Giliam Hamson - The Tectonic Evolution of East Timor and the Band

8/18/2019 Giliam Hamson - The Tectonic Evolution of East Timor and the Band

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The Tectonic Evolution of East Timor and the Banda Arc

Gillian Hamson, #74189

Honours Literature Review submitted as part of the B.Sc.(Hons) degree in the School ofEarth Sciences, University of Melbourne.

Submitted April 30th

, 2004


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I certify that this Literature Review contains less than 4,000 words.

Gillian Hamson


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Table of Contents

1 Introduction............................................................................................................... 1

2 Overview of regional geology................................................................................... 3

3 Tectonic activity in the Banda Arc.......................................................................... 8 3.1 The Timor thrust: deformation in the Timor Trough.......................................... 8

3.2 The Wetar thrust: deformation in the back-arc thrust zone ................................ 9

3.3 Earthquakes......................................................................................................... 93.4 Volcanism ......................................................................................................... 11

4 Models of tectonic evolution.................................................................................. 12 4.1 Overthrust model .............................................................................................. 12

4.2 Imbricate model ................................................................................................ 134.3 Autochthon model............................................................................................. 14

5 Response to tectonism: uplift and exhumation of Timor .................................... 16 5.1 Thermochronological data ................................................................................ 16

5.2 Raised reef terraces ........................................................................................... 17

5.3 Uplift mechanisms ............................................................................................ 19

6 Discussion................................................................................................................. 20

7 Thesis Plan............................................................................................................... 22

8 References................................................................................................................ 23


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Table of Figures

Figure 1.1 Map of the Banda Arc (adapted from Hinschberger et al., 2001) .................... 1

Figure 2.1 Simplified geology of East Timor (adapted from Charlton, 2002a)................. 4

Figure 2.2 Initial continental collision with subduction zone (from Charlton, 2000). ...... 5

Figure 2.3 Pliocene collision at the proto-Timor region (from Charlton, 2000). .............. 6

Figure 2.4 Position of oceanic and continental crust (from Keep et al., 2003)................. 7

Figure 2.5 Schematic cross section of the Banda Arc at Timor......................................... 7

Figure 3.1 Earthquake epicenters in the Banda Sea region (from Milsom, 2001).......... 10

Figure 3.2 Regions of active volcanism in the inner Banda Arc (from Harris, 1991). .... 11

Figure 4.1 Overthrust model (from Richardson and Blundell, 1996).............................. 12

Figure 4.2 Imbricate model (from Richardson and Blundell, 1996)................................ 13

Figure 4.3 Autochthon model (from Richardson and Blundell, 1996). ........................... 14

Figure 5.1 Locality map of East Timor............................................................................ 18

Figure 5.2 Digital elevation model of East Timor (from SRTM data set, USGS)……... 18


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The Tectonic Evolution of East Timor and the Banda Arc Gill Hamson #74189

1 Introduction

East Timor lies at the point at which the leading edge of the Australian continental

margin impinged upon the Eurasian plate, giving a rare insight into the early stages of a

major orogenic event. Subduction of buoyant Australian continental lithosphere

effectively jammed northward subduction beneath the oceanic outer Banda Arc during

the Neogene, resulting in arc-continent collision. Timor, the emergent core of the

resulting Banda Orogen, comprises accretionary material of both Australian and Eurasian

provenance (Bowin et al., 1980; Breen et al., 1989; Keep et al., 2003). The modern Banda

Arc is today bound by an inner volcanic arc and an accretionary outer arc of which Timor

is the largest island (Fig. 1.1).

Figure 1.1 The Banda Arc lies at the intersection of the Pacific, Eurasian and Indo-Australian plates. Thismap shows the position of the inner and outer Banda Arcs, the plates and their direction of movement

relative to the Eurasian plate (adapted from Hinschberger et al., 2001).

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East Timor, on the southern arm of the outer Banda Arc, is located approximately 640 km

northwest of Australia. It consists of the eastern part of Timor island, together with the

small enclave of Oecussi on the north coast of Western Timor, and the islands of Atauro

and Jaco (see Fig. 5.1, p.18). East and West Timor are divided along a 100 km north-

south political boundary located roughly in the centre of the island, and East Timor

extends 250 km to the east.

Geological knowledge of East Timor was acquired over three periods:

• Pre-1975: before Indonesian occupation, foreign access possible: reconnaissance

mapping (e.g. Audley-Charles, 1968).

• 1975-1999: Indonesian occupation: political turmoil, limited foreign access:

studies included seismic surveys and mapping of nearby islands (e.g. Hughes et

al., 1996; Richardson & Blundell, 1996; Snyder & Barber, 1997)

• Post-1999: Independent East Timor; foreign access again possible: studies include

computer modelling, thermochronology, stratigraphic and structural mapping (e.g.

Charlton, 2002a, b; Harris et al., 2000)

An evaluation of the present-day tectonic activity in the Banda Arc region will be

followed by a review of the three dominant tectonic evolution models for East Timor.

Finally, the continuing uplift of East Timor in response to collision will be discussed.

Landscape evolution as a consequence of this geodynamic change can be reconstructed

from the young, variably uplifted rocks in East Timor. My study will involve

constructing a tectonic geomorphological landscape history of East Timor based on the

most recent phase of uplift since arc-continent collision was initiated in the Neogene.

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2 Overview of regional geology

The geology of East Timor has long been recognised as highly complex, and many

theories have been proposed for the island’s tectonic evolution (Audley-Charles, 1968;

Chamalaun & Grady, 1978; Barber, 1979; Hamilton, 1979; Harris, 1991; Charlton,

2000). Despite the conflict of ideas, some broad geological observations allow a

generalised model of the tectonic development of this region since the Neogene.

Gravity surveys have confirmed that the Australian continental crust extends as far as the

north coast of Timor (Chamalaun et al., 1976; Hamilton, 1977). Overlying this gently

deformed Australian basement are rocks derived from the distal Australian passive

margin (para-autochthonous units), formed in response to the Middle-Late Jurassic

breakup of eastern Gondwana and subsequent sea-floor spreading. Passive margin

conditions prevailed until Neogene arc-continent collision, when rocks derived from the

pre-collisional Banda forearc (allochthonous units) were incorporated into the collision

complex. The rocks exposed in Timor (Fig. 2.1) include:

• Early-Permian to Early-Pliocene variably deformed and metamorphosed deep

water sediments of the Australian passive margin (Gondwana and Kolbano

Sequences)

• Late-Miocene-Early Pliocene Bobonaro Scaly Clay, an olistostrome thought to be

emplaced as a gravity slide in response to the southward tilting of Timor during

subduction (Johnston & Bowin, 1981).

• Banda Allochthon: pre-Cretaceous metamorphic rocks overlain by sedimentary

deposits and ophiolites of upper Jurassic to Lower Pliocene age , all of which are

derived from the pre-collisional Banda fore-arc

•

Post-orogenic Upper-Miocene to Recent coral reefs, alluvial terraces and

turbidites, unconformably overlying all other lithotectonic units.

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Figure 2.1 Simplified map of geological units in East Timor (adapted from Charlton, 2002a).

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Australia’s northern convergent margin encompasses New Guinea, Irian, Papua and

Timor. This collision has been markedly diachronous, with collision beginning in the

Oligocene at New Guinea (Fig. 2.2) (Charlton, 2000; Keep & Moss, 2000; Hall, 2002).

Figure 2.2 Initial collision of the Australian continental margin with the Eurasian-Pacific subduction zone

(from Charlton, 2000).

The time at which subduction of continental lithosphere first began at proto-Timor

(Fig.2.3) has been an issue of much controversy. Three different scenarios have been

proposed:

• Mid-Pliocene (Carter et al., 1976; Hamilton, 1979; Bowen et al., 1980; Johnston

& Bowin, 1981; Karig et al.,1987; Hall, 1996; Villeneuve et al., 1999).• Late Miocene (Berry & Grady, 1981; Berry & McDougall, 1986; Charlton, 2000;

Keep et al., 2003). This date coincides with the proposed incorporation of a

microcontinent into the collision complex, inferred to have been the cause of the

metamorphism in the Aileu Formation (Berry & McDougall, 1986).

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• Early-Mid Miocene (Rutherford et al., 2001; M. Harrowfield, pers. comm., 2004)

Rutherford et al. based their early age of collision on the related tectonic escape of

Sumba into the forearc at this time (~16 Ma).

Diachronous collision of an oblique promontory on the Australian continental margin has

been suggested, implying that timing of collision across Timor might have varied by as

much as 5 Myr (Snyder et al., 1996a; Keep et al., 2003). This is further elaborated upon

by Charlton (2002a, b), who claimed that earlier collision in East Timor relative to West

Timor prompted greater uplift and denudation in the eastern half of the island.

Figure 2.3 Initial collision of the Australian continental margin with the subduction zone at the proto-

Timor region (from Charlton, 2000).

Since 3 Ma, Timor progressively emerged from north to south, with southern Timor

becoming fully emergent in the late Pleistocene (Veevers, 2000; Johnston & Bowin,

1981). Oceanic lithosphere to the west of Timor continues to subduct northward beneath

the Eurasian plate (Fig. 2.4) (Audley-Charles, 1975; Chamalaun & Grady, 1978;McCaffrey & Nabelek, 1986; Lorenzo et al., 1998; Charlton, 2000). The island of Sumba,

to the west of Timor is composed entirely of non-Australian-affinity rocks and marks the

transition from subduction to oceanic lithosphere (Charlton, 2000).

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Figure 2.4 Position of oceanic crust (blue) and continental crust (green) south of the subduction zone.

Subduction no longer occurs south of Timor but continues at either end of the Timor Trough (from Keep etal., 2003).

It is clear that subduction and accretion are the driving mechanisms for tectonic activity

in the Timor region. The regional structure is dominated by a divergent thrust style (Fig.

2.5). The surface expression of the south-directed Timor thrust is coincident with a

bathymetric trough south of Timor (Johnston and Bowin, 1981), whereas the Wetar thrust

is north-directed and outcrops north of the inner Banda Arc north of Timor (Richardson

& Blundell, 1996; Harris et al., 2000). A dearth of deep earthquakes beneath East Timor

suggests the presence of a seismic gap in the region, which coincides with the inactive

segment of the inner Banda Arc. Elevated coral reefs of Quaternary age illustrate that

uplift continues today, possibly as a response to thrust formation or isostatic rebound

(Chappell and Veeh, 1978).

Figure 2.5 Schematic cross section of the Banda Arc at Timor.

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3 Tectonic activity in the Banda Arc

3.1

The Timor thrust: deformation in the Timor Trough

Accretion of collision material to the Australian continent is thought by some to have

resulted in formation of the Timor thrust, with its surface expression located south of

Timor in the Timor Trough (Hamilton, 1979; von der Bosch, 1979; Karig et al., 1987;

Masson et al., 1991). Seismic records show that the thrust dips northwards and stepped

south during collision, suggesting that it may have been related to the former interface

between the two plates ( Fig. 2.5) (Richardson & Blundell, 1996). However, this is

inconsistent with evidence that Australian crust underlies the Timor Trough and Timor

itself. The Timor thrust may instead represent a splay emanating from the main

subduction-related thrust structure (M. Sandiford, pers. comm., 2004).

While some authors claim that plate convergence is accommodated on the Timor thrust,

recent work using Global Positioning System geodetic measurements established that

Timor and the inner Banda Arc are moving northward at the same rate as the Australian

continent (Genrich et al., 1996). Thus, convergence may be transferred from the Timorthrust to the back arc region by cross-arc faulting zones (Masson et al., 1991), which

account for the paucity of large thrust earthquakes concentrated at the Timor thrust

(Johnston & Bowin, 1981; McCaffrey, 1988; McCaffrey, 1996). It is thus probable that

movement on the Timor thrust ceased or at least slowed in the recent past. As such, the

Timor Trough, “despite its developmental link with a subduction trench, may now be

regarded as an intracontinental feature” (Johnston & Bowin, 1981).

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3.2

The Wetar thrust: deformation in the back-arc thrust zone

North of Timor, the Wetar back-arc thrust zone evolved in order to accommodate

convergence between Australia and the Banda Sea, through a combination of back-arc

thrust faulting and strike-slip cross-arc faulting (Breen et al., 1989; McCaffrey & Abers,

1991; Snyder et al., 1996b; Snyder & Barber, 1997; Lorenzo et al., 1998; Veevers, 2000;

Rutherford et al., 2001). Lateral shortening and crustal thickening have taken place along

thrust structures dipping antithetic to subduction (Richardson & Blundell, 1996). Such

north-directed thrusting is opposite to that occurring in the Java Trench and previously in

the Timor Trough (Hamilton, 1979; McCaffrey, 1988; Rutherford et al., 2001). The small

degree of shortening along the Wetar thrust suggests that it is a young feature, formed

possibly as recently as 0.15 Ma (McCaffrey, 1996). The transference of convergence

from the Timor thrust to the Wetar thrust is thought by some to represent the early stages

of subduction polarity reversal (Silver et al., 1983; McCaffrey & Nabelek, 1986;

McCaffrey, 1988; Breen et al., 1989; Snyder & Barber, 1997; Harris et al., 1998;

Rutherford et al., 2001).

The degree of convergence located in the Wetar thrust zone is a matter of dispute.

Masson et al. (1991) mapped shallow subsurface tectonic activity around the island of

Timor, and found little evidence for major thrusting north of the Timor Trough. M.

Norvick (pers. comm., 2004) believes that significant shortening is accommodated

northward of the Wetar thrust, in the South Banda Sea. These contrary views suggest that

more work is required to constrain the current convergent activity at the Wetar thrust and

its effects.

3.3 Earthquakes

Shallow thrust and strike-slip earthquakes accommodate some of the collision-induced

convergence, which is distributed throughout the forearc, island arc and backarc basin

(McCaffrey, 1988). Convergence is transferred across the arc via zones of strike-slip

faults such as the left-lateral transcurrent Wetar Fault. This particular fault is thought to

offset the island arc north of Timor by ~50km (Masson et al., 1991). While earthquakes

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show evidence of north-south convergence, normal faulting mechanisms also reveal that

slow east-west extension is occurring in the forearc region (McCaffrey, 1988). This is

supported by evidence of Plio-Pliestocene normal faulting in Timor (Audley-Charles,

1968).

Changes in seismicity are evident along the Banda Arc. Shallow earthquakes have

occurred throughout the region, but deeper seismic activity is concentrated to the east and

west of East Timor (Chamalaun & Grady, 1978). Shallow earthquakes in the vicinity of

East Timor cannot corroborate the reversal of subduction polarity, despite evidence of

northward thrusting in an opposite sense to that of the Timor thrust (McCaffrey, 1988).

Further studies of earthquakes at all depths in the region indicate that a notable seismic

gap exists beneath East Timor (Fig. 3.1) (Milsom, 2001). The seismic gap may be a result

of the detachment of the oceanic lithosphere at the former subduction zone beneath East

Timor (Milsom, 2001). This zone coincides with the inactive section of the volcanic arc,

as discussed below.

Figure 3.1 Earthquake epicenters in the Banda Sea region at depths of less than 100km and 100-125km

(from Milsom, 2001).

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3.4

Volcanism

The Alor/Wetar area of the inner arc directly north of East Timor has been volcanically

inactive during the last 3 Myr (Abbott & Chamalaun, 1978). The severing of the

connection between the magma chamber and the surface during the detachment of the

subducting oceanic lithosphere in this region is a likely explanation for the absence of

volcanism (Chamalaun & Grady, 1978; Johnston & Bowin, 1981). M. Norvick (pers.

comm., 2004) suggested that the disparity in active volcanism along the inner arc is

possibly due to a ‘locking’ of the collision zone at East Timor, a result of its proximity to

the rigid Sahul Platform to the south (Fig.3.2). Locking of the collision zone has caused

subduction to step northward into the Banda Sea, indicated by isolated active volcanism

at Gunung Api, well north of Wetar (Fig. 3.2). According to Johnston and Bowin (1981),

the Banda Sea thus remains an active subduction zone despite the lack of volcanism in

the inner Banda Arc north of Timor,

Figure 3.2 Regions of active volcanism (shaded) in the inner Banda Arc (from Harris, 1991).

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4 Models of tectonic evolution

Timor has been the focus of numerous geological studies since the early 20th

Century.

The seminal work on Timor is that of Audley-Charles (1968) who, despite describing the

close geological ties between Timor and Australia, maintained a completely

allochthonous origin for the material emplaced within the thrust sheets. Hamilton (1979)

labeled the collision complex ‘tectonic chaos’ due to the complexity of the rock

assemblage. Many workers have attempted to unravel the complex geology of Timor, and

a variety of models concerning the island’s tectonic evolution have been proposed.

4.1

Overthrust model

North South

Figure 4.1 Schematic cross-section of the overthrust model for Timor. Allochthonous units are overthrust

onto the folded Australian continental margin (from Richardson and Blundell, 1996).

The overthrust model was developed from early work on the surface geology where

overthrust sheets of allochthonous material are well exposed. Its proponents suggested an

almost completely allochthonous origin for the thrust sheets on Timor (Audley-Charles,

1968; Audley-Charles & Carter, 1972; Carter et al., 1976; Barber et al., 1977). Theyargued that allochthonous strata derived from the Eurasian plate to the north was thrust

onto the Australian crust during the collision process. Large-scale folding and erosion of

Australian continental margin sediments occurred before emplacement of the thrust

sheets, which were not affected by folding.

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The traditional justification for the overthrust model was the close juxtaposition of rocks

of very different types and origins, often of the same age (Bowin et al., 1980). These

rocks must have been widely separated at the time of deposition, then juxtaposed by

compression and overthrusting at the time of collision (Barber et al., 1977). However,

Grady and Berry (1977) amongst others, questioned the validity of the overthrust model

due to the lack of field evidence for basal thrust planes: what should have been near-

horizontal ‘thrust faults’ were in fact steeply dipping faults. Grady and Berry (1977) also

stated that in some areas, allochthonous and autochthonous material were in normal

stratigraphic relationship, and had experienced similar deformation.

4.2

Imbricate model

Figure 4.2 Schematic cross section of the imbricate model for Timor. Imbricated sheets of Australian andEurasian affinity are thrust on top of one another during collision (from Richardson and Blundell, 1996).

Thrust sheets overlying the Australian basement are of both allochthonous and para-

autochthonous origin and were pervasively imbricated during emplacement (Fitch &

Hamilton, 1974; Hamilton, 1979; Charlton et al., 1991; Charlton, 2000). Rocks of

distinctly different provenance were thrust together as a series of slices and are now

juxtaposed in Timor, forming a chaotic complex of imbricated rocks and mélange.

Chamalaun and Grady (1978) disputed this model as their field observations did not

support pervasive imbrication of units. Furthermore, there is little mixing of para-

autochthonous and allochthonous material as would have been expected in the imbricate

model. The incoherent chaotic mélange theory is too simplified a model for the tectonic

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evolution of East Timor (Chamalaun, 1977). Bowin et al. (1980) also disputed the

imbricate model, claiming that any Australian-affinity rocks on Timor were already

present in the Outer Banda Arc prior to collision. However, they did not suggest how

these rocks came to be in this present location: “the manner in which these continental

blocks became detached from the Australian continent and incorporated into the frontal

arc of the southern part of the Banda Arc is not well defined.”

A micro-continent of Eurasian affinity may form some of the crustal material within the

collision complex (Carter et al., 1976; Karig et al., 1987; Whittam et al., 1996;

Richardson & Blundell, 1996; Linthout et al., 1997; Hall, 2002). The proposed micro-

continent lay to the north of the North West Shelf and was incorporated into the collision

complex at around 8 Ma, coinciding with and causing the retrograde metamorphism of

the Aileu Formation on the north coast of East Timor (Berry & Grady, 1981; Berry &

McDougall, 1986). However, palaeomagnetic evidence suggests otherwise, showing

Timor to be part of the Australian allochthon at least during the Upper Permian and

Triassic (Chamalaun, 1977).

4.3

Autochthon model

Figure 4.3 Schematic cross section for the autochthon model. Timor represents the uplifted Australiancontinental margin. Uplift caused south-directed gravity sliding and decoupling of the oceanic slab (from

Richardson and Blundell, 1996).

The autochthon model opposes both the overthrust and imbricate models. In this model,

the accretionary wedge sediments were almost entirely derived from the cratonic

sequence of the uplifted Australian plate (Grady, 1975; Grady & Berry, 1977; Chamalaun

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& Grady, 1978). Material transfer across the plate boundary was limited to olistostrome

mass transport, resulting in a single unit known as the Bobonaro Scaly Clay (Chamalaun

& Grady, 1978; Harris et al., 1998). Proponents of the autochthon model cited a lack of

field evidence for the overthrust and imbricate models. These authors suggested that the

debate could be resolved if evidence for the basal thrust sheets was discovered through

more detailed fieldwork on Timor.

Inherent in the autochthon model is the assumption that the oceanic and continental

portions of the Indo-Australian crust became detached at the collision zone. The

buoyancy of the continental slab caused it to rise rapidly, uplifting northern Timor and

possibly causing reactivation of pre-existing faults, while the detached down-going slab

was absorbed into the mantle (Milsom, 2001). Coupled with this uplift, the Bobonaro

Scaly Clay became a gravity slide, moving southward across the continental margin. This

model suggests a very steep contact between the oceanic crust of the island arc and

continental crust to the south, which has been confirmed by an unusually steep positive

northward gravity gradient on Timor’s north coast (Chamalaun et al., 1976).

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5 Response to tectonism: uplift and exhumation of

Timor

5.1

Thermochronological dataRapid vertical uplift of Timor since the late Neogene has been well documented (De

Smet et al., 1990; Harris et al., 2000; Veevers, 2000). Thermal histories of young

orogenic belts can be reconstructed using apatite fission track analysis. This technique

documents the post-orogenic cooling history below ~110ºC, and can provide estimates of

the timing, magnitude and rates of tectonic uplift and denudation (Gleadow et al., 2002).

Harris et al. (2000) used fission track data to analyse the amount of heating that occurred

since the initial collision process. They determined that there was little or no heatingwithin the collision complex during Neogene uplift and exhumation, most probably due

to the lack of long-term burial suffered by the individual thrust units. Accreted

Australian-margin material on Timor recorded peak palaeotemperatures very similar to

unaccreted material in northwest Australia.

Harris et al. (2000) also concluded that the inversion of apatite fission track ages recorded

(younger over older) was representative of rapid uplift and exhumation due to the

emplacement of thrust sheets during collision. Stacking of thrust sheets of various origins

within the collision complex created an inverted thermal profile with peak

palaeotemperatures decreasing discontinuously downward. One example in a vertical

section from East Timor yielded an abrupt change in fission track age from 280 Ma to 52

Ma over only 25 metres. Such a change is most likely due to the juxtaposition of rocks

which have undergone different thermal histories, rather than due to steep thermal

gradients.

Overall, measurements show a general but discontinuous (due to local disruption by

faults) increase in palaeotemperatures northwards across the island, implying greater

uplift and denudation in the north. This is corroborated by the observations of Price and

Audley-Charles (1987), who observed the exposure of progressively deeper stratigraphic

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intervals towards the north, suggesting that uplift is differential both temporally and

spatially.

Analysis of apatite fission track data indicates rapid cooling and exhumation of the thrust

sheets, which has preserved newly formed fission tracks. This is interpreted as implying

the removal of between 1.2 - 4 km of overburden over the last 2 Myr, with a denudation

rate of 0.6 – 2mm/yr (Harris et al., 2000). Similar denudation rates are derived from

palaeobathymetry and chronostratigraphy of foraminifera (5-10 mm/yr) (de Smet et al.,

1990) and40

Ar/39

Ar dating of the Aileu Complex (~3mm/yr) (Berry & McDougall,

1986).

5.2

Raised reef terraces

Numerous authors have documented the raised reef limestone platforms which exist on

Timor (Fig 5.1 and 5.2) and surrounding Banda Arc islands (Chappell & Veeh 1978;

Hamilton, 1979; Vita-Finzi & Hidayat, 1991; Richardson & Blundell, 1996). Chappell

and Veeh (1978) claimed that the uplift rate of these reef terraces averaged 0.5 mm/yr

over the past 120,000 years, and continues today. The rates of uplift of Quaternary reef

terraces are slower than those of the older rocks of the collision complex, suggesting that

the earlier rapid uplift was a geomorphic response of the landscape to arc-continent

collision. According to Carter et al. (1976), uplifted reef limestones on Timor become

younger from north to south. This may be related to the possible gentle tilting of reefs

observed by Hall and Wilson (2000), with northern Timor experiencing fast uplift than

southern Timor. Extensional deformation may result in terraces of similar age being

vertically offset. Further inquiry into the differential uplift rates and deformation history

of coral reefs across Timor is necessary to correlate the ages of the reefs and establish

their uplift history.

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Figure 5.1 Locality map of East Timor showing towns of Baucau and Lautem on north the coast.

Figure 5.2 Digital elevation model of East Timor showing locations of Baucau and Lautem. The horizontal

nature of elevated coral reef terraces can be seen at the front and rear of the model (derived from SRTMdata set, United States Geological Survey).

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Age-height data collected from Quaternary uplifted coral reefs on the Huon Peninsula,

Papua New Guinea could be used as an analogue for coral reefs on Timor (Ota &

Chappell, 1999). The emergence of coral reefs on the Huon Peninsula during periods of

Holocene sea level change and variable tectonic uplift was studied by Ota and Chappell

(1999). They found that the age of reef emergence was dependent on the nature of uplift

(stepwise vs. uniform) and the rate of reef growth. Such research has not yet been

conducted on the reef terraces in East Timor.

5.3

Uplift mechanisms

The uplift of Timor may be due to a variety of mechanisms. The emplacement of thick

thrust sheets on the Australian continental margin must have caused major isostatic

disequilibrium, prompting rebound-related uplift on steep faults (Grady & Berry, 1977;

Chamalaun & Grady, 1978; Norvick, 1979; Snyder et al., 1996b). Additionally, uplift

may be a response of the landscape to the formation of thrust faults during the collision

process (the Wetar and Timor thrusts). A significant thickening of the collision complex

and crust underlying Timor and the Banda Arc has been indicated by seismic reflection

profiles (Snyder et al., 1996b). This horizontal shortening would also account for the

uplift of Timor and associated downwarping of the Timor Trough to the south (Johnston

& Bowin, 1981).

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6 Discussion

Little is known about the details of early stage orogenesis and the role it plays in ensuing

evolution of orogenic systems, as much of the evidence of these processes is destroyed by

subsequent erosion or deformation. Such information can only be gleaned by studying

young systems such as Timor. As a result of the end of the Indonesian occupation of East

Timor in 1999, the country is once again accessible to foreign scientists. Studying East

Timor and islands of the outer Banda Arc has important implications for understanding

fundamentals of tectonic collision, including (e.g. Bowin et al., 1980; Karig et al., 1987;

McCaffrey & Abers, 1991; Huang et al., 2000):

• early stage processes of collision

•

‘jamming’ of subduction zones

• terminal stages of arc evolution

• the role of changes in subduction polarity

Australia’s northern margin is its only convergent margin. The present tectonic activity at

this margin bears the marks of vigorous tectonism, through its high relief (3 km in

Timor), volcanicity, seismicity, rapid uplift and exhumation, as distinct from most other

Australian margins which have long been inactive (McCaffrey & Nabelek, 1986; Hughes

et al.,1996; Veevers, 2000).Many aspects of this young, evolving arc-continent collision

remain poorly constrained: (e.g. Audley-Charles, 1968; Grady & Berry, 1977;

Chamalaun, 1978; Barber, 1979; Hamilton, 1979; Harris, 1991; Charlton, 2000):

• the timing of initial collision in the proto-Timor region

• the origins of the rocks exposed on Timor

• the mechanisms by which ongoing convergence is accommodated

• the lack of volcanism north of East Timor and related paucity of deep seismic

activity in the same region

• the evolution of the position of the plate boundary

• the role of thrusts, normal faults and strike-slip faults in the Banda Arc

• how the geomorphic expressions of this orogenic event manifested in the

landscape today

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Present-day tectonic activity in the Banda Arc includes deformation along divergent

thrusts, earthquakes, volcanism and significant uplift. Three main models have been

proposed for the tectonic evolution of East Timor: the overthrust, imbricate and

autochthon models. These have been described on the basis of local structural,

stratigraphic and geochemical evidence. The diversity of hypotheses raised suggests that

a broader view of the tectonic process needs to be developed, possibly accommodating a

variety of models of evolution at different stages of the collision process, in order to

constrain models of Neogene collision.

The uplift of East Timor since onset of collision is clearly a response to tectonic

processes including isostasy acting on thickened crust, deformation, erosion, and crustalunderplating. What little is known suggests that uplift occurred in two major phases:

rapid uplift related to emplacement of thrust sheets, followed by slower but continued

uplift until the present day. To date, limited work has been carried out on this aspect of

collision, however, the near-surface uplift history may hold the key to reconciling rival

ideas and providing larger-scale constraints on collisional models. It is this most recent

geodynamic manifestation of the landscape during the second phase of uplift which will

form the basis of my project.

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7 Thesis Plan

The aim of my work is to constrain the more recent uplift history of East Timor. First,

aspects of the geology of East Timor which provide evidence of uplift will be identified.

Using both existing fission track data (Harris et al., 2000) and data to be obtained during

fieldwork this year, ages and denudation rates will be measured, quantifying uplift in

different regions over different timescales. With a lower temperature sensitivity than

apatite fission track thermochronology, apatite U-Th/Helium thermochronology (e.g.

Farley, 2002), will be used to obtain data from the rocks involved in initial uplift. U-

series disequilibria (e.g. Edwards et al., 2003) will be used to date the elevated

Quaternary coral reefs.

An attempt will be made to correlate the reef terraces present at various locations across

northern East Timor (e.g. Fig. 5.2). These terraces, like those of the Huon Peninsula,

Papua New Guinea, may show evidence of sea level change during the Holocene, further

constraining the timing of reef formation (Ota & Chappell, 1999). Data acquired from

both approaches will be combined to establish a first-order model of uplift over different

timescales, providing an analysis of the geomorphic response of the landscape to plate

collision. Uplift may also vary east-west and north-south across East Timor itself,indicated by the slight tilting of uplifted coral reefs. In the case of northern Timor being

uplifted faster than southern Timor, the coral reefs ought to dip gently toward the south,

which may be confirmed through fieldwork.

It is hoped that my work on constraining the recent uplift history of East Timor will add

to the growing body of work, establishing a comprehensive knowledge of the recent

geology of East Timor, and will help in the evaluation of natural hazards, an important

asset in the rebuilding of infrastructure in this emerging nation. A copy of the report

arising from my study will be lodged with the East Timor Department of Energy and

Mineral Resources.

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8 References

Abbott, M.J., Chamalaun, F.H., 1978. New K/Ar age data for Banda Arc volcanics.

Institute for Australasian Geodynamics, Flinders University of South AustraliaPublication 78.

Audley-Charles, M.G. 1968. The Geology of Portugese Timor. Memoirs of the

Geological Society of London No. 4.

Audley-Charles, M.G., 1975. The Sumba Fracture: a major discontinuity between Eastern

and Western Indonesia. Tectonophysics, 26, 213-228.

Audley-Charles, M.G., Carter, D. J., 1972. Palaeogeographical significance of some

aspects of Palaeogene and early Neogene stratigraphy and tectonics of the

Timor Sea region. Palaeogeography, Palaeoclimatology, Palaeoecology, 11, 247-264.

Barber, A.J., 1979. Structural interpretations of the island of Timor, easternIndonesia. Proceedings of the Southeast Asia Petroleum Exploration Society, 4,

9–21.

Barber, A.J., Audley-Charles, M.G., Carter, D.J., 1977. Thrust tectonics in Timor.

Journal of the Geological Society of Australia, 24, 51–62.

Berry, R.F. 1981. Petrology of the Hili Manu lherzolite, East Timor. Journal of the

Geological Society of Australia, 28, 453-469.

Berry, R.F., Grady, A.E., 1981. Deformation and metamorphism of the Aileu Formation,

north coast, East Timor and its tectonic significance. Journal of StructuralGeology, 3, 143–167.

Berry, R.F., McDougall, I., 1986. Interpretation of Ar40/Ar39 and K/Ar dating evidence

from the Aileu Formation, East Timor, Indonesia. Chemical Geology, 59, 43– 58.

Bowin, C., Purdy, G.M., Johnston, C., Shor, G., Lawver, L., Hartono, H.M.S., Jezek, P.,

1980. Arc-continent collision in Banda Sea region. American Association ofPetroleum Geologists Bulletin, 64, 868–915.

Breen, N. A., Silver, E.A., Roof, S. 1989. The Wetar Back Arc Thrust, Eastern Indonesia:

The effect of accretion against an irregularly shaped arc. Tectonics, 8, 85-98.

23


28/32


Carter, D.J., Audley-Charles, M.G., Barber, A.J., 1976. Stratigraphical analysis of island

arc–continental margin collision in eastern Indonesia. Journal of the GeologicalSociety of London, 132, 179–198.

Chamalaun, F.H. 1977. Palaeomagnetic evidence for the relative positions of Timor and

Australia in the Permian. Earth and Planetary Science Letters, 34, 107-112.

Chamalaun, F. H., Grady, A. E., 1978. The Tectonic Development of Timor: A New

Model and its Implications for Petroleum Exploration. APEA Journal, 102-108.

Chamalaun, F.H., Lockwood, K., White, A., 1976. The Bouguer gravity field and crustal

structure of eastern Timor. Tectonophysics, 30, 241–259.

Chappell, J., Veeh, H.H., 1978. Late Quaternary tectonic movements and sea level

changes at Timor and Atauro Island. Geological Society of America Bulletin,

89, 356-368

Charlton, T.R. 2002a. The Petroleum Potential of East Timor. APPEA Journal, 42, 351-369.

Charlton, T.R. 2002b. The structural setting and tectonic significance of the Lolotoi,Laclubar and Aileu metamorphic massifs, East Timor. Journal of Asian Earth

Sciences, 20, 851-865.

Charlton, T.R., 2000. Tertiary evolution of the Eastern Indonesian Collision Complex.

Journal of Asian Earth Science, 18, 603-631.

Charlton, T.R., Barber, A.J., Barkham, S.T., 1991. The structural evolution of the Timorcollision complex, eastern Indonesia. Journal of StructuralGeology, 13, 489–500.

De Smet, M.E.M., Fortuin, A.R., Troelstra, S.R., Van Marle, L.J., Karmini, M.,Tjokrosapoetro, S., Hadiwasastra, S. 1990. Detection of collision-related

vertical movements in the Outer Banda Arc (Timor, Indonesia), using

micropalaeontological data. Journal of Southeast Asian Earth Sciences, 4, 337-356.

Edwards, R.L., Gallup, C.D., Cheng, H. 2003. Uranium-series dating of Marine andLacustrine Carbonates. In B. Bourdon, G.M. Henderson, C.C. Lundstrom and

S.P. Turner (Eds.) Uranium-Series Geochemistry. Reviews in Mineralogy and

Geochemistry, 52, 353-406.

Farley, K. A. 2002. (U-Th)/He dating: Techniques, calibrations and Applications. In C.

Porcelli, C. Ballentine and R. Wieler (Eds.) Noble Gases in Geochemistry and

Cosmochemistry. Reviews in Mineralogy and Geochemistry, 47, 819–843.

24


29/32


Fitch, T.J. and Hamilton, W. 1974. Reply to a discussion by M.G. Audley-Charles & J.

Milsom. Journal of Geophysical Research, 79, 4982-4985.

Genrich, J.F., Stevens, C.W., Subarya, C., Bock, Y., McCaffrey, R., Calais, E. 1996.

Accretion of the southern Banda Arc to the Australian plate margin determined

by global positioning system measurements. Tectonics, 15, 288-295.

Gleadow, A. J. W., Belton, D. X., Kohn, B.P., Brown, R. W., 2002. Fission Track Dating

of Phosphate Minerals and the Thermochronology of Apatite. Reviews in Mineralogy and Geochemistry, 48, 579-630.

Grady, A.E. 1975 A reinvestigation of thrusting in Portugese Timor. Journal of theGeological Society of Australia, 22, 223-228.

Grady, A. E., Berry, R. F., 1977. Some Palaeozoic-Mesozoic stratigraphic-structural

relationships in East Timor and their significance in the tectonics of Timor.

Journal of the Geological Society of Australia, 24, 203-214.

Hall, R., 2002. Cenozoic geological and plate tectonic evolution of Southeast Asia andthe southwest Pacific: computer-based reconstructions, models and animations.

Journal of Asian Earth Sciences, 20, 353-431.

Hall, R., 1996. Reconstructing Cenozoic SE Asia. In R. Hall & D.J. Blundell (Eds.),

Tectonic Evolution of Southeast Asia. Geological Society of America Special

Publication 106, 153–184.

Hall, R., Wilson, M.E.J., 2000. Neogene sutures in Eastern Indonesia. Journal of Asian Earth Sciences, 18, 781-808

Hamilton, W. 1977. Subduction in the Indonesian Region. Island Arcs, Deep SeaTrenches and Back-Arc Basins. In M. Talwani, & W.C. Pitman, (Eds.),American Geophysical Union: Washington, D.C.

Hamilton, W., 1979. Tectonics of the Indonesian region. United States Geological SurveyProfessional Paper, 1078, 1–345.

Harris, R.A. 1991. Temporal distribution of strain in the active Banda orogen: areconciliation of rival hypotheses. Journal of Southeast Asian Earth Sciences, 6,

373-386.

Harris, R.A., Kaiser, J., Hurford, A., Carter, A., 2000. Thermal history of Australian

passive margin cover sequences accreted to Timor during Late Neogene arc-

continent collision, Indonesia. Journal of Asian Earth

Sciences, 18, 47-69.

25

http://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.htmlhttp://newfirstsearch.oclc.org/WebZ/FSQUERY?searchtype=hotauthors:format=BI:numrecs=10:dbname=GEOBASE::termh1=Genrich+J.F.:indexh1=au%3D:sessionid=sp07sw04-60808-dspkkl0m-1zd8ec:entitypagenum=25:0:next=html/records.html:bad=error/badsearch.html


30/32


Harris, R.A., Sawyer, R.K., Audley-Charles, M.G., 1998. Collisional melange

development: Geologic associations of active melange-forming processes withexhumed melange facies in the western Banda orogen, Indonesia. Tectonics, 17,

458–480.

Hinschberger, F., Malod, J.-A., Dyment, J., Honthaas, C., Rehault, J.-P., Burhanuddin, S.2001. Magnetic lineations constraints for the back-arc opening of the Late

Neogene South Banda Basin (eastern Indonesia). Tectonophysics, 333, 47-59.

Huang, C-Y., Yuan, P. B., Lin, C-W., Wang, T. K., Chang, C-P., 2000. Geodynamic

processes of Taiwan arc–continent collision and comparison with analogs in

Timor, Papua New Guinea, Urals and Corsica. Tectonophysics, 325, 1-21.

Hughes, B.D., Baxter, K., Clark, R.A., Snyder, D.B., 1996. Detailed processing of

seismic reflection data from the frontal part of the Timor trough accretionary

wedge, eastern Indonesia. In R. Hall & D.J. Blundell, (Eds.), Tectonic Evolution

of Southeast Asia Geological Society of America Special Publication 106, 75-83.

Johnston, C.R., Bowin, C.O., 1981. Crustal reactions resulting from the mid-Pliocene to

Recent continent-island arc collision in the Timor region. Journal of Australian

Geology and Geophysics, 6, 223-243.

Karig, D.E., Barber, A.J., Charlton, T.R., Klemperer, S., Hussong, D.M., 1987. Nature

and distribution of deformation across the Banda Arc–Australian collision zoneat Timor. Geological Society of America Bulletin, 98, 18–32.

Keep, M., Moss, S. J., 2000. Basement reactivation and control of Neogene structures in

the Outer Browse Basin, North West Shelf. Exploration Geophysics, 31, 424-

432.

Keep, M., Longley, I., Jones, R. 2003. Sumba and its effect on Australia’s northwestern

margin. In R.R. Hillis & R.D. Muller (Eds.), Evolution and Dynamics of the

Australian Plate, Geological Society of Australia Special Publication 22 andGeological Society of America Special Paper 372, 309-318.

Linthout, K., Helmers, H., Sopaheluwaken, J., 1997. Late Miocene obduction andmicroplate migration around the southern Banda Sea and the closure of the

Indonesian Seaway. Tectonophysics, 281, 17–30.

Lorenzo, J. M., O’Brien, G. W., Stewart, J., Tandon, K., 1998. Inelastic yielding and

forebulge shape across a modern foreland basin: North West Shelf of Australia,

Timor Sea. Geophysical Research Letters, 25, 1455-1458.

McCaffrey, R., 1988. Active tectonics of the eastern Sunda and Banda arcs. Journal of

Geophysical Research, 93, 15163–15182.

26


31/32


McCaffrey, R., 1996. Slip partitioning at convergent plate boundaries of Southeast Asia.In R. Hall & D.J. Blundell, (Eds.), Tectonic Evolution of Southeast Asia

Geological Society of America Special Publication 106, 3–18.

McCaffrey, R., Abers, G.A., 1991. Orogeny in arc–continent collision: the Banda Arcand western New Guinea. Geology, 19, 563–566.

McCaffrey, R., Nabelek, J. 1986. Seismological evidence for shallow thrusting north ofthe Timor Trough. Journal of Geophysical Research, 85, 365-381

Masson, D.G., Milsom, J., Barber, A.J., Sikumbang, N., Dwiyanto, B.,1991. Recenttectonics around the island of Timor, eastern Indonesia. Marine and Petroleum

Geology, 8, 35-49.

Milsom, J. 2001. Subduction in eastern Indonesia: how many slabs? Tectonophysics, 338,

167-178.

Norvick, M. S., 1979. The tectonic history of the Banda Arcs, eastern Indonesia: areview. Journal of the Geological Society of London, 136, 519-527.

Ota, Y., Chappell, J. 1999. Holocene sea-level rise and coral reef growth on a tectonicallyrising coast, Huon Peninsula, Papua New Guinea. Quaternary International, 55,

51-59.

Price, N.J., Audley-Charles, M.G. 1987. Tectonic collision processes after plate rupture.

Tectonophysics, 140, 121-129.

Richardson, A.N., Blundell, D.J. 1996 Continental collision in the Banda Arc. In: R. Hall

and D.J. Blundell, (Eds.) Tectonic Evolution of Southeast Asia Geological

Society of America Special Publication 106, 47-60.

Rutherford, E., Burke, K., Lytwyn, J., 2001. Tectonic history of Sumba island, Indonesia,

since the Late Cretaceous and its rapid escape into the forearc in the Miocene. Journal of Asian Earth Sciences, 19, 453-479.

Silver, E.A., Reed, D., McCaffrey, R., Joyodirwiryo, Y., 1983. Back arc thrusting in the

eastern Sunda arc, Indonesia: a consequence of arc-collision. Journal of

Geophysical Research, 88, 7429–7448.

Snyder, D.B., Barber, A. J., 1997. Australia-Banda Arc collision as an analogue for early

stages in Iapetus closure. Journal of the Geological Society of London, 154,

589-592.

27


32/32


Snyder D.B., Milsom, J., Prasetyo, H. 1996a. Geophysical evidence for local indentor

tectonics in the Banda Arc east of Timor. In R.Hall and D.J. Blundell, (Eds.),Tectonic Evolution of Southeast Asia Geological Society of America Special

Publication 106: 61-73.

Snyder, D.B., Prasetyo, H., Blundell, D.J., Pigram, C.J., Barber, A.J., Richarson, A.,Tjokosaproetro, S., 1996b. A dual doubly vergent orogen in the Banda arc

continent–arc collision zone as observed on deep seismic reflection profiles.

Tectonics, 15, 34–53.

Veevers, J.J., 2000. Morphotectonics of the convergent northern margin. In J.J. Veevers

(Ed.), Billion-year earth history of Australia and neighbours in GondwanalandGEMOC Press: Sydney, 29-33.

Villeneuve, M., Harsolumakso, A.H., Cornee, J.J., Bellon, H. 1999. Structure of West

Timor (East Indonesia) along a north-south cross section. Geologie

Mediterraneenne, 26, 127-142.

Vita-Finzi, C., Hidayat, S. 1991. Holocene uplift in West Timor, Journal of Southeast Asian Earth Sciences, 6, 387-393.

Von der Borch, C.C., 1979. Continental-island arc collision in the Banda Arc.Tectonophysics, 54, 169–193.

Whittam, D.B., Norvick, M.S., McIntyre, C.L., 1996. Mesozoic and CainozoicTectonostratigraphy of Western ZOCA and adjacent areas. APPEA Journal, 36,

209-223.

Giliam Hamson - The Tectonic Evolution of East Timor and the Band

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