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A

Critical Evaluation of Plate Tectonic Models for the Development

of

Sumatra

A.J.

Barber1 and

M.J. Crow2

Southeast Asian Research Group Department

of

Geology Royal Holloway University

of

London Egham Surrey

‘ British Geological Survey Keyworth Nottingh am NG12 5GG U.K.

T W 2 0 O X U .K. E-mail: 106731.1236@conzpuserve.com

Over the past

two

decades models have been developed which

suggest that t he Asian continent has been formed by t he accretion

of continental blocks derived from the northern margin of

Gond wanaland . Sumatra which forms the southwes tern margin

of the Southeast Asian promontory (Sundaland) is considered

to be com posed of fragments of continental plates and mag matic

arcs which were derived from Gon dwanalan d during the Late

Palaeozoic and Mesozoic (see Metcalfe, 1996 and references

therein). The core of

Sundaland is formed by the Indochina

Block, exten ding in to the e astern p art of the Malay Peninsula.

The gre ater par t of Sum atra forms part of the Sibum asu Block,

which accreted to th e Indochina Block along the Bentong-Raub

Suture in the Triassic (Metcalfe, 2000). It has been suggested

that the southern par t of the Sibumasu Block in the we stern

part of the Malay Peninsula, and in Sumatra, is divided into

Malacca and Mergui Microplates, separated by the Mutus

Assemblage which also represents a Triassic sutu re (Pulunggo no

and Cameron, 198 4).

A

review

of

th e Permo-Triassic stratigrap hy

of M a l a y a a n d S u m a t r a p r o v i d e s n o s u p p o r t f o r t h i s

interpretation.

Comparison of the Permo-Carboniferous stratigraphy and

palaeontology of northern Sumatra with that

of

the Malay

Peninsula and Peninsular Thailand, and in par ticular the

occurrence of ‘tillites’, links Sumatra firmly to the rest of the

Sibumasu Block to the no rth (Cameron et al., 198 0). Comparison

with the Permo-Carboniferous stratigraphy

of

Bonaparte Gulf

region of northw est Australia (Roberts and Veevers, 1973)

sugges ts a m ir ror image re lat ionship , indicat ing tha t the

Sibumasu Block separated from this part of the Gondwanan

margin in the mid-Permian. On the other hand the Permo-

Carboniferous of Central Sumatra contains a Cathaysian faun a

an d flora, related to the Indochina Block rathe r than t o Sibumasu

(Fontaine and Gafoer, 19 89 ). This anomaly wa s recognised early

in the stu dy of the geology of Suma tra and led to the proposal

o f a D ja m bi N a ppe , t h r u s t ove r S um a t r a f r om the e a s t

v

Y

v

Lower o Mid Permian

carboniferous

Mid

t

Upper Permian

~ E S T UMATRA

,,,,I

with volcanic arc

Medial Sumatra

Q

Tectonic Zone

@

Medial Malaya Line

3 S T MALAYA

~ ~ ~ ‘

Bentong-Raub Suture)

Carboniferous-Permianwithout

SIBUMASU Diamictite sand dominant)

U . . Carboniferous-Permian

ith

Diamiclie Pebbly mudslone)

Fig.

1

Stratigraphic units and tectonicb lock, which have amalgamated to make

up Sum atra and t he Malay Peninsula, modified from Hutchison 1994).

Gondwana Research,

V

4 No. 4 2002

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RODINIA,

GONDWANA AND ASIA

571

(Zwierzijcki, 1930 ). The Cathaysian fa una and flora is associated

with an Early Permian volcanic arc (Fontaine an d Gafoer, 19 89 ).

It has been suggested that this was an independent island arc

accreted to th e western m argin of Sibumasu (Wajzer et al. 1991;

McCourt et al., 19 93 ), but from the relationships of the volcanic

rocks to Permian sediments and the underlying basement, it is

most probable that this arc wa s developed on th e margin of th e

Cathaysian Block.

The most recently accreted pre-Tertiary unit on Sumatra is

the Woyla Group, a Jurassic-Early Cretaceous oceanic volcanic

arc, which together with its associated accretionary complex of

oceanic crustal material was t hrus t over the weste rn margin of

Sumatra in the m id-Cretaceous (Barber,

2000).

There are many

problems still to be resolved in establishing th e stratigr aphy of

the Upper Palaeozoic and Mesozoic rocks of Sumatra, in the

definition of the cru stal blocks and in de term ining the ages a t

which the var ious blocks were accreted to the margin of

Sundaland. In this account, tectonic models which have been

proposed for the evolution of Sum atra (e.g., Zwierzijcki,

1930;

Pulunggono and Cameron, 1984 ; Fontaine and Gafoer, 1989;

Wajzer et al., 19 91 ; Metcalfe, 199 6; Hutchison, 1 99 4) will be

critically assessed,

a

modified interpretation proposed (Fig. ) ,

and those aspects of the geology will be identified w hich require

further detailed studies, with the aim of resolving the many

outstanding problems.

References

Barber,

A.J.

2000)

The origin

of the

Woyla terranes

in

Sumatra and

the

Late

Mesozoic evolution

of

the Sundaland margin.

J.

Asian Earth

Sci. v. 18, pp.

713-738.

Cameron, N.R., Clarke,

M.C.G.,

Aldiss,

D.T.,

Aspden,

J.A.

and Djunuddin,

A. 1980)

The geological evolution

of

northern Sumatra. Indonesian

Petroleum

Association. Proceedings

of

the 9th Annual Convention,

Jakarta,

1980, pp. 149.187.

Fontaine, H. and Gafoer,

S

(1989) The pre-Tertiary fossils of Sumatra

and their environments. United Nations, Bangkok, CCOP Technical

Paper

19.

McCourt, W.J., Gafoer,

S.,

Amin, T.C.,

Andi Mangga, S.,

Kusnama,

Burhan, G.,

Sidarto

and Hermanto,

B.

(1993) The geological

evolution of southern Sum atra. Southern Sumatra geological and

mineral exploration project report series

13,

Directorate

of

Mineral

Resources/Geological Research and Development Centre, Bandung,

Indonesia.

Metcalfe,

I.

(1996) Pre-Cretaceous evolution

of SE

Asian terranes . In:

Hall.

H

and Blundell,

D.J. (Eds.),

Tectonic Evolution of Southeast

Asia. Geol. SOC

London Spl. Publ., No.

106,

pp. 97-122.

Metcalfe, I 2000)

The

Bentong-Raub

suture zone.

J. Asian

Earth. Sci.,

Pulunggono, A.

and Cameron,

N.R.

1984)

Sumatran m icroplates, their

characteristics and their role in the evolution

of

the Central and

South

Sumatra Basins. Indonesian Petroleum Association,

Proceedings of the

13th

Annual Convention,

Jakarta, 1984 I, pp.

Roberts,

J.

and Veevers, J.J. 1973) Summary of

BMR

studies

of

the

onshore

Bonaparte Gulf

Basin 1963-1971.Geological papers 1970 -

71,

Australian Bureau

of

Mineral Resources, Geol. and Geophys.

Wajzer, M.R., Barber,

A.J.,

Hidayat,

S.

and Suharsono (1991) Accretion,

collision and strike-slip faulting: the Woyla Group as a key

to

the

tectonic evolution

of

North Sumatra.

J.

Southeast Asian Earth.

Sci.,

Zwierzijcki,

J.

(1930) Geologische overzichtskaartvan den Nederlandsch

Oost

Indischen Archipel. Toechting

by

blad

8

(Midden Sum atra,

Bangka, Riouw-eilanden). Jaarboek Mijnwezen Nederlandsch Oost

Indie, Verhandlingen 1929 ,

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58,

pp.

73-157.

V

18,

pp.

691-792.

1 2

1 144.

Bull.,

V.139, pp. 29-57.

V.

4, pp. 447-463.

Mineral Chemistry and Temperature Estimates of the Aluminous Granulites

Southern Kamataka India

M. Basavama

Department

of

Geology Karnatak University Dharwad - 580

003

India

Alumino us (Al) granuli tes are extensively distr ibute d

in the high-grade region of southern Karnataka craton. The

A1

r ich granuli tes occur as narrow isolated bands/lenses

showing conformable relation wit h the associated charnockites

and other granulite and amphibolite facies rocks of the area.

These granulites contain cordierite, garnet, biotite, sillinianite

a n d p l a g i o c l a s e . T h e p r e s e n t s t u d y a i m s a t p r o v i d i n g

comprehensive data on the chemistry and P-T estimations of

these rocks.

Electron probe micro analysis of the main mineral phases

show that garnet is essentially almandine-pyrope with 61 to

67Vo almandine and 30 to 35% pyrope and they occupy the

f ie ld of granuli te and bioti te paragenesis (Troger , 1959) .

Cordierite is rich in

Al O

MgO and FeO and poor in CaO and

Na,O. The Fe0:MgO ratio varies from

3

to 1 2. The

K

value

indicates a s trong preference of iron for garnet. Biotite is typically

titanium rich and relatively high in iron. The chemistry of

s i l l imani te does not bea r any s igni f icant va r ia t ions . The

orthopyroxene (Opx) is rich in MgO, FeO and

Al O

and totally

lack alkalis. The

K

values obtained for garnet-biotite, garnet-

cordier i te and bioti te-cordier i te suggest the a tta inment of

equilibrium during the crystallization

of

these minerals. Th e

equilibrium temperature obtained for garnet-cordier ite and

garnet-bioti te pairs is 673°C and 748°C respectively and

comparable to the temperature estimates (766-657°C) by gar-

cpx geothermom etery (Mahabaleswar et al. , 19 84) for part of

the high grade region

of

south ern Karnataka. The mineral

assemblages and their chemistry suggest that these rocks

represent l rich metasediments developed und er granulite facies

conditions. The appearance of cordierite is highly dependent

upo n the bulk composition. The appea rance of hypersthene is

either related to the reaction between biotite and quartz or

controlled by MgO+FeO+Al,O, ratio. The garnet breakdown

r e a c t i o n t o o k p l a c e

as

a c onse que nc e o f i so the r m a l

decompression, probably accompanied by oxidizing condition

that produced magnetite. T he temperature estimates mad e on

Gondwana Research V .4

No.

4 2001