlier estimates from surface sediment compositions. q 1998 Elsevier Science
B.V. All rights reserved.
1. Introduction
The subduction of marine sediment regulates
crustal growth, influences arc volcanism, and refertilizes the mantle. Armstrong Ž1968, 1991. was the
champion of sediment subduction as the primary
control on continental growth. He argued that the
Earth’s crust formed early in the planet’s history, and
has since been at steady-state volume due to a
balance between growth via magmatism and destruction via erosion and sediment subduction. Many
others Že.g., Moorbath, 1977; McLennan, 1988; McCulloch and Bennett, 1994. have had alternate views
of crustal evolution. The subducting sediment mass
flux is a pivotal factor for these models, and recent
estimates Žvon Huene and Scholl, 1991; Rea and
Ruff, 1996. show that it is very significant and
possibly as large as the magmatic growth rate of the
continents ŽReymer and Schubert, 1984.. Even if the
continents are at steady-state in volume, subducting
sediments may gradually change continental composition, since subducted materials are likely to subtract a different composition than what is added
through magmatism. Hence, subducted sediments are
crucial in terms of both mass and composition to the
evolution of the continental crust.
The past ten years have also seen clear evidence
that subducted sediments contribute to arc magmatism. Many isotopic tracers in arc volcanics show the
imprint of sediment Že.g., Kay et al., 1978; Karig and
Kay, 1981; Sun, 1980; White et al., 1985., with
incontrovertible evidence coming from studies of the
cosmogenic isotope, 10 Be ŽTera et al., 1986; Morris
and Tera, 1989.. Its exclusive formation in the atmosphere and fairly short half-life Ž1.5 Ma. make 10 Be
an ideal tracer of young surface materials. The presence of 10 Be in arc lavas, and its absence in lavas
from other tectonic settings, has made sediment subduction and recycling to volcanic arcs not only vi-
able but necessary. Because sediments have much
higher concentrations of many elements than the
mantle, small amounts of sediment can make large
differences in the chemical compositions of convergent margin magmas.
Subducted sediment that makes it past the arc
source is not only a net loss of mass from the
continents, but also a chemical gain to the mantle.
The continuous injection of sediment into the mantle
can impact dramatically the budget and evolutionary
history of various isotopic systems and trace element
ratios. Many models for the origin of the chemical
and isotopic composition of enriched mantle domains, such as EM-I and EM-II, require some form
of sediment recycling to the mantle ŽZindler and
Hart, 1986; Hofmann and White, 1982; Weaver,
1991; Woodhead and Devey, 1993., yet constraints
on the compositional systematics of these sediments
have been cursory.
Given the importance of sediment subduction to
continent growth, arc magmatism, and crust and
mantle evolution, there is a clear need to characterize
the global chemical flux attending subducting sediment. Previous attempts to evaluate the role of sediment have considered only a few sediment cores or
only small portions of sedimentary columns. For
example, Hole et al. Ž1984. and Lin Ž1992. carefully
calculated the bulk sediment composition for individual deep sea sites, then presented them as Pacific
means ŽPAWMS and BWPS.. Ben Othman et al.
Ž1989. published very useful geochemical data for a
selection of piston cores samples, and yet they did
not address how these samples from the upper 10 m
of the seafloor relate to the global subducting mass
flux. Ben Othman’s data have been used extensively
as proxies for various global means Že.g., Devey et
al., 1990; Weaver, 1991.. Rea and Ruff Ž1996. provided global mass fluxes for subducted sediment by
lithology, but for chemical species considered only
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
H 2 O, CaCO 3 and biogenic SiO 2 . Although there
have been some detailed studies to characterize sediment geochemical fluxes in specific regions ŽStern
and Ito, 1983; Kay and Kay, 1988; von Drach et al.,
1986; Briqueu and Lancelot, 1983; Lin, 1992., there
has been no synthesis of geochemical fluxes from
trench to trench, which is required for a good global
estimate.
This study focuses on the diverse aspects of sediment subduction that are necessary to obtain global
geochemical flux estimates. This problem is replete
with details, requiring geochemical analyses, seismic
imaging, core logging, physical properties measurements, and plate motion velocities. We show that the
geochemical variations of tracer elements ŽK, Rb,
Cs, Ba, Sr, U, Th, REE, HFSE. in marine sediments
are strongly linked to lithological variations. Exploiting this link, we present a method to calculate the
bulk chemical composition of deep sea sediment
columns, and evaluate the accuracy of the method.
Fluxes are then calculated for most trenches from
around the world, allowing an assessment of the
variability from one region to another and, in combination with other data, calculation of the global
geochemical flux of subducting sediment. Finally,
we explore implications of these results for the composition of the continental crust and for crust–mantle
evolution.
We presented an earlier set of regional sediment
fluxes for a small number of convergent margins
ŽPlank and Langmuir, 1993. in order to explore the
relationship between sediment inputs and arc volcanic outputs. This paper updates those sediment
flux calculations, provides all the necessary background data for the reader to evaluate them independently, and addresses certain global issues. A companion paper ŽPlank and Langmuir, in prep.. explores further the sediment input-arc output correlations, develops a mass balance of the fluxes, and
provides some new constraints on the process and
net effect of sediment subduction.
2. The geochemical behavior of solid-earth tracers
in marine sediments
The sedimentary columns currently delivered to
deep sea trenches are typically 50–500 m thick,
327
although thicknesses may reach several kilometers in
some regions ŽCascadia, Makran, Antilles; von Huene
and Scholl, 1991.. At face value, determining the
bulk composition of hundreds of meters of sediment
is a monumental task. Sediment lithology and geochemistry may vary on the scale of centimeters, and
thus thousands of chemical analyses would be needed
to characterize a single sedimentary column at the
scale of lithological variability. Another approach is
to sample continuously down-core, mix all of the
samples together and analyze the composite
ŽStaudigel et al., 1989; von Drach et al., 1986.. In
this approach, only one analysis is required, but we
learn little about the variability in a given sedimentary column, the geochemical stratigraphy, or the
phases that contain elements of interest.
An approach that combines the merits of both
approaches is to analyze typical lithological constituents in a sedimentary column, and sum the
analyses based on the stratigraphy. This approach
takes advantage of the abundant lithological data for
each DSDP and ODP drill core, and is successful to
the extent that geochemical variations are linked to
lithology.
2.1. The link between sediment geochemistry and
lithology
Marine sediments are largely physical mixtures of
a few lithological end-members Žcontinental and volcanic detritus, biogenic carbonate and opal, hydrogenous Fe–Mn oxides, etc.., and these end-members
each lie within a fairly restricted range of chemical
composition Že.g., Dymond, 1981.. On this basis,
various statistical techniques have been employed
successfully to invert sediment geochemical variations into lithological mixing proportions ŽHeath and
Dymond, 1977; Dymond, 1981; Leinen and Pisias,
1984; Leinen, 1987; Zhou and Kyte, 1992.. While
the sediment geochemist’s goal is to translate chemical data into lithological data in order to reveal
sedimentation processes, our goal is to do the reverse, to translate lithological data into a chemical
bulk composition for a given sedimentary section.
We discuss below many elements that are useful
tracers of solid earth recycling: the alkali elements
ŽK, Rb, Cs., the alkaline earth elements ŽSr, Ba., the
rare earth elements ŽREE., the high field strength
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T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
elements ŽTi, Nb, Ta, Hf, Zr., and Th and U. Other
important tracers Že.g., Pb, B and Be. cannot yet be
considered in detail for lack of abundant high quality
data for sediments. Nonetheless, preliminary estimates are provided for all major elements and many
trace elements, based on whatever data were available. The following discussion is based on over 1000
compiled analyses of marine sediments, with particular attention to the sample suites for which comprehensive trace element analyses exist. Because much
of the literature data reflects the oceanographic interests of sediment geochemists and so does not generally include elements of use for the study of solid
earth cycles, we obtained more than 250 new analyses of sediment samples near trenches Žfrom ODP
Sites 765, 801 and 701, DSDP Sites 595, 596 and
183, and piston cores in Ben Othman et al., 1989;
Appendix A and Tables A1–A6.. A major source of
oceanic sediments is detritus from the upper continental crust. Thus, we make use of the Post-Archean
Average Shale ŽPAAS., North American Shale Composite ŽNASC. and Taylor and McLennan’s Upper
Continental Crust ŽTMUC. as important comparisons
to oceanic sediment ŽGromet et al., 1984; Taylor and
McLennan, 1985..
2.1.1. Alkalis (K, Rb, Cs): detrital elements
The alkalis are largely contained in detrital phases
in marine sediments. This is illustrated in Fig. 1,
which shows K 2 O and Al 2 O 3 concentrations in sediments of different lithologies, ages and regions. To
first order, sediments have an average upper crustal
K 2 OrAl 2 O 3 ratio, and variations in K 2 O and Al 2 O 3
concentrations are due to dilution of detritus by
biogenic phases Žopal and calcium carbonate., which
are barren of alkali elements. For example, the Cenozoic sediments from ODP Site 765 consist primarily
of carbonate turbidites, which are simple two component mixtures of pelagic clay and biogenic calcium
carbonate redeposited from the Exmouth Plateau
ŽLudden et al., 1990.. The K 2 O and Al 2 O 3 variations in Site 765 turbidites may be explained well by
diluting average continental detritus by calcium carbonate, which plots at the origin of Fig. 1 ŽPlank and
Ludden, 1992.. Second-order controls on K concentrations in marine sediments are Ž1. detrital clay
mineralogy Že.g., illite vs. kaolinite., Ž2. volcaniclas-
Fig. 1. K 2 O and Al 2 O 3 in marine sediments. The line is a
regression through ODP Site 765 Cenozoic carbonate Žcc. turbidites ŽPlank and Ludden, 1992., which show the effect of simple
carbonate dilution on both K 2 O and Al 2 O 3 . The K 2 OrAl 2 O 3
ratio of these sediments is similar to the average upper crust of
Taylor and McLennan Ž1985. ŽTMUC ., and average shales, such
as the Post Archean Average Shale Ž PAAS . composite ŽTaylor
and McLennan, 1985. and North American Shale Composite
Ž NASC . ŽGromet et al., 1984. and loess ŽTaylor et al., 1983..
Thus, to first order, K 2 O and Al 2 O 3 in marine sediments is
controlled by the crustal ratio and the extent of dilution by
biogenic phases Žcarbonate or silica., which have no K 2 O or
Al 2 O 3 . Second order controls include: detrital clay mineralogy,
such as the low K 2 OrAl 2 O 3 kaolinitic detritus from ODP 765;
volcanic detrital composition, such as the low K 2 OrAl 2 O 3 of
Java fore-arc volcaniclastic sediments ŽBen Othman et al., 1989
and Appendix A.; and K uptake during diagenesis, such as the
high K 2 OrAl 2 O 3 of clinoptilolite-rich DSDP 595r6 clays ŽAppendix A. and high K 2 OrAl 2 O 3 of diagenetically altered Cretaceous volcaniclastic turbidites from ODP 801 ŽKarl et al., 1992..
Other data sources: Demerara Abyssal Plain Ž Dem AP . and S.
Sandwich trench Ž SS Tr . sediments ŽBen Othman et al., 1989.;
Site 183 Eocene clastic turbidites, seaward of the Aleutian trench
ŽKay and Kay, 1988 and Appendix A..
tic detritus, and Ž3. diagenetic uptake of K Žsee Fig.
1 for examples..
Rb and Cs generally follow K in marine sediments, and are largely controlled by dilution of
detritus by biogenic material. Thus, RbrK and
RbrCs ratios in sediments are predominantly continental ŽFig. 2a-b.. While RbrCs ratios are fairly
uniform in marine sediments Ž12–18; Fig. 2b., the
RbrK ratio may vary by a factor of three ŽFig. 2a..
High RbrK seems to be characteristic of ancient and
highly weathered sources ŽMcLennan et al., 1990;
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
329
on the seafloor. Modern carbonate oozes have
roughly 1500–2000 ppm Sr ŽFig. 3a., as compared
to 150–200 ppm in shales ŽFig. 3b.. Therefore, Sr
variations in marine sediments are controlled by the
relative proportions of calcium carbonate, clays, and
biogenic opal ŽFig. 3a,b.. Second-order factors that
affect Sr concentrations include Ž1. diagenetic re-
Fig. 2. Ža. Rb vs. K 2 O, and Žb. Cs in marine sediments. Data
sources as in Fig. 1. The single point for Site 183 turbidites is the
A2 composite from von Drach et al. Ž1986. and Kay and Kay
Ž1988.. Site 596 data from Zhou and Kyte Ž1992. and Tables A1
and A2. Different upper crustal Cs estimates: McDUC s
McDonough et al. Ž1992.; PLUCs this study ŽTable 5.. Dem AP
is the Demerara abyssal plain.
Nesbitt et al., 1980; Fig. 2a., while low RbrK is
typical of sediments rich in volcaniclastics Žwhich
are themselves low in RbrK. or sediments that have
experienced K uptake, such as results from diagenetic formation of zeolites ŽFig. 2a..
2.1.2. Strontium: carbonate control
Like the alkalis, Sr is present in continental detritus and excluded from biogenic opal. A far more
important factor for Sr, however, is its substitution
for Ca in calcium carbonate, and its subsequent high
concentration in nannofossil and foraminiferal oozes
Fig. 3. Sr variations in marine sediment. Ža. Sr vs. CaO. The high
Sr Ž ) 2000 ppm. carbonates from Site 765 are from the 200–440
m interval, which contains abundant aragonite ŽCompton, 1992;
Plank and Ludden, 1992.. DSDP Site 530 Paleocene-Eocene
chalks and limestones from Wang et al. Ž1986.. Žb. Sr vs. Al 2 O 3
in carbonate-poor marine sediments. Note difference in scale for
Sr. Loess excludes carbonate-rich Kaiserstuhl samples ŽTaylor et
al., 1983.. Other data sources as in Fig. 1.
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T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
crystallization, resulting in Sr loss from the sediment
column ŽBaker et al., 1982; Renard et al., 1983;
Wang et al., 1986; Compton, 1992.; Ž2. secular
changes in seawater SrrCa ŽGraham et al., 1982;
Renard et al., 1983; Baker et al., 1990.; Ž3. Sr-rich
aragonite; Ž4. Sr-rich apatite from fish-debris; and
Ž5. volcaniclastic detritus, which may be richer in Sr
than average continental detritus Žsee Fig. 3a,b for
examples..
2.1.3. Barium: barite precipitation
The distribution of Ba in deep sea sediments is
variable Ž100–10,000 ppm. and complex ŽFig. 4..
Fig. 4. Ba in marine sediments. Ža. Ba vs. SiO 2 in siliceous
sediments. Žb. Ba vs. alumina. Site 596 data from Zhou and Kyte
Ž1992.; Site 286 volcaniclastics from Peate et al. Ž1997.. Other
data sources as in Fig. 1.
High Ba concentrations are found in sediments deposited in regions of high biological productivity
ŽSchmitz, 1987; Dymond et al., 1992.. Ba is transported to the seafloor as barite particles, which precipitate out of the water column in micro-environments that are rich in sulfate, such as on decaying
organic matter or diatom debris ŽDehairs et al., 1980;
Bishop, 1988.. Although high concentrations of both
Ba and siliceous skeletons are typical of high productivity regions, Ba and SiO 2 do not correlate
simply in seafloor sediments Žvon Breymann et al.,
1990; Fig. 4a.. This lack of a correlation may be
expected for several reasons: Ž1. Both barite and
opal may dissolve in the water andror sediment
column, but at different rates ŽDehairs et al., 1980..
Ž2. Barite precipitated and transported within organic
matter is independent of the rain of siliceous debris,
Ž3. Certain species and shapes of siliceous plankton
are selective to barite precipitation in the water
column ŽBishop, 1988.. Thus, despite an association
between siliceous sediments and sporadically high
Ba concentrations Žup to 10,000 ppm., no simple
relationship exists between Ba and SiO 2 in marine
sediments ŽFig. 4a..
Hydrothermal sediments may also be rich in Ba,
particularly near the source of hydrothermal fluids.
Barium is leached from ocean floor basalts during
high-temperature hydrothermal circulation ŽMottl and
Holland, 1978; Edmond et al., 1982; von Damn et
al., 1985., and forms barite in some hydrothermal
chimneys ŽHaymon and Kastner, 1981.. Because of
its high density and early precipitation from plumes,
hydrothermal barite is fairly restricted in its distribution to active vent sites ŽDymond, 1981; Dymond et
al., 1992.. While only proximal hydrothermal sediments have extreme Ba enrichments Ž) 10,000 ppm.,
distal sediments may preserve associated Ba and Sb
anomalies, attesting to transport of hydrothermal
barite over 1000 km from active vents ŽKarl et al.,
1992; Kyte et al., 1993..
In addition to high biological productivity and
hydrothermal activity, the composition of detrital
phases may also affect Ba concentration in sediments: from ; 600 ppm in PAAS and NASC, to
- 300 in Demerara Abyssal Plain sediments ŽWhite
et al., 1985. to - 200 ppm in some volcaniclastic
sediments ŽPeate et al., 1997. ŽFig. 4b..
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
331
2.1.4. Rare earth elements: the continental REE
pattern, fish teeth and Fe–Mn oxides
The REE pattern of marine sediments is essentially that of the continents, which is itself remarkably uniform ŽTaylor and McLennan, 1985.. This
observation forms the rationale behind the common
practice of normalizing sedimentary patterns to average shales ŽNASC or PAAS.. In general, rapidly
depositing sediments with mature detrital sources
Žtypical of continental margins. have shale REE
patterns ŽMcLennan et al., 1990; e.g., Demerara and
Argo Abyssal Plain sediments in Fig. 5., while other
processes and sources result in perturbations to the
shale REE pattern.
Slowly accumulating sediments have Ce anomalies and higher total REE than shales ŽFig. 5.. Hydrogenous Fe–Mn oxyhydroxides scavenge REE
from seawater, and clays with a high fraction of fish
debris have the highest REE concentrations ŽElderfield and Pagett, 1986; Toyoda et al., 1990; Figs. 5
and 6a.. At the slow sedimentation rates required to
concentrate fish debris, hydrogenous oxides also accumulate in significant quantities, and thus these two
components co-mingle in slowly depositing sedi-
Fig. 5. Sediment REE patterns representative of volcanic detritus,
continental detritus and slow sedimentation rate pelagic clays.
Data sources as follows. High PrMn clay Ž596-13.7., high MnrP
clay Ž596-22., hydrothermal Ž HT . sediment Ž596A-66.7. from
Table A2. Argo Abyssal Plain sample Ž7R., from Site 765,
samples Australian continental detritus ŽPlank and Ludden, 1992..
Samples from Demerara Abyssal Plain ŽGS7605-65., Java fore-arc
ŽV33-79. and S. Sandwich trench ŽV14-55. from Ben Othman et
al. Ž1989.. Volcaniclastic sediment ŽSite 801. is derived from a
Cretaceous Pacific seamount Ž272 mbsf; Karl et al., 1992..
Fig. 6. Relationships between REE and phosphate in marine
sediment. Ža. Covariation of Sm and P2 O5 in deep sea clays,
reflecting the importance of fish debris apatite in controlling REE
concentrations. Pacific clays Ž -12% CaO. from Toyoda et al.
Ž1990.; Sites 595r596 clays from the South Pacific from Tables
A1 and A2; 765 clays ŽCretaceous non-carbonates. from Plank
and Ludden Ž1992.; piston core clays Žexcluding Mn nodules and
biogenic sediments. from Ben Othman et al. Ž1989.. Žb. Relationship between Ce anomaly and MnOrP2 O5 in Site 596 sediments
Ždata from Zhou and Kyte, 1992; excluding ash-rich intervals.. Ce
anomalies reflect deviations from a smooth REE pattern, and may
be calculated from: CerŽLa2r 3 Nd1r3 ., where Ce, La and Nd are
chondrite-normalized values. High MnO clays preferentially scavenge Ce 4q relative to the other REE 3q, and thus have ‘positive’
Ce anomalies Ž )1.. High P2 O5 clays reflect abundant fish debris,
which acquire a ‘negative’ Ce anomaly Ž -1. from seawater.
ments. The magnitude and sign of the Ce anomaly
depends on the relative fractions of these two phases
in the bulk sediment. Fe–Mn flocs scavenge Ce IV
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T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
preferentially, leading to positive Ce anomalies in
their REE patterns, and a negative anomaly in seawater ŽPiper, 1974; Elderfield and Greaves, 1981; Fig.
5.. Apatite fish debris acquire REE during prolonged
exposure to seawater, and inherit the negative Ce
anomaly and isotopic composition of seawater.
ŽWright et al., 1984; Staudigel et al., 1985; Elderfield and Pagett, 1986.. Fig. 6b shows the combined
effects of Fe–Mn oxides and fish debris on sediment
REE in a strong correlation between Ce anomaly and
MnOrP2 O5 ratio in Site 596 pelagic clays.
Aside from the dominant controls on REE concentration by opal and carbonate dilution, and apatite
and hydrogenous oxides scavenging, a second-order
and variable effect is the incorporation of volcaniclastic detritus. Sediments near active volcanic arcs
often posses flatter REE patterns, less well-developed Eu anomalies, and lower REE abundances ŽMcLennan et al., 1990; Figs. 5 and 7.. Sediments
deposited near alkalic seamounts, however, may in-
Fig. 7. Effect of different sediment components and processes on
the REE pattern. LarSm ratio reflects light rare earth element
ŽLREE. enrichment, while YbrSm reflects HREE enrichment.
Continental detritus is enriched in LREE and depleted in HREE,
giving it a steep pattern ŽArgo is average of the Cenozoic section
at Site 765 from Plank and Ludden, 1992.. Sediments derived
from arc volcanics have flatter patterns ŽS. Sandwich trench and
Java fore-arc sediments from Ben Othman et al., 1989.. Pacific
clays from Ben Othman et al. Ž1989. and Site 595 ŽTable A1.
reflect preferential uptake of the MREE by fish-debris phosphate.
N. Atlantic seawater from Elderfield and Greaves Ž1982. Ž2500 m
depth.. Hydrothermal sediment from Leg 92 ŽBarrett and Jarvis,
1988., where arrow connects 4 My to 17 My sample, showing an
effect of diagenesis on the REE pattern.
herit a steep REE pattern from these volcanics ŽFig.
5; Karl et al., 1992.. Finally, hydrothermal sediments
inherit their REE from ambient seawater, due to
efficient scavenging by hydrothermal plume particles
ŽRuhlin and Owen, 1986; Barrett and Jarvis, 1988;
German et al., 1990.. The most distinctive feature of
hydrothermal sediments is the prominent negative Ce
anomaly of seawater ŽFig. 5.. Thus, although basically shale-like, the subtle changes to the REE pattern are useful in identifying the different marine
phases that contribute to seafloor sediments ŽBarrett
et al., 1987; McLennan et al., 1990; Fig. 7..
2.1.5. Thorium: detrital and hydrogenous
The behavior of Th in marine sediments is similar
to that of the REE. Most of the global variability in
Th concentrations is caused by dilution of continental detritus by biogenic phases ŽFig. 8a.; hence sediments typically have continental ThrAl. Some processes and sources cause variation in this ratio: Ž1.
Incorporation of volcanic material lowers ThrAl, Ž2.
Slowly-depositing sediments rich in Fe–Mn oxyhydroxides have high ThrAl because Th is adsorbed
onto metal oxides in the water column Že.g., Bacon
and Anderson, 1982., Ž3. Young source terranes may
contribute low ThrAl detritus Žsee Fig. 8a for examples..
2.1.6. Uranium: redox control
Because U solubility is redox-dependent, the U
distribution in marine sediments is complex. In oxygenated seawater, U forms stable and soluble U VI
complexes, whereas in more reducing marine environments, U VI is reduced to insoluble U IV . Removal
of U from seawater is initiated by the decomposition
of organic matter in sediment, and thus organic-rich
sediments are the largest sink for the U dissolved in
seawater Že.g., Anderson et al., 1989; Klinkhammer
and Palmer, 1991.. In general, slowly depositing
pelagic sediments in the oxidizing open ocean contain little organic matter, and thus U concentration is
largely a function of the concentration in detrital
phases Žcontinental or volcanic. and the extent of
dilution by biogenic carbonate and silica Žwhich
contain little U; Mo et al., 1973.. U and Al correlate
weakly in marine sediments, showing this weak detrital control ŽFig. 8b.. Sediments deposited in coastal
regions may be rich in organic matter, and turbidity
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Fig. 8. Ža. Th and Žb. U variations in marine sediments. Different
upper crustal estimates ŽNASC, PAAS and TMUC. and most
marine sediments have the same ThrAl, which indicate a consistent upper crustal ratio Žlines show TMUC ratio.. Sediments with
lower ThrAl include those near volcanic arcs ŽS. Sandwich and
Java sediments. and those derived from juvenile source terranes
Ž183 turbidites.. Sediments with high ThrAl include red clays,
with a large hydrogenous components ŽTh scavenged from seawater.. U is more complex and correlates weakly with Al 2 O 3 ,
reflecting mixing with detrital components. Sediments low in U
are generally dominated by volcanics; sediments high in U are
generally biogenic or turbidites Žwhere U is fixed in the sediment
in its reduced form, mediated by organic carbon..
currents may transport organic C and reduced U to
abyssal depths. Post-depositional remobilization of U
and C may then occur as oxygenating bottom water
diffuses into the turbidite layer Že.g., Colley et al.,
1989.. Thus, the U concentration in sediments is a
complex function of U and C in the source material
and the burial rate.
333
Fig. 9. High field strength element ŽHFSE. concentrations in
marine sediments. Plots a–c illustrate how Ti, Zr and Nb, respectively, generally follow Al 2 O 3 , and thus the detrital phase, in a
variety of pelagic and terrigenous sediments. Second-order effects
include Ti- and Nb-enriched volcaniclastic sediments from ODP
Site 801 Žderived from the alkalic Magellan seamounts., the
hydrogenous enrichment of Zr in Mn-rich 595r596 red clays, and
heavy mineral Žzircon. concentration of Zr in a single Ben Othman sample Žan Orinoco turbidite.. References as in Fig. 1, and
DSDP 579 and 581 from Cousens et al. Ž1994.. McLennan et al.
Ž1990. muds include the mud phases of various turbidites Žfore-arc,
back-arc and continental arc turbidites are not plotted.. All Ben
Othman et al. Ž1989. piston core sediments are plotted except Mn
nodules. PLUCs upper crustal estimates recommended in this
study ŽTable 5..
334
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
2.1.7. High field strength elements (Hf, Zr, Nb, Ta,
Ti)
Ratios of high field strength elements ŽHFSEs. to
Al 2 O 3 and to one another are fairly constant in
marine sediments ŽFig. 9a–c, Fig. 10a,b., and concentrations vary mostly as a function of biogenic
dilution. Thus, HFSE are largely detrital. Second
order effects include Nb- and Ti- enrichment in
sediments from mid-plate volcanic sources ŽKyte et
al., 1993 and Fig. 9a,c. and hydrogenous enrichments of Zr and Hf in some Mn-rich sediments and
Mn-nodules ŽWhite et al., 1986 and Fig. 9b.. Although heavy minerals Že.g., zircon and rutile.
strongly concentrate the HFSE, they do not seem to
control HFSE abundances of most deep sea pelagic
or terrigenous sediments ŽFig. 9b.. Loess and some
proximal turbidites, however, may be enriched in Zr
and Hf due to concentrations of zircon ŽTaylor et al.,
1983; Patchett et al., 1984 and Fig. 9b.. Nb–Ta and
Hf–Zr may be considered analog element pairs, and
their ratios are fairly constant in marine sediments
ŽNbrTa; 14 and ZrrHf ; 35; Fig. 10a,b..
2.1.8. Summary
For most elements, there are strong links between
sediment geochemistry and lithology. For example,
biogenic oozes will be poor in alkalis, Th, REE, and
HFSE but may be rich in Sr and Ba. Terrigenous
turbidites may have high UrTh ratios and will preserve the KrRb and LarSm ratios of their source.
Pelagic clays will contain REE roughly in proportion
to their fish debris content and inversely proportional
to the sedimentation rate. These clear systematics
can be reduced to a small number of controlling
factors on the compositions of deep sea sedimentary
columns:
Ž1. The relative abundance of biogenic Žcarbonate
and silica. and detrital phases. The proportions of
detrital and biogenic phases is the first-order control
on many element concentrations.
Ž2. The source region of detritus. The detrital
source Že.g. mature continental or young volcanic.
affects many element ratios, such as KrRb, ThrAl,
and LREErHREE, as well as the abundances of
HFSE.
Ž3. The sedimentation rate. The sedimentation
rate is inversely proportional to the concentration of
hydrogenous phases and to the length of exposure of
Fig. 10. Plots of analog high field strength elements in marine
sediments. Nb–Ta and Hf–Zr generally are not fractionated from
one another during most geological processes. Ža. Nb and Ta
define a fairly constant ratio in marine sediments Ž14.2"1.8
calculated from regional averages in Table 4.. DSDP Site 765
values are based on those samples powdered in alumina, not WC
ŽPlank and Langmuir, 1993.; ODP 801 ICP-MS data in Appendix
A ŽTable A5.; DSDP Site 262 Žand Banda piston cores. from
Vroon et al. Ž1995.; Nb and Ta data on Ben Othman samples from
Stolz et al. Ž1996.. Žb. Zr and Hf also define a fairly constant ratio
in marine sediments. Based on the sediment data shown here, a
ratio of 35 was used to estimate Hf from Zr in some trench
sections. Data sources: Ben Othman: ID Hf from Ben Othman et
al. Ž1989. and DCP Zr from Table A3; Site 183: INAA Hf ŽKay
and Kay, 1988. and DCP Zr from Table A4; ODP 765: INAA Hf
and DCP and XRF Zr ŽPlank and Ludden, 1992.; ODP 801:
ICP-MS Zr and Hf from Table A5; McLennan et al. Ž1990.
turbidites: SSMS Hf and Zr; DSDP 579r581: INAA Hf and XRF
Zr ŽCousens et al., 1994..
fish teeth to seawater, both of which can lead to high
concentrations of Th and the REE. High sedimentation rates often reflect turbidites near continental
margins.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Fig. 11. Sedimentary sections being subducted at trenches Žconfidence levels 1 and 2 only, see Tables 1 and 2.. Note that there is no common stratigraphy for these trench
sections. Patterns as in key Ž Z is for zeolites.. Thickness in meters. All sections extend to basement.
335
336
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Table 1
Average sediment conditions by lithography
Oxides in wt%; all others in ppm. Values in italics are estimated Žsee Appendix B.. pc, piston core.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Table 1 Žcontinued.
337
338
Table 1 Žcontinued.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Table 1 Žcontinued.
339
340
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
These three sedimentological factors are much
more indicative of bulk sediment geochemistry than
the more generic ‘pelagic’ vs. ‘terrigenous’ distinction that is common in the subduction recycling
literature ŽGill, 1981; Weaver, 1991.. Pelagic sediments may include chert, chalk, red clays, hydrothermal clays, and mixed lithologies Že.g., radiolarian
clays.. These sediment types generally span the
global range in chemical composition. Likewise, terrigenous sediments may include mature continental
sources, volcanic sources and organic-rich turbidites,
which again may have very different chemical compositions Žespecially for U and Th.. Thus, the terms
‘pelagic’ and ‘terrigenous’, although useful for describing sedimentation processes, are less useful geochemical parameters than the three factors identified
above.
The existence of these chemical systematics means
that it is possible to make educated estimates of the
bulk compositions of sediments from the descriptions of their lithologies, combined with a few chemical analyses. The existence of clear systematics
based on lithology allows far better estimates than
can be obtained by simply averaging published analyses.
3. Calculating the bulk composition of sediment
columns approaching trenches
To calculate bulk compositions of sediment
columns requires lithological descriptions, smear
slide analysis, carbonate analyses and down-hole
geochemical logs, all of which are collected routinely by ODP and DSDP. These data are often
continuously collected down-core and so can be used
to extend ‘spot’ geochemical analyses of core sediments. Generally, the following steps were taken to
Fig. 12. Map of the world with mid-ocean ridges, convergent margins and reference DSDP and ODP drill sites.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
calculate bulk chemical compositions. First, the section was broken into a small number of lithological
units, usually those defined in the DSDP or ODP
Site Reports ŽFig. 11, Table 1, and Appendix B.. If
the unit contained biogenic phases Žcarbonate or
siliceous oozes. then the proportion of that phase in
the unit was estimated from smear-slide modal analyses andror shipboard CaCO 3 analyses. For elements that form simple two-component dilution
trends with biogenic carbonate or opal, the mean
concentration was calculated from the bulk proportion of the biogenic phase in that unit. Within pelagic
clay units, color Žbrown, green, black. and modal
analyses from smear-slides Že.g., percent zeolites or
oxides. were used to subdivide the units and properly weight geochemical analyses. Similarly, within
turbidite units, proportions of sandy, silty and clayey
layers were estimated from core descriptions, and the
geochemical analyses weighted accordingly. Once
averages were calculated for each lithological unit, a
grand, mass-weighted average of the different units
was calculated for the site.
This procedure is straightforward as long as core
recovery is high and abundant analyses exist. Unfortunately, bulk chemical analyses are not standard
procedure for DSDP or ODP cores. If they were, this
project would have been done already. As it is, we
analyzed over 250 sediment samples Ždata in Plank
and Ludden, 1992 and Appendix A., and took advantage of published chemical analyses when available
Žsee Appendix B for references.. When data were
lacking for certain key elements, they were estimated
by ratio to other determined elements, based on the
systematics outlined above. In some cases, down-hole
geochemical logs were used to provide a check on
the averages from core analyses. We found K logs
Žnatural gamma. to be fairly accurate in a groundtruthing experiment with Site 765, where we had
abundant core analyses ŽPlank and Ludden, 1992..
Logs are valuable where core recovery is low, especially if recovery is biased to certain lithologies.
Appendix B outlines the steps taken to calculate
the bulk sediment composition for each region ŽFig.
12., and Table 1 summarizes the results by lithology
and region. The original purpose of these calculations was to compare subducted sediment inputs to
arc volcanic outputs ŽPlank and Langmuir, 1993.,
and so we generally focus on sediment sections near
341
active volcanic arc segments, as well as the lithologies actually getting subducted Žas opposed to those
being accreted in the forearc, see Section 6..
3.1. Accuracy of aÕeraging technique
It is important to estimate the errors involved in
calculating the composition of sedimentary columns.
The errors are tied principally to sampling density. If
continuous samples are taken down-core and analyzed, then the errors are small Ž- 10%.. The question is how large the errors become when there are a
Fig. 13. Results of ‘ground truth’ numerical experiments, to
determine if robust averages can be calculated from small sample
sets. Small sub-sets of the downcore data Ž ns 5 for Site 596;
Zhou and Kyte, 1992; and ns8 for Site 765; Plank and Ludden,
1992. were taken at random within lithologic units and used to
calculate weighted core means. Shown in Ža. is an example of the
distribution of errors for the Site 596 ŽTonga. Th experiment Ž100
random samplings.. Errors are within 23% for 90% of the population. Curve is normal distribution, for reference. Ticks along
horizontal axis show mid-point of each bin Ž1.5% about mid-point..
Shown in Žb. are the results for all experiments from both sites.
Most elements can be estimated at better than 30%, using as few
as 5–8 analyses. See discussion in text.
342
Trench
Subd rate Žmmryear.
Thickness Žm.
Density Žgrcc.
Water Ž%.
Trench Length Žkm.
Confidence level
Tonga
170
70
1.31
62.57
1350
1
Kerm
70
200
1.40
58.00
1400
4
Vanuatu
103
650
1.60
38.35
1800
1
E. Sunda
67
500
1.71
34.89
1000
1
Java
67
300
1.65
40.30
2010
1
Sumatra
50
1400
1.95
24.49
1000
3
Andaman
30
3500
2.05
20.17
1500
4
Makran
35
4200
2.05
20.17
950
3
Philip
90
120
1.31
62.57
0
4
Ryuku
60
160
1.40
58.00
1350
4
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
CO 2
H 2 Oq
59.25
0.488
10.21
7.60
2.21
2.69
2.12
3.96
2.11
0.981
0.00
8.38
58.35
0.669
13.57
6.50
0.85
2.87
2.31
3.24
2.30
0.450
0.00
8.90
56.22
0.558
13.40
4.71
0.21
2.84
7.26
4.21
1.52
0.143
3.94
4.96
53.70
0.591
9.80
4.98
0.36
2.45
9.06
1.28
1.89
0.126
7.04
8.51
60.43
0.710
12.97
5.94
0.42
2.72
2.71
2.14
2.50
0.186
1.07
8.17
62.94
0.69
13.70
4.95
0.12
2.18
3.16
2.46
2.45
0.15
0.14
7.22
61.57
0.69
13.49
5.00
0.09
1.96
3.92
2.57
2.04
0.12
0.05
8.65
53.26
0.75
12.70
6.98
0.64
3.49
7.37
1.52
2.81
0.23
5.08
5.28
44.53
0.55
10.08
6.97
0.93
3.19
13.29
3.35
1.52
0.44
8.63
6.54
50.30
0.63
15.04
6.94
2.06
3.17
2.57
4.06
3.68
1.25
0.00
9.84
Sc
V
Cr
Co
Ni
Cu
Zn
22.0
121
24.6
216.9
251.5
310.2
62.3
18.8
153
69.7
86.9
118.9
141.7
83.7
11.2
98
48.0
18.9
49.5
51.6
42.5
11.7
96
43.6
22.6
63.5
163.0
81.7
14.8
118
70.5
25.9
91.5
122.1
99.9
11.99
90
101.5
18.2
57.5
39.4
95.7
11.74
89
129.3
13.9
63.9
32.8
75.3
17.63
139
64.9
20.4
98.5
99.6
112.7
13.19
160
95.8
80.6
180.3
144.2
71.9
24.16
129
45.9
160.5
353.3
317.1
124.4
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Table 2
Bulk composition of sediment columns subducting at trenches
39.5
2.36
233
1680
173.0
123
3.51
8.44
0.552
55.6
3.19
222
1073
75.0
138
3.62
9.46
0651
22.6
0.85
359
158
25.6
115
2.98
1.99
0.136
63.3
3.86
405
1486
24.6
110
3.33
8.74
0.693
82.1
4.94
218
1068
32.6
145
4.73
10.92
0.848
82.6
5.28
251
543
22.1
165
6.18
11.26
0.803
45.1
2.90
338
491
18.9
167
6.31
10.09
0.714
84.4
4.63
422
851
39.8
149
4.56
11.71
0.925
27.4
1.25
585
1150
70.6
89
2.42
4.51
0.287
79.2
5.45
217
380
238.6
167
4.49
13.17
0.831
La
Ce
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
134.47
196.18
158.20
34.86
8.46
38.22
34.69
20.07
17.01
2.580
61.20
97.78
69.53
15.30
3.70
16.32
14.78
8.55
7.38
1.117
11.31
24.67
15.30
3.56
1.05
3.91
4.02
2.34
2.37
0.383
29.80
74.53
25.44
5.71
1.15
5.27
4.24
2.49
2.43
0.386
39.08
86.08
33.95
7.06
1.43
6.23
5.66
3.35
3.24
0.479
31.15
67.00
28.36
5.24
1.06
4.01
3.98
2.30
2.14
0.322
27.95
60.19
24.20
4.36
1.02
3.30
3.27
1.93
1.85
0.282
40.27
81.68
33.95
7.83
1.59
7.23
6.86
4.03
3.93
0.547
45.80
60.77
50.89
11.12
2.85
12.30
11.76
6.90
6.28
0.975
156.76
236.29
189.09
42.08
9.86
45.75
41.94
23.67
19.86
3.018
Pb
Th
U
113.3
9.89
1.428
49.8
7.78
2.397
9.0
1.44
0.436
20.6
7.73
0.991
25.5
9.78
1.471
24.50
10.28
2.26
17.78
7.56
2.30
27.69
10.31
1.25
48.05
3.94
0.85
56.53
11.58
2.01
87Srr86Sr
143Ndr144Nd
206Pbr204Pb
207Pbr204Pb
208Pbr204Pb
0.70952
0.51234
18.763
15.666
38.784
0.70799
0.51238
18.842
15.659
38.776
0.70530
0.71682
0.51216
18.990
15.741
39.328
0.71682
0.51216
18.990
15.741
39.328
0.73493
0.51191
0.73128
0.51182
18.604
15.664
38.722
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Rb
Cs
Sr
Ba
Y
Zr
Hf
Nb
Ta
343
344
Table 2 Žcontinued.
Mar (800)
455
1.82
23.88
497.9
1.90
22.13
1
59.72
0.61
15.00
5.23
0.59
2.22
3.92
1.40
3.24
0.27
0.00
6.25
Sc
V
Cr
Co
Ni
Cu
Zn
Rb
Cs
Sr
Ba
Y
Zr
Hf
Nb
Ta
La
Ce
Nankai
30
350
2.20
20.00
800
1
1
Marianas
47.5
476.45
1.86
23.00
1400
1
Izu-Bon
50
600
1.86
23.00
1050
4
Japan
105
350
1.64
39.15
800
2
Kurile
90
350
1.64
39.15
1650
2
Kamchat
90
364
1.64
39.15
550
3
Aleut
62
350
1.64
41.54
1900
1
Alaska
70
780
1.80
32.40
800
3
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
CO 2
H 2 Oq
73.61
0.76
5.56
4.94
0.21
3.05
1.56
1.35
1.49
0.21
0.00
6.71
61.68
0.66
5.48
4.66
0.21
4.13
8.52
1.12
1.23
0.22
5.22
6.87
67.65
0.71
5.52
4.80
0.21
3.59
5.04
1.23
1.36
0.22
2.61
6.79
78.89
0.20
3.26
1.89
0.36
0.92
5.31
0.67
0.81
0.27
3.76
4.88
69.17
0.35
8.55
3.80
0.42
1.67
0.65
2.98
1.70
0.20
0.00
10.10
69.17
0.35
8.55
3.80
0.42
1.67
0.65
2.98
1.70
0.20
0.00
10.10
77.71
0.16
3.42
2.07
0.11
0.74
0.46
2.16
0.76
0.21
0.00
11.98
59.63
0.73
13.86
5.61
0.15
2.71
3.41
3.61
2.11
0.15
0.00
8.02
60.55
0.72
14.22
5.43
0.13
2.87
4.16
3.64
1.84
0.13
0.00
6.31
14.95
106
61.8
15.9
37.8
75.0
92.2
140.9
9.52
165
540
36.8
150
4.29
14.31
1.008
7.48
92
134.2
22.3
87.5
75.2
60.4
31.3
1.40
140
442
22.0
99
2.44
12.62
0.869
6.40
87
194.7
21.0
111.6
61.5
68.0
29.4
1.24
183
180
29.8
72
1.36
9.46
0.647
6.94
90
164.5
21.6
99.5
68.4
64.2
30.3
1.32
161
311
25.9
86
1.90
11.04
0.758
3.81
35
24.0
8.5
52.3
71.6
92.4
25.1
1.47
110
244
46.0
48
0.88
3.87
0.239
12.29
84
37.3
30.8
66.6
88.5
76.8
59.9
5.00
87
627
28.9
83
2.10
7.67
0.319
12.29
84
37.3
30.8
66.6
88.5
76.8
59.9
5.00
87
627
28.9
83
2.10
7.67
0.319
5.09
46
23.7
7.0
20.1
42.4
38.6
25.7
2.06
38
254
22.6
35
0.86
4.23
0.133
17.57
145
69.2
26.0
46.0
65.3
86.1
57.0
3.38
245
2074
21.6
131
3.26
7.74
0.545
16.96
144
75.1
18.8
40.7
49.8
57.3
46.4
2.68
289
1276
20.2
115
2.84
7.41
0.522
34.70
74.85
18.78
29.38
22.78
33.71
20.78
31.54
27.26
31.35
21.94
50.11
21.94
50.11
14.39
16.88
17.96
39.03
17.71
38.88
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Mar (801)
Trench
Subd rate Žmmryear.
Thickness Žm.
Density Žgrcc.
Water Ž%.
Trench length Žkm.
Confidence level
30.89
5.62
1.23
5.13
3.80
1.75
1.60
0.250
20.77
4.43
1.13
4.37
3.95
2.10
1.85
0.283
21.28
4.81
1.16
4.02
3.67
2.13
1.87
0.253
21.03
4.62
1.15
4.20
3.81
2.12
1.86
0.268
28.74
6.35
1.46
5.46
5.26
3.15
2.90
0.415
22.03
5.50
1.24
5.03
4.55
2.82
2.82
0.432
22.03
5.50
1.24
5.03
4.55
2.82
2.82
0.432
14.10
3.60
0.82
3.33
3.14
1.91
1.88
0.287
19.07
4.43
1.10
4.31
4.12
2.47
2.31
0.338
18.56
4.05
1.03
3.61
3.65
2.13
2.12
0.333
Pb
Th
U
33.37
14.20
0.99
6.60
2.58
0.51
5.41
2.66
0.66
6.00
2.62
0.58
6.82
2.43
1.19
23.68
6.22
1.39
23.68
6.22
1.39
10.11
2.23
0.71
12.91
5.49
2.39
10.08
4.38
1.69
0.70617
0.51252
18.917
15.646
38.918
0.70810
0.51251
19.025
15.655
39.007
0.70617
0.51252
18.917
15.646
38.918
0.70617
0.51252
18.917
15.646
38.918
0.71121
0.51234
18.816
15.694
38.886
0.71121
0.51234
18.816
15.694
38.886
0.71121
0.51234
18.816
15.694
38.886
0.70635
0.51261
19.042
15.626
38.686
0.70588
0.51267
18.940
15.614
38.641
87Srr86Sr
143Ndr144Nd
206Pbr204Pb
207Pbr204Pb
208Pbr204Pb
Trench
Subd rate Žmmryear.
Thickness Žm.
Density Žgrcc.
Water Ž%.
Trench length Žkm.
Confidence level
Cascadia
35
1500
1.88
30.00
1300
4
Mexico
52
170
1.37
59.01
1450
2
Centam
77
425
1.62
48.69
1450
1
Colomb
70
270
1.64
41.54
1050
3
Peru
100
125
1.37
59.01
1500
4
S. Sand
20
200
1.49
50.00
800
1
N. Ant
24
235
1.66
37.30
400
2
S. Ant
24
1750
1.88
30.00
400
3
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
CO 2
H 2 Oq
57.86
0.77
15.37
5.91
0.12
2.96
2.41
2.85
2.40
0.16
0.00
9.18
54.24
0.57
13.13
11.04
2.33
2.87
1.73
2.50
1.23
0.36
0.00
10.00
23.39
0.17
3.31
3.77
0.43
1.52
34.59
0.83
0.68
0.20
26.55
4.59
35.70
0.04
1.49
0.43
0.14
0.55
28.33
3.10
0.13
0.21
22.26
6.92
33.61
0.31
6.60
4.85
0.43
1.81
24.52
1.28
0.96
0.19
18.49
6.97
71.30
0.46
9.56
4.06
0.06
1.73
1.06
2.58
1.97
0.10
0.00
7.13
52.19
0.71
17.45
7.94
0.17
2.77
1.95
1.85
1.81
0.09
0.59
12.67
54.74
0.87
20.31
6.27
0.07
2.29
0.70
2.51
2.80
0.12
0.08
9.26
Sc
V
Cr
Co
Ni
17.06
170
94.0
16.9
47.5
15.74
252
97.1
36.0
170.9
7.67
103
32.0
30.0
86.0
2.15
17
5.1
6.5
20.4
10.56
104
45.7
31.0
97.4
9.91
84
30.2
32.2
31.7
11.75
239
69.0
22.7
73.6
13.67
189
80.3
22.8
58.1
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
345
346
Table 2 Žcontinued.
Cascadia
35
1500
1.88
30.00
1300
4
Mexico
52
170
1.37
59.01
1450
2
Centam
77
425
1.62
48.69
1450
1
Colomb
70
270
1.64
41.54
1050
3
Peru
100
125
1.37
59.01
1500
4
S. Sand
20
200
1.49
50.00
800
1
N. Ant
24
235
1.66
37.30
400
2
S. Ant
24
1750
1.88
30.00
400
3
Cu
Zn
Rb
Cs
Sr
Ba
Y
Zr
Hf
Nb
Ta
51.0
95.2
64.2
3.64
216
746
22.2
146
3.68
10.00
0.704
287.0
242.7
49.4
3.21
234
2175
42.2
132
3.77
9.58
0.675
167.0
152.3
15.6
0.72
1227
2571
31.7
29
0.84
1.80
0.127
27.2
24.7
2.8
0.15
807
1658
11.9
43
1.24
2.08
0.146
179.3
177.4
25.0
1.49
830
2117
27.0
70
1.69
3.85
0.261
95.1
60.9
68.8
5.46
115
1040
15.0
96
2.37
4.56
0.321
116.8
124.2
83.5
5.64
111
204
23.9
146
4.18
18.33
1.118
92.2
98.1
142.0
10.83
135
402
28.7
170
4.86
21.32
1.300
La
Ce
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
21.75
44.79
21.79
4.77
1.15
4.53
4.06
2.34
2.20
0.329
42.42
87.07
38.71
8.75
1.92
8.19
7.57
4.39
4.22
0.602
15.75
10.62
12.23
2.87
0.63
3.04
3.49
2.07
1.84
0.278
18.01
6.59
13.93
3.24
0.83
3.34
3.61
2.33
1.19
0.350
19.26
21.85
16.96
3.79
0.96
3.85
4.00
2.44
2.30
0.351
9.72
24.05
10.42
2.34
0.56
2.29
2.38
1.47
1.50
0.228
35.54
82.83
31.22
6.18
1.32
5.09
4.68
2.55
2.39
0.359
47.91
105.41
41.64
7.89
1.59
6.36
5.38
2.92
2.76
0.403
Pb
Th
U
15.59
6.63
2.92
106.34
8.64
3.01
7.36
0.93
1.37
0.89
0.38
0.62
26.79
2.89
2.37
22.49
4.86
1.16
25.54
12.08
1.36
30.46
14.94
4.27
87Srr86Sr
143Ndr144Nd
206Pbr204Pb
207Pbr204Pb
208Pbr204Pb
0.70710
0.51253
19.151
15.629
38.747
0.70919
0.51243
18.649
15.633
38.501
0.71788
0.51193
19.318
15.769
39.339
0.71100
0.51204
19.033
15.720
39.150
0.70852
0.51253
18.459
15.515
38.166
Oxides in wt%; all others in ppm.
Trench lengths from von Huene and Scholl Ž1991..
Subduction velocities are orthogonal to the trench. See Appendix B for all details and references.
Confidence levels: 1s highest confidence; 4 s lowest Žsee text for details..
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Trench
Subd rate Žmmryear.
Thickness Žm.
Density Žgrcc.
Water Ž%.
Trench length Žkm.
Confidence level
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
small number of analyses per core Ž- 10.. To address this question, we examine two cores with high
sampling density: DSDP Site 595r596 ŽTonga.,
where Zhou and Kyte Ž1992. analyzed samples taken
every ; 40 cm, and ODP Site 765 ŽJava., where
Plank and Ludden Ž1992. analyzed ; 150 samples.
These two sites provide reliable mean compositions
and also encompass a wide range in sediment
lithologies. The Tonga site consists entirely of pelagic
clays and the Java site includes carbonate turbidites,
radiolarian clay and cratonic detritus. The question
we wish to address is how closely a much smaller
number of random samples combined with our lithological approach would approach this ‘true’ composition. This is not a simple statistical problem, because the data are not normally distributed, and
different lithological units may have different distributions. Therefore we have taken a numerical approach.
At DSDP Site 595 and 596 Ž; 10 km apart. a 70
m section of sediment was drilled on top of Mesozoic basement about 1000 km east of the Tonga
trench. This section is extremely condensed, with the
entire Cenozoic section comprising just the upper 25
m. Zhou and Kyte Ž1992. sampled the Cenozoic
section in great detail Ž55 samples taken at roughly
40 cm spacing. in an effort to characterize red clay
chemostratigraphy in the South Pacific and to geochemically identify the CretaceousrTertiary boundary. Their detailed sampling provides a very accurate
mean for the upper 25 m at 595r6. How closely
would this mean be approached using our method if
there were only 5 randomly selected samples?
The upper 25 m at 595r6 can be subdivided into
two lithological units based on color and smear slide
analyses: an 11 m brown clay unit overlying 14 m of
brown–black metalliferous clay. Two randomly selected samples from the top unit and three random
samples from the bottom unit were used to calculate
a weighted mean for the entire 25 m. For each
selection of five samples, this mean was subtracted
from the true mean based on all 55 of Zhou and
Kyte’s samples to determine the error. After 100
trials using the random selections, the distribution of
the errors becomes well determined. Fig. 13a shows
the error distribution for Th, and Fig. 13b shows the
results for seven elements of interest ŽK, Rb, Cs, Ba,
La, U, Th.. Errors are generally within 15–30% of
347
the ‘true’ mean, for 90% of the trials. The best
elements Žgiving - 20% errors. are K and Ba, for
which the data set has the least variance. These
calculations indicate that by using only 5 samples, a
reasonable mean can still be calculated, with errors
generally less than 30%. Given that analytical errors
can be 10%, and that the global variations in the bulk
composition of sediment columns may be more than
an order of magnitude ŽTable 1., this is a favorable
result.
Although the 25 m section at 595r596 represents
a significant period of time Žthe entire Cenozoic., the
lithology varies little. Therefore, a second ground
truth experiment was conducted on a longer core
with more lithological variability. At ODP Site 765
in the Indian Ocean, 930 m of sediment was drilled
to uppermost Jurassic basement, and three main units
were sampled: 55 m of brown–green radiolarian clay
over 515 m of Cenozoic carbonate turbidites over
360 m of Cretaceous brown and gray streaky clay
with intermixed nannoplankton chalk and radiolarian
clay Žsee Ludden et al., 1990, for complete lithostratigraphy.. An accurate mean can be determined
using the 156 analyses in Plank and Ludden Ž1992..
For the numerical experiment, two samples of the
upper clay unit were selected at random. For the
middle carbonate unit, three samples were selected
randomly, and the average was forced to contain
56% calcium carbonate, an independent constraint
from shipboard CaCO 3 analyses. This step utilizes a
constraint that is normally available Žand indeed was
used for all carbonate-bearing cores; see Appendix
B.. Based on the systematics of global sediments, all
elements except Sr are assumed to be diluted by
CaCO 3 . Finally, for the lowermost unit ŽCretaceous.,
three samples were selected randomly, one from
each of the three 120 m depth intervals. This constraint represents the general practice of sampling at
roughly evenly-spaced intervals down-core. A final
weighted average was calculated using the means
from each of the three units and compared with the
‘true’ mean from Plank and Ludden Ž1992. based on
all 156 samples.
In this case as well, means for most of the
elements of interest ŽK, Rb, Sr, La. are within 20%
of the true mean ŽFig. 13b.. Sr is particularly accurate, because it is directly linked to the percent
carbonate, for which an independent estimate is
348
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
available. The worst case is Ba Žwithin 65% of the
true mean. which varies tremendously in this core
Žfrom 26 to almost 10,000 ppm.. Nonetheless, this
calculation illustrates that as few as 8 analyses can
return a fairly robust estimate of the bulk composition of a 930 m core — within 20% for most
elements. This result is consistent with the conclusion of Plank and Ludden Ž1992. that the main
variation at Site 765 is mixing of average upper
crustal detritus with carbonate, and that a reasonable
average for this site Žwithin 30% for most elements.
can even be calculated ‘blind’ based simply on the
percentage carbonate and an average upper crustal
shale composition.
These numerical experiments generally support
the method used in this paper to estimate bulk
sediment compositions. They demonstrate that geochemical and lithological variations are closely
linked, and that the geochemical composition of a
given lithology can be characterized by a small
number of analyses Ž2–5., especially if independent
data are available on the extent of carbonate Žor
opal. dilution. Bulk estimates carried out in this
paper which include more than 2–5 analyses per
lithology are thus considered reliable to roughly 30%
and assigned the highest confidence levels of 1 and 2
Žsee Table 2..
each trench considered. For approximately 40% of
the sections, no analyses were available for the
sediments from the actual reference sites, and so we
assigned the closest analog geochemical composition. For example, we used analyses from McLennan
et al. Ž1990. of piston core samples from the Ganges
Fan to calculate means for almost the entire Andaman and Sumatran trenches; the Eocene clastic
turbidites near the Aleutian trench ŽKay and Kay,
1988. as an approximation for Cascadia sediments;
and Marianas pelagic units ŽKarpoff, 1992 and Karl
et al., 1992. for the Izu-Bonin sediments. For completeness, a full set of major and trace elements are
given for each trench. The estimates for many of
these elements should be considered preliminary Ži.e.,
transition elements and Pb. as their behavior is not
the focus of this study. Because of the varying
amount of hard data that went into each calculation,
we have assigned confidence levels to each trench
average. Confidence levels 1 and 2 include columns
with adequate geochemical analyses, and these form
the basis for most of our discussions. Levels 3 and 4
trenches are characterized by few if any chemical
analyses andror non-ideal reference sites. Level 5
4. Geochemical variations in bulk sediment
columns approaching trenches
In considering each convergent margin, we started
with Rea and Ruff’s Ž1996. recent compilation of
sediment lithologies near trenches. In most cases we
used the same reference drill sites ŽFig. 12, Table 1.,
but we found their lithological divisions needed further subdivision to be combined meaningfully with
the geochemical data. For example, Rea and Ruff
Ž1996. lump together red clay, volcaniclastics and
clastic turbidites as ‘terrigenous,’ yet these sediment
types have contrasting geochemical compositions.
Therefore, we re-evaluated the terrigenous material
at each site using the following categories: red clay,
siliceous ooze, arc volcaniclastics, ocean-island type
volcaniclastics, cratonic turbidites, and juvenile turbidites. Appendix B provides the details on how
average sediment compositions were calculated for
Fig. 14. Relative sediment mass fluxes at each trench Žfrom table
2 in von Huene and Scholl Ž1991., sediment volume fluxes..
Patterns reflect different confidence levels for chemical flux estimates in this paper Žsee our Table 2.. Confidence levels as
follows: 1sabundant analyses and elements for one or more
reference sites; 2 ssome analyses and elements; 3s few analyses
and elements; 4s no analyses but nearby drill sites; 5s no drill
sites seaward of the trench andror large uncertainties about the
subducted stratigraphy. Note roughly half of the global subducted
sediment flux is virtually unsampled by drilling Žconfidence levels
4 and 5..
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
349
Fig. 15. Bulk composition of subducting sediment columns at the world’s trenches. REE are for confidence level 1 and 2 trenches only
Žindicated as filled circles in b–d.. Vector toward average continental crust ŽTMUC. also shown, along with PAAS, NASC and our GLOSS.
Gray circles are where element of interest was estimated, not determined. Independent estimates for the Marianas sediment are based on
ODP Sites 800 and 801, connected by tie lines to the Marianas average. All data given in Table 2.
trenches lack adequate drilling and so were not
considered ŽNew Britain, Aegean, Chile, New
Zealand, Solomons, Sulawesi.. The pie chart in Fig.
14 shows that there is a significant fraction of the
world’s subducting sediment mass that has yet to be
sampled by drilling.
We can use the whole-core averages to illustrate
the types of compositional variations that occur in
bulk subducting sedimentary columns ŽFig. 15 and
Table 2., in contrast to the variations in sedimentary
components discussed earlier. Rea and Ruff Ž1996.
have already discussed the lithologic diversity of
subducting sediment columns. We focus here on the
geochemistry.
4.1. REE
The REE patterns of sediment columns approaching trenches reflect their constituent components ŽFig.
15a.. Only the sites receiving cratonic terrigenous
material Že.g., Lesser Antilles sediments via the
Orinoco river draining the Guyana shield, and Java
sediments receiving detritus from the Australian cratons. have REE patterns that are as LREE-enriched
as upper crustal composites ŽPAAS and NASC.. All
other sites have less enriched LREE due to seawater
and volcanic sources. Although the net addition of
REE to the oceans has no Ce anomaly, some of the
bulk sediment columns being subducted have bulk
negative Ce anomalies ŽTonga, Guatemala and Marianas., owing to fish teeth and other phases that
inherit REE from seawater. It is notable that Ce
anomalies are also observed in the REE pattern for
volcanics from these same arcs ŽHole et al., 1984;
Carr et al., 1990; Ewart et al., 1994; Elliott et al.,
1997; and our own unpublished ICP-MS data., and
are largely absent in others where the subducting
sediment also lacks a net negative Ce anomaly
ŽVanuatu, Lesser Antilles, Java, Aleutians; e.g., Gorton, 1977; White and Patchett, 1984 and our own
350
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
unpublished ICP-MS data.. With respect to absolute
concentrations, bulk sediments with greater than continental abundances ŽTonga. are rich in fish debris
phosphate, while those lower than continental abundances contain diluting biogenic phases or volcanics
Že.g., Guatemala, Vanuatu.. 147 Smr 144 Nd ratios vary
from 0.11 for the Antilles, Nankai and Andaman
sediments Žmost continental., to 0.14 for Vanuatu
Žarc volcaniclastics.. Thus, the entire marine sedimentary range is higher than upper continental crust
Ž0.104; Taylor and McLennan, 1985., due to LREEdepleted volcanic components as well as MREE-enriched hydrogenous components ŽSee Fig. 7..
4.2. Sr and Ba
The Sr bulk concentration in sedimentary sections
is dependent on the proportion of carbonate, varying
from continental abundances Ž100–300 ppm. to )
1000 ppm in carbonate-rich sections Že.g., Central
America.. The variations in Ba are complex, since
the sources are not always predictably linked to
specific sediment lithologies. Some diatom and radiolarian oozes are very rich in Ba ŽCentral America,
Aleutians, Java., while some cherts and radiolarites
are not ŽMarianas, Antilles.. Hydrothermal fluxes
can also lead to high Ba concentrations ŽTonga and
Mexico., while some detrital sources are very low in
Ba ŽAntilles continental detritus and Vanuatu volcaniclastics.. This complex behavior leads to a decoupling between Ba and Sr, and in fact between Ba
and all other elements.
4.3. Th and U
The ThrU ratio of bulk sediment sections varies
by an order of magnitude ŽFig. 15c., from 10 ŽNorthern Antilles. to - 1 ŽCentral America.. Such extreme variation occurs because Th and U behave
differently in surface and marine systems. High
ThrU ratios may reflect a mature, weathered source
Žwhere U has been preferentially leached relative to
Th, such as continentally-derived Antilles and Java
sediments., or preferential Th scavenging in the
oceans Žred clay-rich Tonga sediments.. Low ThrU
may reflect immature continental detritus ŽAleutians
sediments. or organic-rich hemipelagics Žleading to
enhanced U precipitation under reducing conditions,
as for Central American sediments.. Overall concentrations are mostly controlled by the abundance of
biogenic diluents.
4.4. Alkalis and HFSE
The alkali elements ŽK, Rb, Cs. and high field
strength elements ŽZr, Hf, Nb, Ta. generally covary
in subducted sediments Že.g., Fig. 15d., preserving
roughly continental ratios. Exceptions include Vanuatu and Tonga sediments, which have lower RbrZr
due to volcaniclastic detritus ŽVanuatu. and hydrogenous addition of Zr ŽTonga.. Absolute abundances of
these elements vary inversely with the proportion of
biogenic diluents, and so are highest in terrigenousdominated columns ŽAntilles, Nankai and Java. and
lowest in biogenic-dominated columns ŽCentral
America and Marianas..
To summarize, the global variations in sediment
columns spans more than an order of magnitude for
many of the elements ŽTh, Ba, Sr and REE; Fig. 15..
Furthermore, the geochemical variations among the
sediment columns are complex, with each possessing
its own geochemical fingerprint. These fingerprints
arise because of complex variations in the regional
stratigraphy of the oceans. Indeed, there is no common stratigraphy in the deep ocean ŽFig. 11.. The
‘classic’ deep sea stratigraphy presented in many
textbooks —where carbonate oozes deposited on
ridge crests are covered by siliceous oozes and
abyssal clays and finally topped by continental margin turbidites— exists in few trench columns Žand
none in the Western Pacific.. Use of such a generic
stratigraphy would lead to gross errors in calculating
the bulk composition of a given subducted section.
Hence, the use of global or ocean-wide averages, or
piston core samples Žgenerally restricted to the upper
10 m., to model sediment recycling at a particular
arc or as an average flux into the mantle inevitably
leads to poorly constrained interpretation. Better
models clearly depend on deep sea drilling to obtain
entire sedimentary sections to basement near
trenches. Even such cores, however, are one-dimensional samples of a three-dimensional problem. Thus,
before generalizing our results, it is necessary to
consider to what extent results for specific cores are
sufficiently general to represent the lateral variations
in sediment columns that might occur along an entire
subduction zone.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
5. Lateral variability in sediment columns
While sedimentary columns vary on a global basis, any given region undergoes a common history
that leads to a similar stratigraphic section. For
example, seafloor currently at the Aleutian trench
received turbidites from British Columbia early in its
history, then pelagic diatoms as the plate moved
north, and then gradually more volcanic input as the
arc was approached. The similar transport history of
large sections of the seafloor means that similar
lithological columns exist over substantial regions.
This idea is supported by a study based on over
400 surface sediments from the Nazca plate, where
Dymond Ž1981. identified several large sedimentary
provinces. These include a hydrothermal province
near the East Pacific Rise, a detrital province near
the South American margin, a biogenic province
near the equator, and a hydrogenous province in the
central basin. These provinces are large Žsome are
thousands of km. and mostly continuous. Any core
taken 100 km from any other core is likely to share
the same general sedimentary units. We could take
any point along the northern South American trench,
and estimate the lithological column by vertically
averaging the surface provinces on the Nazca plate.
The section will contain hydrothermal sediments at
the base, overlain by hydrogenous sediment and
detrital sediments, with more or less biogenic material depending upon distance from the equator. The
concept and observation of large sedimentary
provinces in the oceans generally supports the idea
that a single drill site may be an adequate reference
site for a large section of seafloor along a trench.
This discussion, however, is largely theoretical. There
is still the question how well in fact a single sediment column represents its sedimentary province.
In order to approach this answer, we calculated
independent bulk compositions for two sites in the
Marianas region drilled during Leg 129, ODP 800
and 801, which are 600 km apart but in the same
sedimentary province. The general lithologies for the
two sites are similar Žbrown clays, cherts, radiolarites, and volcaniclastic turbidites., although the
stratigraphy and ‘basement’ age differ in detail
ŽLancelot et al., 1990.. The abundant geochemical
analyses ŽKarl et al., 1992; Karpoff, 1992; FranceLanord et al., 1992; Lees et al., 1992. make it
351
possible to calculate fairly accurate bulk compositions for the two sites ŽTables 1 and 2; Fig. 15..
Although core recovery was low Ž28% at 800 and
17% at 801. and possibly biased to the more siliceous
units, geochemical and physical property logs ŽFisher
et al., 1992; Pratson et al., 1992. were used to weight
properly the geochemical analyses Žsee details in
Appendix B.. The differences in the bulk compositions of Site 800 from Site 801 are generally small:
- 20% for the alkalis, 30% for Sr and U, - 10% for
Th and REE, and 60% for Ba. Although some of
these differences are greater than the errors in the
bulk calculation Ži.e., Ba., Fig. 15 shows that either
site would represent well the general characteristics
of the Marianas sediments Žlow Th, U and Ba;
intermediate K., and would occupy the same overall
position with respect to the global distribution, even
for Ba.
One final consideration involves hydrothermal deposits. Significant lateral variability could arise from
hydrothermal activity at the ridge crest, where black
smokers are point sources of hydrothermal elements
like Ba. For example, a two meter hydrothermal
sedimentary section at the base of the Tonga Site
596 contains ) 20,000 ppm Ba. If this extremely
Ba-enriched deposit varied significantly at local
scales, then Site 596 would not be relevant to subduction along the entire 1000 km Tonga trench. Two
lines of evidence suggest that this is not a serious
problem. First, the Ba-rich layer also exists at Site
595, drilled 12 km away from Site 596. Second,
studies by Lyle Ž1986. and Barrett and Jarvis Ž1988.
of DSDP Sites 597–599, three sites along a 1000 km
transect across the East Pacific Rise, allows comparison of the mean composition of the lower 20 m of
hydrothermal sediment. These averages are remarkably similar. For example Ba and La, which are the
worst case elements, vary by only 10% and 20%
about the mean Ž1 sigma., respectively. Thus, even
hydrothermal sediment compositions may be well
averaged enough spatially and temporally to characterize a large sedimentary province.
This does not mean, however, that the problem
will not be better defined by multiple drill holes
along trenches, especially along margins with clear
differences in the predicted sediment lithologies or in
observed volcano compositions. But the existence of
large sedimentary provinces, and the evidence dis-
352
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
cussed above, suggest that a good first order approach is feasible, even with a single drill site per
margin.
6. Calculating sedimentary fluxes into subduction
zones
In order to calculate elemental mass fluxes into
trenches, bulk compositions alone are not sufficient
— sediment thickness, density and subduction rate
must also be considered. The parameters that go into
this calculation are fairly well known. Isopach maps
and global estimates of sediment thicknesses near
convergent margins are widely available ŽLudwig
and Houtz, 1979; Tucholke et al., 1982; von Huene
and Scholl, 1991.; sediment densities have been
routinely measured on core samples by the Deep Sea
Drilling Program ŽDSDP. and the Ocean Drilling
Program ŽODP.; and convergence rates are available
from plate motion models and recent GPS measurements Že.g., DeMets et al., 1990, 1994; Bevis et al.,
1995.. The largest source of uncertainty in the flux
calculation is the extent to which the incoming sedimentary section is lost to the overlying plate by
accretion or underplating in the shallow subduction
zone ŽFig. 16.. Since this sediment is not subducted,
it must be subtracted from the incoming flux to
determine subducted fluxes.
There has been considerable interest in the processes that build accretionary prisms, and many margins have been studied in detail by seismic, drilling
and mass balance techniques to determine the dy-
Fig. 16. Material balance at a convergent margin, after von Huene
and Scholl Ž1991.. The subducted sediment flux is proportional to
the convergence rate, sediment thickness and density of the incoming sediment section, minus the accreted and underplated flux,
plus any forearc erosional flux. In this study, we consider the flux
of sediment beneath the decollement, and do not include underplated or erosional fluxes explicitly.
namic processes that occur ŽKarig and Sharmann,
1975; Davis et al., 1983; von Huene, 1986; Shreve
and Cloos, 1986; von Huene and Scholl, 1991..
Some early attempts to drill into accretionary structures, however, revealed a lack of oceanic sedimentary material ŽHussong and Uyeda, 1982; Moore et
al., 1982., suggesting that in some cases the entire
sedimentary column has disappeared beneath the
fore-arc. Dredging the inner trench wall of some
margins similarly failed to recover off-scraped
oceanic sediments Že.g., Bloomer and Fisher, 1986..
Even where large accretionary prisms have formed,
some portion of the sedimentary pile is still apparently subducted Že.g., Westbrook et al., 1988; von
Huene and Scholl, 1991.. Often a decollement forms,
which may serve as a dynamic plate boundary, separating accreting from subducting material ŽMoore et
al., 1980; Westbrook and Smith, 1983; Moore and
Shipley, 1988.. In other locations, grabens formed
by the bending of the subducting plate also appear to
trap sediments effectively ŽSchweller et al., 1981;
Hilde, 1983.. Thus, sediment accretion is partial
Žvon Huene and Scholl, 1991., and the problem is to
determine the proportions accreted and subducted.
Sediment underplating and forearc erosion also
contributed to the balance of mass across the subduction zone. Underplating is the flux of sediment to the
base of the accretionary complex, and has been
imaged seismically and inferred from material balance at some margins Že.g., Westbrook et al., 1988;
von Huene and Scholl, 1993.. At other margins,
subsidence of the forearc indicates net erosion of the
margin Žvon Huene and Lallemand, 1990., and this
extra material is another crustal input to the subduction zone.
Combining all of these variables gives the following equation for sediment subduction: Žsubducted
flux. s Žincoming flux. q Žerosion flux. y Žaccretion
flux. y Žunderplating flux.. Solving the full equation
precisely may be impossible, given the difficulty in
imaging and sampling the deeper parts of the fore-arc
complex and the likely temporal variability in the
dynamics of sediment subduction. In order to estimate the behavior of the system at depth, it may
ultimately be necessary to rely on predictive models
of sediment dynamics in the fore-arc, such as the
subduction channel model of Shreve and Cloos
Ž1986.. Because the structures within the shallowest
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
levels of the system are the ones best imaged by
seismic techniques and sampled by drilling, and the
deeper and erosional processes are poorly constrained, we consider only the shallow processes.
Specifically, our input fluxes are based on the full
sedimentary column approaching the trench where
no off-scraping is documented, and the column below the decollement where decollements have been
imaged. In terms of the above equation, our subducted fluxes are the incoming flux minus the Žfrontally. accreted flux ŽFig. 16.. Thus, our flux estimates are maxima for margins with underplating and
are minima for margins with fore-arc erosion. When
better estimates of the underplating and erosive fluxes
become available, these can be added to the balance.
In estimating the thickness of subducted sediment
columns, we began with table 2 of von von Huene
and Scholl Ž1991. as a starting point, but in practice
used few of their actual values. Von Huene and
Scholl ŽVH & S. assume 70–80% of the trench sediment is subducted at accretionary margins. The trench
sediment, however, is rarely drilled; therefore, it is
difficult to guess the sediment lithology, let alone the
geochemistry. For example, we use the 270 m pelagic
section approaching the trench Ždrilled at Site 504.
for the Columbia mean sediment, while VH & S estimate a 1.2 km subducted section. This extra km of
material in the trench has yet to be sampled, and so
is difficult to estimate. In other cases, known
decollements have been imaged or drilled that appear
lower in the section than VH & S’s estimates Že.g.,
350 m section beneath the decollement at Nankai
instead of VH & S’s 1.2 km.. Finally, for most nonaccretionary margins, VH & S assign what appears to
be an arbitrary lower limit of 400 m of subducted
sediment, where in many cases less is being subducted Že.g., - 100 m at Tonga.. Thus, our sections
are generally more conservative than VH & S’s, in
that they are based Žby necessity. on actual drilled
oceanic sediment columns approaching the trench,
and this may underestimate in some cases the full
subducted section. We used VH & S’s subduction
thicknesses only in those cases where thick piles of
turbidites have not been completely drilled ŽMakran,
Sumatra, Andaman, Cascadia, and S. Antilles.. Instead of using VH & S’s porosity model, we calculated the mean density and water content from data
published for each reference site. We also updated
353
several convergence rates to include recent GPS
data. Details of the various data needed to carry out
the calculations are given in Appendix B.
Subducted sediment thicknesses vary from - 100
m ŽTonga. to ) 4 km ŽMakran.. At the low end,
sediment supply is the important factor. A thin sedimentary cover means a thin section subducted. In
fact, much of the variability in sediment thickness
for the trenches shown in Fig. 11 Žfrom 70 to 650 m.
is primary variability in the sediment supply to the
site over its history. A thin sedimentary section Ž70
m. is subducted at the Tonga trench because seafloor
in that part of the Pacific is sediment starved, whereas
a thicker section Ž350 m. is subducted at the Aleutian trench because of large diatom accumulations
and terrigenous inputs via turbidites. At the high end
Ž) 1 km., a large sediment supply usually leads to a
large accretionary structure, and complex dynamic
forces may modulate the thickness of sediment that
is subducted. Thus, the greatest uncertainties are for
the thickest sections, which unfortunately make up
the largest potential proportion of the global subducted flux. These sections, however, typically consist of geochemically monotonous turbidites, so the
geochemical uncertainties are low while the mass
flux uncertainties may be high.
The combination of mass flux and chemical concentration data gives the geochemical flux for each
convergent margin. The geochemical flux, F, for any
element, a, is then:
Fa s Ca tL r R
where Ca is the concentration of the element in wt%
Žtaking into account the water content of the sediment., t is the sediment thickness, L is the length of
the subduction zone, r is the sediment density, and
R is the convergence rate. The total global flux can
be calculated by summing the individual fluxes for
each convergent margin. The GLObal Subducted
Sediment composition ŽGLOSS., discussed below,
then reflects the mass proportions of each element in
the global flux.
The global variation in fluxes is not the same as
the global variation in bulk compositions discussed
above, because thickness, concentration, density, water content and convergence rate all factor into the
flux calculations. A thin sedimentary sequence can
have a particularly low mass flux, because thinner
354
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
sections have higher mean water contents than thicker
sections. Table 2 gives the bulk compositions for the
sedimentary sections, and the additional parameters
required to calculate the mass fluxes. Like the bulk
compositions, mass fluxes generally vary by about
an order of magnitude for the different sedimentary
columns. Specific discussion of the variation in mass
fluxes will be discussed in a companion paper ŽPlank
and Langmuir, in prep...
6.1. Correlations between sediment fluxes and Õolcanic rock compositions
One application of this work is to compare regional sediment fluxes to the chemical composition
of corresponding arc volcanics, in order to test ideas
of sediment recycling to the arc. We presented a
preliminary version of this comparison in Plank and
Langmuir Ž1993., showing significant correlations
between sediment input Žper cm arc length. and arc
geochemistry. The high Ba and Sr, and low Th and
K of Guatemala sediments, for example, is a unique
geochemical feature shared by the volcanics. The
sediment fluxes calculated here differ from those
presented in Plank and Langmuir Ž1993. in that they
take into account new sediment data Žfor Vanuatu
DSDP site 286 and Guatemala DSDP site 495, provided by D. Peate and M. Carr, respectively., and
new convergence rate estimates Žincluding NUVEL1a, DeMets et al., 1994 and new GPS measurements,
Fig. 17. Correlation between subducted sediment Rb flux and the
Rb enrichment in associated arc volcanics ŽRb6.0 is the average
Rb concentration in the arc at 6% MgO.. Sediment fluxes calculated from Table 2; arc basalt compositions from Plank and
Langmuir Ž1993.. Using new sediment data compiled in this
study, the correlation has improved from R 2 of 0.50 to 0.77.
e.g., Beavan et al., 1990; Tregoning et al., 1994;
Bevis et al., 1995..
These updates have changed the sediment–
volcano correlations in detail, as might be expected
from the small number of data points, but in general
have led to improved R 2 values Žfrom an average
R 2 of 0.70 " 0.17 to 0.74 " 0.094.. Combining the
new sediment flux estimates here with the volcanic
compositions in Plank and Langmuir Ž1993., none of
the correlations degraded significantly Žthe worst
case is Ba, where R 2 decreased from 0.92 to 0.87.,
and some improved significantly Že.g., the R 2 for Rb
increased from 0.5 to 0.77; Fig. 17.. A companion
paper ŽPlank and Langmuir, in prep.. will explore
these correlations further, and develop a mass balance model based on the sediment input and arc
output fluxes.
7. Global sediment flux estimates
The global subducting sediment composition
ŽGLOSS. differs from previous estimates for large
ocean provinces ŽPAWMS, Hole et al., 1984; BWPS
Lin, 1992., in that we derive a mass-flux-weighted
global mean, taking into account plate convergence
rates, trench lengths and sediment columns. Our
calculations also differ from those by Hay et al.
Ž1988., who considered the total mass of sediment
on the seafloor, including seafloor that is not currently subducting Žsuch as most of the Atlantic.. Our
calculations are very similar in concept to those in
Rea and Ruff Ž1996., but we expand on their study
by providing chemical fluxes.
GLOSS ŽTable 3. includes ; 70% of the global
trench length. Fig. 14 shows that the largest omissions are the entire Chilean margin, for which there
has been no drilling seaward of the trench, and the
Aegean, where subduction is complex and controversy exists over what is actually being subducted
and where the plate boundary resides ŽRyan et al.,
1982; Le Pichon, 1983.. Future drilling, geochemical
analyses, and convergent margin studies will certainly better constrain the GLOSS composition.
7.1. The chemical composition of GLOSS
Oceanic sediment is distinct from the erosional
products of continents, because of the addition of
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
355
Table 3
Global Subducting Sediment ŽGLOSS. composition and flux
GLOSS ave
GLOSS std dev
GLOSS flux
UCC T and M
BCC R and F
58.57
0.62
11.91
5.21
0.32
2.48
5.95
2.43
2.04
0.19
3.01
7.29
2.49
0.04
0.94
0.42
0.13
0.16
1.75
0.20
0.16
0.05
1.44
0.41
1.30E q 15
2.97E q 04
7.62E q 14
8.07E q 12
1.55E q 14
6.78E q 13
4.19E q 12
3.22E q 13
7.74E q 13
3.16E q 13
2.65E q 13
2.45E q 12
3.92E q 13
9.49E q 13
66.00
0.50
15.20
4.50
0.08
2.20
4.20
3.90
3.40
0.40
59.10
0.70
15.80
6.60
0.11
4.40
6.40
3.20
1.88
0.20
Sc
V
Cr
Co
Ni
Cu
Zn
Rb
Cs
Sr
Ba
Y
Zr
Hf
Nb
Ta
13.1
110
78.9
21.9
70.5
75.0
86.4
57.2
3.48
327
776
29.8
130
4.06
8.94
0.63
1.03
10.7
7.06
9.48
14.73
16.07
8.88
6.66
0.50
53.8
137.1
9.92
8.5
0.30
0.94
0.06
1.70E q 10
1.43E q 11
1.03E q 11
2.85E q 10
9.18E q 10
9.76E q 10
1.12E q 11
7.44E q 10
4.53E q 09
4.26E q 11
1.01E q 12
3.88E q 10
1.69E q 11
5.28E q 09
1.16E q 10
8.20E q 08
11
60
35
10
20
25
71
112
3.70
350
550
22
190
5.80
25
2.20
22
131
119
25
51
24
73
58
2.60
325
390
20
123
3.70
12
1.10
La
Ce
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
28.8
57.3
27.0
5.78
1.31
5.26
4.99
2.92
2.76
0.413
6.8
10.3
8.3
1.83
0.44
2.04
1.86
1.06
0.88
0.133
3.75E q 10
7.46E q 10
3.52E q 10
7.52E q 09
1.70E q 09
6.85E q 09
6.49E q 09
3.80E q 09
3.59E q 09
5.37E q 08
30.0
64.0
26.0
4.50
0.88
3.80
3.50
2.30
2.20
0.320
18.0
42.0
20.0
3.90
1.20
3.60
3.50
2.20
2.00
0.330
Pb
Th
U
19.9
6.91
1.68
5.4
0.80
0.18
2.59E q 10
8.99E q 09
2.19E q 09
20.0
10.70
2.80
12.6
5.60
1.40
87Srr86Sr
143Ndr144Nd
206Pbr204Pb
207Pbr204Pb
208Pbr204Pb
0.71730
0.51218
18.913
15.673
38.899
Material flux Žgryear.
Trench length Žkm.
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
CO 2
H 2O
Upper Continental Crust ŽUCC. from Taylor and McLennan Ž1985. ŽT and M.; Bulk Continental Crust ŽBCC. from Rudnick and Fountain
Ž1995. ŽR and F.; Oxides in wt%, others in ppm.
356
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
biogenic, hydrothermal and hydrogenous components. GLOSS, however, contains only about 17%
biogenic components, 7% of which is marine carbonate. We estimate biogenic silica from the SiO 2 enrichment of each site, relative to the background
detritus, and arrive at 10%. These estimates for
biogenic components are similar to those done independently by Rea and Ruff Ž1996., who found 15%
carbonate and 9% biogenic silica. The difference in
carbonate may lie in our omission of the Chilean and
Aegean trenches, where Rea and Ruff include a large
proportion of subducted carbonate. Therefore, the
current GLOSS composition is overwhelmingly terrigenous, in agreement with Rea and Ruff. The
similarity between the lithological make-up of
GLOSS and R & R’s global lithologic percentages is
encouraging, given that they were estimated using
different approaches and independent calculations. If
applied over the global trench length, our total mass
fluxes for sediment Ž1.8 = 10 15 gryear. and H 2 Oy
Ž0.86 = 10 15 gryear of H 2 O lost at 1008C. also
compare favorably to R & R’s Ž1.4 and 0.9 = 10 15
gryear respectively..
In part, the high terrigenous component of GLOSS
is due to the current plate configuration. More than
50% of the global mass flux of subducted sediment
is along four terrigenous-dominated margins:
Makran, Andaman, Sumatra and Vanuatu. With the
exception of Vanuatu, which has a large volcaniclastic section in the reference site ŽDSDP 286., these
margins include terrigenous material of the Bengal
and Indus Fans. The single most effective way to
improve GLOSS would be to obtain more bulk
analyses of these Himalayan-sourced fan deposits.
The low carbonate component of GLOSS demonstrates that subduction of marine carbonate is a
regionally restricted phenomenon; indeed, carbonates
are entirely absent along most currently subducting
margins. When the Atlantic is subducted, however,
the percentage of subducting carbonate may increase
significantly. Hence, the current plate configuration
leads to the possibility of temporally, spatially and
compositionally variable episodes of sediment injection into the mantle.
With its relatively minor percentages of biogenic
components and the predominance of terrigenous
material, it is not surprising that GLOSS is similar to
average upper continental crust ŽUCC.. Fig. 18a
Fig. 18. The elemental composition of global subducting sediment
ŽGLOSS. compared to various crustal estimates. Ža. GLOSS ŽTable 3. normalized to Upper Crustal composition of Taylor and
McLennan Ž1985. ŽTMUC., and including revisions to Ti, Nb, Ta
and Cs abundances as proposed by this study ŽPLUC. Žsee Table
5. Žb. GLOSS ) Žcarbonate, opal and H 2 O-free. normalized to
PLUC, and GLOSS normalized to the bulk continental crust
ŽBCC. composition of Rudnick and Fountain Ž1995., with revisions to Ti, Nb, Ta and Cs as proposed by this study ŽTable 5..
GLOSS ) is calculated assuming 1500 ppm Sr in carbonate Žall
other elements are assumed to have zero concentration in carbonate, opal and water..
shows GLOSS normalized to the UCC composition
of Taylor and McLennan Ž1985. ŽTMUC.. Most
element concentrations in GLOSS are within 50% of
TMUC. The largest enrichments in GLOSS are in
Ba, the middle and heavy REE, and Mn, all of which
are concentrated by marine processes: Ba and Mn by
hydrothermal and hydrogenous phases, and M q
HREE by phosphate scavenging. Elements that are
depleted in GLOSS are those that are dominantly
associated with detrital phases and are diluted by
biogenic phases: the alkalis ŽK, Rb, Na., the HFSE
ŽNb, Zr, Ta, Hf., and U, Th, and Al. In fact, the level
of dilution Ž; 25%. in these detrital elements is
consistent with the sum of biogenic and diluting
components in GLOSS Ž17% biogenic and 7% H 2 O
q ., indicating near quantitative dilution of UCC.
Elements that are equal in the two global averages
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
ŽLREE, Sr, Pb. are balanced by dilution and marine
additions Žhydrogenous and carbonate components..
7.2. Implications for the composition of the continental crust
The composition of the continental crust is one of
the most important and difficult questions in geochemistry, with far-ranging implications. The problem is rather similar to the problem of estimating a
global sediment composition, and both composites
and lithological averaging have been used to make
estimates Že.g. Shaw et al., 1967.. Oceanic sediments
and the systematics we have used to construct GLOSS
provide another perspective on continental composition, because most elements in GLOSS are ultimately derived from the upper continental crust, and
sedimentary processes average diverse compositions
very efficiently. In fact, Taylor has long championed
the use of continental sediments and loess to estimate upper crust compositions ŽTaylor, 1964; Taylor
et al., 1983.. Marine sediments may be just as useful
in estimating upper crustal abundances for elements
that are not significantly fractionated in the oceans.
GLOSS provides an independent evaluation, therefore, of various crustal estimates for detrital elements.
The most recent estimate of the bulk continental
crust composition is that of Rudnick and Fountain
Ž1995., who use Taylor and McLennan’s Ž1985.
values for the upper continental crust ŽTMUC.. Although more than ten years old, TMUC still serves
as the benchmark for crustal compositions. For many
elements, GLOSS conforms well with TMUC, as
discussed above. Some elements, however, differ
considerably: Cs is strongly enriched with respect to
the other alkalis ŽRb, K., and Nb and Ta are depleted
and Ti enriched with respect to the other HFSE ŽHf,
Zr. ŽFig. 18a..
For elements that are not fractionated by weathering, transport or marine deposition Ži.e., the detrital
elements., marine sediments may provide a more
reliable estimate of UCC composition than TMUC.
For one, there are in some cases hundreds of analyses of marine sediments from throughout the globe
with which to calculate crustal ratios. TMUC, on the
other hand, is based on a surprisingly limited database
for some elements. For example, the Nb concentra-
357
tion in TMUC Ž25 ppm; Taylor, 1977. comes from a
study conducted by Shaw et al. Ž1976., who analyzed composite samples from 4 areas on the Canadian shield. Not only were many of the composites
below the detection limit for Nb by their XRF
technique, but the four areas varied widely in Nb
concentration Ž4–50 ppm.. Shaw’s Ž1976. grand
mean thus carries a large 2-sigma uncertainty Ž26
ppm " 24.. For almost 20 years, this value has persisted as the best estimate of the UCC, long ago
detached from its uncertainty. A similar situation
may exist for Cs. Fig. 2b and Table 4 show how
pelagic and terrigenous sediments have a fairly common RbrCs of 15.4 " 0.6, which is completely distinct from the TMUC ratio of 30.
Based on GLOSS and the large marine sediment
database, we recommend revision of the upper crustal
estimates for Nb, Ti, Ta and Cs. The largest discrepancy appears for Nb, which is almost a factor of two
lower in marine sediments than in TMUC. It is
difficult to ascribe this difference to marine processes. For example, a depletion in Nb might reflect
the inability of heavy ŽNb-rich. minerals like rutile
to be transported into the deep sea, but this is
inconsistent with the Ti enrichment in GLOSS ŽFigs.
18 and 19.. Or, juvenile arc volcanic detritus could
contribute significantly to GLOSS, imparting Nb
depletion and Ti enrichment with respect to the
UCC, but these characteristics seem to be present in
all marine sediments, even those with no significant
ash component. Fig. 19 shows Nb and Ti concentrations in a wide variety of marine sediments Žfrom
pelagic clays to terrigenous turbidites.. Virtually all
marine sediments analyzed have a fairly restricted
TirNb ratio of 350 " 20, which is completely distinct from the TMUC ratio of 120 ŽFig. 19.. Given
that we can think of no logical reason why both
pelagic and terrigenous sediments should share a
common TirNb distinct from the UCC, we conclude
that the UCC estimate by Taylor and McLennan
Ž1985. requires revision. Vroon et al. Ž1995. reached
a similar conclusion, based on Nb in East Indonesian
sediments, as did Condie Ž1993., based on his compilation of juvenile crustal domains.
Because TMUC ThrAl 2 O 3 appears to coincide
very well with the marine sediment ratio ŽFig. 8a.,
and because of the abundant precise data for Al, we
use Al as a reference element. Revised Ti and Nb are
358
Table 4
Marine sediment average ratios
Cores
Sediment
type
Nbr
Al 2 O 3
sd
n
TiO 2 r
Al 2 O 3
sd
n
Rbr
Cs
sd
n
Nbr
Ta
sd
n
Indian ŽArgo A.P..
Indian ŽArgo A.P..
Western Pacific
Western Pacific
Global
Global
Lesser Antilles
Western Pacific
S. Pacific ŽTonga.
N. Pacific ŽAleut.
Indian ŽBanda.
Lesser Antilles
ODP 765, Ceno.
ODP 765, Cret.
DSDP 579, 581
ODP 801
Various pc
Various pc
DSDP 543;ODP 671
Various DSDP
DSDP 595r6
DSDP 183
DSDP 262 and pc
piston cores
carb. turbs.
pelagic clays
pelagic clays
red and rad. clays
turb. muds Žnon arc
various
terrigenous
pelagic
red clay
mostly terrig. turbidites
terrigenous
terrigenous
0.79
0.93
0.795
1.07
0.94
0.2
0.19
0.1
0.29
0.32
46
25
9
7
8
0.053
0.0613
0.039
0.061
0.052
0.046
0.037
0.01
0.011
0.014
0.026
0.007
0.009
0.004
87
55
9
23
13
32
58
13.4
16.9
11.8
15.5
2
1.4
1
2.01
4
15
9
7
11.9
12.6
21.8
15.5
1.1
1.6
4.3
2.9
8
7
9
7
0.053
0.05
0.014
0.004
33
36
14.8
14.8
16.2
18.1
17.6
14.5
2.2
1.1
3.2
2.8
0.36
2.2
19
3
7
54
2
15
0.0028 346 15.4
30
0.61
135 14.2 a
11.4
Average
TMUC
a
1.01
1
0.602
1.05
0.12
31
3
0.898
1.645
0.06
130 0.0503
0.033
15.3
13.5
16.4
2.4
1.8
Refs.
1
1
2
3,4
5
4,6
7,8
9
1 10,11,4
12,13,4
15 14
3 15,4
50
Not including NbrTa from DSDP 579 and 581.
pc s piston core; TMUC s Taylor and McLennan Ž1985. upper crust composition.
TiO 2 and Al 2 O 3 in wt%, others in ppm.
Refs.: 1s Plank and Ludden Ž1992.; 2 sCousens et al. Ž1994.; 3s Karpoff Ž1992.; 4 s Appendix A; 5s McLennan et al. Ž1990.; 6 s Ben Othman et al. Ž1989.; 7sWhite et
al. Ž1985.; 8sWang et al. Ž1990.; 9sStern and Ito Ž1983.; 10 s Zhou and Kyte Ž1992.; 11s Zhou Ž1990.; 12 s Kay and Kay Ž1988.; 13s von Drach et al. Ž1986.;
14 sVroon et al. Ž1995.; 15sStolz et al. Ž1996..
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Location
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Fig. 19. Nb and TiO 2 in marine sediments are distinct from the
upper crust estimate ŽTMUC. of Taylor and McLennan Ž1985.. If
marine sediments record the true upper crustal TirNb ratio Ža
ratio of 340 is calculated from regional averages, Table 4., then
TMUC Nb is roughly a factor of 2 too high, and Ti is 50% too
low Žbased on NbrAl 2 O 3 and TiO 2 rAl 2 O 3 in Table 4.. These
suggested revisions to TMUC are shown ŽPLUC.. ODP Site 801
sediments are pelagic clays and radiolarites only and do not
include volcaniclastics Ždata in Table A5..
then calculated from marine sediment TiO 2rAl 2 O 3
and NbrAl 2 O 3 ŽTable 4.. Cs is calculated from
RbrCs, and Ta from NbrTa in marine sediments.
Based on the compilation in Table 4, we propose the
following revisions to continental crust composition:
RbrCss 15.4 " 0.6 Žinstead of 30., Cs s 7.3 " 0.3
ppm Žinstead of 3.7., TiO 2 s 0.76 " 0.04 Žinstead of
0.5., Nb s 13.7 " 0.9 Žinstead of 25., Ta s 0.96 "
0.1 Žinstead of 2.2., and NbrTas 14.2 " 1.8 Žinstead of 11.4.. Some of these revisions are substantial: Nb, Ta and Cs concentrations change by almost
a factor of 2; TiO 2 increases by 50%. These revisions also lead to changes in other important trace
element ratios: LarNb of the UCC increases from
1.2 to 2.2; NbrU decreases from 8.9 to 4.9; RbrCs
decreases from 30 to 15. All of these revisions lead
to an even greater contrast between the UCC and the
oceanic mantle for these same element ratios.
McDonough et al. Ž1992., using sediment data
from the literature, also suggested a revised UCC
value for Cs, using RbrCs of 19. Our compilation of
more marine sediment data ŽTable 4. suggests an
even lower ratio Ž15.4., and consequently higher Cs
concentration. It is possible that processes in the
ocean further fractionate Rb from Cs, but this is
unlikely given that terrigenous turbidites and red
clays have similar RbrCs ratios, and that weathering
359
does not seem to fractionate RbrCs ŽMcDonough et
al., 1992..
Because recent estimates for the bulk continental
crust ŽRudnick and Fountain, 1995. use Taylor and
McLennan’s upper continental crust composition,
these estimates require revision as well for Nb, Ta,
Ti and Cs ŽTable 5.. The largest changes would be to
Nb and Ta, both of which are decreased by about
30%. Again, this leads to 30% increase in LarNb
Žfrom 1.5 to 2.1. and a 30% decrease for NbrU
Žfrom 8.4 to 6.0. for the bulk continental crust
ŽBCC..
With these revisions to UCC and BCC, the distribution pattern for GLOSS relative to continents is
much smoother ŽFig. 18a, solid dots., with Nb, Ta
and Ti behaving more like the other HFSE Hf and
Zr, and Cs more like the other alkalis. The HFSE in
particular are virtually identical between UCC Žrevised. and non-biogenic GLOSS Žrecalculated free of
carbonate, opal and H 2 O q .; after removing these
diluents, HFSE, SiO 2 , Al 2 O 3 , Na 2 O and Sr all plot
at or near 1 in Fig. 18b.
The differences between GLOSS and BCC potentially affect the chemical evolution of the continents.
Subduction of sediments with the composition of
GLOSS will fractionate certain trace elements ratios
in the BCC, independent of other processes such as
continental growth or lithospheric foundering. For
example, GLOSS has higher BarRb, LurHf, and
PbrU than the continental crust, and so sediment
Table 5
Revised continental crust composition
TMUC
Revised UCC
Žqry.
BCC-R and F
Revised BCC
Nb Žppm.
TiO 2 Žwt%.
Cs Žppm.
Ta Žppm.
25
13.7
Ž0.92.
12.00
8.50
0.5
0.76
Ž0.043.
0.700
0.750
3.7
7.3
Ž0.29.
2.60
3.00
2.2
0.96
Ž0.12.
1.1
0.7
TMUC s Taylor and McLennan Ž1985. upper crust composition.
BCC s bulk continental crust; R and F sRudnick and Fountain
Ž1995..
Revised upper continental crust ŽUCC. values calculated from
ratios in Table 4, using TMUC Al 2 O 3 Ž15.2%. and Rb Ž112 ppm..
Uncertainties calculated from standard deviations of the mean
ratios in Table 4.
Revised bulk continental crust ŽBCC. values calculated from
revised UCC and middle and lower crusts given in R and F.
360
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
subduction could lead to a decrease in these crustal
ratios through time. Nonetheless, GLOSS is remarkably similar to BCC for many element abundances
and ratios ŽRbrSr and SmrNd., more similar than it
is to UCC ŽFig. 18b., and so as a first approximation, sediment subduction can be modeled as a quantitative loss of mass, with little fractionation of many
elements.
7.3. Implications for the role of sediment recycling in
mantle eÕolution
While sediment subduction may impart some subtle chemical effects on the evolution of the continental crust, it has a potentially greater effect on the
chemical evolution of the mantle. The crustal and
marine processes that produce GLOSS lead to very
different geochemical characteristics from the mantle, and the continuous injection of sediments can
impact mantle evolution and create enriched compositional domains within the mantle. The logical place
to look for the effects of sediment subduction in the
mantle are in the enriched compositions of ocean
island basalts ŽOIB.. In fact, most models for the
creation of EM-I and EM-II OIB sources call upon
some form of crustal recycling to explain the high
87
Srr 86 Sr and low 143 Ndr 144 Nd compositions. Taking this further, Weaver Ž1991. suggested that EM-I
and EM-II mantle reservoirs are derived from subducted pelagic and terrigenous sediments, respectively, based largely on a presumed difference in
BarTh. Although subducted sediments should create
chemical heterogeneities in the mantle, and although
there are large variations in sediment compositions,
we do not find evidence for a clear chemical signal
distinguishing ‘pelagic’ and ‘terrigenous’ sediments.
Specifically, Fig. 20 shows that there is no obvious
difference between BarTh in pelagic sediments
Žwhich span the global range. and terrigenous sediments. Instead, sediments with high BarTh tend to
be clays with a large hydrothermal component, and
some biogenic sediments Ždiatom oozes and carbonates.. Given the possible lack of a biogenic mechanism to fix Ba in the ancient recycled sediments that
may now be feeding EM-I and EM-II plumes, the
primary mechanism for increasing BarTh in the past
might have been hydrothermal. Further complicating
the picture, a more recent study by Woodhead and
Fig. 20. BarTh in pelagic and terrigenous marine sediments Žfrom
lithologic means in Table 1.. Data were binned from the midpoints of the plotted intervals Ži.e., the ‘0’ bin s 0–12.5; the ‘25’
bin s12.5–37.5, etc... Note that pelagic sediments span the global
range in BarTh, and that there is in fact no clear difference in
BarTh between pelagic and terrigenous sediments, contrary to
suggestions in Weaver Ž1991..
Devey Ž1993. does not find the same high BarTh in
EM-I lavas from Pitcairn seamount, and so calls into
question the correlation between Ba-enrichment and
the isotopic characteristics that traditionally define
EM-I mantle. Since Ba behaves erratically in marine
sediments, it is not surprising that it does not correlate simply with other trace element ratios, such as
the parentrdaughter ratios, UrPb and ThrPb. Thus,
lack of a simple geochemical fingerprint does not
rule out subducting sediments as an important component to isotopic and trace element heterogeneity in
the OIB mantle. A better understanding of the nature
of marine sediment variability through time should
allow a more accurate assessment of the role of
different sedimentary provinces in OIB reservoirs.
Some have argued recently that other trace element ratios preclude significant mixing of sediment
into the mantle. For example, McCulloch and Bennett Ž1994. point out that because sediments and arcs
have similar NbrU Ž- 10., the arc simply inherits
the sediment ratio and low NbrU sediment is returned to the mantle. Because these low ratios are
rarely observed in MORB or OIB Žwhich are virtu-
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
ally uniform at NbrU of 47 " 10, Hofmann et al.,
1986 and Hofmann, 1997., this presents a problem
for large-scale sediment recycling. This argument,
however, is not valid without considering the mass
fluxes across the subduction zone and the preferential loss of some elements out of the sediment ŽU in
this case.. If the mass flux of subducted sediment is
very small relative to the arc magma flux and most
of the Nb comes from the mantle wedge, then the
entire U budget in the sediment could be required to
lower the NbrU in the arc source from the mantle
ratio of 47 to - 10. If this occurred, then the
sediment residues recycled into the deeper mantle
could have much higher NbrU than sediment at the
trench, and so create fewer problems for recycling
models. Thus, a complete consideration of fluxes
across the subduction zone are critical to the problem. Such a flux balance is beyond the scope of the
current paper, because it requires consideration of
each margin and each element individually, and is
discussed elsewhere ŽPlank, 1993; Plank and Langmuir, in prep.. Suffice it to say that the CerPb and
NbrU of the sediments following subduction processing may be substantially higher than the trench
sediment, and that this relaxes considerably the negative implications for sediment recycling that have
been recently proposed by McCulloch and Bennett
Ž1994..
Not all elements, however, are influenced significantly by subduction zone processes. In particular,
the role of sediment recycling for elements that are
the least mobile in fluids, such as the HREE and the
HFSE, can be treated to first order from GLOSS
alone. Lu and Hf are two such elements.
7.3.1. Lu–Hf constraints
Arc basalts are not preferentially enriched in Lu
and Hf, and hence significant fluxes from the slab
are not required to account for the abundances of
these elements. In this case, therefore, ratios in subducting sediment may approximate those in fully
recycled materials.
Patchett et al. Ž1984. set out to study the consequences of sediment subduction on the Lu–Hf and
Sm–Nd isotopic systems, providing the first comprehensive analyses of Hf and REE in sedimentary
samples. They noted a large fractionation of Lu from
Hf in the sedimentary system: continental and shelf
361
Fig. 21. SmrNd and LurHf in bulk trench sediments ŽTable 2.
and GLOSS ŽTable 3.. CHUR is the chondritic uniform reservoir.
Fields for sediment types from Patchett et al. Ž1984.. Permissible
compositions are calculated for f LurHf r f SmrNd s1.3–1.7 Žsee
footnote to table 1 in Patchett et al. Ž1984. for definition of f LurHf
and for CHUR values..
sediments have low LurHf Ždue to detrital zircon.
and pelagic red clays have high LurHf Ždue to a
lack of zircon and REE precipitation from seawater.
ŽFig. 21.. They calculated a global mean for currently subducting sediments based on areal distributions of pelagic sediments, and arrived at LurHf and
NdrHf ratios that failed to reproduce the mantle
array ŽMORB-OIB.. They concluded that subduction
of predominantly pelagic sediments is inconsistent
with mantle Hf and Nd isotopes; red clays in particular have such high LurHf and NdrHf that they
would produce higher e Hf than are ever observed in
mantle-derived magmas. From their calculations, the
only permissible sediment that could be mixed into
the mantle and produce the observed MORB-OIB
array would contain a large terrigenous turbidite
fraction, and would have to have mean sediment
values of NdrHfs 4–6 and f LurHfrf SmrNd s 1.3–
1.7 Žsee Patchett et al., 1984 for definition of f LurHf ..
Patchett et al. considered mixing of turbidites and
pelagic sediments to be unlikely, because they may
be deposited far from one another in the ocean and
may be difficult to mix during mantle convection.
Thus, Patchett et al. Ž1984. concluded that LurHf
fractionation places a severe restriction on the ability
of recycled sediments to explain the range in mantle
isotopic composition.
362
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Patchett et al. Ž1984. emphasized the considerable
physical difficulties in mixing together turbidites
from one site on the ocean floor with pelagics from
another. Much of their discussion, however, is based
on the distribution of surface sediments, where there
are indeed great distances between different sedimentary provinces. The total sedimentary column,
however, contains a larger diversity of sedimentary
materials, because of the thousands of kilometers
traversed by the plate in its journey from ridge to
subduction zone. Plate movement produces total sedimentary columns that contain far more lithologies
than would be evident from the surface sediments
alone. For these reasons, many of our subducting
sediment columns have Lu–Hf parameters similar to
terrigenous sediments ŽFig. 21., even though almost
all contain some pelagic sediments.
Clearly, calculations of the mean composition of
entire sediment columns are more pertinent to the
LurHf problem than estimates from surface samples
alone. Lu and Hf estimates for subducting sediment
are included in Table 2. ŽWhile Hf data are missing
for some column components, it can be confidently
estimated from the common sediment ZrrHf ratio of
35; see Fig. 10b.. Because GLOSS consists of both
deep sea clays and terrigenous turbidites Žsee above.,
the LurHf parameters for the mean subducting sediment ŽNdrHfs 6.8 " 2, and f LurHfrf SmrNd s 1.62.,
are generally within the range that Patchett et al.
calculated for successful sediment recycling models
Žsee above., and far removed from the values for
p elag ic sed im en ts alo n e Ž N d r H f s 1 2 ,
f LurHfrf SmrNd s 0.5.. NdrHf in GLOSS is slightly
high, but falls within the uncertainty of the target
range. In addition, the Ce anomalies and Nd isotope
compositions of arc volcanics require that some Nd
be removed from the slab, which may lead to lower
NdrHf in the sediment returned to the mantle.
Therefore, the globally averaged subducted sediment
could explain the MORB-OIB e Hf– e Nd array.
There are still a few pelagic sections with very
high LurHf ŽFig. 21., such as the sediments being
subducted at the Tonga trench. Such sections of red
clay are necessarily condensed and thin, however,
because they are the result of very slow rates of
sedimentation. For example, the Tonga section is a
mere 70 m, and hence represents a very small volume, a virtual point source of high LurHf that might
easily be lost and smeared out in the mantle. Conversely, terrigenous sections with lower LurHf are
often very thick Že.g. Makran, Andaman, Sumatra,
Antilles., and so constitute a large volume that will
be more important in the recycling process.
One other aspect pertinent to the LurHf problem
concerns the potential effect of biological processes
on the large REE enrichments observed in red clays.
While mechanical separation of zircon does produce
significant fractionation of LurHf during sedimentary processes, it does not account for the extreme
values of LurHf in red clays. These extreme enrichments are currently linked to phosphorous ŽFig. 6a.,
and specifically to an abundance of fish debris,
which effectively scavenges the REE from sea water
ŽToyoda et al., 1990; Elderfield and Pagett, 1986..
Since fish and phosphate shells are a Phanerozoic
phenomena, the large enrichments in the red clays in
the ocean today might not be a feature of the ancient
pelagic sediments that contribute to current mantle
reservoirs.
Based on these various considerations, the LurHf
systematics in the mantle may not pose significant
problems for the hypothesis of sediment recycling
over much of earth history.
7.4. Implications for continental growth and the size
of the plume reserÕoir
von Huene and Scholl Ž1991. noted that the current rate of sediment subduction is approximately 1.5
km3ryear, but after various corrections, they suggested a better long term average was 0.7 km3ryear.
They added an average of 0.9 km3ryear from subduction erosion to arrive at a total of 1.6 km3ryear,
which is virtually the same as Reymer and Schubert’s
Ž1984. estimate of the magmatic continental growth
rate Ž1.65 km3ryear.. Other estimates of continental
recycling are lower. Rea and Ruff Ž1996. and Hay et
al. Ž1988. calculate independently the subducted sediment rate at 0.54 and 0.38 km3ryear, respectively,
although Hay’s estimate is integrated over the maximum age of the oceanic crust Ž180 Ma.. McLennan
Ž1988. uses the recycling model in Veizer and Jansen
Ž1985. along with Nd model ages of sedimentary
rocks to estimate the subduction rate of sediments at
0.75 km3ryear, including some tectonic erosion. The
estimates in this paper sum to 0.51 km3ryear for the
70% of the total trench length that we have consid-
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
ered, or about 0.73 km3ryear globally Žnot including
any tectonic erosion.. Thus, current sediment subduction values seem to be converging at 0.5–0.7
km3ryear. The total recycling of continental material, however, includes tectonic erosion of forearcs,
and large uncertainties still exist in the magnitude of
this process. von Huene and Scholl Ž1991., who have
studied this process in some detail, suggest that
tectonic erosion exceeds the incoming sediment subduction rate. If this is true, then the net effects of
subduction and the addition by igneous activity are
approximately balanced, and continental mass is currently at steady-state. Clearly, further study is needed
to determine the mass and composition of tectonically eroded material.
Even if continental mass is at steady-state, the
crust and mantle may still chemically evolve. While
sediments contribute significantly to some element
budgets in arc lavas Že.g. for Pb., the main mass of
arc magmas is not derived from sediment, but from
the mantle. Hence, current recycling would be returning modified continental material to the mantle,
while extracting primarily basaltic material into the
crust. Taken at face value, current processes lead to
the gradual enrichment of the mantle in incompatible
elements and modification of the continental crust to
more basaltic compositions, both because of basaltic
additions via volcanism and felsic subtraction due to
sediment subduction. These combined processes lead
to even greater problems in making the
intermediate-felsic continental crust at convergent
margins Že.g., Ellam and Hawkesworth, 1988; Rudnick, 1995.. Quantifying the net effects of recycling,
however, requires knowledge of the sediment composition after it has contributed to arc volcanism,
which in turn requires experimental data and detailed
studies of crustal inputs and magmatic outputs at
subduction zones.
Given the composition of GLOSS, and extrapolating it back through time at a constant rate, we can
consider some of the possible long term consequences of sediment subduction. Over 1.6 Ga, subduction of 1 km3 of sediment per year would contribute ; 0.1% by mass to the entire mantle. This
proportion scales directly with the duration of subduction and with the proportion of interactive mantle. For example, for 3.2 Ga of subduction and for
50% of the mantle interacting with the plates, the
363
sediment proportion would be 0.4%. Bulk sedimentmantle mixing calculations result in a maximum of
about 2% sediment addition to the depleted mantle to
create the Nd and Hf isotopes of enriched OIB
mantle ŽPatchett et al., 1984.. While it is possible to
create this OIB source Žwith 2% sediment. by accumulating 4 Ga of subducted sediment at 1 km3ryear
into 10–20% of the mantle, more reasonable box
models involving continuous injection of slabs along
with continuous removal of plume material would
require even more massive sediment recycling in the
past.
8. Conclusions
The strong link between geochemical and lithological variations in marine sediments provides the
basis for calculating the bulk composition of sedimentary columns from a small number of chemical
analyses. Given the existence of Ža. a drill core, Žb.
abundant lithological data Ždetailed core descriptions,
smear slide modal analyses, logs., and Žc. a few
chemical analyses for each main lithological unit,
and given the simplifying systematics of biogenic
dilution and common trace element ratios, a bulk
composition can be calculated with some confidence
Žgenerally to within 30%.. Based on these approaches, different sedimentary columns show clear
regional differences in chemistry and lithology. There
is no common stratigraphy to all deep sea sediment
columns; each regional sedimentary province Žon the
order of 1000 km. possesses its own geochemical
fingerprint. Within a given sedimentary province,
however, the same general stratigraphy persists, and
so even a single drill core can capture the regional
geochemical characteristics of the sediments.
Estimates for the chemical fluxes attending sediment subduction are useful to a number of larger
scale problems. For example, the geochemical composition of arc volcanics seem to reflect the chemical
fluxes from the local subducting sediment. A global
subducting sediment ŽGLOSS. composition can be
calculated by considering all trench sections with
adequate data. GLOSS is dominantly terrigenous,
and therefore similar to upper continental crust in
many ways. Marine processes, however, lead to perturbations on the crustal inputs; Ba, Pb, Sr and the
REE are enriched in GLOSS with respect to the
364
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
alkali and high field strength elements. For detrital
elements, which are least fractionated during erosion
and deposition in the oceans, marine sediments may
provide an independent means to estimate the average composition of the upper continental crust. Based
on over a hundred existing analyses of marine sediment, we suggest important revisions to the current
upper crustal values for Cs, Nb, Ta and Ti. Finally,
GLOSS should prove useful to models of crust–mantle recycling. One example involves a re-analysis of
the coupled Hf–Nd isotopic systems. The Lu–Hf–
Sm–Nd composition of GLOSS provides fewer
problems to deep sediment recycling than previously
thought. Consideration of other isotopic systems requires following the sediments through the subduction process, and documenting the elemental losses
to the arc.
Acknowledgements
We thank the many people who helped us by
generously giving of their time and expertise: John
Compton, Marty Fleisher, Jim Bishop, Paul Baker,
Mitch Lyle, Nathan Bangs, Neal Driscoll, Geoff
Abers, Bill Ryan, David Scholl, Mike Bevis and
John Beavan. Thanks to Bill White, Bob and Sue
Kay, Flip Froelich, and Anne-Marie Karpoff for
providing splits of samples, and to Lei Zhou, Frank
Kyte, Sue Karl, and David Rea for providing
preprints at various times during this project. Michael
Carr and David Peate very generously provided unpublished data. Thanks to Ginger Eberhart-Boitnot,
Mike Cheatham, Dana Stuart and Nate Williams for
technical help. Chris Hawkesworth, David Rea and
Bill White provided very useful reviews. Thanks to
Tim Elliott for a final read and helpful comments.
We acknowledge the Lamont and ODP Pacific core
repositories, and Rusti Lotti and Jerry Bode for their
help. T.P. gratefully acknowledges support from the
Joint Oceanographic Institutions for a Graduate Fellowship and the National Science Foundation for a
Post-Doctoral Fellowship; C.L. acknowledges grants
from the Ocean Sciences Division of the National
Science Foundation.
Appendix A
New analyses of marine sediments appear in Tables A1–A6. Sediment samples were analyzed by
direct current plasma ŽDCP. emission spectrometry
at Lamont Doherty Earth Observatory following
methods described in Plank and Ludden Ž1992..
Most sediment samples had been analyzed previously for trace elements ŽBen Othman et al., 1989;
Kay and Kay, 1988., so our major element data
complete the data set. DSDP Site 595r596 samples
were analyzed for REE by DCP Žfollowing methods
outlined in Miller et al., 1992. and for Pb concentration and isotopes by TIMS Žchemistry at Woods
Hole Oceanographic Institution and mass spectrometry at Cornell University.. ODP 801 samples were
analyzed by ICP-MS at Cornell University Žfollowing methods outlined in Elliott et al., 1997.. Further
details on sample preparation and sample splits appear in table footnotes.
Appendix B. Calculation of bulk sedimentary
compositions subducting at the world’s trenches
Bulk compositions for each sedimentary section
are calculated by first considering the individual
lithologies down-core ŽFig. 11; Table 1., then calculating a weighted mean for each site by averaging
each lithology by mass ŽTable 2.. The details of the
calculations are discussed below. Unless otherwise
noted, orthogonal convergence rates are from von
Huene and Scholl Ž1991., hereafter VH & S. Recovery percentages ŽRec. %. are with respect to the
entire sedimentary column, and not just the sections
cored. References to drilling sites are too numerous
to include formally, and are simply given by site
number. We gratefully acknowledge all scientists
and drilling parties who contributed data for each of
the DSDP and ODP drill sites used below.
Note to Table A1:
Intervals in cm. Depth in core in m. Samples powdered in agate. Analyses reported relative to weight at 1108C. These data are used for the
Tonga sediment mean.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
365
Table A1 DCP analyses of sediments from DSDP Sites 595 and 596 Žeast of Tonga.
Site
Core, sect.
Interval
Depth
Color
Lithology
595A
1,1
47–50
0.47
Yell bwn
Clay
596
1,1
105–108
1.05
Yell bwn
Clay
595A
1,4
87–90
5.37
Bwn
Clay
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
48.40
0.913
16.90
9.71
1.009
2.81
2.24
5.48
2.322
0.460
9.75
51.92
0.827
16.23
8.05
0.900
3.95
1.94
4.66
2.775
0.225
8.52
Sr
Ba
Zr
Y
Cu
Ni
V
Cr
Zn
Sc
210
227
133
92.6
200.5
98.6
155
17.7
57.8
25.4
Site
Core, sect.
Interval
Depth
Color
Lithology
596
1,CC
5.5
Med bwn
Clay
595A
2,3
57–60
6.37
Bwn blk
Clay
596
2,2
65–69
7.65
Yell bwn
Zeol Clay
595A
2,6
128–130
11.58
Dk bwn
Clay
49.65
0.913
16.10
9.09
1.312
3.85
1.76
5.21
2.770
0.294
9.06
48.68
0.917
16.63
9.78
1.000
2.84
2.16
5.37
2.533
0.450
9.64
41.05
0.668
12.38
11.36
4.394
3.49
4.59
5.17
1.897
2.651
12.35
49.02
1.018
16.58
10.92
0.741
3.24
1.85
5.18
1.804
0.229
9.41
216
512
112
35.4
145.0
88.9
152
64.7
63.5
16.5
236
393
132
52.0
167.5
122.6
169
56.3
51.6
18.1
203
251
129
88.4
208.8
114.3
179
30.2
72.9
23.7
350
581
239
416.9
290.0
484.4
216
43.9
65.5
41.5
595A
3,3
95–97
16.15
Dk bwn
Clay
596
3,1
115–117
16.25
Bwn blk
Clay
596
3,5
70–72
21.8
Dk bwn
Clay
596
3,5
80–82
21.9
Dk bwn
Clay
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
49.41
0.599
14.79
7.29
2.977
3.21
2.22
4.79
3.441
1.214
10.06
39.39
0.733
11.66
11.39
4.554
3.54
5.66
5.35
1.797
3.349
12.58
50.59
0.594
15.03
6.72
2.539
3.19
1.72
4.53
3.855
0.877
10.36
Sr
Ba
Zr
Y
Cu
Ni
V
Cr
Zn
Sc
228
567
154
260.4
291.1
437.5
137
24.8
69.0
31.4
389
633
262
576.0
321.8
626.5
226
33.3
67.3
51.8
189
477
147
187.7
256.1
399.6
136
28.3
77.4
27.9
595A
2,CC
12.2
Dk bwn
Mn nod
596
2,6
70–72
13.7
V dk bwn
Clay
595A
3,2
68–72
14.38
V dk bwn
Clay
49.75
0.658
16.16
7.28
1.703
2.73
2.48
5.29
3.588
1.238
9.13
17.84
2.009
7.52
24.54
23.406
3.12
2.86
2.84
.718
0.811
14.34
43.70
0.692
13.95
9.71
3.294
3.24
4.88
4.76
2.280
2.954
10.54
43.93
0.672
13.84
6.84
2.588
3.19
6.29
4.88
2.833
4.005
10.92
174
158
92
42.2
224.5
77.7
159
10.5
71.0
26.8
206
318
124
178.0
200.2
249.2
142
42.5
46.5
21.8
920
1285
671
232.2
1329.2
2147.3
522
24.1
324.5
24.6
326
369
188
549.2
180.9
423.6
172
29.8
44.6
40.7
345
460
217
658.0
174.5
515.2
143
32.1
43.1
54.8
596
3,5
90–91
22
Dk bwn
Clay
596
3,5
100–102
22.1
Dk bwn
Clay
595A
4,1
20–25
22
Dk bwn
Clay
596B
1,2
68–71
26.88
Yell bwn
Clay
595A
4,7
3–5
30.83
Bwnryell
Clay
595A
5,1
74–76
32.14
Bwn
Clayrchrt
50.68
0.609
15.11
6.80
2.523
3.21
1.78
4.34
3.802
0.913
10.24
51.43
0.604
14.93
6.70
2.552
3.16
1.73
4.51
3.837
0.895
9.65
50.92
0.609
14.99
6.81
2.551
3.22
1.76
4.33
3.822
0.884
10.1
49.79
0.761
14.02
7.36
2.528
3.37
2.20
5.03
3.278
1.045
10.62
52.77
0.842
14.67
7.39
1.242
3.29
2.40
4.33
3.579
1.200
8.3
49.43
0.774
13.76
7.95
2.860
3.48
3.25
4.87
2.784
1.530
9.31
61.55
0.288
8.11
7.48
2.096
2.83
1.84
4.23
1.825
0.913
8.84
195
485
144
195.8
260.2
405.2
129
27.2
79.5
28.9
198
493
148
186.4
257.5
357.6
129
24.2
70.3
28.8
195
484
145
186.8
259.9
434.2
133
86.8
81.2
28.2
247
573
175
247.6
315.5
462.7
122
25.9
60.7
30.1
233
317
185
282.7
381.8
301.4
102
26.2
78.5
33.9
300
639
198
327.9
558.4
433.0
118
29.7
79.1
37.9
210
602
95
125.6
417.8
187.9
86
18.5
56.2
17.4
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
366
Table A1 Žcontinued.
Site
Core, sect.
Interval
Depth
Color
Lithology
596B
1,6
80–83
33
Dk bwn
Clay
596
5,2
114–116
36.94
Dk bwn
Clayrchrt
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
47.38
0.538
12.69
10.58
3.258
3.69
2.82
4.49
2.532
1.404
10.62
Sr
Ba
Zr
Y
Cu
Ni
V
Cr
Zn
Sc
595A
5,CC
38
Yell bwn
Porcell
596
5,4
99–101
39.79
Bwn
Clayrrads
596
5,5
18–20
40.48
Bwn
Clayrporc
596
6,1
96–98
40.76
Bwn
Clay
596
6,5
104–106
46.84
Dkryell
Clay
51.49
0.434
11.71
9.39
2.861
3.23
2.47
4.68
3.028
1.235
9.48
88.76
0.108
2.03
2.07
0.506
0.89
0.62
1.16
0.297
0.245
3.31
78.07
0.206
5.19
3.21
0.616
1.97
0.98
2.74
0.954
0.495
5.57
89.99
0.103
1.67
1.80
0.413
0.69
0.50
1.16
0.355
0.262
3.06
46.95
0.634
12.70
9.81
3.177
3.69
3.17
4.94
2.442
1.529
10.96
293
850
192
271.0
605.8
488.5
186
20.8
0.0
30.6
271
654
171
193.2
507.3
256.4
131
14.9
79.0
28.6
51
115
32
29.9
128.1
34.7
14
3.3
40.4
3.7
87
149
46
53.3
236.2
82.7
25
3.8
40.9
10.1
46
117
21
25.1
98.9
25.5
15
y0.5
30.3
3.9
304
776
162
303.5
452.0
472.9
166
24.7
69.1
32.6
Site
Core, sect.
Interval
Depth
Color
Lithology
595A
9,1
70–74
60.9
Dk bwn
Clayrchrt
596A
1,1
70–75
66.7
Dk bwn
Clay
596
9,1
20–23
68.8
Dk bwn
Clayrchrt
596A
1,5
97–101
72.97
Black
Clay
SiO 2
TiO 2
Al 2 O 3
FeO )
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
42.66
0.245
2.68
26.14
8.201
2.04
3.04
3.37
0.630
0.809
10.18
37.93
0.197
2.99
26.38
7.535
3.71
2.93
4.22
1.119
1.178
11.8
59.41
0.148
1.79
17.63
5.589
1.91
1.41
2.84
.510
.360
8.39
11.50
0.237
2.88
51.31
15.797
1.73
4.63
1.81
0.442
2.332
7.33
Sr
Ba
Zr
Y
Cu
Ni
V
Cr
Zn
Sc
894
19359
142
131.6
622.1
211.2
502
20.6
203.6
12.4
898
24404
177
164.2
650.9
172.6
426
7.2
166.4
11.9
535
11262
96
76.9
455.1
165.7
422
15.0
256.4
8.4
960
22435
227
242.6
628.2
207.2
541
8.1
85.1
18.1
595A
7,CC
50.6
Yell bwn
Chert
595A
8,1
107–110
51.67
Yell
Chert
595A
8,5
100–103
57.6
Yell
Chert
60.22
0.305
8.95
6.77
1.891
2.88
2.05
4.54
2.094
1.035
9.25
89.00
0.102
2.16
1.46
0.551
0.68
0.58
1.09
0.396
0.268
3.71
90.05
0.115
1.68
1.96
0.759
0.67
0.47
1.02
0.299
0.225
2.76
78.50
0.253
4.82
3.44
1.330
1.41
0.96
2.42
1.125
0.463
5.27
210
485
113
134.5
347.3
167.8
80
41.5
63.0
18.6
52
161
30
34.9
123.0
43.7
13
1.0
42.2
4.6
98
3344
26
29.2
117.0
40.9
18
0.9
52.5
4.4
152
3424
57
75.6
180.1
146.3
52
11.4
53.0
10.5
Table A2
REE, Rb and clay mineralogy in Tonga sediments
596
595A
596
596
595A
596
596
595A
596B
596
596
596
595A
595A
596A
Core
Top
Depth Žm.
1,1
105–108
1.05
1,4
97–90
5.37
2,2
65–69
7.65
2,6
70–72
13.7
3,3
95–97
16.15
3,5
70–72
21.8
3,5
90–91
22
4,7
3–5
30.83
1,6
80–83
33
5,2
114–116
36.94
5,4
99–101
39.79
6,5
104–106
46.84
8,1
107–110
51.67
8,5
100–103
57.6
1,1
70–75
66.7
La
Ce
Nd
Sm
Eu
Gd
Dy
Er
Yb
Lu
Rb
27.11
68.72
28.61
6.67
1.63
6.49
6.59
3.97
3.73
0.596
19.80
41.12
25.48
6.62
1.93
7.63
8.05
4.75
4.43
0.702
37.6
307.58
483.48
376.68
84.62
19.77
92.24
84.97
49.65
40.16
6.055
132.85
319.15
160.05
37.06
8.65
39.73
36.12
20.54
16.55
2.489
230.79
327.69
283.54
62.56
14.97
69.11
60.65
33.99
28.27
4.259
44.9
45.93
68.66
54.89
11.82
3.10
12.62
11.60
6.75
5.82
0.882
104.11
129.47
118.49
25.51
6.39
28.62
25.96
15.24
13.40
2.032
27.5
25.23
25.68
26.20
5.79
1.49
6.13
5.83
3.48
3.02
0.483
18.6
133.66
38.08
124.03
24.78
6.31
27.91
26.24
15.71
14.22
2.142
9.2
206Pbr
204Pb
207Pbr
204Pb
208Pbr
204Pb
19.09
18.80
19.12
18.56
15.65
15.64
15.66
15.53
38.63
38.72
38.57
37.94
88
102.4
65.0
Pb ŽID-TIMS.73.34
Smectite
Illite
Kaolinite
Qtz
Zeolite
Plag
K-spar
1
2
2
3
0
3
2
3
0
1
2
2
0
2
2
0
2
2
2
2
3
51.4
2
0
2
1
1
2
2
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Site
REE Žppm. by DCP at LDEO following cation column separation after Miller et al. Ž1992..
Rb by DCP at LDEO.
Clay mineralogy courtesy of John Compton ŽUniv. S. Florida, St. Petersburg..
Clay abundance codes: 0 s none; 1s little; 2 ssome; 3sabundant.
Pb by TIMS Žchemistry at WHOI and mass spectrometry at Cornell..
These data are used for the Tonga sediment mean.
367
368
Table A3
DCP analyses of piston core sediments in Ben Othman et al. Ž1989.
V14-55
260
S. Sand.
Trench
V14-56
220
S. Sand.
Trench
V14-57
220
S. Sand.
V14-58
470
S. Sand.
V14-60
220
S. Sand.
Near ridge
EN20-18
101–107
N. Antilles
Fore-arc
V25-5
31–33
NW Atl.
V22-18
5
Puerto Rico
Trench
V15-190
0
Puerto Rico
Trench
GS7605-61 GS7605-65 GS7605-48
240–247
100–107
50–57
Antilles
Antilles
Antilles
Abyssal
Tobago tr
Color
Lithology
Latitude
Longitude
Water depth
Powder
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
Gray
Diat clay
57.58 S
23.97 W
7648
same
65.91
0.614
11.08
6.63
0.152
2.42
4.03
3.41
1.14
0.082
4.53
Brown
Sandy clay
57.57 S
23.97 W
5134
same
63.68
0.624
12.51
6.09
0.170
2.27
3.32
4.08
1.63
0.108
5.53
Gray
Clay
54.57 S
17.10 W
4978
same
64.69
0.581
11.66
5.54
0.171
2.49
2.10
3.75
1.89
0.095
7.04
Lt gray
Foram clay
57.61 S
13.60 W
3543
same
33.96
0.390
7.53
3.81
0.140
1.54
25.29
2.81
0.80
0.059
23.68
White
Diatomite
55.13 S
4.95 W
3193
re-sample
74.76
0.070
0.96
0.52
0.011
0.61
7.62
2.08
0.15
0.037
13.19
Br cream
Foram marl
17.45 N
60.03 W
4030
chips
21.94
0.310
7.20
2.86
0.148
1.74
31.12
2.10
1.18
0.088
31.31
Lt brown
Clay
28.73 N
61.05 W
5813
same
52.24
0.821
18.58
7.39
0.745
3.48
1.09
3.89
3.60
0.211
7.96
Yell brown
Marly clay
19.55 N
66.83 W
8021
same
40.91
0.532
12.60
4.93
0.248
2.38
14.75
2.42
1.72
0.141
19.37
Brown tan
Silt
19.83 N
65.88 W
8341
same
49.03
0.762
17.75
7.13
0.279
3.39
4.36
3.17
2.72
0.176
11.23
Tan gray
Silty clay
14.25 N
52.17 W
5100
chips
55.17
0.891
20.78
5.99
0.057
2.21
0.50
2.62
2.97
0.122
8.69
Red brown
Silty clay
14.43 N
57.65 W
5375
chips
54.00
0.797
19.69
7.18
0.512
2.51
1.05
3.41
2.64
0.155
8.06
Br gray
Foram clay
13.03 N
60.35 W
2430
chips
43.87
0.645
16.02
5.34
0.086
2.00
11.17
3.20
1.77
0.130
15.78
Sr
Ba
Sc
Zn
Ni
V
Cr
Cu
Zr
Y
109
377
19.1
820
20.8
164
22.9
75.4
65
17.7
126
567
16.9
652
22.2
137
29.9
76.9
99
21.7
130
673
14.2
721
34.6
129
36.6
81.9
93
16.5
589
570
13.6
302
16.5
85
18.5
64.3
65
13.1
223
1367
4.8
1465
11.0
14
8.1
3.6
25
5.7
1573
204
8.4
42
31.6
68
51.9
43.5
55
16.2
169
447
15.2
1713
144.5
159
103.6
150.4
164
43.3
1122
281
13.0
4065
52.1
113
101.6
64.6
94
20.8
271
373
16.9
622
76.8
158
123.4
77.2
137
29.3
118
416
14.0
94
55.5
181
82.2
88.1
174
29.5
151
429
14.2
85
66.9
169
88.9
84.2
146
28.4
544
310
14.3
76
30.9
125
61.5
45.6
111
21.8
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Core
Length of core Žcm.
Region
Setting
Table A3 Žcontinued.
GS7605-55
72–80
S. Antilles
GS7605-58
100–107
Antilles
Abyssal
V24-209
45–48
SW Ind. O.
RC14-67
103–107
Sunda
Fore-arc
V28-341
115–118
SundrBanda
Cont margin
V28-343
63
SundarArgo
Abyssal
V28-350
930
Sunda
Wharton B.
RC14-52
1420
W. Sunda
Abyssal
V33-74
322–327
Sundar
Java
Abyssal
V33-75
316–318
Sundar
Java
Fore-arc
V33-77
272–274F
Sundar
Java
Fore-arc
V33-79
33–37
Sundar
Java
Fore-arc
Color
Lithology
Olive gray
Silty sand
Br gray
Silty clay
Yell brown
Clay
Olive
Silty clay
Ol gray
Foram clay
Brown
Silic clay
Brown
Mn clay
Brown
Rad clay
Brown
Mn clay
Yell brown
Foram clay
Latitude
Longitude
Water depth
Powder
11.63 N
57.25 W
4300
chips
10.45 N
53.50 W
4908
chips
34.75 S
39.73 E
5174
same
9.47 S
122.35 E
3230
resample
9.10 S
132.18 E
750
resample
12.32 S
118.30 E
5404
resample
17.73 S
99.77 E
5383
new-IOBC b
10.00 S
12.93 S
102.63 E 106.18 E
5612
5633
new-IORC b new
Ol gray
Clay
wr gl
8.42 S
107.18 E
3396
resample
8.12 S
106.72 E
3014
adj sample
Ol gray
Clay
wr gls
7.90 S
106.40 E
3000
adj sample
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
77.23
0.712
9.89
3.05
0.024
0.89
0.75
1.61
1.58
0.080
4.18
53.39
0.846
19.47
6.38
0.056
2.02
2.04
2.83
2.66
0.140
10.16
54.02
0.900
19.84
7.19
0.095
3.23
0.45
2.53
2.67
0.121
8.94
52.88
0.730
14.05
5.18
0.126
2.83
7.26
2.88
2.19
0.137
11.73
31.76
0.461
11.31
3.59
0.114
2.56
20.50
1.95
1.70
0.145
25.91
55.76
0.688
16.46
5.86
0.312
2.93
0.76
4.58
2.50
0.146
10.01
48.23
0.796
17.24
9.63
1.920
3.12
1.87
3.77
2.70
1.078
9.65
58.64
0.620
15.37
5.02
0.070
2.44
0.85
4.36
2.37
0.094
10.16
50.12
0.781
17.85
7.85
1.872
3.35
1.86
3.24
2.42
1.151
9.51
51.27
0.754
17.74
5.65
0.071
2.28
4.71
2.85
1.64
0.110
12.92
44.87
0.684
15.76
5.73
0.074
2.45
10.36
3.19
1.21
0.129
15.54
52.10
0.691
17.35
5.64
0.085
2.46
4.00
4.20
1.99
0.145
11.35
Sr
Ba
Sc
Zn
Ni
V
Cr
Cu
Zr
Y
85
255
7.1
59
21.3
83
47.5
8.2
327
23.5
171
460
14.3
59
47.0
174
82.2
58.1
183
32.6
119
1054
14.9
138
96.7
145
129.9
99.9
141
30.0
279
317
15.8
56
60.8
119
81.9
30.9
152
29.8
797
333
10.3
85
494.4
88
71.0
602.0
87
17.4
132
814
14.2
57
70.8
126
77.0
155.9
129
26.3
184
323
21.7
67
332.0
187
80.4
240.3
169
157.2
126
1250
13.0
45
57.0
138
55.0
74.0
113
22.3
170
289
21.4
126
485.1
172
95.2
369.9
197
170.7
189
206
13.9
78
25.0
113
50.3
30.0
124
17.1
421
213
16.3
87
27.5
106
53.0
28.9
95
16.8
234
415
15.4
56
35.8
128
47.4
37.6
161
24.7
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Core
Length of
core Žcm.
Region
Setting
369
370
Table A3 Žcontinued.
V34-45
34–37
W. Sunda
V34-47
143–147
W. Sunda
V34-55
314–315
W. Sunda
90 E ridge
V34-62
0
W. Sunda
MW742-SBT4
0
C.Pac
Color
Lithology
Latitude
Longitude
Water depth
Powder
Red brown
Mn clay
10.38 S
94.00 E
5577
resample
Brown
Mn clay
6.10 S
90.62 E
5288
resample
Lt orange
Foram sand
6.03 S
88.95 E
2996
same
Mn nod
5.73 S
88.47 E
4710
same
Mn nod
8.93 N
139.90 W
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
52.70
0.604
18.18
5.89
1.120
3.96
0.87
4.74
1.91
0.305
9.72
51.87
0.651
18.49
6.26
0.666
3.84
0.72
5.11
2.30
0.180
9.91
4.13
0.038
0.85
0.33
0.019
0.33
50.47
0.85
0.16
0.044
42.78
23.26
0.855
5.85
20.09
26.498
2.02
2.98
3.32
1.56
0.822
11.88
Sr
Ba
Sc
Zn
Ni
V
Cr
Cu
Zr
Y
139
1505
17.6
94
260.3
112
54.0
367.8
182
91.2
160
2776
16.5
56
138.1
123
69.5
294.8
154
53.3
1546
812
3.6
11
7.0
10
8.1
19.6
16
22.2
1111
1235
20.7
503
2811.9
393
15.4
1566.5
612
215.4
RC17-198
7
SW Pac
Near Tonga
V18-SBT120
0
SW Pac
V21-147
35
NW Pac
Near Japan
V21-196
212
C.Pac
V24-73
22
C.Pac
Near Hawaii
chips
Brown
Mn clay
20.07 S
163.97 W
4882
same
Mn nod
12.87 S
158.32 W
5066
chips
Gray
Silty clay
39.55 N
162.02 E
5256
same
Brown
Mn clay
9.80 N
136.18 W
4819
same
Brown
Mn clay
16.48 N
166.97 W
5234
resample
15.36
0.648
5.56
7.10
44.924
3.93
2.91
2.85
0.95
0.717
12.91
48.22
0.876
16.06
9.76
1.436
3.82
2.04
5.33
2.69
0.339
9.43
43.72
1.581
15.15
10.97
9.608
1.89
2.93
2.76
4.26
0.451
6.27
58.86
0.582
13.26
7.93
0.143
2.51
1.16
3.63
2.65
0.101
9.16
52.71
0.564
13.69
8.19
1.902
3.38
2.59
3.54
3.26
1.184
8.98
52.98
0.998
16.51
7.17
0.715
3.52
2.67
4.83
3.42
0.836
6.36
667
3319
20.1
1157
7718.0
206
13.5
7426.3
549
250.4
270
1041
17.6
48
130.4
171
73.5
164.9
157
72.3
411
487
28.5
218
1143.7
189
118.6
990.2
378
109.4
135
1247
13.3
1506
84.1
114
70.2
121.9
125
21.3
370
6045
28.1
4549
568.0
120
34.7
513.5
199
246.0
236
1712
23.1
141
166.9
148
114.0
261.4
200
211.6
Samessame powder as in Ben Othman et al. Ž1989.; Chips and resampled sections powdered in agate. Oxides in wt%; trace elements in ppm.
a
Typo in Ben Othman et al. Intervals 372–374 cm.
b
IOBC ŽIndian Ocean Brown Clay. and IORC ŽIndian Ocean Radiolarian Clay. are LDEO lab standards.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Core
Length of core Žcm.
Region
Setting
Table A4
DCP analyses of samples in Kay and Kay Ž1988.
1
2-3,
50–52
6.5
Clay wrdiat
0.3812
2
9-3,
80–82
71.8
Clay wrdiat
0.1109
3
14-1,
143–145
137.43
Diat ooze
0.0641
3.A
17-3,
70–72
167.7
Diat ooze
0.15
4
21-1,
127–129
202.27
Diat wrclay
0.05
5
22-2,
73–75
212.43
Silty clay
0.0922
6
24-3,
83–85
232.83
Clay
0.1516
7.A
26-3,
76–78
251.76
Silty clay
0.1514
7B1
27-3,
10–12
260.1
Clay
0.0393
7B2
27-3,
34–36
260.34
Silt
0.0266
7B4
27-3,
87–89
260.87
Silt
0.0138
7B5
27-3,
99–101
260.99
Clay
0.0091
7B6
27-3,
115–117
261.15
Silt
0.0159
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
57.46
0.911
15.64
6.76
0.132
3.04
4.16
4.69
1.73
0.175
5.3
61.15
0.851
15.24
6.04
0.131
2.69
3.09
4.07
2.17
0.186
4.38
73.21
0.411
7.68
3.03
0.065
1.34
1.48
4.01
1.37
0.073
7.33
80.08
0.207
4.06
1.45
0.049
0.82
0.78
3.03
0.71
0.044
8.77
65.31
0.638
9.93
4.72
0.891
2.20
2.18
4.32
1.14
0.142
8.52
58.98
0.884
17.49
7.06
0.086
3.25
1.00
2.83
3.20
0.181
5.05
54.55
0.901
18.05
8.60
0.100
3.87
0.77
2.56
3.22
0.148
7.25
57.35
0.867
17.64
6.60
0.077
3.54
0.91
2.67
3.00
0.155
7.19
56.57
0.863
18.06
7.01
0.095
3.71
0.95
2.82
3.75
0.166
6
64.33
0.699
15.32
5.44
0.070
2.46
1.55
3.10
2.67
0.155
4.21
66.42
0.773
14.40
5.06
0.068
2.19
1.79
3.17
2.40
0.199
3.54
57.80
0.855
17.84
6.52
0.089
3.52
1.25
2.72
3.36
0.168
5.87
64.12
0.726
15.84
5.23
0.071
2.57
1.43
3.20
2.80
0.149
3.86
Sr
Ba
Ni
V
Sc
Cr
Zn
Cu
Zr
Y
268
1012
34.0
182
20.0
53.8
79.5
66.7
142
26.7
265
802
34.6
151
17.2
62.5
84.5
76.7
160
24.5
133
1866
23.4
55
8.9
16.9
65.9
46.2
85
12.8
107
2588
20.3
25
4.8
9.5
25.4
41.4
43
8.8
460
16382
127.0
78
22.7
21.0
34.9
130.0
163
28.0
186
933
56.6
192
15.7
107.6
121.5
86.5
132
22.9
141
680
52.5
217
17.9
109.1
129.3
55.4
126
25.1
167
743
54.0
190
15.9
105.5
126.4
63.6
130
22.5
166
837
54.4
196
16.9
107.0
138.9
69.4
123
22.6
244
783
49.9
128
11.9
84.2
105.8
30.8
114
17.9
276
753
51.7
122
11.9
88.6
78.9
26.6
175
22.0
183
825
57.2
187
17.3
108.4
106.2
71.0
130
23.0
246
771
46.0
136
11.7
83.4
97.4
49.7
116
17.8
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Sample ID
Core-sect.,
Interval Žcm.
Depth Žm.
Lithology
vD Wt fact.
371
372
Table A4 Žcontinued.
7B7
27-3,
130–132
261.3
Clay
0.04
7
28-2,
133–135
269.83
Silty clay
0.0848
7C
29-1,
124–126
277.24
Silty sand
0.0426
8
31-1,
50–52
295.5
Silty sand
0.0699
8.A
32-1,
106–108
314.06
Clay
0.0302
8B
33-CC
350
Clayey silt
0.0085
9
35-1,
144–146
389.44
Carb sand
0.0286
9A1
36-1,
86–88
416.86
Silty clay
0.0094
9A3
36-1,
135–137
417.35
Clay
0.0326
9B
37-1,
118–120
445.18
Clay
0.0666
10A1
38-1,
106–108
473.06
Clay
0.0409
10A2
38-2,
125–27
473.75
Clay
0.0426
10A3
38-2,
66–68
474.16
Clay
0.0401
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
58.18
0.850
17.51
6.48
0.082
3.33
1.19
2.81
3.27
0.166
6.13
62.12
0.803
15.94
5.59
0.080
3.01
1.55
3.23
2.67
0.174
4.83
69.16
0.615
13.70
4.13
0.066
2.04
2.03
3.32
2.24
0.122
2.59
69.56
0.662
13.42
4.04
0.072
2.07
2.15
3.22
2.13
0.134
2.54
56.14
0.877
17.38
7.00
0.082
3.65
1.09
2.77
2.71
0.171
8.13
61.01
0.802
16.57
6.08
0.072
3.07
1.29
3.11
2.52
0.192
5.29
36.64
0.382
8.24
3.50
0.337
1.79
24.68
1.64
1.17
0.210
21.4
61.84
0.775
15.81
6.17
0.077
3.04
1.79
2.96
2.41
0.307
4.83
57.13
0.875
16.80
7.06
0.074
3.44
1.23
2.93
2.30
0.146
8.01
58.04
0.790
15.11
6.41
0.072
3.02
1.56
3.25
2.25
0.152
9.34
57.90
0.860
17.70
7.12
0.095
3.71
0.98
2.59
2.94
0.161
5.93
57.48
0.874
17.26
7.29
0.109
3.71
1.01
2.62
2.77
0.159
6.72
58.53
0.868
17.24
6.79
0.098
3.56
0.99
2.59
2.75
0.173
6.41
Sr
Ba
Ni
V
Sc
Cr
Zn
Cu
Zr
Y
185
792
52.7
187
16.4
106.3
110.2
59.4
136
22.0
250
777
46.2
157
14.1
87.4
89.8
33.7
143
22.6
304
862
30.8
104
10.3
85.7
76.4
30.2
162
17.0
305
783
33.3
109
11.1
85.6
78.9
11.2
210
19.7
169
734
52.0
208
17.4
108.1
100.5
53.1
141
22.9
205
754
49.1
183
15.0
105.8
93.6
52.5
144
23.7
251
477
21.7
71
7.9
47.2
43.4
17.5
85
10.2
249
869
46.9
164
13.5
93.8
94.7
59.6
133
27.1
200
674
49.2
197
15.7
98.2
102.3
49.9
158
21.3
231
875
47.1
228
13.0
98.9
109.2
71.0
150
20.5
170
769
52.8
186
15.5
98.0
119.4
62.3
139
26.1
177
742
56.4
193
16.6
103.2
101.1
56.7
133
27.2
174
744
59.1
190
16.2
105.5
103.3
54.9
139
25.8
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Sample ID
Core-sect.,
Interval Žcm.
Depth Žm.
Lithology
vD Wt fact.
Table A4 Žcontinued.
10
38-2,
110–113
474.6
Clay
0.0423
10A4
38-3,
33–35
475.33
Clay
0.0425
10A5
38-3,
80–82
475.8
Silty sand
0.0269
10A6
38-3,
137–139
476.37
Silty sand
0.0397
11
39-1,
3–6
500.03
Silty clay
0.0286
12
39-1,
95–97
500.95
Limestone
12.A
39-1,
103–110
501.03
Clay
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K 2O
P2 O5
LOI
59.95
0.854
16.84
6.47
0.088
3.21
1.15
2.68
2.70
0.167
5.91
61.03
0.838
16.59
6.56
0.072
3.42
1.03
2.75
2.72
0.157
4.83
62.35
0.777
15.78
5.95
0.102
2.86
1.36
2.90
2.61
0.144
5.18
60.72
0.746
15.60
6.32
0.078
2.83
1.43
2.87
2.48
0.136
6.79
55.40
0.898
17.86
7.52
0.155
3.65
0.82
2.31
3.07
0.150
8.17
10.40
0.150
3.51
1.06
5.445
2.09
40.38
0.39
0.78
0.133
35.67
52.94
0.820
15.37
9.69
1.983
3.58
2.18
2.58
3.13
0.921
6.79
Sr
Ba
Ni
V
Sc
Cr
Zn
Cu
Zr
Y
198
738
46.7
173
14.1
97.9
105.1
64.7
142
23.3
181
756
81.0
181
14.4
98.3
121.8
48.7
138
21.8
234
894
42.7
147
12.2
88.6
94.2
62.8
122
19.7
227
796
44.9
160
12.9
88.9
93.4
45.3
121
19.6
153
727
60.2
209
15.9
112.5
116.7
75.4
132
25.4
840
120
64.0
33
17.3
12.2
67.4
155.3
108
35.8
222
2670
310.4
149
31.2
21.4
192.0
547.1
233
207.8
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Sample ID
Core-sect.,
Interval Žcm.
Depth Žm.
Lithology
vD Wt fact.
vD weight factor is from von Drach et al. Ž1986.. Oxides in wt%; elements in ppm. These data are used for the Aleutians sediment
mean.
373
374
Table A5
ICP-MS analyses of samples in Karpoff Ž1992.
129-801A
129-801A
129-801A
129-801A
129-801B
129-801B
129-801B
129-801B
129-801B
129-801B
129-801B
1R-1, 40
Pelag clay
red br clay
8.4
KAR-1
3R-1, 63
Pelag clay
red br clay
21.03
KAR-3
5R-1, 13
Pelag clay
yell br clay
39.73
KAR-3
7R-1, 67
Pelag clay
dk br clay
59.67
KAR-1
5R-1-50 ŽGr.
V-clastic
lt ol gray
232.2
KAR-1
5R-1, 52 ŽBr.
V-clastic
gray brwn
232.22
KAR-3
7R-1, 34
V-clastic
pale green
251.34
KAR-1
7R-1, 34
V-clastic
pale green
251.34
KAR-3
24R-1, 54
Br Rad
lt gry wr Mn
401.14
KAR-3
35R-2, 140
RadqClayst
dark red
455.2
KAR-3
35R-3, 19
RadqClayst
dark red
455.49
KAR-3
Rb
Sr
Y
Zr
Nb
Cs
Ba
72.80
180.87
134.30
185.36
16.39
5.629
251.82
101.67
239.45
307.02
186.66
13.74
7.287
353.13
91.45
180.41
265.28
148.58
11.18
6.405
309.92
105.34
162.10
108.88
134.80
11.33
7.101
282.35
20.31
293.55
13.61
127.89
19.69
0.213
43.42
9.23
481.50
23.69
197.48
30.64
0.134
79.47
46.23
257.54
14.05
169.05
33.50
0.396
198.58
49.11
266.92
16.11
169.27
30.67
0.636
201.46
39.95
72.85
17.08
51.26
4.54
2.469
2474.24
94.59
101.17
27.13
152.11
9.68
5.258
2355.87
108.45
91.71
16.56
121.71
11.32
5.994
2415.43
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
69.72
110.29
18.87
82.4
19.52
4.82
22.65
3.939
21.61
4.456
12.41
1.834
11.23
1.731
140.74
159.11
43.65
177.1
39.10
8.88
40.82
6.626
37.97
7.810
20.54
2.883
17.59
2.761
132.40
163.63
40.08
161.2
34.53
7.90
36.79
6.204
34.56
7.268
18.52
2.727
16.32
2.564
78.36
112.55
20.23
85.0
18.30
4.26
19.38
3.262
17.19
3.400
9.27
1.358
8.12
1.196
16.38
32.05
4.44
18.4
3.82
1.10
3.60
0.588
2.86
0.504
1.29
0.179
1.04
0.145
20.47
49.77
7.06
28.5
6.25
1.82
5.57
1.029
5.48
1.017
2.53
0.356
2.11
0.305
19.16
35.02
4.75
19.8
4.00
1.19
3.79
0.612
3.01
0.540
1.42
0.205
1.23
0.175
20.86
42.02
5.54
21.9
4.22
1.17
3.48
0.611
3.10
0.586
1.52
0.219
1.34
0.210
12.93
19.15
3.77
14.3
2.97
0.87
2.95
0.497
2.84
0.619
1.63
0.247
1.54
0.262
19.45
29.08
5.18
21.3
4.72
1.26
4.72
0.860
5.16
1.050
2.96
0.443
3.03
0.500
24.46
28.19
6.48
24.5
4.60
1.16
3.60
0.617
3.23
0.591
1.54
0.216
1.34
0.218
Hf
Ta
Pb
Th
U
U Žcontam. a
4.93
1.032
44.52
5.76
4.25
0.671
69.76
12.06
3.90
0.665
56.11
9.48
3.81
0.874
23.79
10.94
2.24
3.23
1.346
2.20
1.57
0.69
5.50
2.241
6.78
3.45
4.39
2.274
2.84
2.41
0.35
4.39
2.138
2.95
3.27
0.37
1.19
0.347
8.03
3.47
0.55
4.49
0.780
13.66
5.17
1.19
3.19
0.681
9.82
5.40
1.07
49.60
35.58
19.26
9.50
All concentrations in ppm relative to 1108C dry weight; KAR 1s Parr bomb digestion; KAR 3sSavillex beaker digestion.
a
Some samples appear to have been severely contamination by U during powdering or sampling.
These data are used for the Marianas sediment mean.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Hole
Core-sect., cm
Lithology
Description
Depth Žm.
Batch
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
B.1. Kermadec Trench
No drill sites exist seaward of the Kermadec
trench. Sediment thickness Ž200 m. is based on the
isopach maps of Ludwig and Houtz Ž1979.. The
Kermadec sediment section is taken to be the same
as the Tonga section Žsee below., but for an extra
130 m sediment, which is assumed to be composed
of terrigenous turbidites from New Zealand. We use
Aleutian Eocene turbidites Žsee below. as an approximation to the composition of the New Zealand
turbidites.
B.2. Tonga Trench
Reference sites: DSDP Sites 595 and 596 were
drilled only 12.5 km apart ŽRec.s 42.3% and 51.2%.,
about 1000 km east of the Tonga trench ŽMenard et
al., 1987.. Although Site 204 is closer to the Tonga
trench than 595 and 596, the sedimentary section at
204 is dominated by volcaniclastics derived from the
Louisville Seamount Chain, which may not contribute substantially to the main Tonga volcanic arc.
We take the pelagic sections drilled at 595r596 as
more representative of sediments subducting at the
Tonga trench.
Reference units: From youngest to oldest: Ž1. 11
m brown clay with zeolite Žash., Ž2. 16 m brown–
black clay rich in Fe–Mn oxides and fish teeth, Ž3.
41 m dark brown clay interlayered with chert and
porcellanite, Ž4. 2 m black metalliferous Žhydrothermal. sediment.
Sediment thickness: Only ; 70 meters of sediment accumulated at Sites 595r596 on Jurassic crust
Ž; 158 Ma, Menard et al., 1987.. Isopach maps
based on reflection data ŽLudwig and Houtz, 1979.
are consistent with this drilled section, showing less
than 100 m of sediment over basement in this region.
Unit thicknesses are based on the section drilled at
Site 596.
Sediment off-scraping: Well-developed grabens
are apparent in seismic reflection profiles of the
seafloor seaward of the trench Tonga Trench ŽHilde,
1983.. Because the throw on these grabens Žup to
500 m. is greater than the thickness of sediment
Ž- 100 m., these grabens are effective sediment
traps ŽHilde, 1983.. Dredging on the Tonga fore-arc
recovered no off-scraped oceanic sediments, only
basalts, gabbros, volcaniclastics and peridotites
375
ŽBloomer and Fisher, 1986.. We thus assume that the
complete sedimentary section is subducted at the
Tonga trench.
Geochemical data sources: Ž1. New data Žsee
Appendix A.: 36 samples from Sites 595 and 596
analyzed by DCP and a few by ID-TIMS Pb. Ž2.
Zhou and Kyte Ž1992. and Zhou Ž1990.: virtually
continuous sampling Žroughly every 20 cm. of the
upper 25 m Žentire Cenozoic section.; samples analyzed by XRF and INAA.
Unit compositions: In general, with the large
number of analyses of Site 595r6 sediments, most
units can be well approximated simply by averaging
the analyses. Although the analytical coverage is
denser for the Zhou and Kyte data, it does not extend
to below 25 m. We use the sparser DCP data for
consistency down core, and the Zhou and Kyte data
to provide data for missing elements. Details are
given below.
Ž1. Brown clay is based on the average 4 DCP
analyses for brown clay in this interval. Other elements are calculated from the INAA and TIMS data
and ratios to analog elements Že.g., Th was calculated from ThrAl 2 O 3 in the Zhou and Kyte data,
which was then multiplied by the average Al 2 O 3
from the DCP data.. Other ‘analog’ element ratios:
Rb and Cs from ratios to K, U from ThrU and Pb
from CerPb. Some elements were not determined;
throughout the core, Hf was calculated from ZrrHf
s 35; Nb from NbrTas 15.3 Žbased on an unpublished ICP-MS analysis..
Ž2. Metalliferous clay is based on the average of
12 samples from 10–30 m depth ŽDCP data.; nonDCP elements calculated as above.
Ž3. Interlayered clay r chert. This interval is estimated to be 25% chert, based on core descriptions.
Average clay from 30–58 m depth ŽDCP data. is
then diluted by 25% chert Ž100% SiO 2 .. Cs, Th, U
and Co are calculated from CsrRb, ThrAl, UrTh
and CorLa ratios in the metalliferous clay. Mean Pb
is calculated from CerPb of a sample at 46.84 m.
Ž4. Hydrothermal sediment. is the average of 4
DCP analyses from this interval, all of which have
more than 20% FeO and 10000 ppm Ba. Th and U
are calculated from ratios to Al 2 O 3 for distal hydrothermal sediment around 16 m at Site 596 ŽZhou,
1990.. Rb and Cs are calculated from ratios to K,
and Pb from CerPb, for the sample at 66.7 m.
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
376
Table A6
DCP analyses of ODP 701 sediments in Froelich et al. Ž1991.
Hole
Core, sect.
Lithology
Unit
Depth Žm.
Opal Ž%.
701A
1H-4
diat q ash
1A
5.9
94
701A
3H-4
diat q mud
1A
23.7
90
701A
6H-5
diat q ash
1A
53.7
90
701B
1H-5
diat q ash
1A
77.4
98
701B
4H-5
diat q ash
1A
105.9
82
701B
7H-4
diat q ash
1A
132.9
75
701B
9H-5
diat q mud
1B
150
99
701C
17H-5
diat ooze
1B
155.7
96
701B
13X-3
diat ooze
1D
188.4
97
701B
13X-3
diat ooze
1D
188.4
97
SiO 2
TiO 2
Al 2 O 3
FeO )
MgO
MnO
CaO
Na 2 O
K 2O
P2 O5
LOI
79.93
0.286
5.65
2.5
0.97
0.034
1.19
2.19
0.94
0.055
6.25
85.94
0.159
2.91
1.38
0.66
0.019
0.97
1.78
0.614
0.044
5.52
75.97
0.41
8.43
3.21
1.35
0.04
1.21
2.39
1.617
0.068
5.3
72.42
0.473
9.32
3.93
1.5
0.039
1.29
2.53
1.833
0.078
6.58
69.59
0.548
10.97
4.17
1.62
0.047
1.46
2.79
2.075
0.082
6.65
68.93
0.493
10.33
4.75
1.72
0.043
0.9
2.36
2.21
0.081
8.18
85.05
0.127
2.4
1.3
0.49
0.022
0.42
1.86
0.519
0.069
7.74
86.26
0.107
2.08
0.92
0.5
0.03
0.47
2.1
0.475
0.038
7.02
74.43
0.429
9.07
3.45
1.5
0.044
0.83
2.35
1.895
0.07
5.92
74.81
0.424
9.09
3.45
1.49
0.045
0.84
2.3
1.901
0.063
5.58
Rb
Sr
Ba
Sc
V
Cr
Ni
Cu
Zn
Zr
Y
27.71
76.22
847.82
7.84
73.09
17.9
13.27
61.85
38.32
46.15
7.05
17.08
54.02
530.82
3.57
29.72
6.18
7.46
30.82
22.38
31.07
4.19
52.41
109.53
1026.32
9.14
70.86
27.63
14.44
47.83
46.22
85.11
10.68
59.09
119.68
799.73
9.03
75.5
26.67
12.06
50.28
53.03
109.6
13.91
67.94
128.14
940.77
10.23
81.07
30.95
9.42
71.1
59.21
118.14
15.78
75.62
112.49
706.54
10.23
106.96
34.98
31.32
99.15
68.25
109.31
13.65
18.19
40.96
329.67
3.04
13.54
11.83
4.12
60.49
24.64
64.81
7.29
12.2
37.91
331.51
2.76
21.17
6.37
5.1
53.41
16.87
23.13
2.08
63.58
107.18
788.74
9.05
63.88
26.7
24.49
142.26
56.12
101.12
12.58
69.84
106.82
795.34
9.3
77.3
29.9
23.22
120.03
52.94
87.2
10.33
Hole
Core, sect.
Lithology
Unit
Depth Žm.
Opal Ž%.
701C
23H-4
diat q clay
1D
211.7
80
701C
23H-4
diat q clay
1D
211.7
80
701C
27X-2
mud q diat
2A
246.7
20
701C
31X-2
silic clay
2A
284.7
22
701C
34X-4
silic mud
2A
316.2
36
701C
37X-3
silic mud
2A
343.2
25
701C
42X-1
clay
2A
387.7
0
SiO 2
TiO 2
Al 2 O 3
FeO )
MgO
MnO
CaO
Na 2 O
K 2O
P2 O5
LOI
78.77
0.299
6.28
2.79
1.18
0.031
0.6
2.14
1.382
0.059
6.47
79.45
0.294
6.3
2.81
1.17
0.032
0.59
2.19
1.431
0.051
5.68
62.9
0.671
13.85
6.03
2.58
0.05
1.11
2.73
2.643
0.075
7.37
61.38
0.634
13.35
6.11
2.64
0.096
1.34
3.42
2.687
0.143
8.21
66.02
0.586
11.42
4.62
1.94
0.07
1.31
2.99
2.412
0.184
8.45
66.23
0.535
11.46
4.69
2.11
0.078
1.1
3.17
2.562
0.134
7.94
57.23
0.691
15.02
6.62
3.29
0.2
1.09
2.58
3.357
0.272
9.64
Rb
Sr
Ba
Sc
V
51.08
72.26
518.23
7.38
75.51
46.59
69.81
513.74
5.9
60
100.42
159.5
1509.32
13.77
128.72
100.98
154.68
1254.31
14.86
142.02
77.09
156.74
1957.29
12.14
87.09
88.86
130.28
1148.34
11.65
93.56
137.38
157.93
1961.66
14.68
102.48
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
377
Table A6 Žcontinued.
Hole
Core, sect.
Lithology
thoUnit
Depth Žm.
Opal Ž%.
701C
23H-4
diat q clay
1D
211.7
80
701C
23H-4
diat q clay
1D
211.7
80
701C
27X-2
mud q diat
2A
246.7
20
701C
31X-2
silic clay
2A
284.7
22
701C
34X-4
silic mud
2A
316.2
36
701C
37X-3
silic mud
2A
343.2
25
701C
42X-1
clay
2A
387.7
0
Cr
Ni
Cu
Zn
Zr
Y
21.36
17.7
340.71
46.39
83
10.39
19.56
21.1
272.1
44.87
51.6
6.84
43.13
42.71
82.79
105.74
126.95
16.68
51.93
50.55
88.99
66.56
120.37
25.55
29.27
28.45
103.99
69.18
122.4
21.5
34.91
81.45
54
64.44
107.38
22.29
49.66
81.67
144.36
124.08
132.22
27.24
Oxides in wt%; elements in ppm. Analyst: Dana Stuart. Data used for South Sandwich sediment mean.
Sediment isotopes. The isotopic composition for
the S. Tonga sediments is taken from nearby piston
core RC17-198 ŽBen Othman et al., 1989.. North
Tongan sediments may contain a more significant
Samoan component.
Subduction rate. Subduction rates at the Tonga
trench are the highest globally, due in large part to
rapid opening of the northern Lau Basin. Rates
increase to the north, from 164 " 5 mmryear at
Tongatapu Ž; 218S. to 240 " 11 mmryear at Niuatoputapu Ž; 168S. ŽBevis et al., 1995.. At 208S,
where most of the active Tonga volcanoes are located, we use a subduction rate of 170 mmryear.
B.3. Vanuatu Trench
The seafloor outboard of the Vanuatu arc is bisected by the d’Entrecasteaux zone ŽDEZ., which
has clogged the trench, deformed the arc, and caused
uplift in the fore-arc at Espiritu Santo and Malekula
Islands ŽCollot et al., 1992.. We consider here only
the section of the Vanuatu arc south of the DEZ,
where subduction is simpler and a drill site has
penetrated basement ŽDSDP SiteŽ286..
Reference site: DSDP Site 286 ŽRec.s 45%..
Reference units: From youngest to oldest: Ž1. 85
m glass shard ash with radiolarians, nannofossils and
clay, Ž2. 115 m nannofossil ooze and chalk, Ž3. 450
m vitric siltstone, sandstone and conglomerate. Site
286 is dominated by Unit 3, Eocene volcaniclastics
which were probably derived from the Oligocene to
Eocene andesitic seamounts that make up the South
ridge of the DEZ ŽCollot et al., 1992..
Sediment thickness and off-scraping. The sedimentary section drilled at Site 286 is 650 m thick
over basement. Although accretionary dynamics are
more complex near the DEZ, we assume the entire
sedimentary section near Site 286 is subducted at the
Vanuatu trench, based on VH & S classifying the
Vanuatu margin as non-accreting.
Geochemical data sources: Briqueu and Lancelot
Ž1983. report K, Rb and Sr data ŽID-TIMS. for 8
Site 286 sediments. Peate et al. Ž1997. has analyzed
a much more extensive sample set from Site 286: 23
sediment samples analyzed by XRF and ICP-MS.
Unit compositions. Our bulk estimate of 286 is
based entirely on Peate’s data set.
Ž1. Ashy clay. Based on the barrel sheet descriptions, smear slides analyses and CaCO 3 bulk analyses ŽCameron, 1975., the percentages of pure SiO 2
and CaCO 3 were estimated for each core and used to
dilute the analyses in Peate et al. Ž1997., who preferentially sampled the ashy–clayey units. For cores
without analyses, adjacent core analyses were used.
Each core was weighted by the drilled interval.
Despite the impression given in the barrel sheets, the
amount of pure biogenic diluent is minor: we estimate 1.7% pure silica and 2.5% CaCO 3 for this 85 m
unit Žbased on the more quantitative CaCO 3 analyses
in Cameron, 1975.. Sc is calculated from ScrAl in
the nanno ooze. Cu throughout the core was calculated from CurZn in Aleutian sediments.
Ž2. Nanno ooze. As above, the percentage of pure
CaCO 3 was estimated for each core Žwe estimate
around 28% CaCO 3 on average for this 114 m unit..
The analyses in Peate et al. Ž1997. were first re-nor-
378
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
malized to a CaCO 3-free basis, then diluted by the
amount of CaCO 3 appropriate to each core Žextrapolating analyses and interpolating trace element abundances to adjacent cores as necessary.. Core estimates were then weighted by drilled intervals, and a
grand sum calculated.
Ž3. Volcaniclastics. The 15 analyses by Peate et
al. Ž1997. of this unit indicate that the volcaniclastics
are relatively homogeneous. We thus weight the
analyses by the drilled intervals, and calculate a
weighted mean.
Sediment isotopes. The 87 Srr 86 Sr average is from
Briqueu and Lancelot Ž1983..
Subduction rate. The long-term rate of convergence between the Australian–Pacific plates at the
Vanuatu trench is 79–82 mmryear ŽNUVEL-1A:
DeMets et al., 1994.. This rate, however, does not
take into account opening of the North Fiji Basin,
and recent GPS measurements indicate this is a
significant addition to convergence at the Vanuatu
trench, with 103 " 5 mmryear measured at Efate
ŽTaylor et al., 1995.. Convergence at the DEZ is
complicated, and rates reflect a slip deficit Ž41 " 4
mmryear at Malekula. possibly due to very strong
coupling between the DEZ and the arc ŽTaylor et al.,
1995.. It is difficult to know when this coupling
began and over what time scale the rate deficit
applies, but evidence is for fairly recent eastward
displacement and uplift in the DEZ collision region,
within the last 100 ka ŽTaylor et al., 1993.. Since the
sector of the volcanic arc considered here is south of
the DEZ, we will use the Efate rate Ž103 mmryear..
B.4. JaÕa Trench
Reference sites: We estimate lithologies and
thicknesses of sediments entering the Java trench
based on DSDP Sites 211 and 261 ŽRec.s 16% and
24%., which are west and east of Java, respectively
ŽFig. 11.. Although further from Java than 211 and
261, ODP Site 765 ŽRec.s 70%. has been extensively studied, and we use our data and insights from
this reference site as well ŽPlank and Ludden, 1992..
Reference units: The average sedimentary section
subducted at the Java trench is taken to be an
average of Site 211 and 261 lithologies: from
youngest to oldest, Ž1. 125 m brownish and greenish
gray radiolarian clay, Ž2. 45 m clayey sand and silt
Žturbidites. of the Pliocene Nicobar Fan, Ž3. 130 m
brown and gray pelagic clay. Site 261 also contains
carbonate turbidites redeposited from the plateaus
surrounding northwestern Australia, which we assume do not constitute a significant portion of the
sedimentary column as far west as the Java trench.
Sediment thickness. As much as 5 km of sediment
clogs the Sumatra trench, - 1 km fills the western
Java trench, and essentially none exists in the eastern
Java trench. This dramatic thinning of trench sediments from west to east, along with geochemical
evidence for an ancient provenance, is consistent
with a western source of trench turbidites, from the
Himalayan collision zone and deep-sea fans surrounding India ŽHamilton, 1979; Moore et al., 1980;
McLennan et al., 1990.. Sediment thickness on the
incoming plate seaward of the Java trench, however,
is less variable and fairly thin Ž200–400 m, based on
seismic lines in Hamilton, 1979, Moore et al., 1980
and Vema lines 33-8 and 24-10; figs. 4–18 in Plank,
1993.. The average sedimentary section approaching
the Java trench is thinner Ž200–400 m. than the
sections drilled at Site 211 Ž430 m. and Site 261
Ž530 m., probably because of the Nicobar turbidites
from the west and carbonate turbidites from the east
both decrease towards central Java.
Sediment off-scraping: With a lack of more penetrative seismic data to delineate fore-arc structure,
we assume that whatever Quaternary trench deposits
have accumulated off Java are largely scraped off,
and that on average, 300 m of sediment is subducted
along the Java trench, consistent with the thickness
of the oceanic sediment section approaching the
trench. Turbidite off-scraping is also consistent with
VH & S’s classification of the Java fore-arc as accretionary.
Geochemical data sources: Ž1. Incomplete chemical analyses of 4 samples from Site 211 ŽPimm,
1974.. Ž2. Major element and some trace element
analyses of 11 samples from Site 261 ŽCook, 1974..
Ž3. Over 100 samples from ODP 765 were analyzed
by XRF; 40 also by INAA ŽPlank and Ludden,
1992.. Ž4. Piston core samples from around Indonesia ŽBen Othman et al., 1989; McLennan et al.,
1990.. New DCP analyses Žfor major and trace
elements. of Ben Othman and other piston core
samples are given in Appendix A.
Unit compositions: The Java sediment bulk composition is calculated by averaging Site 211 and 261
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
lithologies. In practice, we treat Site 211 and 261
separately, and separate unit averages are given for
the radiolarian clay and lower brown clay units at
Sites 211 and 261 Žthe Nicobar fan unit only exists at
211.. The differences between the two sites reflect
the regional variability in these two units.
Ž1. Radiolarian clay. This bulk composition was
calculated by first estimating the composition of
average clay for the region, and then diluting that
clay by the percentage of biogenic SiO 2 indicated in
the core descriptions for Sites 211 and 261, using our
own SiO 2 analyses and Cook’s to calibrate volume
percent shipboard estimates to wt%. Clay sub-lithologies ŽMn-rich or Mn-poor. were estimated from
the downhole descriptions of the clay color Žbrown
or gray, respectively., and the few analyses that exist
for Site 211 and 261. The composition of the clay
was based on analyses of piston core samples
ŽRC14-52, V33-74. and drill core samples of a similar upper radiolarian clay unit at Site 765. Site 211
radiolarian clay is estimated to be 30% biogenic
silica Žby mass., while Site 261 radiolarian clay is
estimated at 15% silica. Clay compositions were thus
diluted accordingly. Elements for which there are no
data are estimated based on ratio relationships. For
example, the average K 2 OrAl 2 O 3 for Site 211 radiolarian clay is lower than continental values, and
plots towards the Java fore-arc volcanogenic sediments Žsee Fig. 1., which is reasonable because this
site is within a few hundred km of the Java arc.
Thus, for the undetermined elements, ratios intermediate between PAAS and the Java fore-arc sediments
are assumed ŽRbrK 2 O s 36, CsrRb s 0.07,
ThrAl 2 O 3 s 0.55, UrAl 2 O 3 s 0.12.. Further details are given in Plank Ž1993.. Ta was calculated
from NbrTas 11.9, as in Table 4. Pb was calculated from PbrThs 2.35, based on Ben Othman et
al. Ž1989. data.
Ž2. Nicobar fan turbidites: Because no analyses
of these Pliocene turbidites exist, analyses of Quaternary turbidites from the Ganges cone are used instead Žfrom McLennan et al., 1990.. Recovery of the
Site 211 turbidites was poor Ž14–40%., but equal
proportions of fine Žclayey silt. and coarse Žsilty
sand. units are assumed, as was recovered. Thus, the
composition of the Pliocene turbidites is based on an
average of the sand and mud samples from two cores
ŽCC-10 from the Ganges cone and CA-30 from the
379
Java trench, which is isotopically similar to Ganges
turbidites ŽMcLennan et al., 1990.. CC-9 and CC-11
are carbonate-bearing and are excluded.. Rb is calculated from a continental RbrK 2 O ratio of 43. Ta is
calculated from NbrTas 14.2, the global average.
Ž3. Brown clay: Based on limited recovery and
analyses for this unit at Site 211, sediments are
younger than Campanian–Maastrichtian and are Ferich, and the basal sediments are probably hydrothermal. Thus, we averaged similar lithologies from Site
765 Ž3 cores from the Paleocene to Santonian interval Ž22R-24R., and the basal core Ž62R., which is
rich in hydrothermal Fe.. The Cretaceous claystones
at Site 261 are actually a diverse collection of
lithologies Žbrown and gray claystones, nanno claystones, radiolarian clays, carbonate turbidites, and
streaky clays. and very similar to the Cretaceous
section at Site 765. We thus used the average Cretaceous section already calculated for Site 765 for the
section at Site 261 ŽTable 4 in Plank and Ludden,
1992.. Ta was calculated from NbrTas 12.6, as in
Table 4. Pb was calculated from PbrThs 2.81 Žfrom
unpublished ID-TIMS analyses..
Isotopes. The isotopic composition of the Java
sediments is taken from piston core sample V28-343
in Ben Othman et al. Ž1989.. Pb concentrations are
calculated from PbrThs 2.35 Žas determined from
data in Ben Othman et al., 1989..
Subduction rate: The NUVEL-1A convergence
rate for Australia–Eurasia across the Java trench is
71 mmryear ŽDeMets et al., 1994., but recent GPS
measurements indicate a lower rate Ž67 mmryear.
due to either the motion of an independent Southeast
Asian plate or plate margin deformation ŽTregoning
et al., 1994.. We use the GPS-based rate of 67
mmryear.
B.5. East Sunda Trench
The reference site for E. Sunda sediment subduction is DSDP Site 261 ŽRec.s 24%., a 500 m section, including 40 m of radiolarian clay, 100 m of
Cenozoic carbonate turbidites, and 360 m of Cretaceous clay. The two clay lithologies were calculated
above for the Java site, and the same averages are
used here. The bulk composition of the Cenozoic
section at ODP Site 765 ŽTable 4, Plank and Ludden,
1992., which is predominantly carbonate turbidites,
380
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
was used for the Site 261 carbonate turbidite. New
data in Vroon et al. Ž1995. will improve these estimates, but greater uncertainties most likely exist in
the mechanics of subduction, which become increasingly complicated east of Java. The collisions that
characterize the east Sunda-Banda arc sectors will
also affect subduction rates, which are taken here as
equal to Java.
Unfortunately, the trace element XRF data from
Jarrard and Lyle Ž1991. are unreliable, and so an
analog composition was found in the Java 211 clay,
which has similar KrAl, TirAl and FerAl ratios to
the Site 731 turbidites. For the grand Makran mean,
Java 211 clay and East Sunda carbonate turbidites
were mixed together to yield 13% CaCO 3 , the mean
carbonate content for Site 731 turbidites.
B.6. Sumatra Trench
B.9. Philippine Trench
VH & S estimate 1400 m of sediment subduction
at the Sunda trench Ž2000 m)70% subduction.. Since
this section of sediment has never been drilled, we
assume that 300 m of it is equivalent to the Java
section Žessentially the pelagic part of Site 211., and
the rest is made up of Himalayan-derived turbidites,
equal to the Nicobar turbidites in composition. Isotopic compositions are from Ganges-derived turbidites in McLennan et al. Ž1990..
At DSDP Site 291, 120 m of sediment were
drilled over basement ŽRec.s 9.5%., spot coring
four sedimentary units, I: ; 63 m of volcanic-bearing
silty clay, II: ; 17 m of nanno-ooze, III: ; 22 m of
nanno-radiolarian ooze and clay, and IV: ; 18 m of
ferruginous zeolite-rich clay. No chemical analyses
of these sediments are available, aside from carbonate analyses in the Site report. Based on the descriptions and carbonate contents, we assign analog compositions to each of the four units: Vanuatu ashy–clay
for Unit I, Guatemala carbonate ooze for Unit II Žat
80% cc., a mixture of Tonga chertrclay and
Guatemala carbonate for Unit III Žat 40% cc., and
Tonga chertrclay for unit IV.
B.7. Andaman Trench
A very thick section of sediment, part of the
Bengal Fan, is being subducted at the Andaman
margin. VH & S estimate 3500 m of sediment subduction here Ž5000 m)70% subduction.. Since this
section of sediment has never been drilled, we assume that 1400 m of it is equivalent to the Sumatra
section, and the rest is made of Bengal turbidites, the
composition of which is estimated from a single
turbidite sample ŽCC-10. in McLennan et al. Ž1990..
Ta, Rb and Zn were not determined, and are calculated from the global NbrTa of 14.2 and RbrCs of
15.4, and from the CurZn in average Ganges river
sediments ŽSubramanian et al., 1985.. Isotopic compositions for Bengal sediments are from Bouquillon
et al. Ž1990..
B.8. Makran Trench
As for the Andaman margin, the Makran margin
involves subduction of a large fan, the Indus fan.
Drilling during Legs 23 and 117 penetrated sections
of the Indus Fan; the only analyses available are
from Jarrard and Lyle Ž1991. for Sites 723, 728 and
731. Site 731 ŽRec.s 44%., on the Owen Ridge,
contains a large section of Miocene turbidites from
the fan, and provides the basis for our Makran mean.
B.10. Ryuku Trench
At DSDP Sites 294r295, ; 160 m of pelagic
sediment were drilled over basaltic basement, recovering two sedimentary units ŽRec.s 27%.: 100 m of
brown clay overlying 60 m of darker, ferruginous
clay. No chemical analyses of the sediments are
available, and so we used the Marianas ŽSite 801.
red clay and Tonga metalliferous clay as analog
compositions. Pb isotopes are from Sun Ž1980..
B.11. Nankai Trench
At ODP Site 808, the JOIDES Resolution drilled
through the toe of the accretionary prism, through
the decollement and into basement. We only consider the 350 m of Shikoku Basin sediments below
the decollement as input to the subduction zone
ŽRec.s 56%.. Pickering et al. Ž1993. present extensive XRF and ICP analyses for these sediments,
sampled at an interval of ; 7.5 " 5 m. Because the
geochemical compositions are fairly uniform ŽPickering et al., 1993., we calculate a simple mean of the
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
55 samples from this interval Ž910 – 1300 mbsf.. Hf,
Ta, Pb, Cs and U were not measured; they are
calculated from ZrrHf s 35, NbrTas 14.2, PbrTh
s 2.35, and the RbrCs and UrTh in Antilles ferruginous clay.
B.12. Mariana Trench
Reference sites: Recent drilling during Leg 129
has provided a wealth of information about the
seafloor seaward of the Marianas trench. We use two
reference sites from Leg 129: Site 801, the only site
where true Jurassic basement has been drilled in the
Western Pacific ŽLancelot et al., 1990., and Site 800.
Although Sites 801 and 800 are ) 500 km from the
Marianas trench, they are the only sites where coring
has sampled significantly beneath the resistant Cretaceous chert. Seismic lines across the region show
that the sediment thickness and seismic stratigraphy
at Site 800, in particular, ŽAbrams et al., 1992. is
similar to seafloor nearer the Marianas trench Ži.e., at
Site 452, where only 50 m of sediment were penetrated before bit destruction.. Thus, the improved
recovery and more continuous sampling to ‘basement’ at Sites 801 and 800 outweigh the disadvantage of their being some distance from the trench
ŽRec.s 17% and 28%.. Site 802 contains a significant section of Miocene volcaniclastics, derived from
the Caroline platform to the south and which do not
appear to extend north to seafloor near the Marianas
trench ŽAbrams et al., 1992.. Thus, Site 802 is not
included as a reference site.
Reference units: Based on sections at Sites 800
and 801, from youngest to oldest: Ž1. pelagic brown
clay with Fe oxides and zeolites, Ž2. brown chert and
porcellanite" limestone, Ž3. volcaniclastic turbidites
with minor radiolarian claystone pelagic intervals,
Ž4. radiolarite, chert and claystone.
Sediment thickness and off-scraping: At Sites 800
and 801, 400–500 m of sediment were drilled over
basement and include significant sections of volcaniclastic sediments Ž100–200 m. derived from the
Magellan chain seamounts. The volcaniclastic sections should thicken toward the seamount sources,
and sediment thicknesses do in general thicken within
the Ogasawara Fracture ZonerMagellan Flexural
Moat. Nonetheless, seismic reflection profiles show
that 400–500 m is typical for average sediment
thickness throughout the region ŽAbrams et al., 1992..
381
Because the Mariana margin is non-accreting ŽVH &
S., all of this sediment appears to be subducted.
Geochemical data sources: Abundant geochemical data exist for Leg 129 sediment cores ŽXRF and
INAA data in Karl et al., 1992; ICP and arc spectrometry data in Karpoff, 1992; XRF data in Lees et
al., 1992; ICP data in France-Lanord et al. Ž1992.;
and new ICP-MS analyses of the Karpoff samples in
Appendix A.. Additional analyses of DSDP core
samples are published in Stern and Ito Ž1983. and
Lin Ž1992. Žisotope dilution-TIMS., and Meijer
Ž1976. and Woodhead and Fraser Ž1985. Žisotope
ratio data..
Unit compositions: Separate unit and bulk averages were calculated for Site 800 and 801 in order to
determine the variability in two sites that share the
same regional stratigraphy but are ; 500 km apart.
Ž1. Brown Clay. For this relatively homogeneous
unit, the analyses in Karpoff Ž1992. and FranceLanord et al. Ž1992. Ž6 analyses for Sites 801 and
800 each. were weighted by the depth interval and
averaged. For the trace elements not analyzed by
Karpoff, average concentrations were calculated from
ratios using the ICP-MS 801 data Že.g., ICP-MS Rb
was used to determine the characteristic RbrK 2 O
ratio for the clay, and then average Rb for the unit
was calculated from average K 2 O, preserving the
RbrK 2 O ratio. Cs was also calculated from ratio to
K, REE from REErP, Pb from CerPb, U and Th
from Al.. The ratios Že.g., RbrK. determined for the
Site 801 samples were also used for Site 800. Sc was
calculated from ScrAl in the chert. Through the site,
Co and V were calculated from CorFe and VrFe
ratios in the Java 261 pelagic clay.
Ž2. Brown chert. The chert-bearing units of the
Western Pacific have been notoriously difficult to
sample by drilling, due to the alternating hard Žchert.
and soft Žclay. beds. Recovery in the siliceous units
at Site 801 and 800 was predictably poor Žgenerally
- 5%. and possibly biased towards the more resistant, siliceous beds. From a geochemical standpoint,
an average composition for these units based on the
descriptions of the recovered material alone could be
over-diluted by silica, and deficient in many of the
trace elements of interest.
In order to estimate better the average composition for the in situ chert unit, the geochemical logging data were used. Pratson et al. Ž1992. and Fisher
382
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
et al. Ž1992. found that the logging data agreed
reasonably well with core analysis, and the logs
show trends consistent with the down-core lithological changes as well as the predicted variations among
the elements Že.g., most elements vary inversely with
silica as a function of dilution due to biogenic opal
dilution.. We used the SiO 2 logging data to calculate
the average SiO 2 content for each unit, renormalizing the SiO 2 to take into account the addition of
MgO, MnO, Na 2 O and P2 O5 to the major element
sum Žexcluded in the logging data.. The SiO 2 averages were then used to adjust the core analyses in
Karl et al. Ž1992. to the correct level of dilution.
Only the samples with SiO 2 - 85% from Karl et al.
Ž1992. were used in the average, in order to minimize analytical errors for the elements that are diluted by silica. Pratson and Fisher both noted that the
SiO 2 logs tended to be lower than the core analyses
Žon the order of a few percent SiO 2 .. This may be
due to preferential sampling of the siliceous samples
Žas noted above., or to errors in the accuracy of the
geochemical logs. In the absence of more rigorous
ground-truth experiments, we assume here that the
logs are accurate.
For Unit III at Site 800, chert and limestone, the
logging data ŽFisher et al., 1992. were also used to
determine the average CaO Žas calcium carbonate.,
and dilute the elements Žexcept Sr. accordingly.
Ž3. Volcaniclastic turbidites. For Site 801, we
averaged the 13 samples of the volcaniclastic turbidites analyzed by Karpoff, which are more representative of the whole unit that those analyzed by
Karl, who preferentially sampled the siliceous
lithologies, and of those analyzed by Lees, who
preferentially sampled the coarse turbidite bases. The
Karpoff average was then adjusted to the average
SiO 2 calculated from the logging data Žas for the
Chert unit above.. Other element averages were estimated from the ICP-MS analyses Žas for the Clay
unit above.. For Site 800, geochemical logging was
not completed through this unit, and so the 43 combined analyses from Karpoff, Karl and France-Lanord
were simply weighted by interval and averaged.
Ž4. Radiolarite. For Site 801, the average composition for this unit was calculated as for the Chert
unit above. For Site 800, geochemical logging data
were not collected in this unit, and the 17 published
analyses were weighted by interval and averaged.
Isotopes. Brown clay: Nd, Sr and Pb isotopic
values from Site 452 composite of the upper clay
unit ŽWoodhead, 1989 and Woodhead and Fraser,
1985.. Siliceous lithologies: Nd and Sr isotopes from
Site 198 chert ŽLin, 1992. and Pb isotopes from Site
196 chert ŽMeijer, 1976.. Volcaniclastics: Nd, Sr and
Pb isotopic values from Site 585 ŽWoodhead, 1989
and Woodhead and Fraser, 1985.. The Pb isotopic
composition of the volcaniclastic unit is distinctly
high in 206 Pbr 204 Pb, similar to the inferred Magellan seamount sources Žas for Himu and Hemler
seamounts in Staudigel et al., 1991..
Comparison to BWPS. Lin Ž1992. calculates an
average composition for Bulk Western Pacific Sediment ŽBWPS. based on DSDP cores from the Marianas-Izu region. We chose to calculate new bulk
compositions here, to take into account of the wealth
of new data generated during ODP Leg 129, which
post-dates Lin’s work. Because drilling efforts prior
to Leg 129 focused on the southern part of the
region, or were unsuccessful in coring through the
resistant cherts, BWPS is not entirely representative
of sediment columns subducting beneath the Central
Marianas. Specifically, BWPS contains too much
carbonate for the average sedimentary column entering the central and northern Marianas trench. Carbonate increases to the south of the region, due to
carbonate turbidites shed off the Caroline platform,
but is a minor component of pelagic sedimentation in
the region seaward of the active Marianas islands.
Similarly, the Ash analyzed by Lin and included in
BWPS Žhis table 2. is based on Miocene tuffs derived from Caroline volcanism, and not the Cretaceous volcaniclastics that contribute so significantly
to the sediments that feed the active Mariana arc
further north. The Chert average calculated by Lin is
too diluted in trace elements for average chert and
radiolarite units, as sampled by Leg 129 drilling and
downhole logging. The average Clay calculated by
Lin, however, agrees very well with the Pelagic
Clays estimated here, which might be expected because the upper clay unit is the most homogenous
unit throughout the region. The agreement between
our estimates is encouraging, however, given that the
averages were calculated from different samples,
analyses, and methods.
Subduction rate: The convergence rate at the Marianas trench is not very well known due to uncertain-
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
ties in the motion of the Philippine sea plate, the
opening of the Marianas trough, and the convergence
vector along the trench. A GPS campaign under way
should lead to better estimates Že.g., Beavan et al.,
1990.. For this work, we have used estimates from
Seno et al. Ž1993. of Pacific-Philippine trench-normal convergence Ž35 mmryear at 188N and 22
mmryear at 228N., and of Hussong and Uyeda
Ž1981. of Mariana trough opening Ž33–43 mmryear
at 188N.. Subduction velocities slow to the north due
to an increase in convergence obliquity Žaccording to
Seno’s model. and a decrease in the rate of back-arc
basin opening Ževentually to zero north of 228N.. We
take the average orthogonal subduction velocity between 18–228N Žroughly the position along the arc
of volcanoes considered. to be 47.5 mmryear.
B.13. Izu-Bonin Trench
There are currently no adequate reference drill
sites seaward of the Izu-Bonin trench. Seismic reflection records indicate approximately 600 m of pelagic
sediment ŽLarson, pers. comm... We assume these
sediments are similar to the pelagic units seaward of
the Marianas, and use ODP Site 800 as an analog.
The following Site 800 units are used: 38 m of
pelagic clay; 370 m of chert; 150 m of mixed
chert-limestone; 49 m of radiolarite. Thus, the section is identical to Site 800, but for an extra section
of chert, and a lack of volcaniclastics, which are
absent to the seafloor to the north Ždue to a lack of
seamounts.. Clearly, a drill site to sample the actual
Izu-Bonin lithologies is desirable.
B.14. Japan-Kurile trench
The same sediment composition is calculated for
the Japan and Kurile trenches, using the analyses in
Cousens et al. Ž1994. for sites DSDP 579 and 581
sediments. The two sites together provide a good
composite stratigraphy, with Site 579 providing excellent recovery ŽRec.s 89%. through the upper 150
m, and Site 581 providing good recovery ŽRec.s
45%. through the lower 185 m. Lithologies are based
on Site 581: 240 m of diatom clay over 30 m pelagic
clay over 65 m clay-chert Žtotal thicknesss 335 m..
V is calculated from VrFe in Aleutian diatom ooze.
383
B.15. Kamchatka Trench
Drilling at ODP Site 881, seaward of the Kamchatka-Kurile trench, penetrated 364 m of sediment
ŽRec.s 71%.. Although basement was not reached,
the drilled section at Site 881 may be virtually
complete, as seismic estimates place acoustic basement at ; 400 m. The stratigraphy at Site 881
consists of 164 m of diatom clay over 200 m of
diatom ooze. Only Pb data exist for Site 881 sediments ŽKersting and Arculus, 1995.. Thus, the Kurile
diatom clay was diluted with SiO 2 until it reached
the Pb concentration measured for the Kamchatka
diatom clay Ž; 14 ppm.. The Kurile chert-clay was
used as an analog for the Kamchatka diatom ooze
Žand it is within the range of Pb concentrations
measured by Kersting and Arculus, 1995..
B.16. Aleutian Trench
Although the Aleutian trench stretches over 2000
km, the seafloor south of the trench has been drilled
in only one location, Site 183, seaward of the Eastern Aleutiansrlower Alaska Peninsula. Thus, we
consider only this region of the arc-trench system.
Other drill sites in this part of the Pacific are in the
forearc region ŽDSDP 186 and 187. or on the flanks
of Emperor seamounts in the far western Pacific
ŽODP 884., and thus not typical of seafloor converging at the Aleutian trench.
Reference site: DSDP Site 183 ŽCreager and
Scholl, 1973.. Recoverys 30%.
Reference units: From youngest to oldest: Ž1.
ash-rich diatom ooze, Ž2. greenish gray clay, Ž3. silty
clay with sand Žclastic turbidites.. Chalks were recovered in two intervals in the site, in a 1–9 m layer
below the green clay, and in limited amounts at the
base of the sediment column. Because of their minor
but undetermined size Ždue to poor recovery., the
chalks have been excluded from the bulk calculation.
The buried, Eocene turbidites are part of the Zodiac
Fan, and were derived from the margin of N. America, at a high latitude ŽCreager and Scholl, 1973..
One candidate for the source terrane of the turbidites
is the Coast Mountains Batholith of northern British
Columbia, which experienced extensive Ž10–30 km.
and rapid Ž2 mmryear. uplift in the Paleocene and
Eocene ŽHollister, 1979, 1982.. Although another
384
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
unit may have overlain and been eroded off the
Coast Mountains Batholith, the turbidites at Site 183
have a Nd isotopic composition similar to the exposed Coast Mountains batholith Žvon Drach et al.,
1986; Samson et al., 1991.. This suggests that the
batholith itself or comparable bodies may be the
source of the turbidites.
Sediment thickness and off-scraping: Seismic reflection data across the Aleutian trench near the
Shumagin Islands indicates more than a km of sediment in the trench ŽVH & S.. At Site 183, however,
only 500 m of sediment were drilled above basalt.
The extra thickness of sediment in the trench is due
largely to the addition of trench turbidites, which
appear to be mechanically separated from the lower
oceanic sediment section by a decollement ŽVH & S..
We thus assume the trench turbidites are being accreted while the oceanic section of sediments, similar
to that drilled at Site 183, is subducted beneath the
decollement. Although 500 m of oceanic sediment
were drilled at Site 183, the isopach maps of Ludwig
and Houtz Ž1979. and Winterer Ž1989. show an
average of only 350 m of sediment along the arc
sector for which the most volcanic data have been
published ŽRecheschnoi to Cold Bay.. This difference is probably due to a decrease in the thickness of
the Eocene turbidites to the west, and sediment
thickness thins dramatically west of 1708W, to 100–
200 m. We thus estimate that a 350 m section of
sediment is subducted along the Recheschnoi-Cold
Bay sector of the arc, and use a stratigraphy similar
to that drilled at Site 183, but with a thinner section
of Eocene turbidites.
Geochemical data sources: von Drach et al. Ž1986.
combined 35 individual samples of Site 183 sediments into two composites, corresponding to the
upper Žpelagic. and lower Žturbidites. sections. The
composites were created by physically mixing the
individual samples together, weighting each sample
by the appropriate thickness and density. These composites were analyzed for Sr and Nd isotopic composition, as well as Rb, Sr, Sm, Nd, K and Ba concentrations Žvon Drach et al., 1986.. Kay and Kay
Ž1988. report INAA data, and we report DCP data
for the same 35 individual samples Žsee Appendix
A..
Unit compositions: For the sake of consistency,
we did not use von Drach’s weighting factors, but
calculated the bulk composition of Site 183 in a
similar way to the other sites discussed here.
Nonetheless, for the elements in common, our bulk
compositions agree very well with von Drach’s composites, based on different averaging approaches and
different analytical techniques.
Ž1. Ash-rich diatom ooze. The percentage of diatoms Ž50%. and ash Ž7%. are estimated for this
interval from core descriptions in Creager and Scholl
Ž1973.. The core descriptions provide volume percentages, however, and the two samples described as
100% diatoms average 75 wt% SiO 2 . Using this
relationship, we estimate that 50% diatoms corresponds to 65% SiO 2 , and dilute the analyses Žcalculated silica-free. from this unit accordingly. Because
von Drach purposefully avoided ash layers in sampling the upper unit, average Aleutian andesite was
added as a component, based on our arc database
ŽPlank and Langmuir, 1988.. Rb was calculated from
the RbrK 2 O ratio of composite A3 in von Drach et
al. Ž1986.. Throughout the core, Nb was calculated
from the global average NbrTa of 14.2, and Pb was
calculated from PbrThs 2.35 Žbased on data in Ben
Othman et al., 1989..
Ž2. Greenish gray clay. Samples that have been
analyzed from this unit include a silty clay and a
greenish gray clay. From the core descriptions, silty
clay, clay and nannofossil ooze are estimated to
make up 37.5%, 50% and 12.5% of this unit, respectively. The 2 analyzed samples are taken as representative of the silty clay and clay, and the nannofossil
ooze is taken to be 56% CaO, 44% CO 2 and 1000
ppm Sr. Rb is calculated as above.
Ž3. Clastic Turbidites. The 28 samples that were
analyzed from this chemically homogeneous turbidite unit ŽKay and Kay, 1988. are averaged by
weighting them by the appropriate interval and
lithology. The proportions of sand, silt and clay were
estimated from the core descriptions; uncored intervals were assumed to be an average of the adjacent
cores. Rb was calculated from the RbrK 2 O ratio of
composite A2 in von Drach et al. Ž1986..
Isotopes. Sr and Nd isotopes for the site are from
the composites analyzed by von Drach et al. Ž1986.:
A3 for the upper pelagic units, A2 for the turbidite
unit. Pb isotopes and concentration for pelagic units
are from sample RC10-199 in Sun Ž1980.. Pb isotopes for the turbidite unit are from McDermott and
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Hawkesworth Ž1991.; with Pb concentration calculated from PbrThs 2.35 ŽBen Othman et al., 1989..
Subduction Rate: NUVEL-1A for Pacific-North
America at 1608W is 62 mmryear ŽDeMets et al.,
1994..
B.17. Alaska Trench
780 m of sediment were drilled at DSDP Site 178
ŽRec.s 27%., consisting of similar lithologies to
Site 183, but with a greater thickness of turbidites.
Although some of these turbidites are probably part
of the Zodiak Fan as well, younger material no doubt
also derives from Alaska. Thus, we have used the
300 m of Site 183 sediments, along with 480 m of
turbidites with a composition of two shallow piston
cores, SS13 and 14, from McLennan et al. Ž1990..
P2 O5 in the piston cores are calculated from Smr34
Žas in Fig. 6a.; Zn and Rb are calculated from the
ZnrCu and RbrCs ratios in the Aleutian diatom
ooze; Ta is calculated from NbrTas 14.2, the global
mean. Pb isotopes are from Sun Ž1980..
B.18. Cascadia Trench
Approximately 1500 m of sediment subducts in
the Cascadia system, as estimated by VH & S. Although these sediments have been drilled at DSDP
Site 174 ŽRec.s 23%. and ODP Site 888 ŽRec.s
64%., no chemical analyses are available. The sediments are predominantly fan deposits and more distal turbidites. Thus, the closest analog is the Aleutian
clastic turbidite of the Zodiak Fan.
B.19. Mexico Trench
Reference site: The only drilling near the Mexican
trench took place during Leg 66, at ; 168N. DSDP
Site 487 was drilled seaward of the trench ŽRec.s
66%., Site 486 was drilled in the trench ŽWatkins et
al., 1982.
Reference units: The sediments cored at Site 487
consist of 100 m of a hemipelagic gray muddy silt,
overlying 70 m of brown pelagic clay ŽWatkins et
al., 1982.. The silt fraction of the upper hemipelagic
unit consists primarily of quartz, feldspar and mica,
suggesting derivation from the crystalline rocks of
the Mexican margin. The lower brown clay unit is
enriched in Fe and Mn, probably of hydrothermal
385
origin ŽLegget, 1982.. The relatively thin sediment
cover reflects the young age of the oceanic crust
ŽMiocene., and the near-lack of carbonates indicates
that the section at Site 487 was below the CCD.
Sediment thickness and off-scraping: Based on
seismic reflection profiling, the oceanic crust that
approaches the Mexican trench delivers on average
100–200 m of sediment ŽLudwig and Houtz, 1979.,
similar to the 170 m oceanic section drilled at Site
487. Sediment thickness in the Mexican trench, however, reaches a maximum of 450 m, although it
varies along strike with the location of submarine
canyons ŽMoore and Shipley, 1988.. Drilling of the
trench sediments was attempted at Site 486, but the
hole was abandoned after drilling only 35 m of
extremely coarse, quartz-rich sand. Seismic reflection data suggest that these trench turbidites are
mechanically decoupled from the oceanic sediments
below, which appear to be underthrust along with the
downgoing plate. Moore and Shipley Ž1988. identify
a decollement that forms roughly 200 m above basement, similar to the thickness of the oceanic sediments approaching the trench. Thus, the section
drilled at 487 is taken as representative of the subducted oceanic sediment.
Geochemical data source: Legget Ž1982. analyzed 45 sediments from Site 487 by ICP.
Unit compositions:
Hemipelagic silt: The analyses reported by Legget
Ž1982. of Site 487 clays are averaged in 10 m
intervals, and then averaged down-unit. The
hemipelagic unit has continental CrrAl 2 O 3 and
LarAl 2 O 3 ratios. Rb, Cs, Sm and Th are therefore
estimated from continental ratios ŽRbrK 2 O s 40,
CsrRbs 0.065, LarSms 5.6, ThrAl 2 O 3 s 0.66..
SiO 2 was calculated from the sum of the major
elements, assuming 10% LOI. U, Nb, Zr and the
REE pattern were calculated from UrTh, NbrAl,
ZrrAl and the REE pattern for the Aleutian clastic
turbidite. Y was calculated from 10)Yb; Ta from
NbrTas 15.2; Hf from ZrrHf s 35.
Pelagic brown clay: As above, except UrTh,
NbrAl, ZrrAl, and the REE pattern from Java 211
pelagic clay.
Sediment isotopes: No isotope data are available.
Subduction Rate: NUVEL-1A for Cocos-North
America at 178N is 52 mmryear ŽDeMets et al.,
1994..
386
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
B.20. Sediment subduction at the Central American
Trench
Reference site: DSDP Site 495, south of
Guatemala ŽRec.s 74.5%..
Reference units: The sediment drilled at Site 495
consists of 175 m of hemipelagic, diatom-rich mud
overlying 250 m of pelagic carbonates. The sediments mark the movement of the Miocene oceanic
crust beneath an equatorial zone of high biologic
productivity Žhigh rates of carbonate deposition. to a
coastal zone of upwelling Žhemipelagic mud and
diatom deposition..
Sediment thickness and off-scraping: Sediment
thickness at Site 495 is 425 m ŽAubouin et al.,
1982., which is consistent with the 400 m average
indicated by seismic reflection profiles in the region
ŽLudwig and Houtz, 1979.. One of the objectives of
Leg 67 was to study the presumed accretionary
structures of the Guatemalan margin. Drilling in the
fore-arc, however, failed to recover pelagic sediment
derived from the down-going plate. These results
suggest that thousands of kilometers of oceanic crust
have been subducted, with no accretion of sediment
to the continental margin Žvon Huene and Aubouin,
1982.. We thus assume the entire 425 m of sediment
at Site 495 is subducted.
Geochemical data sources: DCP, ICP-MS and
isotopic analyses of 19 samples of Site 495 sediments were provided by M. Carr, and discussed in
Carr et al. Ž1990..
Unit compositions: Generally, the percentage of
diluent Žbiogenic opal or carbonate. is estimated
from the core descriptions, smear slide analyses, and
shipboard carbonate ‘bomb’ analyses ŽAubouin et
al., 1982.. Clay compositions are then diluted by
these percentages.
Hemipelagic diatom mud. Site 495 smear slide
percentages of diatoms, radiolarians, sponge spicules
and silicoflagellates give an average of 35% biogenic
opal for this unit. As for the Aleutian sediments, the
shipboard modal Žvolume. analyses of biogenic silica
are roughly a factor of two higher than wt% SiO 2 .
Thus, the average SiO 2 content for this interval is
taken to be 57%, consistent with 17 wt% biogenic
opal. The six analyses from this unit average close to
57%, and so a simple average is used. Co and Zn are
calculated from CorFe and CurZn in Aleutian di-
atom ooze. Hf and Ta are calculated from ZrrHf s
35 and NbrTas 14.2.
Pelagic carbonate. The average calcium carbonate of this interval is 80%, based on Leg 67 shipboard carbonate bomb analyses. Thus, the average of
the 13 analyses provided by M. Carr for this unit is
adjusted to 80% calcium carbonate Ž45% CaO.. Co,
Zn, Hf and Ta are calculated as above.
Sediment isotopes: Sr and Nd isotopic analyses
for mud and carbonate samples from Carr Žpers.
comm.. and Carr et al. Ž1990..
Subduction rate: NUVEL-1A for Cocos-Caribbean at 148N is 77 mmryear ŽDeMets et al., 1994..
B.21. Colombian Trench
Drilling at DSDP Site 504 and 504B penetrated
approximately 270 m of sediment over basement
ŽRec.s 72%.. These sediments consist of mixed
siliceous and carbonate lithologies Žnannofossil and
radiolarian oozes, chalk and chert.. Carbonate bomb
analyses indicate approximately 50% carbonate for
the bulk core. Hein et al. Ž1983. present an average
analysis for a partly silicified chalk; we dilute this
average to 50% total CaCO 3 . Sc, Rb, Cs, Nb, Th and
U are calculated from ScrAl, RbrK, RbrCs, NbrZr,
ThrAl and UrTh of Guatemala diatom clay. Yb is
calculated from YrYbs 10, and the rest of the REE
are calculated from the Peru REE pattern. Hf, Ta and
Pb are calculated from ZrrHf s 35; NbrTas 14.2;
PbrThs 2.35.
B.22. Peru Trench
Drilling at DSDP Site 321 penetrated 124 m of
sediment over basement ŽRec.s 64%.. Sediments
consist of 35 m of siliceous green clay over 24 m of
brown pelagic clay over 66 m of nanno ooze. No
geochemical data exist for this site. We use the
Guatemala diatom mud for the green clay, and the
Mexico silty clay for the brown clay. Some trace
element data exist for the nanno ooze in nearby Site
320 ŽHole et al., 1984., which we use for the 321
nanno ooze unit. All other elements are taken from
the Guatemala carbonate.
B.23. South Sandwich Trench
The closest drill site to the South Sandwich trench
is ODP Site 701, ; 350 km north of the volcanic arc
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
ŽRec. ) 69%.. There, approximately 500 m of diatom-rich sediment was drilled, with some nannobearing lithologies encountered deeper in the hole.
15 samples of diatom oozes and clays from the upper
400 m of the site Žsqueeze cakes of pore fluid
samples given in Froelich et al., 1991. were analyzed
by DCP Appendix A.. Seafloor immediately seaward
of the South Sandwich trench is younger than that
drilled at ODP Site 701, and the sedimentary section
is generally thinner Ž0–500 m; 200 m on average,
based on Islas Orcadas seismic profiles.. Thus, we
use a thickness of 200 m of sediment, with a composition of the weighted average of our DCP analyses
of Site 701 diatom oozes, for the South Sandwich
average. Elements not determined by DCP were
estimated from element ratios in a nearby piston core
ŽV14-57; Ben Othman et al., 1989.: Hf, U, Th, Pb
from HfrZr, UrLa, ThrLa and PbrLa in V14-57.
The REE were calculated from the REE pattern in
V14-57, using YrYbs 10 to constrain the absolute
abundances. Nb and Co were calculated from CorFe
and NbrAl in the Aleutian diatom ooze.
B.24. Northern Antilles Trench
Sediment thickness and off-scraping: There is a
large north-to-south gradient in sediment thickness
outboard of the Lesser Antilles arc. North of the
Barracuda rise, only 200–300 m of sediment overlies
basement ŽTucholke et al., 1982., whereas several
1000 m of sediment have accumulated in the south.
This gradient in sediment thickness reflects a S.
American source, via the Orinoco river system and
turbidites derived from the Venezuelan margin. This
enormous supply of sediment has resulted in a large
accretionary complex in front of the southern Lesser
Antilles, which has been well studied by seismic
methods Že.g., Westbrook et al., 1988; Torrini and
Speed, 1989; Ladd et al., 1990. and drilling during
DSDPrODP Legs 78, 110, and 156. A pervasive
feature of the accretionary wedge is a prominent
decollement that forms between 300 and 1 km above
basement, separating sediments that are off-scraped
from those that are underthrust along with the basaltic
oceanic crust ŽWestbrook and Smith, 1983; Westbrook et al., 1988; Moore et al., 1988.. In some
places, the decollement is observed to step down
section Že.g., Ladd et al., 1990.. Thus, despite the
387
growth of a spectacular accretionary structure in the
Antilles fore-arc, much of the incoming sedimentary
pile is subducted beneath a decollement. Indeed,
VH & S estimate that most of the sediment is subducted Ž70%..
Reference sites: Drilling outboard of the deformation front Žtoe of the accretionary prism. has been
restricted to a latitude of around 158N ŽSites 543 and
672., north of the Tiburon Rise. The sediments at
Site 543 thin to 400–500 m, largely because the
Tiburon Rise dams the northern flow of turbidites.
The sediments at Site 672, only 20 km to the south
of Site 543, are thicker due to a thicker section of
distal turbidites, because of its position further up the
flank of the Tiburon Rise ŽDolan et al., 1989..
Sediment thickness between the Tiburon and Barracuda rises varies between 500 and 800 m, and thins
dramatically to 200–500 m north of the Barracuda
rise ŽTucholke et al., 1982.. Extensive geochemical
data are available for Site 543 only ŽRec.s 66%.,
and thus is the reference site chosen. Sediment thickness at Site 543 is more appropriate for seafloor
north of the Barracuda rise and the section of the
volcanic arc north of Guadeloupe.
Reference units: Sediments at Site 543 consist of
4 main units Žfrom youngest to oldest.: Ž1. 170 m of
ashy mud Žarc derived., Ž3. 140 m of radiolarian
clay, Ž4. 65 m of Mn- and zeolite-rich clay, Ž5. 30 m
of calcareous, ferruginous claystone. Based on results from both Legs 78A and 110, the decollement
is observed to form at the top of the radiolarian clay
unit Žearly Miocene., where porosities are anomalously high, and sediments are weaker than the adjacent, lower porosity sediments ŽMoore et al., 1988..
Thus, only the lower three units are subducted beneath the accretionary prism, and included in the flux
calculation.
Geochemical data sources: White et al. Ž1985.
present isotope ratio ŽSr, Nd, Pb. and isotope dilution ŽU, Th, Pb, Rb, Sr, Sm, Nd. data for 13
sediment samples from Site 543, as well as some
additional ID-REE, Ba, Cs and K data. Davidson
Ž1987. presents trace element and isotope data for 4
additional Site 543 sediments. Wang et al. Ž1990.
present major element data for nearby ODP Site 671.
Ben Othman et al. Ž1989. and White et al. Ž1985.
also provide analyses of piston core samples from
the region.
388
T. Plank, C.H. Langmuirr Chemical Geology 145 (1998) 325–394
Unit compositions:
Radiolarian clay. The average biogenic opal for
this interval Ž170–313 m. is 17%, based on smear
slide analyses. Since no major element data are
available for Site 543 sediments, a different method
must be applied than one based on ground truth wt%
SiO 2 , as for other sites above. A good relationship
between Rb concentration and percent opal from the
smear slide data is used to determine the average Rb
concentration for the unit ŽRb is diluted by radiolarians and varies inversely with percent opal.. This
average Rb actually turns out to be similar to the
simple average of the 11 analyses reported by White
et al. Ž1985. for this interval. The other elements are
thus simple averages of the analyses. Major elements
are estimated using data in Wang et al. Ž1990. from
ODP Site 671. Radiolarian clay analyses were averaged to equal K 2 O in the Site 543 average.
Zeolite and Mn bearing clay. Only three samples
from this unit Ž313–379 m. have been analyzed: a
Mn-rich clay ŽWhite et al., 1985., a clay, and a
zeolite-bearing clay ŽDavidson, 1987.. The proportions of the zeolite, Mn-bearing clay, and clay are
estimated from the barrel sheets as 50%, 20%, and
30%, respectively. The three analyses are weighted
accordingly. Davidson Ž1987. did not measure Th or
K, and so they are estimated from ThrRb and KrRb
ratios in the adjacent samples analyzed by White et
al. Ž1985. Cs is estimated from the CsrRb ratio of
the overlying radiolarian clay unit. Major elements
as above.
Ferruginous and calcareous clay. The proportions
of Fe-rich and carbonate-rich clays are estimated to
be roughly equal, based on the barrel sheet descriptions. The analysis of a carbonate-rich sample in
White et al. Ž1985., and the analysis of the ferruginous clay sample in Davidson Ž1987. are thus averaged. Th, K and Cs and major element concentrations are estimated as above.
Sediment isotopes and other trace elements: The
abundant isotopic data for Site 543 sediment ŽWhite
et al., 1985; Davidson, 1987. permit weighted averages to be calculated for the units described above.
The remaining trace elements were calculated from
ratios in nearby piston core GS-7605-61 ŽBen Othman et al., 1989; Appendix A; Stolz et al., 1996.: Sc,
V, Cr, Ni, Cu, Zn, Zr, Nb and Ta from ScrAl,
VrFe, CrrAl, NirFe, CurFe, ZnrCu, ZrrAl,
NbrAl and NbrTa. Co was calculated from CorFe
in the Aleutian clastic turbidite, and Y from YrYb
s 10 and Hf from ZrrHf s 35.
Subduction rate: NUVEL-1A for Cocos-North
America at 178N is 11.5 mmryear ŽDeMets et al.,
1994.. Sykes et al. Ž1982. have argued that convergence rates should be higher Ž37 mmryear., based
on seismic considerations and thermal models for the
length of the slab. Until this disagreement is settled
with independent data Ž10–15 year GPS; Dixon et
al., 1991., we use an average of the Sykes and
DeMets estimates Ž24 mmryear. and include a 50%
uncertainty on the sediment fluxes.
B.25. Southern Antilles Trench
VH & S estimate 1750 m of sediment subducting
beneath the Barbados prism. There has been no
drilling south of the area described above, in the
thicker parts of the prism. We estimate the composition of the southern Antilles sediments starting with
the northern Antilles average Ž250 m. and adding
1500 m of a sediment having the composition of the
terrigenous piston core GS-7605-61 ŽBen Othman et
al., 1989..
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