Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia By PETEIR H. STAUFFER, Kuala Lumpur*) With 11 figures

Zusammenfassung Teile Sfidost-Asiens besitzen offenbar pal~iozoische oder/iltere kontinentale Erdkruste. Diese umfassen Heine Fragmente in den Archipelen der Philippinen und Indonesiens, Neuguinea mit anliegenden Schelfen, und (das Hauptgebiet) eine grol3e Masse, die fast das ganze Festland S/idost-Asiens, den Hauptteil Sumatras, das siidwestliche Borneo und Teile des angrenzenden und dazwischenliegenden Meeres einschliegt. Ophiolitgiirtel, die wahrscheinlich Suturlinien darstellen und dariiberhinweg sehr gegens~itzliche Geologie deuten an, dab diese Hauptmasse ein Mosaik aus verschiedenen Fragmenten oder Bl6cken ist. Nachdem seit einem Jahrzelint eine umfassende Durchsicht der Herkunft und Gesehiehte dieser B16cke erfolgt ist, liegen neue Kenntnisse vor. Einige herausgearbeitete Suturlinien wurden zwar neu interpretiert, doch wird das Hauptgebiet der alten kontinentalen Erdkruste immer noch als aus mindestens zwei und vielleicht drei verschiedenen B16cken bestehend verstanden. Neue paliiomagnetische Messungen fiir das Pal/iozoikum deuten auf eine Lage in mittelhohen (wahrscheinlich siidlichen) Breitengraden (48 ~ ftir NW-Malaya) f/Jr einen Tell Siidost-Asiens im friiheren Pal~iozoikum bin und fiir das sp/itere Pal/iozoikum auf die M6glichkeit einer mittleren siidliehen Lage (24 ~ fiir Zentral-Thailand). Neue Daten aus spiitpaNozoisehen F1oren best~itigen mehr, dab Kathaysischen Floren auf dem Rand des Gondwanakontinents auf dem Arabischen Schild welt verbreitet waren und die floristischen Daten k6nnen jetzt verstanden werden im Sinne einer friiheren Anbindung yon Teilen Siidost-Asiens an Gondwana. Eine auffallende Zone von ger611f/ihrenden Schlammsteinen des Karbons, die jetzt in einer Verbreitung von 2000 km yon Sumatra bis Burma bekannt ist, wurde neu interpretiert als wahrseheinlich glaziomariner Herkunft und nicht als tlutsehungsmassen. Die Deutung dieser Gesteine ist yon kritiseher Bedeutung: falls die ger611fiihrenden Sehlammsteine von submarinen Rutsehungen stammen, wurde das westliche Siidost-Asien wahrscheinlich im sp~iteren Pal~iozoikum von einem unbekannten Kontinent abgespalten; jedoch, wenn sie glaziomarinen Ursprnngs sind, dann war das westliche Sfidost-Asien nahezu zweifellos an Gondwana angebunden und die Abspaltung und Losl6sung gesehah sp/iter, wahrscheinlich wiihrend des sp~iteren Mesozoikums.

Abstract Parts of Southeast Asia show evidence of having Paleozoic or older continental crust. These include small fragments in the Philippine and Indonesian archipelagoes, New Guinea and adjoining shelves, and (the main area) a large mass consisting of nearly all of mainland Southeast Asia, most of Sumatra, southwestern Borneo, and parts of the bordering and intervening seas. Ophiolite belts, probable sutures, and contrasting geology across them indicate that this main mass is a mosaic of different fragments or blocks. Since a comprehensive review of the origins and histories of these blocks a decade ago, new information has appeared. Some inferred sutures have been reinterpreted, 9 *) Address of the author: Dr. P. H. STAUFFEIR, Department of Geology, University of Malaya, Kuala Lumpur 22-11, Malaysia. Geologische Rtmdschau, 72, 8, 1061--1080, Stuttgart 1983

"106"1

P. H. STAUFFEB though the main area of old continental crust is still seen as consisting of at least two and possibly three separate blocks, tteeent paleomagnetie determinations for the Paleozoic suggest a position in moderately high (probably southern) latitudes (48 ~ for NW Malaya) for part of Southeast Asia in early Paleozoie, and the possibility of a southern temperate position (24 ~ for central Thailand) in Late Paleozoie. New data on Late Paleozoie floras establish more firmly that Cathaysian floras were widespread on the edge of the Gondwana continent in the Arabian shield region, and the floral data can be seen now as supporting former attachment of part of Southeast Asia to Gondwana. A prominent zone of Carboniferous pebbly mudstones, now recognized to extend over 2000 km from Sumatra to Burma, has been reinterpreted to be of probable glacial marine, rather than slump, origin. The interpretation of these rocks is of critical significance: ff the pebbly mudstones are submarine slump deposits, western Southeast Asia probably rifted off some unknown continent during Late Paleozoic; if they are glacial marine sediments, then western Southeast Asia was almost certainly attached to Gondwana and the rifting and separation took place later, probably during the later Mesozoic. B6sum6

Plusieurs r6gions d'Asie du sud-est attestent l'existenca d'une crofite continentale pal6ozoique ou plus ancienne. On trouve ainsi de petits fragments dans les archipels philippin et indon6sien, en Nouvelle Guin6e, et surtout une vaste masse qui comprend presque toute l'Asie du sud-est continentalc, la majeure pattie de Sumatra, le sudouest de Born6o et des r6gions c6ti6res ou entre les mers. Des ceintures d'ophiolithe, des sutures probables et une g6ologie contrastante montrent qua cette masse principale se compose d'une mosa~que faite de diff6rents fragments ou blocs. Depuis une 6rude compr6hensive de l'origine et de l'histoire de ces blocs datant d'une dizaine d'ann6es, de nouvelle informations sont apparues. Certaines de ces sutures ont fait l'objet d'une nouvelle interpr6tation, bien qua la zone principale de l'ancienne crofite eontinentale soit encore consid6r6e comma se composant d'au moins deux et peut-Stre de trois blocs s6par6s. De r6centes d@erminations pal6omagn6tiques pour le Pal6ozoique sugg6rent une situation (probablement australe) de latitude mod6r6ment 61ev6a (48 ~ pour le Nord Ouest de la p6ninsule de Malaisie) en ce qui concerue des r6gions d'Asie du sud-est au Pal6ozoique Inf6rieur, et la possibilit6 d'une situation australe temp@6e (24 ~ pour la Thailande centrale) au Pal6ozoique Sup6rieur. De nouvelles donn6es sur la flora du Pal6ozo~que Sup6rieur montrent plus clairement qua la flora eathaysierme s'6tendait largement ~ la limite du continent de Gondwana dans la r6gion du bouelier de l'Arabie; les donn6es sur la flore peuvent maintenant confirmer l'attachement d'une partie de l'Asie du sud-est au Gondwana. Une longue zone d'argile ~ blocaux earbonff6re, maitenant reeonnue comma s'6tendant sur plus de 2000 km de Sumatra ~ la Birmanie, a fait l'objet d'une nouvelle interpr6tatiou; elle est ~ pr6sent consid6r4e comma 6tant d'origine glaciomarine plut6t qua de glissement. L'interpr6tation de ces roches comporte une signification particuli6re: si l'argile bloeaux est un d6p6t dfi ~ des glissements sous-marins, la pattie oecidentale de l'Asie du sud-est s'est d6tach6e probablement d'un continent inconnu au cours du Pal4ozoique Sup6rieur; si, en revanche, ce sont des s6diments glaciomarins, cette partie oceidentale 6tait alors presque certainement attenante au Gondwana, et la d6rive ainsi qua la s~paration ont eu lieu plus tard, probablement au M6sozoique sup6rieur.

~paTKoe co~ep~aHHe B OT~e~H~IX peFHOHaX~F0-BOCTOqH0~A3HH coxpaHH~aC~ Ha~eo30~cKaH, H~H ~ a ~ e 50~ee ~ p e B H ~ MaTepHKOBa~ ~ o p a . E e H a x o ~ T B BH~e OT~e~H~IX Ma~eH~KHX ~paFMeHTOB Ha & p x H n e ~ a P a x : ~ H ~ H n H H L I , ~ H ~ O H e 3 H H , HoBaH ~BHHeH C

1062

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia npH~erai-o~tg~MH 30HaMH me~i~qba ~, Na~ 0CHOBI-IytO Naccy, npocTHpam~.~ymc~ II0~THtITO qepe3 sec~ tOFO-BOCT0qHLI~I MaTepHE A S H t t , FJI. o6p. Ha CyMeTpe, ~oro3aHa~e BopHeo H B Mopax, Haxo~a~i~xca Me;~y H~MH, ~Jn~ r~pHJ~era~-o~.~HxK HHM. OC1)HOJIHTOB~Ie no~ica~ H p e ~ c T a B J I a H ) ~ H e c 0 5 0 ~ , B e p 0 ~ T H O , IIIBI~I, -- I~eoJIOFHtO EOTopI~IX T p F ~ H 0 ' i I p H B e C T H K O~HOMF 3HaMeHaTeJII-0 --, y K a 3 l ~ I B a t O T H a TO, ~IT0 ~ T a 0CHOBHaY/ M a c c a n p e ~ C T a B J i a e T c 0 5 0 ~ M o 3 a H K F H3 pa3JIHtIHI~IX q b p a r M e H T O B H 5 ~ 0 KOB. B o J I e e ~ e C ~ T H . ~ e T H ~ I ~ 3 y q a J I H I ~ p o H c x c 3 K ~ e H H e H ~ICTOpH~0 3THX 5JIOKOB, e o S p a B HOBtJIe CBe~eHHYl. i e K o T 0 p I : , I e H3 IIIBOB n 0 J I y t I H J I t t HHFK) I~HTepnpeTaI~HtO, ~IeM Hpe~e, ~ 0 0CHOBttaFI ~IaCTI~ ~peBHe~I M a T e p H K O B 0 ~ K 0 p ~ I n p e ~ C T a B J I e H a ~BFM~'t, HJII~, MOH~QT 6I~ITB, T p e M H pa3JIHtlHI~IMH 6 n o K a M H . i O B e ~ I I I H e IIaJIeOMaFHHTHI~Ie H 3 MepeHHYI I I p 0 6 n a J I e O 3 o H pacnoJiaI~aJIHCI~ B c p e ~ H H X I n H p 0 T a X , B e p O H T H e e BceI~O B I-OHfHI~IX (43 o) ~ n ~ Beel~o c e B e p o - s a ~ a ~ a ~V~aJIa3HH, a B HO3~:][HeM Y i a J I e o 3 o e - , BO3MO~KHO, B 2 4 0 ( ~ n a ~ e H T p a J ~ H O r O T a ~ J ~ a H ~ a ) . H O B B I e ~(aHHBIe 0 n O S ~ H e H a ~ e o -

3o~c~o~ qbnope nO~TBep~amr TOT ~aET, HTO ~YI0pBI Cathaysian 5~inz mHp0~0 pacnpocTpaHeH~ Ha apa5c~oM I~Hwe no ~pam MaTep~a I~OH~:~BaHBI H 3TH ~aHH~e MOH~HO HCTOJIKOBaTB B CMBICJIe p a H H e F O n p 0 c 0 e ~ H H e H H H ~IaCTeI~I IOI~O-BOCTO~HO~I A3HH K ~OH~BaHe. 1-IpoHcxo~eHHe 3OHI~I H3 HJIOBI~IX OTJIOH~eHH~I C BHJUO~IeHHHMH r a ~ b ~ H i~apSoHa, H3BeeTHO~IHa IIp0THY~eHHH5o~ee 2 0 0 0 I ~ OT C y ~ a r p ~ ~0 BHpMBI, H H T e p n p c ~ r H p y t O T TeIIept,, i~aE B0~MOH~HLIe JIe~HHKOBO-M0pCKI4e OTJIOHs a He, I~aH 0HOJI3eHt~. TO~tHaH H H T e p I I p e T a I ~ H H YIpOHCXOYE~eHHH DTHX n o p o ~ BaHs eeJIH 3TH HJIHCTI~Ie I I o p 0 ~ B I , HecyII~He PaJII~Ky, HpoH3OIHJIH B pe3yJII~T&Te HO~BO~HI~IX OHOJIDHe~, TO 3 a I I a ~ H a H ~IaCTI~ tOFO-BOCTOKa ~L3HH OTKOJIOJIaCI~ OT HeH3BeCTH01"O HOHTHHeHTa~ BepOHTHO~ B H O 3 ~ H e M H a J I e O 3 O e ; HO, eCJIH 0 H a FJIaI~HaJII~HO-IVIOpCHOrO H p O H C X O ~ e H H H , T0 O H a 5BiYla, BHe BCHE01"O COMHeHHH~ C B H 3 a H a C InOH~BaHO~I H 0 2 ~ e J I H J I a C B OT n o c J I e ~ H e ~ I 3HaHHTeJn~HO n o 3 m e , B e p o H T H e e B c e r o , B HO3~HeM Me3o3oe.

Introduction

Southeast Asia, taken here to include all the territory between India, China, and Australia, can be broadly divided into two types of geologic terrane. One of these comprises the volcanic-magmatie-tectonic belts formed mainly in later Mesozoic to recent times along convergent plate boundaries. These belts are largely expressed as island arcs developed in regions of originally oceanic crust, and they constitute the bulk of the Philippine and Indonesian archipelagoes. The other type of terrane includes the areas of mainly continental and intermediate crust, in which the basement rocks are of P a l e , z , i t or older age. These areas of older and continental-type basement include several small fragments within the island ares, such as the Sula and Banggai Islands (inferred to have been faulted off northwestern New Guinea and translated westward; see HAMILTON, 1979, 156-159), the North Palawan block (possibly rifted off from South China; see HOLLOWAY, 1981), and Timor (consisting in the main of dislocated fragments of the edge of the Australian continent; see HAMILTON1979, 121--182). The Sahul and Arafura Shelves and most of the island of New Guinea also consist of such older continental crust, which there is clearly part of the Australian craton, merely separated by shallow submergence of the shelf. But the largest area of old crust in Southeast Asia is that which projects down from Asia in the north and includes nearly all of mainland Southeast Asia (Ind.china, Thailand, eastern Burma, and 'Peninsular Malaysia), most of Sumatra, west-central Borneo, and portions of intervening and adjoining shallow seas, especially those constituting the Sunda Shelf. This area has been referred to by many names and was shown by MURPHY (1975) as the "Pretertiary core" of Southeast Asia (Fig. 1). It is locally overprinted (especially along the southwest side of 68 Geologische Bundschau, Bd. 72

10113

P. H. STAUFFER

Sumatra) by the later Mesozoic and younger arc systems, and it contains within itself remnants of older (pre-Jurassic) arcs. The crust underlying this '~!d' region has been inferred to be largely of continental character, on the bas'is of topography, gravity, composition of igneous bodies, and the character of the Paleozoic and Mesozoic sediments. Actual Precambrian basement has been confirmed by radiometric dating only in Vietnam, where gt number of datas between 650 and 2800 Ma have been obtained (BAo et al., 1981), though other crystalline rocks in some areas, such as western Thailand, are suspected to be of Precambrian age. Within this block of inferred old continent, however, there are several possible and probable sutures between blocks that had independent histories up to the time they collided, forming the sutures. These features are marked by tectonic lineaments, contrasting geology, and belts of basic and ultrabasic rocks which have been called, with varying degrees of justification, 'ophiolite' (see HUTCHISON, 1975). The older portion of Southeast Asia is therefore a composite block - - a mosaic of juxtaposed fragments. Deciphering the story of this mosaic and working out the separate histories of the fragments has been and remains one of the more interesting problems of Southeast Asian geology. This problem was reviewed nearly a decade ago, using what evidence was available from several different kinds of data (STA~:FFEa, 1974). The major conclusions from that review were as follows: 1. That the old core of Southeast Asia consisted of three fragments (referred to as the 'West Malaya Block', 'East Malaya Block' and 'Indochina Block'), divided from each other by probable sutures and from South China by a major suture belt in northern Vietnam, the Song Ma - - Song Da ("Black River") belt (Fig. 2). 2. That the western fragment ('West Malaya Block') represented the marginal part of a large Preeambrian continent formely attached on the (present) west side, this fragment being possibly Continuous northward into Tibet or western China; the central fragment ('East Malaya Block') represented a probable island arc which formed not far from the West Malaya Block and collapsed against it by Triassic; and the Indoehina Block represented a small separate microcontinent. 8. That South China collided with the Indochina Block, and Indochina with the East Malaya Block, in the Triassic, by which time the last also collapsed against the West Malaya Block. 4. That the unified cluster of these fragments rifted off the large continent to its (present) west probably in the Jurassic. 5. That the continent to which the Southeast Asian cluster was formerly attached was part of Gondwana, and perhaps most likely the North African --Arabian portion (see Fig. 8). 6. That such a hypothesized connection with Gondwana was not ruled out by the "Cathaysian' Carbo-Permian floras of Southeast Asia, since an essentially Cathaysian flora was known from the Permian of Hazro, Anatolia, on a part of the Arabian Shield and hence on the Gondwana continent. In this paper I wish to examine the new data and interpretations that have come to light since this review of the problem, and see to what extent these earlier Conclusions must be modified or extended. 1064

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia

Fig. 1. Index map of Southeast Asia showing approximate extent of the main area underlain dominantly by Paleozoie or older continental basement, here called the 'Pretertiary Core'. Also shown are present plate boundaries and motions. Modified from Mu~nY (1975).

Fig. 2. Component blocks making up the old continental part of Southeast Asia, according to STAUFFEa(1974). Later work shows only one probable suture in Thailand/Laos, and therefore the 'E. Malaya Block' cannot be recognized there as a separate unit. 1065

P.H. STAUFFER

J

I I 1,5o JURASSIC

, ~

..fsour.

c.~NA

I

1oo~ 4~o

IN

Equot( r - -

3 0 o- - -

45 ~

(

I 60 ~

\

-'--7

~

75 o - -

Fig. 8. Positions of Southeast Asian fragments and some other continental blocks in Jurassic, as inferred from paleomagnetic data. From STAVFFEa(1974). If Southeast Asia riftet off a large continent at about this time, the most likely candidate appears to be Africa/Arabia.

Boundaries of block and fragments Our picture of the constituent blocks that make up the old core of Southeast Asia has been somewhat modified by recent work, and the extent and relationships of some of the blocks are the subject of varying and sometimes speculative interpretations. The more western of the two probable ophiolite belts noted by HUTCHISON(1975) in northern Thailand and Laos (the 'Lampang-Houei:Sai Line') has been shown to be a late Carboniferous volcanic arc (MAcDoNALD & BAR~, 1978), leaving only one likely suture belt (the 'Uttaradit-Luang Prabang-Pok Lay Line' of H~:TCmSON, 1975 - - see THANASUTHIrlTAK,1978) in that region. Therefore the 'East Malaya Block' of STAUFFER(1974) may be merely part of the Indochina Block, and MITCHELL (1981), in his delineation of the boundaries of tectonic blocks in Southeast Asia, has shown it as such (Fig. 4). The interesting thing in MITCHELL'Sinterpretation is his extension of the Indochina Block and the 'Western Southeast Asia Block' through narrow slivers into Central and Southern Tibet, respectively (see Fig. 4). This extension is based on geological similarities and inferred continuity of the bounding 'sutures' and remains to be tested by either paleomagnetic determinations or continuous mapping. The nature and indeed the reality of the 'suture' belt between 'Western Southeast Asia' (the belt from Sumatra and western Malaya to at least northeast Burma and southwest Yunnan) and the block(s) to the east of it has been the subject of 1066

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia I'

8' 0 ~

'

90 ~

'

I00 ~

'

I10 ~

Fig. 4. Component blocks and their bounding sutures in the Southeast Asian region, according to MITCHELL(1981). Note the extension of the Southeast Asian fragments into Tibet, and the implied inclusion of eastern Malaya into the Indochina Block. controversy and speculation. In particular, the Malayan portion of this 'suture', the Bentong-Raub Line, though classed by HUTCHISON(1975) as a definite though dismembered ophiolite, in fact shows few of the features of a well-developed ophiolite (TAN & Kaoo, 1981). It consists instead of a discontinuous and somewhat scattered belt of serpentinite bodies, possibly related metamorphosed basic igneous rocks, and very rare peridotites, associated with some prominent geologic contrasts and tectonic features. If the Bentong-Raub Line is continuous with the belt through Uttaradit in Thailand (THANASUTHII'ITAK,1978), as MITCHELL(1981) has interpreted it to be, then the better developed ophiolites of the Thai portion would allow the entire belt to be taken as a suture marking the site of a closed ocean basin. But these two parts may represent separate entities, as inferred by STAUFFER (1974) and more recently by PtIDD (1980), who retains a separate 'East Malaya Block' but does not extend it northward through Thailand (see Fig. 5). In that case the Bentong-Raub Line must be interpreted purely from the evidence in the Malay Peninsula. The two segments are not differentiated by age, as both appear to represent late Paleozoic to Triassic events, although dates are imprecise. 1067

P.H. STAUFFER

Fig. 5. Component blocks and their bounding sutures in Southeast Asia, according to RIDD (1980). Note the retention of a separate block for eastern Malaya and southwestern Borneo, distinct from the Indochina Block. Despite the absence of a good ophiolite along the Bentong-Raub Line, I feel this line is still best considered as the western edge of a suture belt marking the site of a closed oceanic basin. Evidence in support of this interpretation includes: 1. The great geologic contrast across the line (see Fig. 6): To the west the geology is dominated by Paleozoic shallow-water and continent-derived sedimentary rocks and granitic intrusive rocks; immendiately to the east are Carboniferous to Triassic sedimentary rocks, in large part of deep marine deposition and of volcanic are derivation (see, for instance, METCALFEet al. 1982). 2. Gravity values: A gravity profile across the line (RYALL 1982) shows a marked negative anomaly over the Main Range batholith, changing eastwards (across the line) to a marked positive anomaly. The abruptness and magnitude of the change indicate a sharp and profound geologic boundary. Depending on the densities assumed for the sediments in the central graben, the gravity values east of the Bentong-Raub Line can be interpreted as indicating a very thin or absent "granitic layer" (continental crust). 8. Manner of occurrence of serpentinite bodies: Among the scattered serpentinite bodies found along and near the Bentong-l~aub Line are some which have apparently squeezed up along the faulted crests of anticlinal structures in the Paleozoic sedimentary and metasedimentary rocks (see KRISltNAN, 1975). This situation seems to indicate a widespread or pervasive underlying basement of 1060

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia I

~

I

102~

I 104o

0

50

IOU

KILOMETRES -6 ~ z

tin

=m ~

~ ++++

~70 '~:iiii: ':':'":v.

4o

% %

Ca

~v"

+ ++ + §162

KEY

t" .~

::'::-<'. ...:.:......

~?~

:i~ii~-~- EPIZONAL LATE CRETACEOUS GRANITES EPIZONAL PERMO-TRIASSIC GRANITES ['~'-~ MESOZONAL PERMO-TRIASSIC GRANITES

~::i.;~ ? '~? ~ ~

o "

TR,ASS,C EP,ZONAL G.AN,'rES

;NL~US'VLmmmm, E .,GH

\

GRADE METAMORPN,C ROCKS

I

----='= BENTONG- RAUB LINE --?-- UNCERTAIN EXTENSION MAJOR FAUTS

(02~ I

~? 104 o. l

I

Fig. 6. Tectonic belts and granite types, in the Malaya Peninsula, after HUTCHINSON (1977). Note the Bentong-Raub Line and the limitation of inferred mesozonal granites to the belt just west of it. already serpentinized basic or ultrabasic rocks, ready to form cold intrusions upward where fractures give such opportunities. 4. Character of the Main Range batholith: The characteristics of this very large granitic mass (see Fig. 6) have been interpreted (MITcrtELL, 1977) to have resulted from 'collision', i. e. the impingement of the western continent against the volcanic

1069

P.H. STAUFFER

are of an eastward-dipping subduction zone, leading to depression, heating and anatexis of the continental edge (Fig. 7). Such an inferred origin seems best able to explain the special characteristics of this batholithic belt. Data on the granites of western Thailand (BECKINSALEet al., 1979) support MITCHELL'Sinterpretation, in that the characteristics of the Triassic granites (low NaeO, high SrSVSrs6 ratios, and relatively reduced oxidation state of Fe) imply a magma deriving from continental crust, the melting of which is most easily explained by depression in a collision event. The existence of a Permo-Triassic calc-alkaline volcanic belt to the east of these granites (across the Uttaradit ophiolitic zone) is consistent with eastward subduction and closure of an ocean or marginal basin prior to the collision, as pointed out by BECKINSALEet al. (1979). The Thai data therefore indicate a Permian and Triassic history closely analogous to that inferred for Malaya by MITCHELL (1977). If we can accept the Bentong-Raub Line and the associated belt to the east of it as the traces and remnants of a closed ocean basin, the question remains how wide this basin was. The existence of a tin belt in eastern Malaya, paralleling the western tin belt associated with the Main Range granites, suggests a geological relationship most easily explained if the closed ocean was a narrow one, perhaps of marginal basin type.

Paleomagnetie data Southeast Asia remains a region for which the paleomagnetic data, especially for the pre-Mesozoie, are still few, scattered, and often of uncertain reliability. HAILE (1978) reviewed the data available up to 1975, most of which was taken account of in STAVFFER (1974). New data published since 1975 are relatively few and mostly concern Mesozoic and Cenozoic rocks. Data from both Jurassic (BuNoPAS et al., 1978) and Middle Triassic to Jurassic rocks (BA•R et al., 1978) indicate that eastern and western Thailand (i. e. the Indochina Block and the Western Southeast Asia Block) have been united since those times, which is consistent with their having collided and fused during Triassic. Data from Cretaceous rocks of Malaya and west Borneo (HAmE, 1978) similarly indicate those two areas have formed parts of one tectonic block since at least Cretaceous. Two sets of new results from Paleozoic rocks have been published and are of considerable interest. Data from one site in the Kaeng Krachan Formation (late Paleozoic pebbly mudstones) in Thailand (BuNoPAs et al., 1978) yield an inferred paleolatitude of 24 ~ S for central Thailand. Though this result is unsupported by study of other sites, it is interesting because it is more consistent with paleolatitudes inferred for the pebbly mudstones from other evidence (see below) than are the paleomagnetic results for late Paleozoie of McELHINNYet al. (1974). Paleomagnetic data from Ordovician/Silurian limestones in the Setul Formation of northwest Malaya (HAILE, 1980) yield a paleolatitude of 43 ~ Such a relatively high latitude of origin for the Setul Formation, which includes dolomites and oolitic limestones (JONES, 1968), seems unlikely, although recent work (RAO, 1981) suggests caution before ruling out a temperate zone origin for the formation. Even if a somewhat lower latitude is assumed, the inferred position of Southeast Asia in the early Paleozoic is interesting (Fig. 8). If the Earth's field was normal at the 1070

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia

CONTINENTAL FORELAND

A.

.

.

.

B.

OCEANOR MARGI BASINAL

r ~ co

=:~ ~~ co

:~ ~ "~ '~

LATE PERMIAN-EARLY TRIASSIC

.

.

.

.

.

~"i~

~~

"ANATECTICGRANITE

END TRIASSIC

Fig. 7. Diagrams showing the possible origin of the Main Range granites by depression of the continental edge in an eastward-dipping subduction zone, and consequent anatexis. After MITCHELL(1981). time, the old part of Southeast Asia would be placed in the northern hemisphere, in a position possibly farther north than any other known continental block or fragment, and with no likely larger continent to which to be attached. If the field was reversed, the indicated position would be in the southern hemisphere and rotated nearly 180 ~ from its present orientation. That position would allow of attachment to the Gondwana continent at two places (see Fig. 8). Because of the evidence that this fragment of Southeast Asia was attached to a continent on its (present) west side (see STAUFFER, 1974), the more likely position in the early Paleozoic would be next to the Iranian portion of the Gondwana margin, a position not far different from that inferred by STAVFFER(1974). Nevertheles, not very much significance can be attached to these paleomagnetic results until they are corroborated by further studies and tests to rule out later overprinting.

Late Paleozoic floras No new data on late Paleozoic floras have appeared which conflict with the inferences drawn earlier (STAUFFER, 1974). Indeed the inference that Cathaysian floras were established on parts of the margin of the Gondwana continent in the 1071

P. H. SThUFFER Permian has been strengthened by the report ol a distinctly Cathaysian Middle to Upper Permian flora from a site underlain by the Arabian Shield in western Iraq (~TYROKY~ 1973). This occurrence, along with a lew other Middle to Upper Permian floras, has been added (Fig. 9) to the map of CHALONER & LACEY (1973) showing the distribution of latest Carboniferous/early Permian floras. This map shows clearly that the Gondwana continent was host not only to Gondwana (Glossopteds) floras but also, in its lower-latitude portions, to Cathaysian floras such as were characteristic of China and of Southeast Asia. Thus the inference of a former attachment of parts of Southeast Asia to Gondwana (RIDD~1971; TARZINC, 1972; A~LEY-CHARLES et a]., 1972; STAUFFER, 1974; HAMILTON, 1977) may now even be said to be supported by the Permian floral distributions. A tantalyzing recent floral find was the discovery (AzHAR, 1977) Of a single lea/ tentatively identified as Gangamopteds in Carbo-Permian deposits in eastern Malaya (the occurrence shown as a doubtful 'tilloid' on Fig. 10). The precise age is not known, but this find is interesting in view of the inferred presence of a Carbo-Permian glacial facies in western Southeast Asia (see below). It also sug-

SOUTHEAST ASIA (NORMAL)

,oo

-

--

60~

....

i

- - - -

-

Fig. 8. Position of Southeast Asia in the Ordovieian based on paleomagnetic evidence from Langkawi, Malaya, after HAmE (1980). If the magnetie field was reversed, attachment to Gondwana is allowed at two sites (though the West African site is improbable - - see text). I f normal, Southeast Asia would have been the northernmost known continental block, and no likely attachment sites are evident. Note that Indoehina rides With western Southeast Asia, though other evidence implies they were separate at this time. 1072

Unraveling the mosaic of Paleozoie crustal blocks in Southeast Asia "~ 11/ A m e r / c o n

9 Ca/hays/

9 Euromer/on

Cothayszdn/ 9 M~;red Glossop/erLr

o

o

r~o

Glossopler/s

@ MLred GlossopterLr

a 11ngaro

o---

~

~j o

-60~

o

o o

."i

....,...~... ~:S o

o

o

o

o

O~

@O@o o oo o

~ o

o

J

Fig. 9. Distribution of some Permian and latest Carboniferous-floras on a 'pre-drift' reconstruction of the continents for Permian (based on paleomagnetic data). After the map of CnALONER&' LAtEr (1978) showing Early Permian and latest Carboniferous floras, to which have been added some Middle and Late Permian Cathaysian floras from Southeast Asia and Middle East. Inferred tropical floras shown by solid symbols. Dashed line bounds those parts of Asia which were probably in low latitudes and not attached to Eurasia in the present positions as shown here.

gests that a re-evaluation should be made of the previously reported Glossopteris floras elements in the Permian of Thailand, which have been regarded either as stray migrants (KoN'NO, 1963) or as a case of parallel evolution (AsAM& 1966).

Possible Late Paleozoie glacial facies One of the most interesting recent developments in the Paleozoic geology of Southeast Asia concerns the late Paleozic pebbly mudstone facies found along the western edge of Southeast Asia's old core. Such pebbly mudstones have long been known from the Phuket area of southern Thailand (MANTAJITet al., 1979), and from the Lankawi Islands off northwestern Malaya (AHMAD,1978), where the unit containing them (the Singa Formation) is bracketted by fossiliferous late Devonian and early Permian strata, indicating that the pebbly facies is essentially and perhaps entirely Carboniferous. These pebbly rocks have 1073

P,H. STAUFFER traditionally been explained by "slumping", although the possibility of ice-rafting of the megaclasts was considered (and rejected) by several authors. Recent work, however, makes a glacially-related (mainly glacial marine) origin for these pebbly mudstones more likely (STAUFFER, 1980). The evidence supporting such a reinterpretation (partly based on work in progress by P. H. STAUFFER and C. P. LEE) includes the following: 1. The great lateral extent of the facies - - from central Burma through southern Burma and southern Thailand to Malaya - - was made evident by a recent compilation of the data (STAUEFER & MANTAJIT,1981). Similar rocks have also been recorded over wide areas of northern Sumatra (CAMERONet al., 1980). This pebbly facies therefore occurs in a belt stretching more than 2000 km (Fig. 10), and such a great extent is easier to reconcile with an'event of continental or global scale, such as glaciation, than with more local events such as slumping. 2. The megaclasts in the pebbly facies typically exhibit the blocky and facetted shapes characteristic of coarse glacial debris. Many occur in laminated rocks and show a 'dropstone' character. Included among the megaelasts are many examples of (pre-Carboniferous) granitic plutonie rocks. Such rocks are not known to be exposed anywhere near the pebbly mudstone belt today and must be regarded as exotic. One of these from Malaya has yielded a probable Precambrian radiometric age (STAUFFER• SNELLING,1977). 3. Trace fossils of typically shallow-water type occur in the pebbly facies in Malaya (in the Singa Formation), where they include vertical burrows transeeting tight 'slump' folds. In many places the matrix of the dropstone-bearing rocks is rhythmically, if vaguely, laminated, and the monotonous repetition of very thin sand layers, often rippled, and silty muds is suggestive o.f tidal influence. The implication from these features of very shallow water is not consistent with slumping on a major (e. g. continental) slope, but could be consistent with very local slumping in rapidly deposited glacial debris or even with superficial folding produced by movement of grounded icebergs or shelf ice. 4. Diamonds which have turned up in alluvial tin mines both in the Phuket area of Thailand and in Sumatra are almost certainly weathered out of the late Paleozoie pebbly mudstones forming the bedrock in those areas. If these diamonds are derived ultimately from kimberlite pipes scattered on a continental eraton, it would be difficult to move them to the continental edge (where they might become involved in 'slumping') by ordinary transport mechanisms. Transport to the sea would, however, be easy and expected if continental ice sheets were eroding the eraton surface. This proposed glacial interpretation of the pebbly mudstone facies has obvious and important implications. It would contradict earlier interpretations (e. g. STAUFFER & GOBBETT, 1972; STAUFFER~1974) of the Late Paleozoie lithologies and faunas of the Malay Peninsula as indicating tropical or subtropical conditions. Indeed these earlier ideas are in need of revision. The notion that thick extensive carbonate formations imply warm water has been shown to be false (RAO, 1981), and fossils from the pebbly mudstones themselves have been interpreted as indicating cool water conditions (WATERHOUSE,1982). HOW one interprets the Origin of this pebbly mudstone facies is critical for the 1074

Unraveling the mosaic of Paleozoie crustal blocks in Southeast Asia

KEY Mandalay "~?

~1

'--.;:.41

l f ~1 '

:"~

Late Paleozoic

tilloid-bearing units

,...d I §

International

"~. '-'Jr

boundary

0

)00

200 mi

16o260 3;Okr~

I

I

;

I

9

THAILAND

-15~

~ iso_ {

A NDA MA N

,r

SEA

~'x~.

i

Mergui '

-,0~

~

~i CAMBODIA

~~,~ ~o %

0

Phuket ~176 ~~ .~ ~ Langka-~-~"~... j

"~, ~ 5 ~ --

~.~,~k.~

.~

(~t, - " ~ &

I~K u an t a n

- ~ "~Kuala Lumpur~'-]

Fig. 10. Distribution of Late Paleozoic stratigraphie units containing the Carboniferous pebbly mudstone ('tilloid') facies in western Southeast Asia. After STAUFFER& MANTMIT (1981). Pebbly mudstones form only a part of the units whose extent is shown here.

1075

P.H. STAUFFER

inferred paleotectonic history of the region. To the east of the pebbly rocks in Malaya and South Thailand are contemporaneous sedimentary rocks of what appear to be normal (non-glacial) offshore shallow marine facies. Therefore, if the pebbly mudstones are glacial sediments formed in very shallow water or under the edge of a continental ice sheet, then that continental was on the (present) west side (which is the traditional view of the paleogeography), and the rifting and separation of it from Southeast Asia must have been a post-Carboniferous event. Consistent with this interpretation, recent studies of Permian brachiopod faunas (ARcHBOLD et al., 1982) indicate proximity or connection of Gondwana (New Guinea) and at least part of western Southeast Asia (southern Thailand) as late as the early Permian. If, on the other hand, one interprets the pebbly mudstones as formed by slumping on a major marine slope, then deeper ocean must have been to the west, and any continent previously attached on that side might been just beginning to rift away, in the process producing the major slope. RIDD (1980) proposes exactly thaL However, the evidence for compressional folding, calc-alkaline volcanism, and associated magmatism in a north-south belt through central Thailand in the Carboniferous (BAuM et al., 1970; BUNOPAS & VELLA, 1978) imply continued plate convergence during that period rather than major rifting. CAMERON eta]. (1980) also want (for other reasons) to have the continent on the west rifted off early (before Carboniferous), yet they propose a glacial origin for the belt of pebbly mudstones, requiring them to infer a small ice cap in the area of the present Malacca Straits. However, such a small local ice mass would make it difficult to explain the great north-south extent of the pebbly facies, the presence of abundant 'exotic' old granitic clasts, and the derivation of the diamonds. There are some other interesting implications of a glacial interpretation of the late Paleozoic pebbly mudstones. The hint of a Glossopteris flora (AZHAR, 1977) in possibly contemporaneous rocks in eastern Malaya may indicate that at least parts of the eastern Malaya/Indochina block(s) were also in cold latitudes and therefore perhaps not far separated from western Southeast Asia and its attached continent. This would support the inference that the Bentong-Raub Line in Malaya does not represent the closure of a major ocean, but at most of a marginal basin or narrow sea. The interpretation of a 2000 + k m glacial marine facies in the Late Paleozoic would virtually establish the attachment of (western) Southeast Asia onto Gondwana, since only Gondwana is known to have had extensive ice sheets reaching the sea in the Late Paleozoic. The glacial marine character of the belt also puts constraints on possible attachment sites on the Gondwana margin. A map of late Paleozoic glaciation in Gondwana (Fig. 11) shows that major glaciers reached the (known) edge of the continent along three portions of its margin. One of these (southwestern South America to the Antarctic Peninsula) can be ruled out as an attachment site for Southeast Asia, as it would require an impossibly long and roundabout journey for the latter to reach its present site. A second area (southeastern Australia to Antarctica) is also a quite improbable site for similar reasons. Clearly the most likely site of former attachment of Southeast Asia to Gondwana is the stretch from northwest Australia, across the poorly-known margin on 1076

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia

t/. 0 0

Areas of Glaciation between 250 and 3 0 0 million years ago with arrows indicating known directions of ice movement /

Boundaries of continental

blocks

Limit of Gondwana glaciation Sites of C a r b o - P e r m i a n Cathaysian (or mixed Cathaysian) floras on the Gondwana continent

Fig. 11. Map of the Gondwana continent and its glaciation in Late Paleozoic times. After TAaLING& TAaLING(1971, fig. 18), with the sites of Cathaysian or partly Cathaysian floras on the Gondwana continent added.

1077

P.H. STAUFFER

the outer edge of 'Greater India', to Arabia. That the Arabian Peninsula was affected by late Paleozoie glaciation has been strongly indicated by recent work (see ROLAND, 1978; McCLURE & YOUNG, 1981). This segment of the Gondwana margin is also the general region where Cathaysian floras or partly Cathaysian floras are known to have existed on the Gondwana continent itself in the late Paleozoie (see Fig. 11). An attachment near the Arabian-Iranian region would be consistent with the limited paleomagnetic data for Southeast Asia in the early Palezoic (HALLE, 1980) as shown in Fig. 8 and with some of the limited data for late Paleozoie (BuNoPASet al., 1978).

Conclusions That the old continental part of Southeast Asia is a mosaic of several fragments seems reasonably well established, though the number, nature and position of the boundaries between fragments remain subjects of debate. The unified block formed of these fragments was constructed by a series of collisions terminating in Triassic times. During Paleozoio and earlier times the fragments had partly independent histories. The westernmost fragment, which extends from south Sumatra to at least southwestern China and possibly into Tibet, is inferred to have formed part of the margin of the Gondwana continent, most likely in the sector from Arabia-Iran across Greater India. It remained attached there through the Carboniferous, when it was affected by the Gondwana glaciation, but rifted off the continent at some subsequent time. Though considerable progress has been made in deciphering this story through combined use of geological, paleontological, paleomagnetie, and other information, much uncertainty remains and many questions are as yet unanswered.

Acknowledgements I am grateful to a number of people, whose comments and discussions have helped to clarify ideas on the early history of Southeast Asia, particularly to my colleagues in the University of Malaya Geology Department and to Dr. A.H.G. MITCHELL. The figures were drafted by Ching Yu Hay and photographed by Jaafar Haji Abdullah. The German and French abstracts were prepared with the assistance, respectively, of Dr. G. H. Teh and Mr. L. Metzger. Finally, I wish to thank Dr. Ian Metcalfe and anonymous reviewers for reading the manuscript and making helpful suggestions for improvement.

References AHMADBIN JANTAN:Stratigraphy of the Singa Formation (Upper Paleozoic) in the southwestern part of the Langkawi Island Group, West Malaysia, 250 p., Kuala Lumpur, M. Sc. thesis, University of Malaya, 1978. ARGHBOLD, N. W., C. J. PIGRAM, N. RATMAN,and S. HAKIM:Indonesian Permian brachiopod fauna and Gondwana - - Southeast Asia relationships, Nature, 296, 556--558, 1982. ASAMA,K.: Permian plants from Petchabun, Thailand, and problems of floral migration from Gondwanaland, Geol. and Paleont. Southeast Asia, 2, 197--285, 1966. 1078

Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia AUDLEY-CnAI~LES, M. G., D. J. CANTER, and J. S. MILSOM: Tectonic development of eastern Indonesia in relation to Gondwanaland dispersal, Nature phys. Sei., 239, 8~-89, 1972. AZHAa HAJI HVSSIN: Geology of the Bukit Jaya area, Pahang, 63 p., Kuala Lumpur, B. Sc. (Hons.) thesis, Department of Geology, University of Malaya, 1977. BAO, NGUYEN XUAN, HUYANH TEUNG, NGUYEN THAC NHAN, and PHAN VIET KY: (Abs.) The main stages of tectonomagmatic activities in Vietnam, Fourth reg. Conf. Geol. Min. Energy Resourc. Southeast Asia, Manila, Nov. 1981, Abstracts of Papers, 1, 1981. BANE, S. M., A. S. MACDONALD,and N. S. HAILE: Reconnaissance paleomagnetic measurements on Triassic and Jurassic sedimentary rocks from Thailand, Geol. Soc. Malaysia Bull., 10, 53--62, 1978. BACM, F., E. YON BRAUN, L. HAHN, A. HESS, K.-E. Kocrt, G. KRUSE, H. QUARCH, and M. SIEZENH/~NER: On the geology of Northern Thailand, Beih. geol. Jb., 102, 24 p., 1970. BECKINSALE, R. D., S. SUENSlLPONG,S. NAKAFADtJNGRAT,and J. N. WALSH: Geochronology and geochemistry of granite magmatism in Thailand in relation to a plate tectonic model, Jour. Geol. Soc. London, 186, 529--540, 1979. BUNOPAS, S., and P. VELLA: Late Palaeozoic and Mesozoic structural evolution of Northern Thailand - - a plate tectonic model, Third reg. Conf. Geol. Min. Resourc. Southeast Asia, Bangkok, Nov. 1978, Proc., 138--140, 1978. BVNOPAS, S., P. VELLA, K. PITAKPAIVAN,and J. SUKROO: Preliminary paleomagnetic results from Thailand sedimentary rocks, Third reg. Conf. Geol. Min. Resourc. Southeast Asia, Bangkok, Nov. 1978, Proc., 25--32, 1978. CAMERON, N. R., M. C. G. CLAI~KE,D. T. ALDISS,and J. A. ASPDEN: The geological evolution of northern Sumatra, 53 p., Ninth Indonesia Petroleum Assoc. Convention, Jakarta, May 1980, 1980. CnALONEa, W. G., and W. S. LACEr: The distribution of Late Palaeozoic floras, Palaeont. Assoc. Spec. Pap. in Palaeont., 12, 271--289, 1973. CTYRo~, P.: Permian flora from the Ga'ara region (Western Iraq) N. Jb. Geol. Paliiont. Mh., 383~388, 1973. HALLE, N. S.: Progress report on palaeomagnetic research in Southeast Asia, Reg. Conf. Geol. Min. Resourc. Southeast Asia, Jakarta, 1975, Proe., 38--36, 1978. HAILE, N. S.: Palaeomagnetic evidence from the Ordovician and Silurian of northwest Peninsular Malaysia, Earth planet. Sci. Lett., 48, 233----236, 1980. HAMILTON, W.: Subduction in the Indonesian region, Island arcs, deep sea trenches and backarc basins, Am. geophys. Union, Maurice Ewing Ser., 1, 15--31, 1977. - - : Tectonics of the Indonesian region, U.S. Geol. Surv. Prof. Pap., 1078, 345 p., 1979. HOLLOWAY, N. H.: The North Palawan Block, Philippines: its relation to the Asian Mainland and its role in the evolution of the South China Sea, Geol. Soc. Malaysia Bull., 14, 19---58, 1981. HUTCHISON, C. S.: Ophiolite in Southeast Asia, Geol. Soc. America Bull., 86, 797~806, 1975. - - : Granite emplacement and tectonic subdivision of Peninsular Malaysia, Geol. Soc. Malaysia Bull., 9, 187--207, 1977. JONES, C. R.: Lower Paleozoic rocks of Malay Peninsula, Am. Assoc. Pet. Geol. Bull., 52, 1259--1278, 1968. KoN'r~o, E.: Some Permian plants from Thailand, Jap. Jour. Geol. Geogr., 34, 139--159, 1963. KnlSnNAN, D.: Geology of the Bentong area, Pahang, West Malaysia, 88 p., Kuala Lumpur, B. Sc. (Hons) thesis, Department of Geology, University of Malaya, 1975. 69 GeologischeRtmdschau, Bd. 72

"107~

P. H. STAUFFER MACDONALD, A. S., and S. M. BAD.It: Tectonic significance of a Late Carboniferous volcanic arc in northern Thailand, Third reg. Conf. Geol. Min. Resourc. Southeast Asia, Bangkok, Nov. 1978, Proc., 151--150, 1978. MANTAJIT,N., W. TANTIWANIT,and L. RAXSASAKULWONC:Stratigraphy of Phuket-Phang Nga area (Permo-Carboniferous), Geol. Soc. Thailand Jour., 1979. McCLUD.E, n., and G. M. YOUNG: Late Palaeozoic glaciation in the Arabian Peninsula, Earth's pre-Pleistocene glacial record, 275--277, Cambridge, 1981. McELHINNu M. W., N. S. HAILE,and A. R. CaAWFOD.B:Palaeomagnetic evidence shows Malay Peninsula was not a part of Gondwanaland, Nature, 252, 641--645, 1974. METCALFE, I., S. P. SIVAM, and P. H. STAUFFED.:Stratigraphy and sedimentology o~ Middle Triassic rocks exposed near Lanchang, Pahang, Peninsular Malaysia, Geol. Soc. Malaysia Bull., 15, 19--80, 1982. MITCHELL, A. H. G.: Tectonic setting for emplacement of Southeast Asian tin granites, Geol. Soc. Malaysia Bull., 9, 128--140, 1977. - - : Phanerozoic plate boundaries in mainland SE Asia, the Himalayas and Tibet, Jour. Geol. Soc. London, 188, 109--122, 1981. MuD.PHY, R. W.: Tertiary basins of Southeast Asia, S. E. Asia Petroleum Explor. Soc., Proe., 2, 1--36, 1975. RAO, C. P.: Criteria for recognition of cold-water carbonate sedimentation: Berriedale Limestone (Lower Permian), Tasmania, Australia, Jour. sed. Petr., 51, 491--506, 1981. RIDD, M. F.: Southeast Asia as a part of Gondwanaland, Nature, 284, 581--588, 1971. - - : Possible Palaeozoic drift of SE Asia and Triassic collision with China, Jour. Geol. Soc. London, 187, 685--640, 1980. ]=~OLAND,N. W.: Jungpal~iozoische Glazialspuren auf dem Arabischen Schild, EiszeitalteI u. Gegenw., 28, 188--188, 1978. I~YALL,P. J. C.: Some thoughts on the crustal structure of Peninsular Malaysia - - results of a gravity traverse, Geol. Soc. Malaysia Bull., 15, 9--18, 1982. STAUFFED.,P. H.: Malaya and Southeast Asia in the pattern of continental drift, Geol. Soc. Malaysia Bull., 7, 89---188, 1974. - - : (Abs.) The Singa Formation: is it a glacial deposit? Warta Geologi, 6, 88--34, Kuala Lumpur, 1980. STAUFFED., P. H., and D. J. GOBBETT: Southeast Asia a part of Gondwanaland? Nature phys. Sci., 240, 189--140, 1972. STAUFFED.,P. H., and N. MANTAJIT:Late Palaeozoic tilloids of Malaya, Thailand and Burma, Earth's pre-Pleistocene glacial record, 881-~87, Cambridge, 1981. STAUFFED.,P. H., and N. J. SNELLING:A Precambrian trondhjemite boulder in Palaeozoic mudstones of NW Malaya, Geol. Mag., 114, 4 7 9 4 8 2 , 1977. TAN, B. K., and T. T. KHOO: (Abs.) Serpentinites in Peninsular Malaysia and their tectonic implications, Fourth reg. Conf. Geol. Min. Energy t~esourc. Southeast Asia, Manila. Nov. 1981, Abstracts of Papers, 21, 1981. TARLING,D. n.: Another Gondwanaland, Nature, 288, 92---98, 1972. TAItLING,D. H., and M. P. TARLING:Continental drift. 112 p., London, 1971. THANASUTHII'ITAK,T.: Geology of Uttaradit area and its implications on tectonic history" of Thailand, Third reg. Conf. Geol. Min. Resourc. Southeast Asia, Bangkok, Nov. 1978, Prec., 187--197, 1978. WA~ED.rIOUSE,J. B.: An early Permian cool-water fauna from pebbly mudstones in south Thailand, Geol. Mag., 119, 887--854, 1982.

1080