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TECTONIC CONTROLS OF GEOCHEMICAL EVOLUTION IN ARC MAGMATISM OF SE ASIA
Tectonic controls of Geochemical Evolution in
Arc Magmatism of SE Asia
C G Macpherson1 and R Hall1
ABSTRACT
Subduction zone magmatism is a direct response to tectonic and chemical
processes operating at convergent margins. Changes in the tectonic
configuration of plate boundaries in SE Asia during the Cenozoic had
consequences for the nature and volume of magma produced. Retreat or
advance of the trench hinge has probably been an important process in
controlling the presence or absence of magmatism in SE Asian
subduction zones. This process also provides a means of replenishing the
mantle wedge and counteracting the effects of melt extraction in
depleting the wedge. Changes in the nature of recycled material and
lithologies of the over-riding plate also have the potential to influence the
lavas that are erupted in arcs. Several locations in SE Asia have
experienced magmatism bearing the geochemical signature of subduction
but are remote from coeval subduction zones. Such magmatism requires
an earlier period of mantle enrichment by subduction but may result from
localised extension. The distribution of such magmatism may provide
information of tectonic value. Some adakitic magmatism occurred in
tectonic settings where there is no evidence for subduction of young
oceanic crust at the time of magma genesis. Slab melting in such settings
is not possible and alternative mechanisms are required to explain the
occurrence of, at least some, adakitic lavas.
INTRODUCTION
The recognition that the linear chains of volcanoes in island arcs
were related to subduction was very quickly incorporated into
tectonic models once the plate tectonic theory of the Earth was
accepted at the end of the 1960s. Subsequent research has led to
revision of many ideas relating to the causes of melting, and the
relative importance of tectonic processes. Early models (eg
Oxburgh and Turcotte, 1970) emphasised magmatism due to
frictional heating on the Benioff zone, melting of the subducting
slab and compressional shortening of the over-riding plate in the
arc-trench gap. In contrast, melts are now seen as originating
primarily in the mantle wedge above the subduction zone, they
are thought to result from the input of volatiles that lower the
mantle solidus, and extension of the over-riding plate is now
recognised as a common feature in arc settings. Tectonics may
influence magmatism at a regional and local scale, for example,
by inducing melting during extension, by providing pathways for
magmas, or by varying the rate of supply of volatile components.
The character of magmatism is of particular interest in tectonic
interpretation if, for example, the geochemistry of igneous rocks
can be used reliably to infer the tectonic setting (eg Pearce and
Peate, 1995).
Subduction and volcanic arcs in Southeast Asia
Volcanic arcs occur in SE Asia at the boundaries between the
Eurasian, the Indian - Australian and the Pacific plates (Figure
1). In addition, the Philippine Sea plate lying between the Pacific
and Eurasian plates plays a crucial role in tectonic structures.
There are three major zones. The first is between the Eurasian
and Indian - Australian plates and extends from Myanmar in the
west to the Banda Islands in the east. Within this zone the Sunda
arc comprises the islands of the Andamans, Sumatra, Java and
Nusa Tenggara and results from subduction of Indian Ocean
lithosphere beneath Sundaland. Mesozoic magmatism is known
1.
SE Asia Research Group, Department of Geology, Royal Holloway
University of London, Egham, Surrey, TW20 0EX, United Kingdom
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in Sumatra and Java (Katili, 1975; Rock et al, 1982) while the
oldest magmatic rocks in Nusa Tenggara are of Miocene age
(Abbott and Chamalaun, 1978). The eastern part of this convergent
zone is the Banda arc where the Australian continental margin is
being subducted towards the north (Vroon et al, 1993). The second
zone of convergence occurs where lithosphere of the Pacific Ocean
is subducted towards the west. A subduction zone extends from
Japan, through the Izu – Bonin and Mariana trenches to the Ayu
Trough. Magmatism has occurred in this arc since the Eocene
(Cosca et al, 1998) and involved the opening of several marginal
basins within the Philipine Sea plate: the Parece Vela Basin, the
Shikoku Basin and the Mariana Trough. The third zone of
convergence runs from southern Japan, past the Ryukyu Islands,
through Taiwan and the Philippine Islands to the Molucca Sea
region in the south. Excepting the Nankai and Ryukyu trenches
in the north where the Philippine Sea plate is subducted beneath
east Asia, this is a complex region with subduction zones dipping
both east and west beneath the Philippine Islands and linked by
strike-slip faults. The Philippine Sea plate is subducted towards
the west at the Philippine trench. Eastward subduction at the
Manila, Negros and Cotobato trenches consumes oceanic
lithosphere of the South China, the Sulu and Celebes Seas,
respectively. This oceanic crust formed in Cenozoic extensional
and backarc basins at the eastern margin of Sundaland. The
Celebes Sea is also being subducted towards the south beneath
the northern arm of Sulawesi. All of these subduction systems are
very young but at the southern end of the Philippines the Molucca
Sea plate is being subducted to the east and west beneath the
Halmahera and Sangihe arcs, respectively. The greatest ages yet
obtained for volcanism associated with subduction of the Molucca
Sea are Middle Miocene (Baker and Malaihollo, 1996; Elburg
and Foden, 1998), although a Late Cretaceous – Eocene phase of
subduction magmatism is recorded in the Halmahera basement
(Hakim and Hall, 1991). Further to the east young subduction
systems and oceanic basins result from complex convergence and
strike slip faulting linking the New Guinea margin to the
Melanesian arcs at the boundary of the Australian and Pacific
plates.
In SE Asia most new Cenozoic subduction systems appear to
have been initiated close to the boundary between thick and thin
crust after collision events or plate reorganisations. From the
viewpoint of the present-day region we can distinguish three broad
categories of tectonic settings linked to arc magmatism:
1. ‘normal’ tectonic settings in which there is magmatism
associated with a subducting slab;
2. tectonic settings where there is subduction but no magmatism;
3. tectonic settings where there is magmatism of arc character
but no subduction.
In all cases it is also necessary to consider carefully the history
of subduction. Hamilton (1988, 1995) emphasised the necessity
of viewing subduction in a dynamic way, as opposed to static
concepts which represent only a single instant and usually
portray the subducting slab rolling over a stationary hinge and
sliding down a slot fixed in the mantle. Viewed in a dynamic way
Hamilton (1995) argued that most subduction zones are
characterised by retreat of the hinge with time, or rollback, and
that the mantle wedge above the subduction zone is constantly
replenished by an inflow of hot, undepleted mantle. In this way
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Proceedings 4 PACRIM Congress, 1999, Australian Institute of Mining and Metallurgy, 359–368.
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FIG 1 - Map of SE Asia highlighting major tectonic plates and plate boundaries. Subduction zones are indicated by lines with triangles on the over-riding
plate. Key to subduction zones not noted in Fig: 1. Manila Trench; 2. Negros Trench; 3. Cotobato Trench; 4. North Sulawesi Trench; 5. Halmahera
Trough (also frontal thrust of Sangihe arc); 6. Seram Trough; 7. New Guinea Trench; 8. Manus Trench; 9. New Britain Trench.
steady-state arc magmatism can be maintained. In principle there
is no reason why there should not be subduction zones
characterised by hinge retreat, hinge advance and fixed hinges.
However, Figure 2 shows that as far as SE Asia and the SW
Pacific are concerned most subduction zones have indeed been
retreating as Hamilton suggested. Future improvements in
tectonic models may make it possible to examine the tectonic
history of different regions in greater detail but from current
models there appear to be some general relationships between
hinge movement and volcanic activity. For the period since 25
Ma slab rollback was accompanied by significant arc volcanism
and in most cases by marginal basin formation. In contrast,
periods of hinge advance seem to be marked by reduction or
cessation of volcanic activity.
Geochemical Characteristics of Arc Magmatism
Lavas erupted in subduction zones frequently display
geochemical characteristics that can be used to distinguish them
from melts generated in other tectonic environments, particularly
mid-ocean ridge basalts (MORB). Lavas from many island arcs
are often chemically ‘depleted’ relative to MORB. This is
observed as depletions in the relative and absolute concentration
of non-mobile trace elements such as the high field strength
elements (HFSEs) (Ewart and Hawkesworth, 1987; McCulloch
and Gamble, 1991). Such depletion suggests that the mantle
wedge has been stripped of a basaltic component to varying
degrees prior to the present phase of magmatism (Woodhead et
360
al, 1993) and demonstrates that the wedge exerts important
controls on general geochemical characteristics of arc lavas (eg
Woodhead, 1989).
As a consequence of the cooling effect of the slab and the
refractory nature of peridotite in some mantle wedges, volatilerich slab-derived fluid or melt is probably necessary to induce
melting beneath the arc front (Morris et al, 1990; Ryan and
Langmuir, 1993). Any portion of the sedimentary cover that is
subducted with the lithosphere may also be prone to melting
at, or close to, the depths at which the mantle wedge melts.
Therefore, the recycled component can display dual provenance
within individual arcs (Elliot et al, 1997; Turner et al, 1996).
The presence of crustal material within the source region of
arc magmas provides a reservoir not present during MORB
genesis. The nature of this material and the mechanisms of
mass transport between slab and wedge can be resolved by
examining enrichment of trace elements that are mobile, relative
to HFSEs, and characteristic departures of isotope ratios from
upper mantle values (Tatsumi and Eggins, 1995; Turner et al,
1996; Hawkesworth et al, 1997). For example, fluid transport
from slab to wedge can induce chemical fractionation between
elements such as La and Nb that display similar behaviour
during magmatic processes (Tatsumi et al, 1986; Thirlwall et
al, 1994; Brennan et al, 1995; Keppler 1996; You et al, 1996).
Taken together, these observations have caused considerable
rethinking of early ideas on the mechanisms and nature of
sources operating in subduction zones (eg Woodhead, 1989;
Hawkesworth et al, 1991; Elliott et al, 1997).
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TECTONIC CONTROLS OF GEOCHEMICAL EVOLUTION IN ARC MAGMATISM OF SE ASIA
A
25-5 Ma
Japan
25-5 Ma
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25-5 Ma
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Mariana
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Sangihe
Sunda
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Halmahera
15-5 Ma
Solomons
Sunda-Banda
20-10 Ma
New
Hebrides
10-5 Ma
Tonga
15-10 Ma
Hinge
Advance
Hinge
Retreat
Kermadec
25-5 Ma
B
A: Andaman Sea
BS: Banda Sea
Bi: Bismarck Sea
L: Lau Basin
M: Mariana Trough
NF: North Fiji Basin
Wd: Woodlark Basin
5-0 Ma
Japan
Ry
yu
Izu
Bonin
Phil
Sa
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ippi
Manila
Trench
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Halmahera
North
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Solomons
Bi
BS
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Wd
NF
New
Hebrides
Hinge
Advance
L
Tonga
Hinge
Retreat
Kermadec
FIG 2 - A: Regions and intervals of significant movement of subduction hinges in the Neogene based on the reconstructions of Hall (1998). The map
represents the interval between the regional plate reorganisations of 25 Ma and 5 Ma. Major continental outlines are shown at 25 Ma for reference. For
subduction zones shown without shading there was no significant movement of hinge. B: Regions of significant movement of subduction hinges since 5
Ma based on the reconstructions of Hall (1998). Bold letters indicate areas of young marginal basin formation. Major continental outlines are shown at
5 Ma for reference.
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C G MACPHERSON and R HALL
Variation in steady-state settings
There are many possible tectonic causes for variation in the
character of magmatism in a steady-state setting. Changes in the
rate of subduction could vary both the rate at which the mantle
wedge is replenished and the fluxes of material (fluids and melts)
derived from the down-going slab. The nature of subducted
material may influence magmatism and may, in some
circumstances, provide a chemical tracer of tectonic history. If
magmas interact with the crust, the character of crust in the
over-riding plate will be important. For example, in east
Indonesia it is possible to identify changes in character of crust
from the geochemistry of the Neogene volcanic rocks (see
below). In the case of oblique subduction, there may be changes
in the character of crust where there are trench-parallel strike-slip
faults as in Sumatra and the Philippines.
Evolution of Recycled Components
Turner and Hawkesworth (1997) have shown that the nature of
recycled crust can influence the chemistry of melts erupted
through an arc. The nature of recycled materials, and recycling
processes, may also change. For example, Elburg and Foden
(1998) have suggested that the recycled component in southern
Sangihe arc lavas was derived mainly from altered oceanic crust
during the Middle Miocene but is presently dominated by a
sediment-derived melt. This evolution can be compared with data
for Neogene (Forde, 1997) and Quaternary (Morris et al, 1983)
magmatism in the Halmahera arc. An orthogonal collision
between the Sangihe and Halmahera arcs is consuming the
Molucca Sea plate. Therefore, the crust and sediments being
subducted beneath both arcs may be similar.
Figure 3 shows the changes in Zr/Nb in the Halmahera lavas
during differentiation of suites of lavas from Halmahera. The
Zr/Nb ratio is considered relatively sensitive to additions of
sediment-derived melt to the mantle wedge that produces low
values in the erupted lavas (Elliott et al, 1997). There is
considerable variation in Zr/Nb between the different Neogene
centres investigated by Forde (1997), but most appear to have
evolved from (high MgO) parental magmas with Zr/Nb ratios
that were similar to, or higher than, N-MORB (Figure 3). None
of the phenocryst phases present in Halmahera lavas are able to
produce significant changes in the Zr/Nb ratio during fractional
crystallisation. Lavas from Obi have relatively constant Zr/Nb
close to the MORB range while ratios increase through Central
362
100
C. Halmahera
Bacan
Obi
Quaternary
80
Zr/Nb
Following generation, melts must traverse the plate that
overrides the subduction zone prior to eruption. This transport
provides an opportunity for chemical differentiation, either
through melt-solid-vapour partitioning, or through open system
processes, such as magma-mixing, crustal contamination or
assimilation with fractional crystallisation (AFC). The
contaminants involved in these processes can resemble the
materials being subducted and care must be taken to fully
account for the influence of the overriding plate if recycled
fluxes are to be accurately constrained (Davidson and Harmon,
1989; Macpherson et al, 1998).
The studies conducted to formulate new theories on melt
generation in subduction zones have largely focussed on active
and recently active arcs. Much progress has been made by
investigating spatial variations within individual arcs that allow
evaluation of changes in the balance of different processes. Each
of the major processes influencing petrogenesis also has the
potential to vary in time (eg Turner and Hawkesworth, 1997;
Elburg and Foden, 1998). Therefore, geochemical studies have
potential to yield information on the evolution of tectonic events
at convergent margins. This is particularly relevant to SE Asia
where relatively rapid changes in plate configuration and the
rates of tectonic processes have occurred throughout the
Cenozoic.
60
40
N-MORB
20
0
0
2
4
6
8
MgO (wt.%)
FIG 3 - Plot of MgO (wt. %) content versus Zr/Nb for Neogene and
Quaternary to Recent volcanics from the Halmahera Arc. Zr/Nb ratios
higher than the value for MORB infer residual mantle wedge while low
values can reflect incorporation of subducted sediment. Halmahera data
from Forde (1997) and Morris et al (1983) and N-MORB from Sun and
McDonough (1989).
Halmahera and Bacan. High values for Zr/Nb ratios occur in melts
derived from mantle that has experienced previous melt
extraction (Woodhead et al, 1993) and probably require a
relatively high fluid flux to induce melting. Thus, the Neogene
data for Halmahera are consistent with a mantle wedge that was
variably depleted, with respect to the MORB source, being
fluxed by a slab-derived fluid.
The majority of Quaternary lavas from Halmahera also have
Zr/Nb ratios that are similar to N-MORB (Figure 3). A few
Quaternary lavas also have Zr/Nb in excess of N-MORB. This
suggests that, like Neogene magmas, the majority of these lavas
were derived from mantle that was similar to or more depleted
than the MORB source. However, a number of Quaternary lavas
display Zr/Nb lower than any observed from the Neogene arc.
Normal mantle processes, such as previous melt extraction or
fractional melting, are unable to produce melts with low Zr/Nb
ratios suggesting a significant input from a reservoir
characterised by low Zr/Nb. Sediments provide such a reservoir
(Elliott et al, 1997) and partial melting of sediment, as opposed to
bulk additions to the mantle, may further lower the ratio.
Therefore, Zr/Nb ratios can be used to infer that Quaternary arc
lavas may contain a more significant contribution from
subducted sediment than lavas erupted during the Neogene. In
this respect, the Neogene to present day evolution of the
Halmahera and Sangihe arcs has been similar. However, unlike
the Sangihe arc mass transport of recycled components by both
fluid and melt appears to have been important in different parts
of the Halmahera arc from the Neogene until the present.
Figure 4 compares Pb and Nd isotope data for the arcs
colliding in the Molucca Sea region. This figure also illustrates
the less extreme time dependence of mass transfer processes of
the Halmahera arc compared to Sangihe. The younger (Pliocene
to Quaternary) Sangihe volcanics are successively displaced
closer to the field of sediments than their Neogene counterparts
(Elburg and Foden, 1998). In the Halmahera arc there is
considerable overlap between lavas of different ages, although
the Quaternary rocks are again more concentrated towards the
field of sediments. The most conspicuous feature of this plot is
the distinct offset between the fields for the two arcs; the
Halmahera lavas possess consistently higher 206Pb/204Pb. This
may be interpreted in several ways. It may be incorrect to assume
that similar sediment is subducted under each arc and that
sediment has higher 206Pb/204Pb in the east. Alternatively, the
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TECTONIC CONTROLS OF GEOCHEMICAL EVOLUTION IN ARC MAGMATISM OF SE ASIA
same sediment may enter both subduction zones but mixes with
isotopically distinct mantle wedges. The isotopic characteristics
of both arcs, throughout their Neogene to Recent history, favour
derivation from mantle similar to the source of Indian Ocean (I-)
MORB. I-MORB show a sufficiently large isotopic range to
accommodate the range of sources required to account for the
differences between Halmahera and Sangihe lavas (Figure 4). A
final possibility is that the same sediment is being subducted
beneath both arcs where it is contaminating mantle wedges that
have similar isotopic characteristics but different Pb/Nb ratios,
resulting in greater sensitivity to Pb contamination in the low
Pb/Nd wedge (Halmahera).
0.5131
Indian Ocean MORB
143
Nd/144Nd
0.5130
0.5129
0.5128
0.5127
0.5126
17.8
Halmahera Neogene
Halmahera Quaternary
Sangihe Neogene
Sangihe Pliocene
Sangihe Quaternary
18.0
Sediments
18.2
18.4
206
18.6
18.8
204
Pb/ Pb
FIG 4 - 206Pb/204Pb versus 143Nd/144Nd in lavas from the Molucca Sea
collision zone. Lavas from the Sangihe arc show a clear temporal
progression towards lower 143Nd/144Nd. While there is more overlap
between Neogene and Quaternary arc lavas, in the Halmahera data a
similar overall progression exists. Halmahera data from Forde (1997),
Sangihe data from Elburg and Foden (1998) and Indian Ocean MORB
from Michard et al (1986), Ito et al (1987) and references therein.
Evolution of Mantle Wedge
Progressive melting of the mantle wedge might be expected to
result in increasingly depleted lavas being erupted in the later
stages of an arc’s activity. However, lavas from the Quaternary
Halmahera arc show no significant evidence for greater depletion
of the mantle wedge when compared to the Neogene arc (Figure
3). This suggests that fresh material has been available to
maintain the fertility of the zone of melting beneath the
Halmahera arc since the Neogene.
Upwelling of asthenosphere from the backarc region is a
significant control on the depletion of the mantle wedge. Mantle
can be ‘processed’ through the backarc region before being
advected into the mantle wedge (McCulloch and Gamble, 1991).
Where melting is minimal, or absent, in the backarc region this
will allow the mantle wedge to be replenished with fertile
peridotite. Therefore, arcs that are tectonically susceptible to
asthenospheric upwelling may be less likely to show a
progressive depletion in wedge fertility. Upwelling will be an
inevitable tectonic response in subduction zones when hinge
retreat occurs (Hamilton, 1995). Figure 2A shows that the
boundary between the Molucca Sea plate and the Philippine Sea
plate, to the west of Halmahera, migrated relatively rapidly
westwards through the Neogene resulting in substantial hinge
retreat west of the Halmahera arc. Peridotite from beneath the
Philippine Sea plate or deeper in the asthenosphere must have
been drawn into the mantle wedge during this process.
Recharging of the mantle wedge by asthenospheric peridotite
could reduce, or even suppress, the overall wedge depletion
throughout the lifetime of an arc.
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This process may also play a factor in the relative volumes of
arcs. Volumetrically, the Halmahera arc is considerably larger
than the Sangihe arc on the opposing side of the Molucca Sea
collision zone. During the Neogene there was negligible
movement of the subduction hinge at the Sangihe arc, separating
the Molucca Sea plate and the Eurasian plate (Figure 2A). This
situation would not favour upwelling of fresh fertile peridotite
beneath the Sangihe arc, thus limiting the volume of magmatism.
Replenishment of the Halmahera mantle wedge would provide a
greater reservoir of fertile mantle from which to construct a
larger arc.
Evolution of Crustal Interaction
The basement upon which island arcs are constructed are
relatively poorly known. To a large extent, this is due to the
poor exposure of basement rocks that have often been blanketed
by the products of the arc. Geophysical techniques can be used to
indirectly examine the nature of arc basements, but, interactions
between the crust and passing melts can produce distinctive
geochemical signatures in the melts. Where local basement rocks
have been geochemically characterised such signatures can be
exploited to understand the degree and processes of interaction
(eg Macpherson et al, 1998). Conversely, where the basement is
not exposed, suites of lavas displaying geochemical trends that
can be attributed to crustal interactions may reveal something of
the nature of the arc basement. Where the age of magmatism is
known this may also provide tectonic constraints on the
development of crustal domains (Vroon et al, 1996).
The island of Bacan, in the Halmahera arc, provides an
example. Morris et al (1983) noted that dacitic lavas in southern
Bacan, erupted near areas of metamorphic basement, possess
exceptionally radiogenic strontium and lead isotopic ratios
(87Sr/86Sr: 0.7198-0.7240, 206Pb/204Pb: circa 40.2). In conjunction
with elevated alkali contents in the lavas, Morris et al (1983)
used the isotopic ratios to suggest that the dacites were
contaminated by crust of continental origin. Neogene dacites
displaying elevated isotopic ratios indicate that this continental
material was present in the arc crust prior to the Late Miocene
(Vroon et al, 1996; Forde, 1997). However, the locally exposed
basement (Sibela Metamorphic Complex) has lead and strontium
isotopic ratios that are too low to produce the values found in the
dacites requiring older basement material to be available in the
crust (Forde, 1997). In the western part of Bacan isotopic ratios
of Late Miocene basaltic andesites show 87 Sr/ 86 Sr and
143
Nd/144Nd ratios typical of oceanic arcs, whereas Pliocene lavas
in the same part of the island have higher 87Sr/86Sr and lower
143
Nd/144Nd that are consistent with contamination by the rocks of
the Sibela Complex. This implies either:
a. a change in magma dynamics leading to interaction
between melts and parts of the crust that were previously
unaffected by magmatism; or
b. tectonic movement - possibly associated with the Sorong
Fault Zone (Hall et al, 1991) – introducing previously
unavailable material.
The latter scenario suggests that strike slip faulting in the
region would have been active in the late Neogene as implied by
palaeomagnatic studies (Ali and Hall, 1995).
Subduction without magmatism
In some areas there is subduction but no arc magmatism.
Changes in rates of subduction are a possible explanation but
where subduction has been effectively continuous other
explanations are required for temporal changes in arc volcanic
activity. It has been suggested that backarc basin formation leads
to a cessation of arc volcanism. From early studies of the
Philippine Sea plate Karig (1983) suggested arc volcanism
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C G MACPHERSON and R HALL
continued during backarc basin opening whereas ODP drilling in
the Mariana arc led other workers (Scott et al, 1980; Scott and
Kroenke, 1980; Hussong and Uyeda, 1981) to advocate an
alternation of arc activity with backarc basin opening. It now
seems that arc volcanism generally does continue during backarc
basin opening (Taylor and Natland, 1995). In search of other
causes Cambray et al (1995) used ODP and DSDP cores to infer
periodicity in volcanic activity based on the distribution of ash
deposits in the western Pacific. They interpreted the temporal
variations in volcanic activity to reflect variations in shallow
stress fields in some arcs (Japan and Bonin), but where this
explanation did not apply they appealed to variations in the
amount of subducted hydrated sediment in other Philippine Sea
arcs. McCourt et al (1996) suggested periodicity in magmatism
in Sumatra may mark variations in plate motions and changes in
obliquity of subduction but it is not yet entirely clear if the
variations they infer, based largely on K-Ar dating, are real or an
artefact of the dating method and database. East of Java volcanic
activity in the Sunda arc declines significantly in the period
between about 20 and 10 Ma although there is no evidence for
changes in direction or rates of motion. This may reflect the
movement of the subduction hinge and the reconstructions of
Hall (1998) suggest that this region experienced hinge advance
during this interval (Figure 2A). Carlson and Mortera-Guitierrez
(1990) have also related variations in rates of hinge advance to
backarc basin formation in the Philippine Sea plate. Elsewhere,
hypotheses of slab breakoff (eg Richardson, 1993) or formation
of gaps in the subducting slab (Thorkelsen, 1996) are plausible.
Until now these types of explanation have been difficult to test
because of the complex configurations of slabs under many parts
of SE Asia, as is well illustrated by the Molucca Sea region
(McCaffrey, 1982; Hall et al, 1995; Lallemand et al, 1998).
Continued improvements in the seismic database and detailed
tomographic studies may offer the means to test these types of
model.
Magmatism without subduction
It is not unusual to find arc-like magmatism in regions where
subduction is not active. Several magmatic provinces in SE Asia,
including parts of the Philippines, south Sulawesi and east
Indonesia, can be described in these terms. Like similar
magmatism in other parts of the world – such as the Aeolian
Islands, Italy (Ellam et al, 1989) and the Basin and Range
province of SW USA (Fitton et al, 1991) - lavas from these
settings display distinctive geochemical signatures indicating their
origins are linked to subduction processes.
The presence of potassic volcanoes at convergent margins and
in post-collisional settings argues for some link between
subduction and the origin of this type of magmatism. Various
models have been proposed including melting of subduction
modified mantle (Johnson et al, 1978), melting of subducted
sediment (Rogers et al, 1987) and melting of crustal material
(Bergman et al, 1996). In several regions, such as western and
southern Sulawesi, magmatism clearly post-dates active
subduction suggesting that an origin through mantle enrichment
or crustal melting is likely. The rapid reorganisation of plate
boundaries that are known to have affected SE Asia during the
Cenezoic may have caused dispersion of mantle domains that
developed distinctive characteristics.
Mantle Enrichment Events
Bergman et al (1996) used isotopic data to infer that potassic
magmatism in the Kalosi region of western Sulawesi is the result
of crustal melting during the Middle Miocene to Pliocene. They
suggested that the Makassar Strait is a foreland basin between
two converging thrust systems. The potassic magmatic province
of Sulawesi extends beyond Kalosi to the southwestern tip of the
364
island (Polvé et al, 1997) and plate tectonic reconstructions can
be used to show that this portion of Sulawesi was adjacent to
Java during from the Paleogene until late Oligocene (Figure 5).
At that time, the regions of SW Sulawesi that subsequently
experienced potassic magmatism were located along strike from
the locations of Plio-Pleistocene ultra-potassic volcanism in
northern Java (Figure 5B). A link between potassic magmatism in
southern Sulawesi and Java has previously been suggested by
Leterrier et al (1990). The plate reconstruction of Hall (1996)
provides a tectonic framework for this link showing that the
mantle sources of these regions could have been established
simultaneously above a single subduction zone and subsequently
separated by tectonic processes (Figure 5).
A link between potassic magmatism in Java and Southern
Sulawesi is further suggested by similarities in trace element and
isotopic compositions. Trace element characteristics of lavas in
both regions (eg enrichment of large ion lithophile elements
relative to high field strength elements) provide clear evidence
that the sources are enriched in many elements, with respect to
MORB, and that the enrichment event was subduction-related
(Edwards et al, 1994; Macpherson, 1994; Elburg and Foden,
1997; Polvé et al, 1997). Strontium and neodymium isotopic
ratios are also very similar in lavas from the two areas (Edwards
et al, 1994; Macpherson, 1994; Elburg and Foden, 1997).
Isotopic ratios of strontium, neodymium and lead in the Javan
lavas strongly point towards melting of enriched mantle rather
than crustal melting (Figure 6). Melting was probably induced by
later tectonic events since the location of potassic magmatism in
northern Java coincides with major structural lineaments in the
basement (Soeria-Atmadja et al, 1988). This is a feature that the
Javan volcanoes share with other post-subduction potassic
volcanics, such as the Basin and Range province of the United
States (Fitton et al, 1991).
These findings imply that a crustal source may not be
necessary to explain potassic magmatism throughout western and
southern Sulawesi, weakening arguments for a foreland basin
origin for the Makassar Strait. Processes such as loading in a
collision zone (Bergman et al, 1996) or underthrusting (Priadi et
al, 1994), which are necessary to achieve melting of continental
crust in western Sulawesi, need not be required in the
southwestern arm of the island if the potassic magmatism has a
mantle source. In this case, a major discontinuity in magmatic
(and tectonic?) processes must be inferred to exist to the south of
the Kalosi region (Elburg and Foden, 1997). Polvé et al (1997)
suggested that within plate extension might provide a mechanism
to induce melting of enriched mantle beneath SW Sulawesi. This
may be associated with extension in the Gulf of Bone to the east
of the SW Sulawesi peninsula. The axis of inferred extension lies
sub-parallel to the alignment of the southern Sulawesi potassic
volcanoes and extension is thought to have commenced in the
Middle Miocene (Guntoro, 1995) at the same time that
magmatism was initiated (Polvé et al, 1997).
Adakitic Melts
In parts of the Philippines adakitic rocks have been inferred to
result from subduction of young, hot crust with resultant slab
melting (Defant and Drummon, 1990). However, adakitic lavas
in Mindanao interpreted to be related to subduction at the
Cotobato trench (Sajona et al, 1994 and 1997) seem unlikely to
have been generated in this way. These adakites have ages
greater than 1 Ma, the age of the subducted crust is Eocene and
the subducted Celebes Sea slab is still currently only at depths of
about 80 km. At the time of magmatism the slab would not have
penetrated even to this depth. Thus, the availability of a suitable
adakite reservoir from the subducted Celebes Sea lithosphere is
questionable. In Mindanao and in the Bacan region of east
Indonesia (Forde, 1997) there is an obvious relationship of these
rocks to strike-slip faults. This suggests that rather than melting
Bali, Indonesia, 10 - 13 October 1999
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TECTONIC CONTROLS OF GEOCHEMICAL EVOLUTION IN ARC MAGMATISM OF SE ASIA
s
Palawan
A: Present
Mindanao
s
r enc
ine T
s
Sulu
Sea
SUNDA
SHELF
h
s
Malaya
pp
Phili
10oN
s
Celebes
Sea
s
s
Molucca
Sea
Halmahera
s
Borneo
s
Sula
Platform
assa
r Str
ait
0o
Su
nd
a
Sulawesi
Mak
Sumatra
ng
Soro
t
u
Fa l
Seram
Java Sea
Tre
n
Banda Sea
ch
da Arc
Inner Ban
Java
Java Tren
10oS
Timor
ch
Sumba
h
roug
or T
Tim
INDIAN PLATE
100 E
110oE
o
120oE
130oE
10oN
Proto
South China
Sea
SUNDA
SHELF
B: 45 Ma
Sumatra
0o
Borneo
a
nd
Su
Celebes
Sea
Java Sea
Tre
n
Java
Jav
a Tr
10oS
100oE
it
tra
ch
s
as
k
Ma
S
ar
Philippine
Sea
West
Sulawesi
enc
h
AUSTRALIAN PLATE
INDIAN PLATE
110oE
120oE
130oE
FIG 5 - A: Present day plate configuration of the southern Sundaland margin. Locations of post-Middle Miocene ultra-potassic volcanoes in Java and
southern Sulawesi (Letterier et al, 1990; Polvé et al, 1997) are shown are black triangles. B: Plate tectonic reconstruction of the same region during the
Eocene (Hall, 1998). The locations of post-Middle Miocene potassic magmatism in Java and southern Sulawesi form a zone parallel to the Java Trench
at that time.
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365
C G MACPHERSON and R HALL
REFERENCES
0.5133
Indian
MORB
0.5132
0.5131
143Nd/144 Nd
0.5130
0.5129
0.5128
Guntur
Cereme
0.5127
0.5126
Muriah
Banda Arc
0.5125
0.5124
Sediment
0.5123
0.702
0.704
0.706
0.708
0.710
0.712
87Sr/86Sr
Fig 6. 87Sr/86Sr versus 143Nd/144Nd for volcanic rocks from the Sunda
Arc. Symbols represent different lava groups from the potassic Ringgit
Formation in eastern Java (Edwards et al, 1994; Macpherson, 1994).
Although displaced from probable local mantle compositions (Indian
Ocean MORB) the Ringgit lavas, and other potassic lavas from the Java
(eg Muriah) have isotopic ratios that are not consistent with the
involvement of old continental crust. This contrasts with the Banda arc
(Vroon et al, 1993). Other data from Michard et al (1986), Ito et al
(1987), Ben Othman et al (1989), Stolz et al (1990), Edwards et al
(1991), Van Bergen et al (1992), Vroon (1992), Edwards et al (1993).
the subducted slab the rocks are produced by melting of the
mantle wedge and/or lower crust. Recent slab rollback on the
west side of the Philippines (Figure 2B) would have caused an
inflow of hot mantle with additional heat provided by ductile
shearing in the lower crust or upper mantle as suggested for other
major strike-slip zones (Thatcher and England, 1998). A similar
explanation would apply in the Halmahera arc where there has
been massive rollback of the Molucca Sea slab in the last 10-15
Ma.
SUMMARY
The timing and location of magmatism in SE Asia can be related
to recent models for the evolution of plate boundaries. Hinge
retreat appears to be important in controlling the volume of melt
produced at an active margin. Furthermore, the dynamic nature
of subduction zones suggests that this process may also
encourage mantle circulation through the mantle wedge with
implications for the chemistry of arc magmas. Changes in the
balance between recycled fluxes of slab-derived fluid and
sediment melts also appear to be possible and the presence of
faults and thrusts in the overriding plate may lead to changes in
the crust available to interact with melts during transport to the
site of eruption. Finally, mantle that has been enriched by
dehydration and/or melting of subducted material may be
sampled by later magmatic events. Plate reconstruction models
can be used to trace the provenance of such mantle and identify
regions that may formerly have comprised part of the same
supra-subduction zone complex.
ACKNOWLEDGEMENTS
Funding from the Southeast Asia Research Group supported by
Arco, Canadian Petroleum, Exxon, LASMO, Minorco, Mobil,
Union Texas and Unocal is gratefully acknowledged. The
comments of an anonymous reviewer helped improve this
contribution.
366
Abbott, M J and Chamalaun, F H, 1978. New K/Ar age data for Banda
arc volcanics, Institute for Australian Geodynamics Publication 78/
5, 34pp.
Ali, J R and Hall, R, 1995. Evolution of the plate boundary between the
Philippine Sea Plate and Australia: palaeomagnetic evidence from
eastern Indonesia, Tectonophysics, 251: 251-275.
Baker, S and Malaihollo, J, 1996. Dating of Neogene igneous rocks in
the Halmahera region: arc initiation and development, in, Tectonic
evolution of Southeast Asia, (Eds: Hall, R and Blundell, D J), pp
499-509 (Geological Society of London Special Publication 106).
Bergman, S C, Coffield, D Q, Talbot, J P and Garrard, R A, 1996. Tertiary
tectonic and magmatic evolution of western Sulawesi and the
Makassar Straight, Indonesia: evidence for a Miocene continentcontinent collision, in, Tectonic evolution of Southeast Asia, (Eds:
Hall, R and Blundell, D J), pp 391-429 (Geological Society of London
Special Publication 106).
Ben Othman, D, White, W M and Patchett, J, 1989. The geochemistry of
marine sediments, island arc magma genesis and crustal-mantle
recycling, Earth and Planetary Science Letters 94: 1-21.
Brennan, J, Shaw, H F, Phinney, D L and Ryerson, J F, 1995. Mineral –
aqueous fluid partitioning of trace elements at 900°C and 2.0Gpa:
Constraints on the trace element chemistry of mantle and deep crustal
fluids, Geochimica et Cosmochimica Acta 59: 333-3350.
Cambray, H, Pubellier, M, Jolivet, L and Pouclet, A, 1995. Volcanic
activity recorded in deep-sea sediments and the geodynamic evolution
of Western Pacific island arcs, in, Active Margins and Marginal
Basins of the Western Pacific, (Eds: Taylor, B and Natland, J), pp
97-124 (American Geophysical Union Geophysical Monograph 88).
Carlson, R L and Mortera-Guitierrez, C A, 1990. Subduction hinge
migration along the Izu-Bonin-Marian arc, Tectonophysics 181: 331344
Cosca, M A, Arculus, R J, Pearce, J A and Mitchell, J G, 1998. 40Ar/39Ar
and K-Ar geochronological age constraints for the inception and early
evolution of the Izu – Bonin – Mariana arc system, The Island Arc
7: 579-595.
Davidson, J P and Harmon, R S, 1989. Oxygen isotope constraints on the
petrogenesis of volcanic arc magmas from Martinique, Lesser Antilles,
Earth and Planetary Science Letters 95: 255-270.
Defant, M J and Drummond, M S, 1990. Derivation of some modern arc
magmas by melting of young subducted lithosphere, Nature 347:
662-665.
Edwards, C M H, Menzies, M and Thirlwall, M F, 1991. Evidence from
Muriah, Indonesia, for the interplay of supra-subduction zone and
intraplate processes in the genesis of potassic alkaline magmas,
Journal of Petrology 32: 555-592.
Edwards, C M H, Morris, J D and Thirlwall, M F, 1993. Separating mantle
from slab signatures in arc lavas using B/Be and radiogenic isotope
systematics, Nature 362: 530-533.
Edwards, C M H, Menzies, M A, Thirlwall, M F, Morris, J D, Leeman, W
P and Harmon, R S, 1994. The transition to potassic alkaline
volcanism in island arcs: the Ringgit – Beser Complex, east Java,
Indonesia, Journal of Petrology 35: 1557-1595.
Elburg , M A and Foden, J D, 1997. Magmatism in west Sulawesi,
Indonesia: geochemical characteristics and economic implications,
Geological Society of Australia Abstracts 45: 21-23.
Elburg, M A and Foden, J D, 1998. Temporal changes in arc magma
geochemistry, north Sulawesi, Indonesia, Earth and Planetary
Science Letters 163: 381-398.
Ellam, R M, Hawkesworth, C J, Menzies, M A and Rogers, N W, 1989.
The volcanism of southern Italy: role of subduction and the
relationship between potassic and sodic alkaline magmatism, Journal
of Geophysical Research 94: 4589-4601.
Elliot, T, Plank, T, Zindler, A, White, W and Bourdaon, B, 1997. Element
transport from slab to volcanic front at the Mariana arc, Journal of
Geophysical Research 102: 14991-15019.
Ewart, A and Hawkesworth, C J, 1987. The Pleistocene – Recent Tonga –
Kermadec arc lavas: interpretation of new isotopic and rare earth
data in terms of a depleted mantle source model, Journal of Petrology
28: 495-530.
Bali, Indonesia, 10 - 13 October 1999
PACRIM ‘99
TECTONIC CONTROLS OF GEOCHEMICAL EVOLUTION IN ARC MAGMATISM OF SE ASIA
Fitton, J G, James, D and Leeman, W P, 1991. Basic magmatism associated
with late Cenozoic extension in the western United States:
compositional variation in space and time, Journal of Geophysical
Research 96: 13683-13711.
Forde, E, 1997. The geochemistry of the Neogene Halmahera Arc, eastern
Indonesia, PhD Thesis (unpublished), University of London.
Guntoro, A, 1995. Tectonic evolution and crustal structure of the central
Indonesian region from geology, gravity and other geophysical data,
PhD Thesis (unpublished), University of London.
Hakim, A S and Hall, R, 1991. Tertiary volcanic rocks from the Halmahera
arc, eastern Indonesia, Journal of Southeast Asian Earth Science 6:
271-287.
Hall, R, 1996. Reconstructing Cenezoic SE Asia, in, Tectonic evolution
of Southeast Asia, (Eds: Hall, R and Blundell, D J), pp 153-184
(Geological Society of London Special Publication 106).
Hall, R, 1998. The plate tectonics of Cenozoic SE Asia and the distribution
of land and sea, in, Biogeography and Geological Evolution of SE
Asia, (Eds: Hall, R and Holloway, J D), pp 99-131 (Backhuys
Publishers, Leiden, The Netherlands).
Hall, R, Ali, J R, Anderson, C D and Baker, S J, 1995. Origin and motion
history of the Philippine Sea Plate, Tectonophysics 251: 229-251.
Hall, R, Nichols, G, Ballantyne, P, Charlton, T and Ali, J, 1991. The
character and significance of basement rocks of the southern Molucca
Sea region, Journal of Southeast Asian Earth Sciences, 6: 249-258.
Hamilton, W B, 1988. Plate tectonics and island arcs, Geological Society
of America Bulletin 100: 1503-1527.
Hamilton, W B, 1995. Subduction systems and magmatism, in, Volcanism
associated with Extension at consuming plate margins, (Ed: Smellie,
J L,), pp 3-28, (Geological Society of London Special Publication
81).
Hawkesworth, C J, Hergt, J M, Ellam, R M and McDermott, F, 1991.
Element fluxes associated with subduction related magmatism,
Philosophical Transactions of the Royal Society of London A335:
393-405.
Hawkesworth, C J, Turner, S P, McDermott, F, Peate, D W and van
Calsteren, P, 1997. U-Th isotopes in arc magmas: implications for
element transfer from the subducted crust, Science 276: 551-555.
Hussong, D M, Uyeda, S, 1981. Tectonic processes and the history of the
Mariana arc: a synthesis of the results of DSDP Leg 60, in, Initial
Reports DSDP 60, (Eds: Hussong, D M, Uyeda, S et al) 909-929.
Ito, E, White, W M, Göpel, C, 1987. The O, Sr, Nd and Pb isotope
geochemistry of MORB, Chemical Geology 62: 157-176.
Johnson, R W, Mackenzie, D E and Smith, I E M, 1978. Delayed partial
melting of subduction-modified mantle in Papua New Guinea,
Tectonophysics 46: 197-216.
Karig, D E, 1983. Temporal relationships between back arc basin
formation and arc volcanism with special reference to the Philippine
Sea, in, The Tectonic and Geologic Evolution of Southeast Asian
seas and islands, Part 2. (Ed: Hayes, D E), pp 318-325 (American
Geophysical Union Geophysical Monograph 27).
Katili, J A, 1975. Volcanism and plate tectonics in the Indonesian island
arcs, Tectonophysics, 26: 165-188.
Keppler, H, 1996. Constraints from partitioning experiments on the
composition of subduction-zone fluids, Nature 380: 237-240.
Lallemand, S E, Popoff, M, Cadet, J-P, Bader, A-G, Pubellier, M, Rangin,
C, and Deffontaaines, B, 1998. Genetic relations between the central
and southern Philippine trench and the Sangihe trench, Journal of
Geophysical Research 103: 933-950.
Leterrier, J, Yuwono, Y S, Soeria-Atmadja, R and Maury, R C, 1990.
Potassic volcanism in Central Java and south Sulawesi, Indonesia,
Journal of Southeast Asian Earth Sciences 4: 171-187.
Macpherson, C G, 1994. New Analytical Approaches to the oxygen and
carbon stable isotope geochemistry of some subduction-related lavas,
PhD Thesis (unpublished), University of London.
Macpherson, C G, Mattey, D P and Gamble, J A, 1998. Oxygen isotope
geochemistry of lavas from an oceanic to continental arc transition,
Kermadec-Hikurangi margin, S.W. Pacific, Earth and Planetary
Science Letters 160: 609-621.
McCaffrey, R, 1982. Lithospheric deformation within the Molucca sea
arc-arc collision: evidence from shallow and intermediate earthquake
activity, Journal of Geophysical Research 87: 3663-3678.
PACRIM ‘99
McCourt, W J, Crow, M J, Cobbing, E J and Amin, T C, 1996. Mesozoic
and Cenozoic plutonic evolution of SE Asia: evidence from Sumatra,
Indonesia, in, Tectonic evolution of Southeast Asia, (Eds: Hall, R
and Blundell, D J), pp 321-335 (Geological Society of London Special
Publication 106).
McCulloch, M T and Gamble, J A, 1991. Geochemical and geodynamical
constraints on subduction zone magmatism, Earth and Planetary
Science Letters 102: 358-374.
Michard, A, Montigny, R and Schlich, R, 1986. Geochemistry of mantle
beneath the Rodriguez Triple Junction and the Southeast Indian Ridge,
Earth and Planetary Science Letters 78: 104-114.
Morris, J D, Jezek, P A, Hart, S R and Gill, J B, 1983. The Halmahera
Arc, Molucca Sea Collision Zone, Indonesia: A geochemical Survey,
American Geophysical Union Monograph 27: 373-387.
Morris, J D, Leeman, W P and Tera, F, 1990. The subducted component
in island arc lavas: constraints from Be isotopic and B-Be systematics,
Nature 344: 31-36.
Oxburgh, E R and Turcotte D L, 1970. Thermal structure of island arcs,
Geological Society of America Bulletin 81: 1665-1688.
Pearce, J A and Peate, D W, 1995. Tectonic implications of the composition
of volcanic arc magmas, Annual Reviews of Earth and Planetary
Sciences 23: 251-285.
Polvé, M, Maury, R C, Bellon, H, Rangin, C, Priadi, B, Yuwono, S, Joron,
J L and Soeria-Atmadja, R, 1997. Magmatic evolution of Sulawesi
(Indonesia): constraints on the Cenozoic geodynamic history of the
Sundaland active margin, Tectonophysics 272: 69-92.
Priadi, B, Polve, M, Maury, R C, Bellon, H, Soeria-Atmadja, R, Joron, J
L and Cotton, J, 1994. Tertiary and Quaternary magmatism in Central
Sulawesi: chronological and petrological constraints, Journal of
Southeast Asian Earth Sciences 9: 81-93.
Richardson, A, 1993. Lithosphere structure and dynamics of the Banda
Arc collision zone, Eastern Indonesia, Bulletin of the Geological
Society of Malaysia 33: 105-118.
Rock, N M S, Syah, H H, Davis, A E, Hutchison, D, Styles, M T and Lena
R, 1982. Permian to Recent volcanism in northern Sumatra,
Indonesia: a preliminary study of its distribution, chemistry and
peculiarities, Bulletin Volcanologique 45: 127-152.
Rogers, N W, Hawkesworth, C J, Mattey, D P and Harmon, R S, 1987.
Sediment subduction and the source of potassium in orogenic leucites,
Geology 15: 451-453.
Ryan, J G and Langmuir, C H, 1993. The systematics of boron abundances in
young volcanic rocks, Geochimica et Cosmochimica Acta 57: 1489-1498.
Sajona, F G, Bellon, H, Maury, R C, Pubellier, M, Cotten, J and Rangin,
C, 1994. Magmatic response to abrupt changes in geodynamic
settings; Pliocene Quaternary calc alkaline and Nb enriched lavas
from Mindanao (Philippines), Tectonophysics 237: 47-72.
Sajona, F G, Bellon, H, Maury, R C, Pubellier, M, Quebral, R D, Cotten,
J, Bayon, F E, Pagado, E and Pamatian, P, 1997. Tertiary and
Quaternary magmatism in Mindanao and Leyte (Philippines):
Geochronology, geochemistry and tectonic setting, Journal of Asian
Earth Sciences 15: 121-154.
Scott, R B and Kroenke, L, 1980. Evolution of back arc spreading and
arc volcanism in the Philippine Sea: interpretation of Leg 59 DSDP
results, in, The Tectonic and Geologic Evolution of South east Asian
Seas and Islands (Ed: Hayes, D E), pp 283 291 (American
Geophysical Union Geophysical Monograph 23).
Scott, R B, Kroenke, L W, Zakariadze, G and Sharashkin, A, 1980.
Evolution of the South Philippine Sea, Deep Sea Drilling Project
Leg 59 Results, in, Initial Reports of the Deep Sea Drilling Project
59, (Eds: Kroenke, L W, Scott, R B et al), pp 803-816.
Soeria-Atmadja, R, Maury, R C, Bellon, H, Yuwono, Y S and Cotton, J,
1988. Remarques sur la répartition du volcanisme potassique
quaternair de Java (Indonésie), C. R. Acad. Sci. Paris 307: 635-641.
Sun S S and McDonough, W F, 1989. Chemical and isotopic systematics
of oceanic basalts: implications for mantle composition and processes,
in, Magmatism in the ocean basins, (Eds: Saunders, A D and Norry, M J),
pp 313-345 (Geological Society of London Special Publication 42).
Stolz, A J, Varne, R, Davies, G R, Wheller, G E and Foden, J D, 1990.
Magma source components in an arc-continent collision zone: the
Flores – Lembata sector, Sunda arc, Indonesia, Contributions to
Mineralogy and Petrology 105: 585-601.
Bali, Indonesia, 10 - 13 October 1999
367
C G MACPHERSON and R HALL
Tatsumi, Y, Hamilton, D L and Nesbitt, R W, 1986. Chemical
characterisation of fluid phase released from a subducted lithosphere
and origin of arc magmas: evidence from high-pressure experiments
and natural rocks, Journal of Volcanology and Geothermal Research
29: 293-309.
Tatsumi, Y and Eggins, S, 1995. Subduction Zone Magmatism, 209p
(Blackwell Science).
Taylor, B and Natland, J, 1995. Active Margins and Marginal Basins of
the Western Pacific. American Geophysical Union Geophysical
Monograph 88.
Thatcher, W and England, P, 1998. Ductile shear zones beneath strikeslip faults: implications for the thermomechanics of the San Andreas
fault zone, Journal of Geophysical Research 103 (B1): 891-905.
Thirlwall, M F, Smith, T E, Graham, A M, Theodorou, N, Hollings, P,
Davidson, J P and Arculus, R J, 1994. High field strength element
anomalies in arc lavas: Source or process? Journal of Petrology 35:
819-838.
Thorkelsen, D J, 1996. Subduction of diverging plates and the principles
of slab window formation, Tectonophysics 255: 47-63.
Turner, S and Hawkesworth, C, 1997. Constraints on flux rates and mantle
dynamics beneath island arcs from Tonga – Kermadec lava
geochemistry, Nature 389: 568-573.
Turner, S, Hawkesworth, C, Van Calsteren, P, Heath, E, Macdonald, R
and Black, S, 1996. U-series isotopes and destructive plate margin
magma genesis in the Lesser Antilles, Earth and Planetary Science
Letters 142: 191-207.
368
Van Bergen, M J, Vroon, P Z, Varekamp, J C and Poorter, R P E, 1992.
The origin of the potassic rock suite from Batu Tara volcano (East
Sunda Arc, Indonesia), Lithos 28: 261-282.
Vroon, P Z, 1992. Subduction of continental material in the Banda Arc,
Eastern Indonesia: Sr – Nd – Pb isotope and trace-element evidence
from volcanics and sediments, PhD Thesis (published), University
of Utrecht.
Vroon, P Z, van Bergen, M J and Forde, E J, 1996. Pb and Nd isotope
constraints on the provenance of tectonically dispersed continental
fragments in east Indonesia, in, Tectonic evolution of Southeast Asia,
(Eds: Hall, R and Blundell, D J), pp 445-453 (Geological Society of
London Special Publication 106).
Vroon, P Z, van Bergen, M J, White, W M and Varekamp, J C, 1993. SrNd-Pb isotope systematics of the Banda Arc, Indonesia: Combined
subduction and assimilation of continental material, Journal of
Geophysical Research 98: 22349-22366.
Woodhead, J D, 1989. Geochemistry of the Mariana arc (western Pacific):
source composition and processes, Chemical Geology 76: 1-24.
Woodhead, J D, Eggins, S and Gamble, J A, 1993. High field strength
and transition element systematics in island arc and back-arc basin
basalt: evidence for multi-phase melt extraction and a depleted mantle
wedge, Earth and Planetary Science Letters 114: 491-504.
You, C -F, Castillo, P R, Gieskes, J M, Chan, L H and Spivak, A J, 1996.
Trace element behaviour in hydrothermal experiments: implications
for fluid processes at shallow depths in subduction zones, Earth
and Planetary Science Letters 140: 41-52.
Bali, Indonesia, 10 - 13 October 1999
PACRIM ‘99