Mesozoic-Cenozoic rift-drift sequence of Asian fragments from Gondwanaland

317

TL’c.rr,rlopll,.s,c..s,15s (1988) 317-330 Elsrv~er Science

Publishers

B.V.. Amsterdam

- Printed

Mesozoic-Cenozoic

in The Netherlands

rift-drift sequence from Gondwanaland

M.G. AUDLEY-CHARLES,

of Asian fragments

P.D. BALLANTYNE

and R. HALL

llepurm7enr o/ Grologlcul Sw3lc~e.~. C’nirwrl!,~ (‘olky Limlorl,Lon~f~,ll IL’.K I (Received

July 25. 1986: revised version

accepted

June 25. 19X7)

Abstract

Audlry-Charles.

Ballantyne.

Gondwanaland.

In:

P.D. and Hall, R., 198X. Mesozoic-Cenozoic

C.R.

Scotese

and

W.W.

Sager

(Editors).

rift-drift

Mesoroic

sequence

and

of AhIan fragments

Cenozoic

Plate

from

Rccon\tructions.

T
The University diaperial

of Cambridge

of continental

Atlas map-plotting

blocks from eastern

Ma). The geological

basis for the reconstruction

and Sumatra

been part of the eastern

having

reconstruction the Late

This

rifting

It was associated

the Cretaceous

in the Jurassic.

di\rupted

these rock sequences

The date of the rifting

of South Tibet. Burma. during

tectonic

during

New

Guinea. correlatmn

Burma.

western

The

the late Palaeozo~c of central

preserved

of the Outer

Banda

that these arear and associated

ThaIland.

and rarlv

Nw

Meaoro~c. The

(;(~nd\~analan~i

Gulnca

by profound

Arc from Scram

formed

to Timor,

part of thih rifted

maJor strlkc-slip

movement\

111

.md northern

in the floor of the northeastern followed

(IO

Malava

Indi,ln

huhsldrnce

in

and the \lmllar

northern

margin

have &formed

01 and

the Calnozolc. South Tihrt.

in favour

Burma.

of the rifting of the

western

eplsodr

observations

identification

with the Banda Thailand

anomalies

implie\ collision

we\trrn

blocks were rifted from ea\tcrn margin

of the

(160 Ma) until the Late Miocene

upllft in the Middle Jurassic

in the islands

are stratigraphic-structural

htratigraphic

ThaIland

having

continental

hlockh

and Malaya

occurred

on the northwestern

Arc and New Guinea

and Malaya

Auatrallan

remwed

and partI>

h\

rather

than

In the

shelf. 111the Banda .Arc and 111 thi\

on indications

with Abia wa\ a Late C‘retaceous

from (;ond\\,~nal,~~~~l I\

in the Jurahric rlftlng

i\ hased

partI\

on

that the age of colllw)n

event and not Tria\\lc-Jura\\lc

of ;I\ I\

held.

There are very few reliable land-baaed continental available

fragments Indian

ocean-floor tectonic

continent

spreading

of crustal

that removed

The indications

Permo-Triassic

generally

Gondwana

Sulaweai

Subsequent

haa been used to plot a reconrtructl~~n

gave rise to the continental

exposed

facies in eastern

Australia

controversial.

episode

the Indication

and Palarogene.

Jurassic-Cretaceous

Tibet.

rest\ on the concept

with the sea-floor

The model considers

central

program

from the Late Jurassic

ih also hased on the wew that these Asian continental

Jurassic.

Australia. Ocean.

computer

Gonduanaland

from

Ocean

data

associated

collision

processes

palaeomagnetic

Gondwanaland.

sea-floor

spreading

with the rifting that occurred

measurementa

The computer-generated data

although

and dispersal

0040-1951/x8/$03.50

of the northern Guinea region of

” 19XX Elsevier Science

Publishers

B.V

arc

the movements

rrcon~tructlons

not

of these continental

at the Asian continental

Introduction In this paper the break-up margin of the Australia-New

the?

to constrain map

umque

\olutionh.

fragment\

of thew dl\perwd

put forx+xd Much

hcrc

111 the

01 the crltlcal

ha\ heen de\tr~~\ed

in the

margin.

Gondwana during the Late TriassicLatt: Jurassic is discussed. The dispersal of the rifted continental fragments removed from thia part of eastern Gondwanaland during the Jurassic ia plotted by

.:1h means

of a series of reconstructions

for 160. 120.

90, 40, 30 and 10 Ma. The palaeomagnetic control

these reconstructions

the model put forward available

Metcalfe

(1988)

movements

data of these

has

of poor dating. and

Carboniferous western

Asian

He found

the presence

lack of fold

the

blocks

of penetrative tests

the Permian

block determined

Peninsula

of northeastern

Thailand

defor-

from western

land and the Malay Peninsula (Maranate and Vella. 1986:

vertebrate

palaeontological

northeastern Thailand part of the Indochina

evidence

South

and

Nujiang

phase

compressional

and

Thai-

that

was palaeogeographically block during the Mesozoic

and. we would argue, during the late Palaeozoic, and was separate from western Thailand and Malaya (Audley-Charles, 1983, 1984). No reliable palaeomagnetic data relevant to the late Palaeozoic and Mesozoic appears to be available for western Thailand and the Malay Peninsula. but a major sampling of the Jurassic was undertaken recently from which we await the results. There are very little palaeomagnetic data bearing on the date of the collision of South Tibet, Burma. western Thailand, the Malay Peninsula and Sumatra with mainland Asia (Jarrard and Sasajima, 1980). In their review Achache et al. (1983) conclude that, in the Late Cretaceous, South Tibet was at about 15” N, while the Malay Peninsula was at about lOoN and Sumatra at about 5 o N. Jarrard and Sasajima (1980) regarded the palaeomagnetic data for Sumatra “with a precision of marginally reliable” as indicating that

Cretaceous

closely

Peninsula evidence

in the South Tibet between

80 and

Tibet

along

If that is correct

the

deformation

between Bangong--

it would

to the age of the only

(Harbury to support

block

60 Ma.

the effects of collision

North

suture.

and

fauna not (Buffetaut, and land suggests

folding

spond

by a tectonic suture Metcalfe, in press),

has a Laurasian terrestrial vertebrate found in western Thailand and Malaya the palaeomagnetic 1985). Thus,

important

and

the Jurassic and Cretaceous and probably during the Triassic. It is significant that northeastern which is separated

Achache et al. (1984) point out that before the collision with India in the Eocene, there was an

This may represent

Vella, 1986) revealed that northeastern Thailand occupied approximately its present latitude during

Thailand,

in the early Mesozoic.

de-

by McElhinny

(Maranate

had drifted north to ahwt it\ present in the Late Cretaceous from Hbout 20 “S

in the Late

et al. (1974) and Bunopas (1982) are unreliable. However, more recent and reliable data on the Mesozoic

Sumatra position

the

that on grounds

poles for the Malay

Thailand

available

to determining

Southeast

but

all the

reliable.

reviewed

relevant

rived from Gondwana. mation

is very limited

here accommodates

data which are considered

palaeomagnetic

data to

corre-

Mesozoic

we saw in the Malay

et al., in prep.). We found no the widely discussed Triassic

compressional deformation reported from the peninsula (Mitchell, 1981; Sengor. 1986). Two compressional events that are well expressed appear to be of Permian and Cretaceous age. This suggests that the reported Permian (Helmcke. 1982) and Mesozoic (Mitchell, 1981) deformation events in Burma and western Thailand need careful reinvestigation. The presence ported

to have

of

the

been

Donqiao

thrust

over

ophiolite,

re-

Middle-Upper

Jurassic flysch (Girardeau et al., 1984). has been interpreted (Allegre et al., 1984) as indicating that South Tibet collided with North Tibet not later than

Late Jurassic.

This conclusion

may be chal-

lenged on the grounds that Tethyan-type ophiolites do not seem to correspond to with arc-continent or continent-continent collisions (Hall, 1984). Emplacement of this type of ophiolite pre-dates such collisions,

as may be seen in Taiwan

(Pelle-

tier and Stephan, 1986). As much of the palaeomagnetic data from the relevant parts of the oceans has been destroyed by N-directed subduction associated with the dominantly E-W orientated spreading systems, the critical palaeomagnetic data will have to be sought in the continental blocks now in Asia whose geology indicates they originated in Gondwanaland. The model indicates where land-based palaeomagnetic measurements are required to test this hypothesis. The geological indications in favour of South Tibet, Burma, western Thailand, Malaya and Sumatra having been part of Gondwana during the late Palaeozoic have been summarised briefly

by Audley-Charles

(1983, 1984). This view is based

on the affinities stratigraphic

of fauna,

sequence

flora

and

correlation,

episodes

of

volcanism and p~utonism and the phases of deformation described by McTavish (1975), Hamilton (1979). Bally et al. (19801, Cameron Mitchell

(1981),

Archbold

and Hsu (1984). Metcalfe (1988). In particular,

et al. (1980),

et al. (1982),

Sengor

(1988) and Sengor et al.

South Tibet,

Burma.

western

Thailand

and Malaya

reveal strong geological

relations

as pointed

out by Bally

Mitchell

cor-

et al. (19X0),

(1981) and Sengor and Hsu (1984). There

are implications that these regions were united or very closely associated along strike and formed a geological province which shared common p~~lae~)~eographical eIements at its margins. Thus. in plotting a reconstruction for the late Palaeozoic and Mesozoic it is difficult to avoid regarding these Asian

blocks

as forming

one elongated

as the result of island-arc ern margin

lithofacies,

nar-

row block. The shape of this block itself suggests that it is a rifted continental sliver whose length

of Tethys

Gondwanaland western

subduction

around

(including

Thailand,

at the south-

the eastern South

Malaya.

margin

Tibet.

Sumatra,

of

Burma.

New Guinea

and Australia). The evidence deformation neously

of Permo-Triassic having

occurred

in these Asian

the southern

margin

now. adjacent and eastern northern

penecontempora-

blocks

while they were at and in, what

of Tethys

parts

are

of Asia such as Indo-China

Thailand

margin

rnagm~~tisnl and

but which

of the Tethys

formed

the

Ocean (Sengor

then

and

us with a fundamentime we c;tn observe

Hsu, 1984) does not present tal problem. At the present

contemporai~eous subduction of a major ocean (the Pacific) on its eastern, western and northern margins

associated

is possible

with local deformation.

to conceive

penecontemporaneously southern (Gondwana)

of subduction

Thus it occurring

at the northern (Asia) and continental margins of

well with the reconstructed Mesomargin of northern Australia (Fig.

Tethys. The picture is complicated because the subsequent rifting of the Gondwanaland margin led to the collision of these continental margins.

The main question that arises is not whether this elongated narrow block was derived from

One particular feature of the Triassic magmatism concerns the granites (some of which arc tin bearing) in Burma, western Th~~iland. Malaya.

accommodates zoic continental 1).

Gondw~~naland, as that seems generally agreed (as references cited above indicate), but instead, when was this block rifted from Gondwanaland and

Sumatra, Bangka (1986) have found

when did it collide with the mainland Asian continent‘? These questions are central to any interpre-

read

tation and

of Tethyan-Gondwana reliable

solution

palaeomagnetic

palaeogeography, data

to guide

their

Probably the most imthat have been made which

are not available.

portant observations

indicate that this ~ontinentai sliver was rifted from Gondwana in the Permo-Triassic are the occurrences of Permo-Triassic talc-alkaline vofcanics and granitic plutons. The general view is that these eruptive rocks resulted from subduction at the Asian margin on the north side of Tethys (Sengor and Hsu. 1984). and that during the Late Triassic these continental blocks with their Permo-Triassic eruptive rocks collided with the Asian continental margin (Mitchell, 1981). An alternative inte~retation has been put forward by Audley-CharIes Permo-Triassic

(1983, 1987) which regards the magmatism in these Asian blocks

tinctive

and Billiton. C‘obhing et al. that these granites have a dis-

geochemical the

same

signature.

signature

It is possible

in

the

Triassic

tc,

Mole

granite of eastern Australia (Plimer and K&man. 1985). Hamilton (1979) has pointed out the ohvious possible

correlation

(which

with these Triassic granites bearing granites) of eastern

is followed

here)

(including the tinAustralia which ex-

tend northwards to the Kuhor Range of New Guinea where the trend was abruptly t~rInin~~te~i by Early Jurassic continental rifting. It could he worth testing this hypothesis by looking at the geochemistry of the Triassic Kuhor Range granite and those granites (including the tin-bearing type\) of the Sula and Banggai islands of eastern Indonesia. Another type of Permian magmatism involves the Panjal traps of South Tibet, which continue westwards to Kashmir. They have been regarded as indicating that South Tibet was rifted from Gondwana in the Permian (Searle. 1983). How-

ever. rift-type volcanics of this age also occur in Timor and on the northern Australian shelf (Bird. 1987). These Permian to an important sponsible seismic

event

may all be related which

for the extensional-type survey

shelf (Powell.

was also re-

faulting

data from the northern 1976). This rifting

least as well explained of blocks Burma,

volcanics

rifting

western

Thailand.

the removal

side of South Malaya

and

Timor

of siliciclastic

Triassic been

age (Cook.

derived

continental

is. in our view, at

by postulating

from the Tethyan

seen in

Australian

while they remained part of Australian (iondwana during the Permian-Jurassic. The presence in

Timor

from block

Sumatra

the

Bird.

Tethyan

to have been

of Permian

and

1987) that

have

side

require

a

present

north

of

at that time.

The pre-rifting

Tibet,

turbidites 1986;

location

at the

northern

cannot

be controlled

of the Asian

Australia-New with

fragments

Guinea

precision.

margin

They

have

W BORNEO

ANTARCTICA

Fig. 1. Reconstruction continental

of Australian

Gondwanaland

fragments modified from Audley-Charles

the northern Australian-central elements of the overthrust

v \

1

at 160 Ma (Late Jurassic) based on Smith et al. (1981). Positions (1983). Note schematic

position

New Guinea margin (after Pigram and Panggabean,

sheets now in the Outer Banda Arc islands considered

with which the Australian

continental

of Asian

of the spreading ridge related to the rifting of 1984). The Banda atlochthon

represents those

to have been derived from the forearc basement

margin collided in the Pliocene (Audley-Charles,

1986). Coastlines

for reference only.

been

reconstructed

qualitative

here on the basis of the best

fit using present

do not take account other deformation during

suffered

their tectonic

margin

account

duced

the

Cainozoic

by

Asia.

margin

has been before

accumulations

and in defining

into

New Guinea

blocks

of the position

the taking

and

with mainland

Guinea

sedimentary

were formed

shortening

by these Asian

coltision

on an estimate

post-Jurassic

These shapes

of the crustal

The rifted Australia-New based

outlines.

its location

of the deformation collisions

and of Australia

the

at this

with

pro-

here to account between

eastern

(Sikumbang. Malay

for the strong Borneo

1986) and

Peninsula

and

of the Australia-New Other

western

the affinity

western

1988). The case for regarding Cainozoic

geological

and

between

Borneo

eastern

Guinea

as part

in the pre-

has been put by Audley-Charles

workers

(Katili.

197X:

(197X).

Hamilton.

1979:

Silver et al., 1983) take the view that eastern

of northern

western

the volcanic

However,

Sulawesi

were linked

the stratigraphic

the

(Metcalfe,

Sulawrsi

margin

affinity Sulawesi

and

in the pre-Cainozoic. evidence

of Sukamto

The reconstrucrifted margin in

and Simandjuntak (19X3) and Simandjuntak (1986) reveals the strong geological affinity between the

central New Guinea (Pigram and Panggabean, 1984) follows the suggestion of Hamilton (1979). The present outline of Sumatra cannot of course

Mesozoic of eastern Sulawesi and the Bnngpai and Sula islands that are generalty agreed to he a detached

represent

tinental

Banda Arc has been attempted. tion of Sumatra at the Jurassic

the shape of the continental

fragments

now present

in Sumatra

fragment

been attached to central New Guinea before Mesozoic rifting that removed Sumatra. The reconstructions

were plotted

versity of Cambridge Department ces. Atlas map-drawing program

or

that could have the

using the Uniof Earth Sciendeveioped from

plotting programs written by R.L. Parker and successively modified by D. McKenzie. A.G. Smith. A.M. Hurley and L.A. Rush. The area reconstructed is bounded by latitudes 30 o N and 70”s and by longitudes 60” E and 160” E and is plotted using the Mercator projection. The reconstructed positions of the major continental fragments, i.e. Eurasia, India, Australia and Antarctica, were

taken

from

Smith

et al. (1981).

The

ap-

proximate coastlines of the other. smaller fragments. with which this article is concerned, were digitised using the ISIS digitising facility in the University Coilege London Department of Geography and then rotated into their desired positions between the major continental blocks.

part of the Australia-New margin

for the Late

Jurassic:

Oxfordian

The basis for locating the Banda allochthon (Fig. 1) adjacent to Sumatra and western Sulawesi as part of Mesozoic Sundaland was indicated by Audley-Charles (1983). The western and eastern Borneo separation is the tentative solution adopted

1979).

con-

Furthermore.

the absence

of a well marked

the Banggai but instead

and Sula islands and eastern Sulawrsi the presence of a strong tectonic su-

ture between

eastern

suture zone between

and western

Sulawesi,

marked

by a wide zone of blueschists, makes a good case for separating eastern and western Sulawesi. especially as there is good structural

evidence

for this

central blueschist zone being regarded as a collision suture of Middle Miocene age (Sukamto and Simandjuntak, 1983). The indication of Early Jurassic rifting of central New Guinea (Pliensbachian-Sinemurian. 200 Ma) has been presented by Pigrnm and Panggabean (1984). The geological indications for dating the Middle margin Timor

Jurassic

rifting

in the region between have been discussed

of the Australian

eastern Sulawesi and by Audley-Charles

(1987). There are abundant indic~~tions (Falvey and Mutter. 1981: Pigram and Panggabean, 1984) of major tectonic rifting of the northwestern Australian

Reconstruction (160 Ma)

(Hamilton,

Guinea

continental

margin

west of Timor

dur-

ing the Late Jurassic (Oxfordian. 160 Ma). Oil company seismic reflection surveys of the northwestern Australian shelf and Exmouth Plateau regions (Willcox and Exon, 1976) together with palaeomagnetic data from the Wharton Basin (northeastern Indian Ocean) adjacent to this shelf leave no room for doubt that a ma,jnr tectonic rifting episode removed a long block from this

part

of

Australian

Gondwanaland

Oxfordian.

This block is interpreted

Tibet

Burma

and

available

been

continental

derivation side during

data

without

the rifted

is the

the Permian

Bird, 1987). That

sediment

of course

the

conflict.

One for

from the Asian (Cook,

does not

remove

block that rifted

all

from

to accommodate

any other candidate and it does independent land-based indicate where palaeomagnetic measurements could be directed to test this hypothesis. Allegre et al. (1984) argued that if South Tibet was part of Gondwanaland it must have been from

Gondwana

no later

than

in the

Early Jurassic or Late Triassic because they suggest it accreted to Eurasia before the end of the Jurassic, Their strongest argument (1984) in favour of a Late Jurassic collision with the South Tibet block is the observation that the Donqiao ophiolite is thrust southwards over Middle-Upper Jurassic flysch in South Tibet (Girardeau et al., 1984). The ophiolite overlain (120-100

and the flysch are said to be

unconformably Ma) subaerial

by Aptian-Albian to shallow-marine-

posits. Girardeau et al. (1984) correlate with that producing similar structures

Australia could

(30”s)

in the Oxfordian

have reached

by ocean

for 80 Ma. following

This

a similar

30 Ma and (Molnar

then

(160

its Late Cretaceous may

spreading

at 5.5 cm/y1

be compared

path at 10 cm/yr 5 cm/yr

and Tapponnier.

Ma) it (80 Ma)

with

India

for the first

for the next

40 Ma

1975).

1986;

northwestern Australia during the Oxfordian has been correctly identified but it would be difficult

separated

Thus, if South Tibet was rifted from northwestern

palaeolatitude

as having

in Timor

and Triassic

that the continental

below,

blocks

evidence

of siliciclastic

the

can accommodate

any apparent

for regarding

doubts

as explained

palaeomagnetic

this proposal reason

and,

during

here as South

de-

this event in Burma

(Mitchell, 1981) as part of the neo-Cimmerian (loo-80 Ma) tectonic crisis along the southern Eurasian margin. However, if these deposits, unconformable on the Donqaio ophiolite, are Early Cretaceous (= 120 Ma) in age, there is no conflict, as the postulated rifting of South Tibet could have moved the 4500 km northwards between 160 and 120 Ma (at 11 cm/yr). Alternatively, the emplacement of the Donqaio ophiolite may have occurred at the Gondwana margin associated with rifting and spreading and then have been carried northwards to Eurasia on the South Tibet allochthonous terrain. The palaeomagnetic data (Allegre et al., 1984) suggests a Late Cretaceous (80-60 Ma) palaeolatitude of between 10” and 15’N for South Tibet.

Reconstruction

for the Early Cretaceous:

Aptian

(120 Ma) The position of the Tethys Ocean III spreading centre is partly controlled by the position of the magnetic Indian Tethys

anomalies

present

in the northwestern

Ocean (Fig. 2). The spreading III is determined by the need

ridge for to locate

South Tibet between 10” and 15” N by 80 Ma (Allegre et al., 1984). Comparison of Fig. 1 with Fig. 2 shows that for South Tibet to be transported north to Asia it was necessary for the new spreading axis of Tethys III to propagate westwards north of Greater India. This was essential to separate Greater India. The case for the subduction continental

margin

South

Tibet

from

zone at the Asian

has been made by Parker

and

Gealey (1985) among others and is followed here. This allowed South Tibet to converge on Asia (North Tibet) until, in our view, it colhded in the Late Cretaceous (80-60 Ma) as indicated by the intense deformation of that age, predating the India collision (Achache et al., 1984).

Reconstruction for the Late Cretaceous: Cenomanian (90 Ma) Indian Ocean palaeomagnetic anomalies indicate that India had rifted from Australia (Larson, 1977). It appears from the model presented here that India drifted north following much the same route taken earlier by South Tibet, which arrived at 10”N at about 80 Ma. The initial rifting of Australia from Antarctica (Fig. 3) is taken to have occurred between 110 and 90 Ma (Cande and Mutter, 1982), with a period of very slow spreading lasting until the Eocene (43

323

AUSTRALIA

ANTARCTICA Fig. 2. Reconstruction fragments

rifted

of Australian

from northern

South Tibet is postulated to the north Larson

of Australia

Gondwanaland

at 120 Ma (Early

Australia-central

to have drifted plotted

et al. (1979) and Doutch

New Guinea

north by a spreading

from Larson

dotted

Ma) when

relatively

rapid

northward

regime between

(1975) and Doutch

(1981) (this information

Cretaceous)

have drifted (1981),

is presented

lines. Coastlines

movement

of Australia began. The presence of Cretaceous granites in Sumatra (Cobbing et al., 1986) requires a subduction zone which could also accommodate continuing spreading of Tethys III and new spreading, albeit modest in amount, of the Indian Ocean between Australia and Antarctica. There are also indications in the Banda allochthon Palelo Group of arc-related

based

northward

on Smith

itself and India. and those

as dashed

for reference

volcanism

et al. (1981). The continental

by the spreading Indian

of the Tethys

Ocean

magnetic

to the west of Australia

lines).

Postulated

magnetic

Ocean

anomaly

111. data

from Mark1 (1978). anomalies

shown

as

only.

of Late

Cretaceous

age (Earle,

which implies

that subduction

Reconstruction

for the Late Eocene (40 Ma)

1983)

was active.

The apparent absence of Palaeogene magmatism from the Sunda Arc (Hamilton, 1979) may indicate that N-dipping subduction below the Sunda Arc of Java-Sumatra temporarily ceased to

PACFIC OCEAN

E.BOf?NEO

BANDA

AUOCHTHON

--_.

AUSTRALIA

Fig, 3. Reconstruction of Australian Gondwanaland at 90 Ma (Late Cretaceous) based on Smith et al. (1981). Continued spreading-of Tethys Ocean III caused Burma-western Thailand and Sumatra to migrate north. Schematic strike-s&pmotion between iriumatraand .MaIaya is related to plate movement in the West Pacific. Indian Ocean magnetic anomaly ~nf~~rna~~ presented as in Fig. 2 and taken from Larson (1977), Mark1 (1978), Larson et al. (1979) and Doutch (1981). Incipietit spreading between Australia and Antarctica schematically depicted after Cande and Mutter (1982). Coastlines for reference only.

be active at the end uf the Cretaceous. Alternatively the reported absence of Palacogene eruptive rocks may need revision, depending on their future discovery, or they may be present but completely unexposed. The amount of Palaeocene northward subduction below the Sunda Arc may have been very small if the subduction direction was oblique. The model put forward has postulated a series of strike-slip movements in the eastern part of proto-Indonesia, associated with the effect of the

plate movement reorganisatiun related to the shift in Pacific plate movement from n~r~-no~h~~t to northwest at 45 Ma (Engebretson et -al., 19SS). The postulated strike-slip movements c&d have served to bring together the somewhat scattered fragments of Indonesia as the northwed movemerrt of Australia and. the n~~wes~w~d movement of the Pacific fstarting~ at 45 MaJ-began the major Cainozoic process of corrvergence with Southeast Asia. Northern India and already coltided with the

PACIFIC OCEAN

INDIA W.BORNEO

/-‘b

E.BORNEO !

.O

W.SULAWESI

uu \\

JAVA

,

BANOA

ALLOCHTHON

& d

N GUINEA

9N OCEAN AUSTRALIA

ANTARCTICA

Fig. 4. Reconstruction Eurasia

at about

New Guinea.

of Australian

Gondwanaland

X0 Ma and India began

Indian

Ocean

magnetic

at 40 Ma (Late Eocene)

to collide with South Tibet at about

anomaly

data presented

based on Smith et al. (1981). South Tibet collided 44 Ma. Note the arc-continent

as in Fig. 2 and plotted

from Doutch

collision

(1981). Coastlines

with

Just north

of

for reference

only.

volcanic arc at about 75 Ma (Searle, 1983) and its continuing northward movement would have resulted in collision with South Tibet at about 44 Ma (Fig. 4). Reconstruction

for the Oligocene (30 Mu)

Subduction below the Sunda Arc, if it ceased or waned at the end of the Cretaceous, appears to have been active by the Oligo-Miocene (25 Ma) as indicated by the presence of talc-alkaline volcanics in Sumatra (Karig et al., 1979).

Australia began to drift northward by relatively rapid spreading of the India-Antarctica Ridge from 43 Ma (Fig. 5) (Smith et al., 1981: Cande and Mutter, 1982). Westward dipping subduction below western Sulawesi is indicated by volcanic products of Oligo-Miocene age (Sukamto and Simandjuntak, 1983). while eastern Sulawesi and the Banggai and Sula islands expose platform carbonates without any volcanics (Sukamto and Simandjuntak, 1983: Simandjuntak, 1986). Thus. the model proposes the convergence of eastern and western Sulawesi resulting in the tectonic

PACIFIC OCEAN

ANTAR-

Fig. 5. Reconstruction

of Australian

Gondwanaland

at 30 Ma B.P. (Late Oligocene)

its relatively rapid northward drift. Coastlines

collision in the Middle Miocene (15 Ma) as dated by the unconformable molassse facies on the deformed pre-hrliddle Miocene rocks (Kundig, 1956; Simandjuntak, 1986). The tectonic suture is indicated by the wide belt of blueschists and related metamorphics in central Sulawesi that now separates the eastern and western parts of the island (Hamilton, 1979). The Banda allochthon began to develop as an Eocene-Oligocene volcanic arc associated with N-dipping subduction of the Indian Ocean related to Australia’s (post 43 Ma) northward drift. These Eocene-Oligocene volcanics are exposed in Sumba

based on Smith et al. (1981). Australia continues

for reference only.

(the Banda forearc) and in the Banda allochthon as the Palelo volcanics, now also exposed on Timor (Earle, 1983; Audley-Charles, i985). Following the Middie Miocene collision of eastern and western Sulawesi the Sunda Trench propagated eastward, leading to the development of the volcanic islands of the eastern end of the Banda Arc. Reconstruction

for the Late Mhcene

(IO Ma)

By this time most of western Indonesia appears to have consolidated into its present general form.

321

PACIFIC OCEAN

BANGGAI-SULA

ANTARCTICA

Fig. 6. Reconstruction Sulawesi

collided

of Australian

at 15 Ma. Seram

Gondwanaland and Timor continues

at 10 Ma (Late

on the northern ita northward

Miocene)

Australian

drift. CoastlInes

Eastern Indonesia was undergoing rapid evolution as the convergence of the Australia-New Guinea margin with Southeast Asia continued. The volcanic Sunda-Banda Arc was still linked to continuing N-dipping subduction of the Indian Ocean associated with the northward movement of the Indian Ocean-Australia plate. This led to the continuing development of the Banda Arc volcanism until the continental margin of northwestern New Guinea collided with the eastern end of the Sunba Trench in the region of Seram (Audley-Charles et al.. 1979) at the end of

hased

margin

on Smith

collide

for reference

Eastern

and western

at 5 and 3 Ma respectively

et al. (1981).

as Australia

only.

the Miocene (5 Ma) (Fig. 6). The collision Australian continental slope with the

of the Sunda

Trench in the Timor region (Audley-Charles, occurred in the Middle Pliocene (3 Ma).

1986)

Conclusions By means of the Atlas map-plotting computer program we have drawn a series of schematic reconstructions for Australia converging on Southeast Asia during the late Mesozoic and Cainozoic. We have also included the rift-drift

movements blocks

of a number

postulated

Australian

include

trends

from

Ocean. data

from

Sumatra,

Tibet.

The pathways from they

magnetic

from

anomaly

followed

Gondwana

accord

Thailand

with

our

unique

donesia:

Nature.

solutions

view of the regional

are abundant

indications

rifting

event

affected

the

margin

in the Late Jurassic.

that

northern

a major

This paper

margin

extending

from northwestern could have been

for more

than

from

6000

km

Australia to Papua New Guinea South Tibet, Burma. western

Thailand and Sumatra. Much of the critical ocean-floor associated with this rifting episode has been destroyed by subduction, so this model can only be tested by land-based palaeomagnetic meathe

Malay

Peninsula did not collide with the Asian mainland until the Cretaceous are found in the structural history of those blocks and are in accord palaeomagnetic data from Tibet.

M.G..

with the

tectonic

Audley-Charles.

Cobbing

for

discussion, two anonymous referees for constructive suggestions, Janet Baker and Mike Gray for help with the artwork and Steve Kaye for his expert digitising

more

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