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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 ) 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 - 2 326 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 328 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. 330 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 332 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. 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