Peninsular Thailand

8/3/2019 Peninsular Thailand

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Geological Society, London, Special Publications

doi: 10.1144/GSL.SP.2005.004.01.17 1974; v. 4; p. 301-315Geological Society, London, Special Publications

Cedric Keith BurtonPeninsular Thailand

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P E N I N S U L A RT H A I L A N DC E D R I C K E I T H B U R T O NCi t i es Serv i ce I n t e rna t i ona l , I nc . ,60 Wa l l T ower , New York , N .Y . 1000 5, U .S .A .

C O N T E N T SA . G e n e r a l d a t a o n t h e s e g m e n tB . S ubd i v i s i on o f t he s e gme n tC . D a t a on ind i v i du a l s t r uc t u r a l z ones1 . I n t e r na l P os i t i ve z one2 . E uge osy nc l i na l z one3 . M i oge a n t i c l i na l z one4 . M i oge o sync l i na l z one4A . S he l f z oneD . Re f e r e nc e s

30 130931031031031 231 3314314

A . G E N E R A L D A T A O N T H E S E G M E N T1. T H E S E G M E N T S T U D I E D

T ha i l a nd p r e se n t s t he spe c i a l c ase o f a s e c t ion o f a ge osy nc l i na l c ompl e x ,l y i ng be t w e e n w e l l ma r ke d c onve n t i ona l o r oge n i c be lt s , i n w h i c h as o m e w h a t a t y p i c a l o r o g e n h a s d e v e l o p ed , i n w h i c h r a t h e r m o d e r a t e l yf o l d e d s e d i m e n t s h a v e b e e n h e a v i l y i n v a d e d b y g r a n i t e s . T h e o r o g e nde sc r i be d he r e i s a s e c t i on o f t he T r i a s s ic - Ju r a s si c Y un na n - M a l a y a nor oge n a nd i s t he on l y one o f t he e a r l y M e soz o i c o r oge ns o f e a s t e r nA s i a de a l t w i t h i n t h i s vo l ume .T he d e sc r i p t i on w h i c h f o l low s i s ba se d on P e n i nsu l a r T ha i l a nd on l y ,b u t d a t a f r o m h y d r o c a r b o n e x p l o r a ti o n ( n o t y e t a v a i l a b le f o r p u b l ic a -t i on ) i nd i c a t e t ha t t he c onc l us ions a pp l y e qua l l y t o t he G u l f o f T ha i l a ndto the eas t .Segment: t h i s ha s a l e ng t h , me a su r e d N - S a l ong s t r i ke , o f 1080 km.Bo t h t he w e s t e r n a nd e a s t e r n pa r t s o f t he o r oge n a r e l a r ge l y be ne a t ht h e s e a . O n t h e e a s t , t h e Y u n n a n - M a l a y a n o r o g e n m u s t a b u t a g a i n s tt he Ca m bod i a n S h i e l d ( ' I nd os i n i a ' ) . E a s t o f t he l a t t e r li e s t he A n-n a m i t i c c o r d i l le r a , a n o t h e r f o r m e r g e o s y n c l i n al t r a c t w h i c h p r o b a b l yc o n n e c t e d w i t h t h e Y u n n a n - M a l a y a n g e o s y n cl i n e i n t h e I n d o c h i n a -C h i n a b o r d e r a r e a . O n t h e w e s t , t h e Y u n n a n - M a l a y a n o r o g e n i so v e r l ai n b y t h e y o u n g e r s t r a t a o f th e A n d a m a n S e a , i n t u r n b o r d e r e db y t h e ' s t r e tc h e d ' o r o g e n o f t h e A n d a m a n - N i c o b a r I s la n d s . T h e w e s tm a r g i n o f t h e o r o g e n ic b e l t d e s c l i b e d h e r e is u n k n o w n a n d t h e w i d t ho f t h e o r o g e n ic b e l t c a n n o t b e m e a s u r e d : i t m a y b e c . 7 0 0 k m , o f w h i c hon l y 150 km l i e s a bove s e a l e ve l.Zones: the se gm e n t i s de sc r i be d i n t e r ms o f fou r z one s , l i s te d f r om e a s tt o w e s t a s ( 1) I n t e r na l P os i ti ve z one o f P a l a e oz o i c r oc ks i n t r ude d bygr a n i t e s ; ( 2) a E uge osyn c l i na l z one i n w h i c h a P a l a e oz o i c / M e soz o i cse r i e s w i t h vo l c a n i c s ha s be e n s t r ong l y f o l de d a nd ove r l a i n by l a t e rM e soz o i c r oc ks; ( 3 ) a M i og e a n t i c l i na l z one o f mi l d l y me t a m or ph ose dP a l a e oz o i c ge osync l i na l r oc ks on l y ; a nd ( 4 ) a M i oge osync l i na l z one ,f r on t i ng t he I nd i a n O c e a n , w i t h de f o r me d P a l a e oz o i c ove r l a i n by t h i nM e soz o i c r oc ks : she l f - li ke c ond i ti ons w i t h i n p a r t o f th i s z one ha ve be e nd i s t i ngu i she d a s sub - z one 4A .History: r e c o r de d ge o l og i c a l h i s t o r y i n t he s e gme n t c omme nc e s w i t h aCa m br i a n t o S i l u r i a n qua r t z i t e - c a r bona t e , s t a b l e she l f s e que nc e i nsub- z one 4A . M i oge osy nc l i na l c ond i t i ons i n z one 4 w e r e e v i de n t l yi n i t ia t e d i n l a te O r d o v i c i a n t i m e s a n d a p p a r e n t l y s l i g h t ly p r e - d a t e d t h ei nc e p t i on o f t he e uge osync l i ne ( z one 2 ) . G r a n i t e i n t r us i on a n d o r oge n i cm o v e m e n t s a p p e a r t o h a v e o c c u r r e d l o c a l l y i n t h e l a t t e r h a l f o f t h eCa r bon i f e r ous pe r i od . I t s e e ms t ha t z one 1 w a s up r a i s e d a t t h i s t i me ,pos s i b l y ne ve r a ga i n t o be subme r ge d .

S h a l l o w w a t e r l im e s t o n e a c c u m u l a t e d w i d e l y i n P e r m i a n t i m e s( z one s 2 t o 4 ) , w i t h some vu l c a n i sm i n z one 2 . G e osync l i na l c ond i t i onsr e t u r ne d t o muc h o f t he be l t i n t he T r ia s s i c a nd vu l c a n i sm oc c u r r e d i nz one 2 . T ow a r ds t he e nd o f t he T r i a ss i c , o r oge n i c mov e me n t s , i nc l ud i ng


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302 P E N I N S U L A R T H A I L A N Dd e f o r m a t i o n a n d m a j o r g r a n i t e e m p l a c e m e n t , to o k p l a c e . S e d i m e n t a t i o nw a s r e n e w e d i n l a t e s t T r i a s s i c to l a t e J u r a s s i c t i m e s w i t h t h e d e p o s i t i o no f r e d m o l a s se , a n d w a s t e r m i n a t e d b y g e n t l e f o ld i n g a n d u p l if t ,p r o b a b l y a c c o m p a n i e d b y m i n o r g r a n i t i c in t r u s i o n , t o w a r d s t h e e n d o ft h e J u r a s s i c . W r e n c h f a u l t i n g a ls o o c c u r r e d a b o u t t h e n . S h a l l o w w a t e rs e d i m e n t a t i o n t o g e t h e r w i t h v u l c a n i s m w a s r e s u m e d i n z o n e 2 i n l a t eJ u r a s s i c t o e a r l y C r e t a c e o u s t i m e s . S u b s e q u e n t l y t h e b e l t h a s b e e nq u i e s c e n t, w i t h o n l y C e n o z o ic s e d i m e n t a r y b a s i ns o f g e n e r a l l yl i m i t e d e x t e n t a n d s p o r a d i c v u l c a n i s m d e v e l o p e d .

2 . SHAPE OF THE OROGEN IN PLANin The Yunnan-lVfal aya orogen is continuous along s trike over a

NORTH A NDA HA N

IDDLE ANDAMAN

I~JSOUTH ANDAHAN

A N D A M A N

ISLANDSBURM.A

~) LITTLE ANDAHA N-tO" ANDAMAN SEA

~t~ NI COB A RISLANDS

~)GRE A T NI COB A R

l e n g t h o f a t l e a s t 3 3 0 0 k in , f r o m t h e I n d o n e s i a n T i n I s l a n d s t o Y u n n a n .I t s n o r t h e r n e n d i s n o t c l e a r l y d e f i n e d , f o r i n C h i n a i t s p li ts i n t o t w o o rt h r e e b r a n c h e s , c o m p r i s i n g p a r t o f t h e a n a s t o m o s i n g s y s t e m o f o r o g e n i cb e l ts w h i c h c o n s t i tu t e s t h e e a s t e n d o f T e t h y s . T o t h e s o u t h - e a s t t h eb e l t p a ss e s b e l o w t h e J a v a S e a a n d t h e y o u n g e r r o c k s o f B o r n e o .2 4 G en e r a l t r e n d : f r o m t h e I n d o n e s i a n T i n I s l a n d s to n o r t h e r n T h a i l a n dt h e b e l t f o r m s a n a s y m m e t r i c , r e v e rs e d s i g m o i d , c u r v i n g t h r o u g h s o m e9 0 w i t h a r ad i u s o f cu r v a t u r e o f c . 60 0 k i n .

3. SURFACE SHAPE OF THE SEGMENT IN ELEVATION30 Highest 5% of groun d: 1500 to 2000 m. Avera ge hei ght of: ~1 west

f ITI-IAILAND 10S"

C A M B O D I A

~ ULF OF THAILAND:HUMPHON

. - - " i

THANIVIET NAM

tlWAT

SOUTH CHINASEA

--5"

I 2SOkm MENTAWAI IS.

SUMAT RA k L%,.\ M A L A Y AIGAPORE~:~::~ ~ _s ~ tJ

Figure 1. Map of the segment described here showing structural zones and m ajor faults in Thailand andadjacent are as. Faults are identified by letter: L = Lebir, B = Bok Bak, K = Khlong Marui, R = Ranong.


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PENI NSULA R THAILAND 303mar gin of belt, 2670 m below sea level (the 'deep terr ace' bo undi ngthe Central Andam an trough, Rodolfo 1969); 33 east margin of thebelt, 60 m below sea level (beneath the Gul f of Thai land ).3 3 G e o m o r p h o l o g i c a l s u r f a c e s : a tilted gradation plane seems to be presentin the Ma lay penins ula, risi ng from 190 m beside the Straits of Singa-pore to 1380 m. A feature of similar morphology and constitutionattains 1318 m in north-east Thailand, but has not been identifiedover most of the segment. The feature is largely formed by U. Jurassicto L. Cretaceous strata and stands well above the Cenozoic basindeposits (of ?Miocene to Pleistocene date) and so is thought to be ofU. Cretaceous to early Terti ary date. Another depositional or erosionalsurface may exist at 70-90 m; palaeogeographic reconstructionssuggest it is approximately early Pleistocene in age (Burton 1964,1969).Submarine surfaces have been recognized in the Andaman Sea at< 100 m (Inne r shelf) a nd fro m 150 m (13 N.) to 539 m (8 N.)(Mer gui terrace, Rodolfo 1969). Both surfaces, which may representa single feature disrupted by faulting, are covered by some 200 m ormore of unconsolidated sediments, resting on a basement which isrelated to the Sunda Shelf and probably formed in late Miocene timesto judge from sedimentation rates (Rodolfo 1 9 6 9 , p. 1213). Another,higher (buried) erosion surface (Rodolfo 1969, fig. 8), thought to beof late Pliocene age, ma y possibly correlate with a surface recognizedaround the perip hery of the segment on the basis of high level laterites(Brown e t a l . 1951, pp. 42-3) and from borehole data (Alekseev &Takaya 1967).

5. PRESENT-DAY ACTIVITY6 8 S e i s m i c a c t i v i t y : the region is virtually quiescent, although there areverbal reports of an earthqu ake in north-west Malaya (Burton 1965).

6. TIME RELATIONS85 The oldest undeforme d rocks in the segment belong to the S apha ngconglomerate (Upper Khorat Gp) and are probably Cretaceous in age,to judge f rom their close correlation with strata detailed in Ward &Bunnag (1964). S3The youngest deformed strata in the segment be-long to the Fang Daeng Fm (Lower Khorat G p) of Jurassic age(Hayami 1960; Ward & Bunnag 1964).sx The oldest rocks deformed for the first time dur ing the Triassic-Jurassic orogeny belong either to the Rat Buri gp of early (Sakmarian)to late Permian date (Sakagami 1963, 1966, 1968A, B, C) or to thelate Cambrian Tarutao quartzite (Kobayashi 1957), which in placesmay have escaped the effects of the late Carboniferous orogeny.

Table 1PHASES OF MOBILITY

91 Phase 93 NatureA ge

93 Max imum 94 Min imum 9s Ev idence fo r age3Late Juras sic Strong plift (inphase; Pahang part ) and g e n t l e(Malaya) and foldingof latenorth geosynclinaledPeninsular molas se; ossibleThail and emplacement flate graniticstocks

Late Jurassic

2Late Triassic Strong plift, 200 m.y.phase; nort h- granit e mplace- (Norian)west Malaya, ment,wide-Songkhla spread uplift(Thailand) (changerommarine to non-marine sedi-mentation)

?180 m.y.(?Het-tangian)

Fossil evidence indi-cates that the de-formed red molasseis late Triassic tolate Jurassic and theoverlying unde-formed sandstone islate Jurassic to earlyCretaceous

Flysch facies strataare of Carnian to?Norian date;4 Rb/Sr dates a rea v a i l a b l e o n l a t ekinematic graniteswhich have intrudedCarnian to ?Norian,plus K/Ar d a t e s(Shellinget al. 1968) ;l a t e o r o g e n i c strataare probably of U.Triassic to U. J u r a s -s i c a g e

1Early Triassic Wid esp rea d Pr oba bly lenekian K/Ar dates of 210 tophase; Kelan- uplift,genera- 220 m.y. on schisttan (north-east tion of granite and granite pod inMalaya), gneiss, gneiss schist (Snelling?Narathiwat and schist 1965); schists appear(Thailand) to be formed fromPermian strata;Olenekian strataa p p e a r t o b e missingeverywhere

76-80 B a s e m e n t r o c k s : no true basement (pre-U. Cambrian) for the wholeorogenic cycle has been found. The 'basement' for the Triassic-Jurassic orogeny is only locally of the U. Cambri an to L. Carboniferoussuccession which, although partially invaded by late Carboniferousgranite, was frequently but slightly tectonized and metamorphosed inthe late Carboniferous orogeny.


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304 PENINSU LAR THAILAND7. SEDIMENTARY RELATIONS

Table 2SUMMARY OF STRATAL DATA IN THE OROGEN

P re-o ro g en ic S yn -o ro g en ic P o s t-o ro g enic~7 Age spanfrom

to9s Maximum thickness9~ Estimated volume per100 km length of segment--and probable error inthis estimate

lO O ~facies

Late (or possib ly Anisi an Late JurassicM.) CambrianInduan Late Jurassic Recent12,600 m 4000 m 4560 m77,000 km3 1250 km3 I000 km850% 50% 30%Flysch-like rocks Flysch Fluviatile-(associated with estuarine (ChaoCarboniferous Phraya faultorogeny) trough)

Percentage of th e t otal volume occupiedb y - -and the errora01 Dominant facies 36 + 5%loa Volcanic rocks 4 + 2 %lo3 Sedimentary rocks with 23 _+5%over 90% carbonatex0~ Sedimentary rocks wi th 15+ 4%over 95% quartz

55+20% 70+20%7+5% 2+1}%8+5% 3+2%

Low Moderate

The figures given in Table 2 are biased (especially those relating tovolcanic rocks) by the submergence of much of the eugeosynclinalzone. The total volumes relate only to land outcrops, which form only150 km of the possible 750 km overall wid th o f the orogen. Also, themaximum thicknesses are cumulative, they are not developed at anyone point.106 Defor mati on has been t aken int o acc ount in assessing the strata lthicknesses given above: they mostly come from the miogeosynclinalzone where deformation is not very intense.108 Pre- an d syn-orogenic sedimentation was apparent ly interrupt edover a wide are a on a numb er of occasions. A late Siluri an erosionsurface has not been found but is suspected, for no Ludlovian fossils areknown from a rather prolific fauna in the U. Ordovician to L.Devoni an succession of the miogeosyncl inal basin o f north-w estMalaya. The Khlong Kaphon fm (M. Devonian to L. Carboniferous)overlies L. to M. Devonian and earlier rocks with disconformity orparaconformity. Late Carboniferous erosion is evidenced by the un-conformity beneath the L. Permian, which tests on L. Carboniferousstrata over a wide area. L. Triassic strata are apparentl y missing over a

very wide area, implying erosion: M. Triassic strata usually succeedM. (to ?U.) Permian or older rocks.

8 . STRUCTURAL RELATIONS111-16 M a j o r f a u l t s : Fault 1--the Bok Bak fault (Burton 1965) is aNW-SE sinistral, transcurrent fault along which movements com-menced in the Rhaetic to Cretaceous interval, prob ably in late Jurassictimes, and ceased in the late Jurassic to early Quate rnar y interval,probably in M. Cretaceous times. Displacement amounted to 52-58 kmand mylonite occurs on the fault. The fault is probably a reactivatedearlier fracture. Faults 2 and 3--the Khlong Marui and Ranong faults(Garson & Mitchell 1970) are NE-S W, sinistral transcurrent faultsalong which movements commenced in the Rhaetic to late Tertiaryinterval, probabl y in late Jurassic times, and ceased in the earlyJurassic to early Quaternary interval, probably in late Cretaceous toearly Tertiary times. Displacements amounted to at least 150 km(Khlong Marui) and 20 km (Ranong), as evidenced by the displace-ment of batholithic granite outcrops and associated belt of tin mineral-ization. Mylonke occurs on both faults. Fault 4 the Lebir fault(Burton 1967D) is a NNW-S SE, sinistral transcurr ent fault which showslater movements of dip-slip nature, downthrowing to the east. The ageof the fault movements is not well known: they had commencedat least by Rhaetic times, and ceased no longer ago than the Permian.Displacements are large and mylonite is associated with the fault.117 T ype of ev idence used to assess the displacements: Fault 1, displacement ofstratigraphic marker horizons; 2, displacement of batholithic graniteoutcrop; 3, abrupt delimitation of physical features (e.g. mountainrange) a nd of numerous rock units.124M eg atec to n ic s : the Khlong Marui fault cuts across the entirepeninsula and possibly across the entire belt, effecting a 200-220 kmdisplacement.

9 . REVIEW OF OROGENIC DEVELOPMENT1 26 REGIONAL CHRONOLOGY AND CORRELATIONIn recent years considerable advance has been made in geochrono-logical investigations in Thailand and Malaya. This work indicatesthat the Yunnan-Malaya orogen exhibits only limited polarity andthat lithostratigraphic units maintain their character and time-relations over long distances.

The Ordovician-Silurian Thung Song Limestone appears to formpart of a regional shelf facies on the west margi n of the geosyncline;it extends into north-west Malaya and has been reported from northThailand (Baum & Koch 1968). Westwards, in the Shan States ofBurma, synchronous limestone is intercalated with sandstones andsandy shales (La Touche 1913; Brown & Sondhi 1933A, B). Twothin (few metres) horizons of carbonaceous argillite occur high in and


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P E N I N S U L A R T H A I L A N D 305ab o v e th e Th u n g S o n g . Th e lo wer ca r r i e s ea r ly S i lu r i an g r ap to l i t e s ,wh i l s t t h e u p p e r b ea r s ea r ly to M. Dev o n ian t en t acu l i t e s , g r ap to l i t e san d t r i l o b i t e s . Th es e mar k e r b an d s r ecu r i n n o r th - wes t Ma lay a , i n t h es o u th e r n S h an S ta t e s ( B r o wn & S o n d h i 1 9 3 3 A, B ) an d in t h e n o r th e r nS h an S ta t e s ( a s t h e P an g h s a - p y 6 g r ap to l i t e b an d an d th e Zeb in g y is t ag e o f L a To u c h e 1 9 1 3) . I n t h e Th a i - M a lay p en in s u la t h ey f o r mwes te r ly ( i.e. s h e l f -war d ) s a l ien t s o f a l a r g e b o d y o f g r ap to l i t e - a n dt e n t a c u l it e - b e a r in g b l a c k s h al e ( t h e B a n n a n g S a t a g p a n d t h e M a h a n gF m an d B a l in g g p in Ma lay a , B u r to n 1 9 67 B ) b e l i ev ed to h av e b eeng en e r a t ed in a mio g eo s y n c l in a l b a s in . Th e f ac i e s i s r ep r e s en ted b y th eB an N a s h a le o f S i S awa t a t t h e n o r th o f t h e s eg men t , an d b y th e F an gs h a le i n n o r t h T h a i l a n d ( B u r to n 1 9 6 7C ; Ja e g e r et al. 1968) . Correla tedh e r ew i th a l s o a r e t h e J en h o ch iao s e ri e s ( g r ap to l it i c s h a le s ) an d th eWas h ih f m ( y e l lo w s h a le , s h a ly an d ch e r ty l imes to n e wi th g r ap to l i t e s ,t en t acu l i t e s an d s h e l ly f au n a ) o f Wes t Yu n n an ( S u n & S ze tu 1 9 4 7 ) .Ex cep t ap p a r e n t ly in Y u n n an ( Yin & L u 1 9 3 7) , fo ss il s o f L u d lo wa g e s e e m t o b e w a n t i n g t h r o u g h o u t t h e r e g io n .T h e B a n n a n g S a t a g p o f T h a i l a n d i s o v e r l ai n b y t h e P h u k e t g p ,wh ich i s f l y s ch - l ik e an d ch a r ac t e r i zed b y Posidonia becheri v a r . s iam en s isi n t h e lo wer p a r t wh i l s t t h e u p p e r p o r t io n i s c lo s e r t o mo la s s e an ds ig n a l i zed b y f en es t r a t e b r y o zo a . Th e s ame b io - l i t h o f ac i e s can b er eco g n ized f a r t o t h e s o u th , wes t an d n o r th ( Tab le 3 ) .

Table 3N O M E N C L A T U R E O F C O R R E LA T A B L E U N I T S O FT H E P H U K E T G P

MALAYA THAILAND BURMA/ Kubang / Pathiu fm { Lower 'Moulmein| Pasu fm l | beds' (excludingSinga gp ] (Jones, in ms) Mergui | l imesto ne, Oldham(Jones in ] Phu ket series ] 1856)Koop man s~ gp (Brown &1 9 6 5 ) | K a m p o n g | K h l o n g H ero n 1 92 3) ' M er g u i s er ie s'[ Sena fm | Kaphon | (Oldham 1856)\ (Burton 1967B) \ f m k

I n th e P e r mian , r eg io n a l s h e l f - l i k e o r ' q u as i - c r a to n ic ' co n d i t i o n sp r ev a i l ed an d v as t t r ac t s o f s h a l lo w- wa te r l imes to n e wer e l a id d o w nt h r o u g h o u t T h a i l a n d ( S a r a b u r i l i m e st o n e o f t h e R a t B u r i g p ) , i nn o r t h M a l a y a ( C h u p i n g l i m e s t o n e o f J o n e s , in K o o p m a n s 1 9 6 5 ;G u a M u s a n g f m o f Y in , in I c h i k a w a & Y i n 1 9 6 6 ) , i n B u r m a ( M o u l -me in l imes to n e o f R ao 1 9 30 ) a s we l l as i n s o u th - wes t C h in a an dI n d o ch in a ( S au r in 1 9 5 6) .Th e M. to U . T r i a s s i c Na th awi f m co n s t i t u t e s a s eco n d d ev e lo p men to f fl y sch an d i s d i s t i n g u i s h ed b y th e o ccu r r en ce o f b ed d e d c h e r t an dby var ious species of Halobia, Daonella, Posidonia p lu s s ev e r al amm o n i t e s .I n n o r th - wes t Ma lay a th e u n i t i s k n o wn a s t h e S eman g g o l f m ( B u r to n ,i n K o b a y a s h i et al. 1967) and to the wes t is rep laced by l imes tone.To the eas t , c las t ic rocks of s imilar facies and foss i ls rea ppe ar in theeu g eo s y n c l in e b u t w i th v o lcan ic r o ck s in p l ace o f b ed d ed ch e r t .S t r a t a s i m i l a r i n f a u n a a n d c h a r a c t e r t o t h e N a t h a w i f m a r e a l s o

k n o w n i n t h e L a m p a n g d i s t r i c t o f n o r t h T h a i l a n d b u t a r e t h e r ea u g m e n t e d b y a s t r o ng d e v e l o p m e n t o f l i m e st o n e .Ma lay an r ad io me t r i c ev id en ce s u g g es t s t h a t t h e ma in in t r u s iv e r o cke m p l a c e d d u r i n g t h e o r o g e n i c / p l u t on i c r e v o l u t i on a t t h e e n d o f t h eTr i a s s i c was th e co a r se ly p o r p h y r i t i c ad ame l l i t e . S o me s imi l a r ad am e l -l i t e ap p ea r s , h o wev e r , t o b e l a t e C a r b o n i f e r o u s ( S n e l l i n g et al. 1968)wh i l s t a t R an o n g in s o u th Th a i l an d an in d i s t i n g u i s h ab le r o ck h as b eend a ted ( R b /S r ) a s M. C r e t aceo u s .Th e p r in c ip a l p o s t - o r o g en ic u n i t i s t h e Kh o r a t G p , o f o x id i zedmo las s e f ac i e s , r e s t in g wi th an g u la r u n co n f o r mi ty o n mo s t o ld e r r o ck san d g en e r a l ly o ccu p y in g e l ev a ted s i t u a t io n s . Th es e c r i t e r i a s e r v e toc o r re l a te t h e K h o r a t w i t h t h e T e m b e l i n g F m ( K o o p m a n s 1 9 68 ) a n dt h e G a g a n G p o f M a l a y a a n d w i t h t h e r e d b e d s o f M e r g u i , B u r m a( R aG 1 9 3 0 ) . Th e Kh o r a t i s f u r th e r p h y s i ca l ly co n t in u o u s wi th th em i d d l e a n d u p p e r I n d o s i n i a n o f I n d o c h i n a ( W a r d & B u n n a g 1 9 64 ).F o r t h e m o s t p a r t t h e C en o zo ic r o ck s o f t h e s eg men t co m p r i s e p a r t i a l l ymar in e co a l - b ea r in g s ed imen t s , d ep o s i t ed in f au l t - d e t e r min ed b as in san d k n o wn a s t h e Kr ab i s e r i e s o r , mo r e co r r ec t ly , Kr ab i g p . I n t h en o r t h e r n h a l f o f T h a i l a n d a n u m b e r o f s i m i la r o c c u r re n c e s h a v e b e e ns ep a r a t e ly d i s t i n g u i s h ed , o win g to an ev id en t l a ck o f mar i n e co m-p o n en t s , a s t h e M ac S o t s er i es ( B r o wn et al. 1 9 5 1 ) . Th e Mac S o t b a s inex ten d s in to B u r ma , wh e r e o th e r i s o l a t ed co a l - b ea r in g C en o zo icb as in s a r e k n o wn an d s imi l a r b a s in s a l s o o ccu r i n Ma lay a .12 7 MIGRA TION OF TROU GHS OF SEDIMENTATIONTh e mio g eo s y n c l in a l ( zo n e 4 ) an d eu g eo s y n c l in a l ( zo n e 2 ) b a s in se s t ab l i s h ed in Or d o v ic i an to Dev o n ian t imes ev id en t ly ma in ta in edth e i r g eo g r ap h ic p o s i t i o n s wi th r emar k ab le co n s i s t en cy th r o u g h o u tth e g eo s y n c l in a l h i s to r y o f th e s eg m en t ( i.e. u n t i l t h e l a t e T r i a s s ic ) a n dwer e n o t s ig n i f i can t ly d i s p l aced b y th e C a r b o n i f e r o u s o r o g en y . Wh i l s tJ o n es ( 1 9 68 ) accep ted th a t d u r in g m o s t o f P a l aeo zo ic t ime th e g eo -s y n c l in a l zon es o ccu p ied th e s i t u a t io n s in d ica t ed in t h e p r e s en t r ev iew,h e co n ten d ed ( p . 1 2 7 6) th a t i n t h e l a t e P a l aeo zo ic an d Mes o zo ic th e s ei s o p ic zo n es wer e lo ca t ed s o me d i s t an ce f a r th e r ea s t . Th i s v i ew can n o tb e s u s ta in ed . Wi th in th e s ed imen ta r y r o ck s o f t h e P e r m ian ' q u as i -c r a to n ' t h e p r e - ex i s t i n g eu g eo s y n c l in a l an d mio g eo s y n c l in a l zo n es canb e d i s t i n g u i s h ed b y th e r e s p ec t iv e p r e s en ce an d ab s en ce o f v o lcan icr o ck s an d th e T r i a s s i c ( s eco n d g eo s y n c l in a l ) zo n es a r e a lmo s t ex ac t lys u p e r imp o s ed o n th e i r P a l aeo zo ic co u n te r p a r t s . Th i s p e r man en ce i sc l ea r ly a f u n c t io n o f t h e s i t u a t io n a l co n s e r v a t i s m o f th e wh o le g eo -syncl inal t ract , w hils t the mor e specif ic pers is tence of the euge o-s y n c l in a l an d mio g eo s y n c l in a l f u r r o ws may b e d u e l a r g e ly to t h elo n g ev i ty o f t h e i r d e l im i t in g g ean t i c l in e s, wh ich f ea tu r e s wer e p r o b a b lyr e in f o r ced b y th e emp lacem en t i n t h em o f C a r b o n i f e r o u s g r an i t e .Wi th in th i s en d u r in g t ec to n ic f r amewo r k ex p an s io n an d co n t r ac t io no f t h e d ep o s i t i o n a l r eg ime h av e t ak en p l ace f r o m t ime to t ime .Th e U. Or d o v ic i an to L . Dev o n ian eu x in i c f ac i e s was l a r g e lyco n f in ed to t h e mio g eo s y n e l in a l f u r r o w b u t o n two o ccas io n s , i n t h e


7/16

3 06 P E N I N S U L A R T H A I L A N De a r l y S i l u r i a n a nd e a r l y / mi dd l e D e von i a n r e spe c t i ve l y , i t e x t e nde dw e s t w a r d on t o t he she l f t o ge ne r a t e t w o w e l l - m a r ke d b l a c k a r g i l l it eho r i z ons w i t h i n t he l i me s t one suc c e s s i on . S i mi l a r l y , s e d i me n t a t i on i nt he e uge osync l i ne s e e ms t o ha ve c omme nc e d ( i n t he e a r l y D e von i a nor be f o r e ) i n a na r r ow be l t , r e ga r de d a s a ge o t e c t oc l i ne , on t he i nne r( e a s t ) s i de o f t he mi oge a n t i c l i ne . S ubse que n t l y , t he ba s i n o f s e d i -me n t a t i on sp r e a d t o e mbr a c e , by t he e a r l y Ca r bon i f e r ous , t he w ho l eo f the e uge osyn c l i na l t r a c t . T he f l ysc h fa c i es o f t he M . D e von i a n t oe a r l y Ca r bon i f e r ous t r a nsg r e s se d f r om t he mi oge osync l i na l t r ough f a rw e s t w a r ds on t o t he she l f , bu t t he e nsu i ng o r oge ny e v i de n t l y r e s t r i c t e dde pos i t i on o f t he M . Ca r bon i f e r ous ( ?) t o L. P e r m i a n P a t h i u f m t ot h e n o r t h e r n h a l f o f p e n i n s u l a r T h a i l a n d a n d t o t h e T h a i l a n d - M a l a y abor d e r a r e a ( F ig . 3 ) . I n t he P e r mi a n , how e ve r , t he de pos i t i ona lba s i ns a ppa r e n t l y e xpa nde d a ga i n t o un i t e t he e u - a nd mi oge osync l i ne s .E a r l y T r i a s s i c t e c t on i c move me n t s e v i de n t l y r e susc i t a t e d t he mi o -ge a n t i c l i ne , r e - s e pa r a t i ng t he mi oge osync l i ne a nd e uge osync l i ne s ,w h i c h f u r r ow s now oc c up i e d subs t a n t i a l l y t he s a me pos i t i ons a s p r i o rt o t he Ca r bon i f e r ous o r oge ny .133 T R A N S C U R R E N T O R S T R I K E - S L I P F A U L T I N GS t r i ke - s l i p f a u l t i ng w a s show n t o be w i de sp r e a d i n M a l a ya ( Bur t on196 5) a nd ha s subse que n t l y be e n r e c ogn i z e d i n T ha i l a nd ( Bur t on196 7A ; G a r son e t a l . 1971) . I n M a l a ya t he se f a u l t s c ons t i t u t e t w oc o m p l e m e n t a r y s e t s a r r a n g e d i n a t y p i c a l A n d e r s o n -t y p e w r e n c h f a u l tpa t t e r n bu t t he o f f s e t s a r e i n t he oppos i t e s e nse t o t ha t i mp l i e d by t hed i spos i t i on o f t he f a u l ts . T hus t he ma i n d i sp l a c e me n t s a r e s i n i s t ra l i n

MIOGEOSYNCLINE MIOGEANTICLINEW

s e ns e a n d a l o n g f a u l t p l a n e s a l i g n e d N N W - N W w h i l st s u b s i d i ar yde x t r a l shi ft s ha ve oc c u r r e d o n N N E - N E f r a c t u re s . I t w a s t he r e f o r ep r opose d t ha t t he se d i sp l a c e me n t s r e p r e se n t l a t e ( Ju r a s s i c - Cr e t a c e ous )move me n t s on p r e - e x i s t i ng f a u l t p l a ne s i n i t i a t e d by d i f f e r e n t f o r c e s .L a t e r i t w a s sugge s t e d ( Bur t on 196 7A , 1970B) t ha t t he you nge r d i sp l a c e -me n t s m i gh t be a c onse que nc e o f e x t e ns i on r a t he r t h a n c omp r e s s i on ,p r o d u c e d a s G o n d w a n a l a n d d i s i n t e g r a t e d a n d t h e M a l a y a - T h a ipe n i nsu l a d r i f t e d a w a y f r om t he I nd i a n S h i e l d i n t he w a ke o f A us t r a l i a .I t w ou l d s e e m, how e ve r , t ha t t he pos t u l a t e d e x t e ns i ona l t e nde nc yha s no t be e n ope r a t i ve i n t he no r t he r n pa r t o f t he pe n i nsu l a . T w o l a r ge ,N E - S W d i r e c t e d t r a ns c u r r e n t f a u l ts ( F i g . 1 ) ha ve r e c e n t l y be e nde sc r i be d fr om sou t h T ha i l a n d ( G a r son & M i t c he l l 1970 ; G a r sone t a l . 1971) . Bo t h e xh i b i t ' no r ma l ' ( s i n i s t r a l ) t r a ns l a t i on w i t h , r e spe c -t iv e ly , a m i n i m u m o f 1 5 0 k m ( K h l o n g M a r u i f a ul t ) a n d 2 0 k m( Ra n ong f a u l t ) o f s t r i ke s l i p d i sp l a c e me n t . T he se f e a t u r e s ha ve be e ne xp l a i ne d i n t e r ms o f p l a t e t e c t on i c s a s t r a ns f o r m f a u l t s due t o d i f fe r -e n t i a l m o v e m e n t w i t h i n t h e S u n d a S h e l f c o n t i n e n t a l p l a t e i n r es p o n s et o n o r t h - e a st w a r d s p r e a d i n g o f t h e I n d i a n O c e a n .T he w r e nc h f a u l t i ng s e e ms t o be cl ose in t i me t o e mp l a c e m e n t o f la t e -s t a ge s t a nn i f e r ous g r a n i t e s a nd i n some c a se s , a t l e a s t , t he f a u l t p l a ne sa pp e a r t o ha ve c o ns t i t u t e d c ondu i t s f o r the up r i s e o f g r a n i t i c ma gm a .134 T H E O V E R A L L E V O L U TI O N O F T H E B E L TP e n i n s u l a r T h a i l a n d f o rm s p a r t o f t h e Y u n n a n - M a l a y a o r o g e n w h i c he x t e n ds f r o m t h e T i n I s l an d s o f I n d o n e s i a t h r o u g h M a l a y a , s o u t h a n dw e s t T h a i l a n d a n d e a s t B u r m a i n to Y u n n a n . P r e - C a m b r i a n r o c k s

EUGEOSYNCLINE

Psb

i . . .

I 50krn IMainly arenaceousMainly argillaceousMainly calcareousVolcanic rocks

Tkr Krabi frn PCp Pathiu fm -~ Phuket Gp.Klk Khorat Gp CDkk Khlong Kaphon fm JTRn Nathawi fm DSbs BannangSara fm.Psb Saraburi Ist.lRat Dstrn Tan Yong-Mar fm.

!Pm Matsi Fm. JBuri SOts Thung Song Lst. ]Gp. Ont Nai Tak Fr n. . j~ Satun Gp.

-(:t Tarutaoqtz,Figure 2. Diagrammatic cross-section of Peninsular Thailand/North Malaya showing original thickness variation o f thesedimentary rocks. Note that the Miogeosyncline is d epicted accurately, but the Eugeosyncline is largely diagrammatic.


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P E N I N S U L A R T H A I L A N D 30 7ha ve be e n po s t u l a t e d i n t he no r t he r n p a r t o f t he be l t. Wi t h i n a n da d j a c e n t t o t he s e l e c t e d s e gme n t , how e ve r , r e c o r de d ge o l og i c a l h i s t o r yc o m m e n c e s w i t h a C a m b r i a n t o S i l u r i a n o r t h o q u a r t z i t e - c a r b o n a t ef a c i e s , a ppa r e n t l y r e p r e se n t i ng r a t he r s t a b l e , she l f - l i ke c ond i t i onsl a r ge l y p r e c e de n t t o t he ge osync l i na l s t a ge .T he ge osync l i ne w a s e v i de n t l y in i t i a t e d i n t he l a t t e r pa r t o f t heO r do v i c i a n a n d t h r ou gho u t i ts e x i s t enc e c ompr i s e d a mi oge osy nc l i na lz one i n t he w e s t a nd a e uge osync l i na l z one t o t he e a s t . T he e a r l i e s tknow n c om pone n t o f t he ge osync l i na l suc c es s i on i s a n O r dov i c i a n t oe a r l y D e von i a n e ux i n i c f a c i e s , be s t de ve l ope d i n t he mi oge osync l i neo f n o r t h - w e st M a l a y a a n d r e c u r r in g a t v a r io u s p o i n t s i n p e n i n s u l a ra nd w e s t T ha i l a nd ( Bur t on 196 7C) . T o t he sou t h t h i s b l a c k sha l e i sr e p l a c e d b y li me s t one a n d t o t he e a s t i t be c ome s i n t e r c a l a t e d w i t hl i me s t one s a nd a r e n i t e s , t hou gh t t o be i nd i c a t i ve o f sha ll ow e r a ndbe t t e r a e r a t e d c ond i t i ons a bou t a ( mi o ) ge a n f i c l i ne w hose up r i s e ma yha ve be e n t he d i r e c t c a use o f r e s t r i c te d c i r c u l a t i on i n t he e ux i n i c ba s i n .T he o l de s t da t e d r oc ks o f t he e uge osync l i ne a r e L . D e v on i a n sha l es ,c he r t s a nd oph i o l i te s , pos s i b l y ge ne r a t e d i n a t e c t oc l i ne w hosed e v e l o p m e n t m a y h a v e c o i n c i d e d w i t h d i s i n t eg r a ti o n o f t h e m i o -ge a n t i c l i ne i n t o a c ha i n o f i s l ands . T he r e a f t e r a f l y sch - l ike suc c e ss i onof M . D e v on i a n t o e a r l y Ca r bon i f e r ous da t e i s a w i de sp r e a d f a c ie s int h e m i o g e o s y n c l i n e f r o m n o r t h - w e s t M a l a y a t o n o r t h - w e s t T h a i l a n d ,de t r i t u s e v i de n t l y be i ng f u r n i she d bo t h f r om a f o r e l a nd t o t he w e s ta nd f r om t e c t on i c l a nds t o t he e a s t . T o t he sou t h , i n M a l a ya , a nd t ot he w e s t , l i me s t one c on t i nue d t o f o r m, pos s i b l y i mp l y i ng g r e a t e rs t a b i l i t y , w h i l s t t o t he e a s t l i me s t one s w i t h sha l e s w e r e de pos i t e d i nt he e uge osync l i na l t r ough o f a x i a l M a l a y a . N e a r t o t he e a s t c oa s t o f t ha tc oun t r y a r g i l li t e i s dom i na n t ov e r c a r bona t e i n t he L . Ca r bon i f e r ouss t r a t a ( F i t c h 1959) . A r e n i t e a l so oc c u r s he r e , be c omi ng a bunda n t no r t h -w a r ds . Fos s i l be n t hos , p l a n t r e ma i ns , a nd r i pp l e ma r ks po i n t t o c on t e m-por a r y shoa l i ng o f t he s e a a nd s e e mi ng l y t o t he oc c u r r e nc e he r e e i t he r o fa no t h e r ge a n t i c l i na l w e l t ( e uge a n t i c l i ne ) o r o f a n e x t e ns i on f r om sou t hI ndo c h i na o f h e sh ie l d - li ke f e a t u r e know n a s ' I ndos i n i a ' ( F r om a ge t 1941) .A n i n t r ag e o s y n c l i n a l o r o g e n y o f T a c o n i c o r A n t l e r t y p e e v e n t u a t e di n t he l a t t e r h a l f o f t he Ca r bon i f e r ous , a s e xe mpl i f i e d by t he w i de sp r e a doc c ur r e nc e o f L . Ca r bon i f e r ous f l y sc h , by t he f re que n t p r ox i m i t y o ft h i s l i t ho fa c i e s t o P e r m i a n c a r bona t e s , by t he a bse nc e o f M i dd l e a ndl a t e Ca r bon i f e r ous b i o t a f r om t he f os s i l r e c o r d a nd by t he r e c ogn i t i on ,t h r o u g h R b / S r d e t e r m i n a t i o n s , o f la t e C a r b o n i fe r o u s g r a n i t e i n b o t hM a l a y a ( S h e l l i n g e t a l . 1968) a nd T h a i l a n d ( Bur t on & B i gne l l 1969) .I n s o m e l o ca t io n s , h o w e v er , a s i n C h u m p h o n ( T h a i l a n d ) , M e r g u i( Bur ma ) a nd P e r l is ( M a l a y a ) e v i de nc e o f Ca r bon i f e r ous o r oge ne s i s isw a n t i ng a nd t he U . P a l a e oz o i c suc c e s s i on a ppe a r s t o be unbr oke n .T he l a t e Ca r bon i f e r ous move me n t s ha d pa l a e oge ogr a ph i c e f f e c t s o fr e g i o n a l i m p o r t a n c e . A d i r e c t r o u t e t h r o u g h t h e H i m a l a y a n r e g i o nw a s now e s t a b l i she d a s t he p r i nc i pa l c onne c t i on be t w e e n t he Y unna n-M a l a y a g e o s y n c li n e a n d t h e E u r o p e a n T e t h y s r a t h e r t h a n , a s h e r e to -f o r e, v i a c e n t r a l Ch i n a . Fu r t h e r mo r e , m uc h o f t he sou t h - e a st A s i a na r e a a ppe a r s t o ha ve now be e n c onso l i da t e d , f o r i n P e r m i a n t i me s

s h a l lo w w a t e r l i m e s t o n e w a s g e n e ra t e d o v e r m o s t o f T h a i l a n d a n d t h ea d j a c e n t p a r t s o f B u r m a , L a o s , C a m b o d i a a n d M a l a y a . T h i s l im e s t o n ee x t e nde d , a ppa r e n t l y w i t hou t i n t e r r up t i on , a c r os s t he loc us o f t hemi oge a n t i c l i ne a l t hough t he e uge osync l i na l z one c a n s t i l l be d i s c e r ne dby t he p r e se nc e o f vo l c a n i c ma t e r i a l i n t e r c a l a t e d w i t h t he c a r bon a t e s ,a n i nd i c a t o r , pe r ha ps , t ha t ge osync l i na l i t y w a s subdue d , r a t h e r t ha ne l i mi na t e d , a t t h i s t i me .I n e a s t e r n a nd sou t he r n M a l a ya t he P e r mi a n l i m e s t one is l a r ge l yr e p l a c e d b y b l a c k s h a l e - - a c i r c u m s t a n c e w h i c h m a y i m p l y b a r r i n gof t he de pos i t i ona l b a s i n by t he pos i t i ve t e c t on i c e l e me n t i n f e r r e d he r ei n t he e a r l y Ca r bon i fe r ous~ w h i c h w a s a s i te o f l a t e Ca r bon i f e r ousg r a n i t e e m pl a c e m e n t a nd w ho se pe rs i s te nc e is i nd i c a t e d by P e r m i a np l a n t r e m a i n s . P e r m i a n f l o r a a n d s h a l lo w w a t e r s t r a t a i n t h e P e t c h a b u na n d L o e i a r e as o f n o r t h - c e n t r al T h a i l a n d d e m o n s t r a t e t h e p r o x i m i t y o fl a nd t he r e a l so .G e osync l i na l c ond i t i ons w e r e r e s t o r e d ove r mu c h o f t he be l t i n t hee a r l y pa r t o f t he T r i a s , t h i s r e ve r s ion be i ng a c c om pa n i e d b y r e ne w e dt e c t on i c a nd p l u t on i c a c t i v i t y i n t he e uge osync l i na l t r a c t . T he s t r i c tc on f i ne m e n t o f T r ia s s i c vo l c a n i c r oc ks to t he e uge osyn c l i ne a ndbe dde d c he r t t o t he mi oge osync l i ne sugge s t s t ha t t he mi oge a n t i c l i new a s now r e susc i t a t e d a s a phys i c a l ba r r i e r be t w e e n t he se t w o z one s .I n b o t h f u r r ow s m uc h o f t he T r i a s s ic s e d i m e n t a t i on w a s o f f l y schc ha r a c t e r a nd n e a r t o t he e nd o f t he pe r i od ge osync l i na l e vo l u t i onc u l m i n a t e d i n a n o r o g e n i c/ p l u to n i c r e v o l u t i o n w h e r e i n v a s t a m o u n t so f g r a n i t e w e r e e mpl a c e d ne a r t o t he e uge osync l i na l - mi oge o sync l i na lbo r de r a nd a l so w i t h i n t he mi oge osync l i ne .T he l a t e o r oge n i c suc c e s s i on be ga n i n t he l a t e s t T r i a s s i c w i t h al i m i t e d d e v e l o p m e n t o f m a r i n e b e d s, s o o n r e p l ac e d b y m o r e w i d e -sp r e a d ' c on t i ne n t a l ' ( non- m a r i ne ) r oc ks , ma ny o f r e d mol a s se f a c ie s .T he se s t r a t a a r e w e l l d i sp l a ye d i n t he f o r me r e uge osync l i ne a nde x t e nd on t o t he I ndos i n i a n S h i e l d ( e a s t T ha i l a n d ) a nd a r e a l so t o bef ound i n t he o l d mi oge osync l i na l t r a c t . I n e a s t M a l a ya t he r e i s somee v i de nc e t ha t pa r t o f t h is c l a s ti c ma t e r i a l i s o f e a s t e r n p r ove n a nc e ,a g a i n p o i n t i n g t o a n e m e r g e n t z o n e i n t h e r e g io n o f th e S o u t h C h i n aS e a . D e pos i t i on w a s t e r mi na t e d by l ong w a ve l e ng t h f o l d i ng a nd up l i f to f a p p r o x i m a t e l y l a t e J u r a s s ic d a t e w h i c h m a y h a v e c o i n c id e d w i t h t h ei n t r oduc t i o n o f l a t e g r a n i t i c s t oc ks , i nc l ud i ng t hose r e spons i b le f o r t i nmi ne r a l i z a t i on . A t a bou t t h i s t i me t oo , e x t e ns i ve w r e nc h f a u l t i ng t ookp l a c e , c onc e i va b l y r e l a t e d t o t he a n t i c l oc kw i se d r i f t o f t he M a l a y - T h a ip e n i n s u la a w a y f r o m t h e I n d i a n S h i e ld a s G o n d w a n a l a n d d i s i n te g r a t ed(see be low) .S h a l l o w w a t e r s e d i m e n t a t i o n w a s l a t e r r e n e w e d i n t h e o l d e u g e o -sync l i na l z one w he r e pos t - o r oge n i c vu l c a n i sm, i nc l ud i ng e f f us i on o fba sa l ts , oc c u r r e d . N e a r t he e nd o f t he M e soz o i c , e pe i r oge n i c w a r p i n ga nd up l i f t t ook p l a c e . S ubse que n t l y t he be l t ha s be e n r a t he r qu i e sc e n t ,a l t houg h t he a t t i t ude o f t he c i r c umsc r i be d Ce noz o i c ba s i n de pos i ts( f l uv i a t i l e - l a c us t r i ne w i t h , i n pa r t , ma r i ne i n t e r c a l a t i ons ) a nd t hei nc i de nc e o f l a t e vo l c a n i c r oc ks de mo ns t r a t e t ha t b l oc k f a u l t i ng a ndi gne ous a c t i v i t y ha ve spo r a d i c a l l y r e c u r r e d .


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3 08 P E N I N S U L A R T H A I L A N DI t I

5


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P E N I N S U L A R T H A I L A N D 30 9Suggested explanation of divergences: f r om e a s t t o w e s t , t he f o l l ow i ngt e c t on i c un i t s c a n be r e c ogn i z e d i n t he M a l a y - T ha i pe n i nsu l a w i t hva r y i n g de g r e e s o f c e r t a i n t y , ( 2 ) , (3 ) a nd ( 4 ) be i ng w e l l - e s t ab l i she d :( 1 ) e uge a n t i c l i na l r i dge , ( 2 ) e uge osync l i na l f u r r ow , ( 3 ) mi oge a n t i c l i na lr i dge , ( 4 ) mi oge osyn c l i na l f u r r ow , ( 5 ) shel f. T h i s a r r a ng e m e n t s t r ong l ysugge s ts t o the p r e se n t a u t ho r t h a t a c on t i ne n t o r c r a t on l a y t o t he w e s t ,i n w h i c h d i r e c t i on t he ne a r e s t s t a b l e b l oc k is t ha t o f pe n i nsu l a r I nd i a ,some 2000 km d i s t a n t . T he t r i a ngu l a r sha pe a nd c ons i de r a b l e de p t ho f t h e i n t e r v e n i n g b o d y o f w a t e r , t o g e t h e r w i t h t h e a p p r o x i m a t ema t c h i n sha pe o f t he e a s t e r n sho r e l i ne o f I nd i a a nd t he w e s t e r n sho r eo f T h a i l a n d - M a l a y a , e n g e n d e r t h e s u g g e s ti o n t h a t t h e B a y o f B e n g a lm a y b e a s p h e n o c h a s m , f o r m e d b y r o t a t i o n a l d r i ft o f t h e Y u n n a n -M a l a y a o r o g e n a w a y f r o m t h e I n d i a n c r a t o n . I n a c c o r d a n c e w i t h t h i shypo t he s i s i s t he s i n i s t r a l o f fs e t, e v i de n t l y Ju r a s s i c - Cr e t a c e ous i n da t e ,o f t h e d o m i n a n t l y N W - t r e n d i n g w r e n c h f a u l ts i n t h e T h a i - M a l a ype n i nsu l a ( Bur t on 196 5, 196 7A ) a nd t he f a c t t ha t mos t o f t he l a nd a r e ab e t w e e n T h a i l a n d a n d I n d i a i s o f C r e t ac e o u s o r y o u n g e r o r ig i n .M or e o ve r , d i a m ond s ha ve be e n f ound , q u i t e ou t o f ge o l og i c a l c on t e x t ,a t P h u k e t a n d P h a n g n g a o n t h e w es t co a s t o f T h a i l a n d ( A r a n y a -ka no nd 1955 ; S t e phe ns et al. 1966) , wh ich loca l i t ies f a l l adjac ent tot he I nd i a n 'G o l c on da ' d i a m ond f i el d w he n t he t w o coa s t -l i ne s a r ef i t t e d t oge t he r . S i mi l a r l y , w h i l s t t he r e i s no obv i ous sou r c e i n sou t h -e a s t A s i a f o r t he g r a n i t e de t r i t u s i n t he M i dd l e D e von i a n t o e a r l yCa r bon i f e r ous f l y sc h ( t he K h l ong K a phon f m a nd i t s c o r r e l a t i ve s ) ,t he r e e x i s t i n pe n i nsu l a r I n d i a l a r ge vo l ume s o f P r e - C a m br i a n g r a n i t i cr o c k s . T h e Y u n n a n - M a l a y a o r o g e n m a y f o r m e r l y h a v e c o n s t i t u t e dp a r t o f a g e o s y n c l i n al s y s te m p e r i p h e r al t o t h e o ld G o n d w a n a c o n t i n e n t( Bur t on 1970A ) . T h i s c ond i t i on w ou l d a c c o un t f o r some o f t he d i f fe r -e n ce s b e t w e e n t h e Y u n n a n - M a l a y a g e o s y n cl i ne a n d A u b o u i n ' s i d e a l.I f , a s s e e ms l i ke l y , G ondw a na l a nd ha d be gun t o d i s i n t e g r a t e a s t hege osync l i ne a t t a i ne d t he o r oge n i c s t a ge , t he h i gh p l u t on i sm a nd l owt e c t o n i s m m a n i f e s t b y Y u n n a n - M a l a y a m a y a l s o b e e x p l i c a b l e .F i s s i pa r ous f o r c e s w ou l d t he n be t e nd i ng t o de t a c h t he o r oge n f r omt he f o r e l a nd a nd he nc e w ou l d be a c t i ng i n oppos i t i on t o t he ' ge o -sync l i na l fo r c e s ' te nd i n g t o t h r us t t he f o r e l a nd be n e a t h t he ge osync l i ne .T h i s c oun t e r a c t i on w ou l d d i mi n i sh c r us t a l sho r t e n i ng a nd r e duc e t hei n t e ns i t y o f t he te c t oge ne s is . A t t he s a me t i m e , ge o f r a c tu r e s r e l a t e d t oc on t i ne n t a l d i s r up t i on ma y ha ve f u r n i she d c ondu i t s f o r t he e mpl a c e -me n t o f g r a n i t i c ma t e r i a l w h i c h w a s a va i l a b l e a t t h is c u l mi n a t i ngs t a ge o f t he ge o sync l i na l c yc l e .Later Stages of Tectonic Evolution in the Region: T h e w r i t e r ' s c o n c e p tt h a t t h e f o r m a t i v e s ta g es o f t h e Y u n n a n - M a l a y a o r o g e n t r a n s p ir e d i n as i t u at i o n m a r g i n a l t o G o n d w a n a l a n d i s i n o p p o s i ti o n t o t h e o p i n i o nof p r ev . ious w or ke r s w ho ha ve r e ga r de d t he o r oge n i c e vo l u t i on o f theM a l a y - T ha i pe n i nsu l a a s pa r t o f a r e gu l a r p r oc e s s o f sou t h - w e s t w a r dou t g r o w t h o f t he A s i a n ( 'Ca t ha ys i a ' , 'L a u r a s i a ' ) l a ndm a ss . I t a ppe a r s ,h o w e v e r , t h a t s u b s e q u e n t t o t h e d e t a c h m e n t o f t he o r o g e n f r o m t h eI nd i a n S h i e l d , t e c t on i c e vo l u t i on i n S uma t r a ha s p r oc e e de d byge osync l i na l / o r oge n i c mi g r a t i on t ow a r ds t he Ba y o f Be nga l , i.e. i n t he

d i r e c t i on pos t u l a t e d by Be m me l e n ( 1949 , 1954) . Fu r t h e r e v i de nc e o fsuc h a p r oc e s s oc c u r s i n t he A nda ma n a nd N i c oba r I s l a nds , w h i c hoc c upy t he s a me r e g i ona l s t r i ke pos i t i on a s t he w e s t S uma t r a n M e n t a -w a i I s l a nds . T he t h i c k p r e - l a t e M i oc e ne T e r t i a r y suc c e s s i on i n t heA n d a m a n a r e a is o f n o r t h - e as t e r ly p r o v e n a n c e a n d R o d o l f o ( 1 96 9 ,p . 1 2 2 4) b e l i ev e d t h a t ' . . . t h e a r e a o f t h e M a l a y c o n t i n e n t al m a r g i nw a s a h i gh s t a nd i ng sou r c e ' f o r t he se s e d i me n t a r y r oc ks . P r e se n t l y t heA n d a m a n a n d N i c o b a r I s l a n d s a r e s e p a r a t e d f r o m t h e c o n t i n e n t a ls l op e o f t h e M a l a y - T h a i - B u r m e s e p e n i n s u l a b y t h e A n d a m a n B a s i n ,w h i c h f e a t u r e Rodo l f o a sc r i be d t o l a t e M i oc e ne t o Re c e n t r i f t i ng - -e v i de n t l y a c on t i nua t i on o f t he t a ph r oge ne s i s pos t u l a t e d f o r thege ne r a t i on o f the Ba y o f Be nga l .

B . S U B D I V I S I O N O F T H E S E G M E N TTable 4

3ol Z O N E S A N D E L E M E N T S W I T H I N T H E S E G M E N T

Elements

Zones1 2 3 4In ternal E ug eo - Mio g e- Mio g eo - 4Apositive synclinal anticlinal sytw linal Shelfzong z.one zon~ ZO?~ zone

a Older alluvium (?early Pleistocene)b Cenozoic basin deposits (?Miocene to?early Pleistocene)c Upper Khorat Gp (late Jurassic toCretaceous)d Lower Khorat Gp (red molasse,late Triassic to late Jurassic)e Second geosynclinal sequence(Olenekian to Norian or R haetian)f Perm ian shelf or quasi-cratonsequence; Sakmarian to late Permianor e arly Triassic (Induan)g Main geosynclinal (and pre-geosynclinal) sequence (late or midCambrian to Sakmarian)

x ?

x ? x

X "~ X X

X ? X X

X X X X X

20 2 Ba si s f o r the c o r r e l a t i on o f e l e me n t s be t w e e n z one s : c , r oc ks o fs i m i l a r l i t h o l o g y a n d m o r p h o l o g y t o t h e t y p e d e v e l o p m e n t i n z o n e 2a r e f ound t o a l i mi t e d e x t e n t i n z one 4 ; d , roc ks o f s i mi l a r fa c ie s a nds t r a t i g r a ph i c pos i t i on t o t hose i n z one 2 a l so oc c u r i n z one 4 ; e ,pa l a e on t o l ogy , l i t ho f a c i e s a nd s i mi l a r t e c t on i c pos i t i ons ; f , s i mi l a rl i t ho - a nd b i o - f a c i e s , pos s i b l y o r i g i na l l y c on t i nuous f r om z one 2 ,a c r os s z one 3 , a nd i n t o z one s 4 a nd 4A ; g , c on t i nuous f r om z one s 4a nd 4A t o t he f l a nks o f z one 3 , r e c ogn i z e d i n z one 2 by f os si ls a nd byi t s pos i t i on be ne a t h t he P e r m i a n qu a s i - c r a t on i c s e que nc e , a nd i nzone 1 on foss il evidence .


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3 10 P E N I N S U L A R T H A I L A N D

C . D A T A O N I N D I V I D U A LS T R U C T U R A L Z O N E S

1. I N T E R N A L P O S I T I V E Z O N EI n t he e x t r e me e a s t o f t he sou t he r n pa r t o f t he s e gme n t t he r e i s al i mi t e d t r a c t , oc c u py i ng on l y a f e w hund r e ds o f squa r e k i l ome t r e s i nT h a i l a n d b u t b e t t e r d e v e l o p e d t o t h e s o u t h i n M a l a y a , w h i c h h a se xh i b i t e d a t e c t on i c a l l y pos i t i ve t e nde nc y ove r a l ong pe r i od . Wi t hsome reserva t ions , s ince so l i t t le i s known about i t , this t r ac t i s dis-t i ngu i she d he r e a s a z one . I t i s c ompose d o f g r a n i t i c r oc ks i n t r us i vei n t o a s e d i me n t a r y s e que nc e , w h i c h l a t t e r i s ve r y poor l y e xpose dw i t h i n t he s e gme n t . T o t he sou t h t h i s s e que nc e i s s ee n t o be c omp r i s e dof a r g i ll i t es a nd a r e n i t e s ( w h i c h a r e some t i me s p r e dom i na n t ) w i t hc a r bona t e l e nse s . Fos s i l s de mons t r a t e a V i sda n a ge ( F i t c h 1952) . T hebe n t ho n i c c h a r a c t e r o f t he f a una , t he i nc i de nc e o f p l a n t r e ma i ns , t her a t he r c oa r se l y e l a s ti c na t u r e o f t he s t r a t a a nd t he c on t a i ne d r i pp l ema r ks a l l po i n t t o shoa l i ng on t he e a s t e r n s i de o f t he e uge osync l i ne .I n M a l a y a t o o , t h r e e R b / S r w h o l e - r o c k a g e d e t e r m i n a t i o n s o n t h eg r a n i t e a l l ind i c a t e a l a t e Ca r bon i f e r ous da t e .S i nc e t h i s g r a n i t e i s o f ba t ho l i t h i c d i me ns i ons a nd l a t e o r oge n i ca spe c t i t i s c onc l ude d t ha t t he z on e su f f e re d l a t e Ca r bon i f e r ous o r oge ny .N o s u b s e q u e n t o r o g e n i c / t ec t o n i c / m e t a m o r p h i c a c t i v it y h a s b e e ne s t a b l i she d ( a l t houg h m i nor i gne ous a c t i v i t y o f Ju r a s s i c / Cr e t a c e ou s

da t e ma y ha ve a f f e c t e d t h i s a r e a ) . N e i t he r ha ve a ny younge r s e d i -m e n t a r y r o c k s ( a p a r t f r o m Q u a t e r n a r y a l l u v i u m ) b e e n p r o v e n h e r ea nd i t s e e ms t ha t subse que n t t o t he Ca r bon i f e r ous o r oge ny t he z one ha sc ons t i t u t e d a s t a b l e a nd l a r ge l y suba e r i a l f e a t u r e . T ow a r ds i t t heP e r m i a n l i me s t on e o f t he e uge osync l i ne i s r e p l a c e d b y b l a c k sha l e ,w h i c h pos s i b l y ow e s i t s e ux i n i c c h a r a c t e r t o r e s t r ic t i on o f c i r c u l a t i on i nt he ba s i n by t he e l e va t e d t r a c t pos t u l a t e d i n t he e a s t . P l a n t r e ma i nsa r e f ound i n t h i s sha l e . P a l a e oc ur r e n t c r i t e r i a f r om t he e qu i va l e n t s o ft he l a t e T r ia s s i c t o la t e Ju r a s s i c L ow e r K ho r a t i n sou t h M a l a y a( K oop ma n s , 1968) a nd S i nga p or e ( F . E . S . A l e xa n de r 1950) bo t hpo i n t t o de r i va t i on f r om a f o r me r l a ndm a ss s i t ua t e d t o t he e a s t o f t hepe n i nsu l a .T he na t u r e o f t he I n t e r na l P os i ti ve z one ha s no t be e n f u l l y e l uc i da t e d .T he v a s t vo l ume o f g r a n i t e he r e , p l us it s a c i d na t u r e a s c ompa r e d w i t ht he g r a n i t e o f the e uge osy nc l i na l f u r r ow , i mp l i e s a t h i c k s i a l i c sub -s t r a t e . I t ma y be t ha t t h i s pos i t i ve f e a t u r e w a s a e uge a n t i c l i na l r i dgei n t he s e nse o f A ub ou i n ( 196 5). I t s ge ogr a ph i c s i t ua t i on a l so a ll ow sof t he pos s i b i l it y t ha t t h i s z one c ons t i t u t e d a s ou t hw a r d e x t e ns i on o ft he a nc i e n t I ndos i n i a n ma ss i f , a c t i ng a s a h i n t e r l a nd t o t he Y unna n-M a l a y a o r oge n o r c onc e i va b l y a s a z w i sc he nge b i r ge be t w e e n t heT h a i - M a l a y a n a n d A n n a m i t i c m o b i l e b e l t s .

2. E U G E O S Y N C L I N A L Z O N E~o~-s Zone margins: t he e a s t e r n ma r g i n i s i nde f i n i t e , i t l i e s ma i n l y

IMIOGEOSYNCLINE _1_ MIO -IWEST

~ . ~ " A N D A M A N S E A j ~ ' ~' % ~0 [ Q ~ S O t s c ~ '~ T K r T ~ _ ~ x " . . ~ ~

. . . . . . , . , - . . . . . . . . . . . . = - - / , ,PSb DSbsPC p

L C D k kGEANTICLINE ~ sots~J - ~:t EUGEOSYNCLINE . ~ e ~ ' ~ . - ~ ' ~' ~

- ~ ~ . . . . - " rs o i%. - . - ~ ~ ~=1/~~" ~ I I rs o Psba ' ~ ~ 4 , ~ l ~ ~ " - . / ~ ! / ' ~ ~ / ", . r s o ~ ~ Q Q \ o ~ 0 I IO k m; - i

/Granitic rocks, mainly biotite or two mica graniteM e l a n o c r a t i c [ r ~ n i ~ i c rocks

- bearing graniteornblendeFigure 4. G e o l o g i c a l p r o f il e f r o m t h e A n d a m a n S e a t o th e S o u t h C h i n a S e a . F o r l e g e n d t o r o c k u n i t s s e e F i g . 2 .


12/16

P E N I N S U L A R T H A I L A N D 311b e n e a t h t h e G u l f o f T h a i l a n d a n d e l se w h e re s e e m s to b e b r o a d l yg r a d a t i o n a l t o z o n e 1 . T h e w e s t e r n m a r g i n i s b r o a d l y g r a d a t i o n a l( > 3 k m ) . 3 0 s -n A p p r o x i m a t e a r e a s of t he z one oc c up i e d by t he ou t c r opof r oc k t ype s : vo l c a n i c 5 - 10% ; p l u t on i c 25% ; s e d i m e n t a r y 6 2%( i nc l ude s 26 % of Q u a t e r n a r y a l l uv i a l c ove r ) ; me t a mo r ph i c 6 %( e xc lude s bo t h 13% of g r a n i t e w h i c h i s gnei s sose , a nd s l i gh t l y me t a -m o r p h o s e d o l d e r s e d im e n t s ) .312-14E l e m e n t s : t h e u n d e f o r m e d r o c k s o f t h e U p p e r K h o r a t G p ( e l e m e n tc ) re s t u n c o n f o r m a b l y o n L o w e r K h o r a t s t r a ta ( e l em e n t d ) . T h e l a t t e rha ve b e e n up l i f t e d , b r oa d l y f o l de d a nd t he r e f o re s l i gh t l y f o r e shor t e ne d ;t he y ove r l i e t he s t r a t a o f e l e me n t e w i t h un c onf o r m i t y , d i s c onf o r m i t yo r l a t e r a l /ve r t i c a l g r a d a t i on . Roc ks o f t he s e c ond ge osync l i na l s e que nc e

Table 5S T R A T I G R A P H Y I N Z O N E 2

833 Elemen t3~oAge and 822 Thickness m in whichevidence or these rocks319 Un it age 821 Litho logy Average occur

Upper Late ut to Co arsel y ross- 300-Khorat Gp early Cret; be dd ed , ather 600(Thailand)- plant fossils mature sand-Gagau Gp stone and con-(Malaya) glomerate(non-marine)Lower Late Trias to Red sandstone,Khorat Gp late Jur ( to siltstone, on-(Thai land) - ?ear lyCret) ; glom erate, hale,Tembeling plant fossils plus minorFm (Malaya) and sporadic volcanicshelly fa un a intercalations

(mainly non-marine)Gu no ng Ladin-Cam; Sha le , mmatureRabong fm fossil mo llusca sandstone,(Malaya) conglomerate,volcanic rock

3000

1000-5000

Saraburilimestone(Thailand)-Gu aMusang fm(Malaya)Tan YongMat fin(Thailand)-'FoothillsFm '(Malaya)

Sakm-Olenek; Pa le imestonemarine fossils with volcanics

?Ordovic to Arg illite,Gedinn; fossils quartz ite, con-near top of glom erate, hert,sequence ophioliteBase not seen

2500

C3650

( e l e me n t e ) ha ve be e n f o l de d a nd r a t h e r s t r ong l y f o r e shor t e ne d a ndove r l i e e l e me n t f unc on f o r ma b l y . T he s t r a t a o f e l e me n t f a r e mod e r -a t e l y f o l de d a nd ha ve be e n a ppr e c i a b l y f o r e shor t e ne d ; t he y ove r l i ee l e m e n t g p r o b a b l y a t a n u n c o n f o r m i t y . E l e m e n t g h a s b e e n a f f e c t e dby s t r ong f o l d i ng , i nc l ud i ng ove r f o l d i ng a nd i s s t r ong l y f o r e shor t e ne da n d t h i ck e n e d .315--16 O u t c r o p a r e a s o f t h e e l e m e n t s : c , > 1 . 5 x0 . 3 k m ( ve r y e x t e ns i veb e y o n d t h e s e g m e n t ) ; d , e x t e n d s f r o m t h e s o u t h e r n m a r g i n o f t h ese gme n t f a r sou t hw a r ds i n t o M a l a y a ( K oop ma n s 1965) ; e , < 10 x 28k m ; f , > 9 5 x < 6 6 k m ; g , < 1 8 0 x 4 5 k m .3 2 6- 3 2 I g n eo u s a c t i v i t y : E pi sode 1 - - i n t r a ge osync l i na l vu l c a n i sm, t her e pe a t e d ge ne r a t i on o f t u f ts a nd l a va s o f va r y i n g c ompo s i t i on , oc c u r r e ddur i ng t he a c c um ul a t i on o f e l e me n t s g , f, a nd e in ? O r dov i c i a n t o la t eT r i a s s i c t i me . E p i sode 2 - - sma l l , ma i n l y s e r pe n t i n i z e d , dyke s a nd s i l l so f u l t r a ba s i c r oc k ( oph i o li t e s) i n t r u de e l e m e n t g a nd p r oba b l y f o r m e di n S i l u r ia n t o G e d i n n i a n t im e s . T h e y o c c u r m a i n l y o n t h e w e s t m a r g i no f t he z one . E p i sode 3 - - m e soz o na l , g r a n i t i c ba t ho l i t h s w e r e i n t r ude di n t o e l e m e n t g d u r i n g t h e m i d t o l a t e C a r b o n i f e r o u s o r o g e n y ( R b / S rw ho l e r oc k r a d i ome t r i c d a t e s o f 280- 300 m . y . ; S ne l l i ng et al . 1968)a n d h a v e a n e s t i m a t e d v o l u m e , w i t h i n t h e s u b a e r i al p a r t o f t h e s e g m e n t ,o f c. 10 , 000 km 3 ( a s sumi ng a de p t h o f 10 km) . E p i sode 4 - - - g r a n i t i cr oc ks i n t r ude d e l e me n t s f a nd g pos s i b l y du r i ng ? e a r l y T r i a s s i c t i me s( K / A r mi ne r a l r a d i om e t r i c da t e s o f 200- 220 m . y . ; S ne l l i ng 196 5 ,196 6) . T he y ha ve a n e s t i ma t e d vo l ume w i t h i n t he s e gme n t , o f c .2 0 ,0 0 0 k m 3 ( a s su m i n g a d e p t h o f 1 0 k m ) a n d a r e m a i n l y m e s o z o n a la nd a l so me so- ka t a z on a l . E p i sode 5 - - sm a l l , e p i z ona l g r a n i t i c bod i e si n t r ud e d e l e me n t g i n ? e a r l y T r i a s s i c t o l at e Ju r a s s i c / e a r l y Cr e t a c e oust i me s ( Rb / S r w ho l e r oc k c onf i r ma t i on o f t he e a r l ie r da t e a nd you nge rK / A r mi ne r a l da t e s o f 130- 140 m. y . ) . E p i sode 6 - - pos t - o r oge n i c l a va s ,t u f ts a nd dyke s o f a c i d t o ba s i c c ompo s i t i on oc c u r spa r se l y i n e l e me n t sc a nd d a nd a r e o f l a t e T r i a s si c t o ? e a r l y Cr e t a c e ous da t e .335-42 M e t a m o r p h i s m : P h a s e 1 - - m e t a m o r p h i s m i n t h e M . D e v o n i a n t oS a k m a r i a n i n t e r v a l, p r o b a b l y o f N a m u r i a n d a t e ( b y c o m p a r i s o n w i t he p i sode 3 a bove ) , i s s t r ong l y suspe c t e d t o ha ve p r oduc e d t he musc ov i t esc h i s t s i n e l e me n t g . P ha se 2 - - 1a t e ge osync l i na l me t a mor ph i sma f f e c t e d e l e me n t s f a nd g i n t he G ua da l up i a n t o A n i s i a n i n t e r va l ,p r o b a b l y i n O l e n e k i a n t i m e s : P e r m i a n s t r a ta a r e m e t a m o r p h o s e d a n dr a d i om e t r i c K / A r m i ne r a l da t e s o f 210 a nd 220 m. y . on s c h i st a nda s soc i a t e d g r a n i t e s g i ve a mi n i mum da t e . P e l i t i c r oc ks c on t a i n kya n i t e ,s i l l i ma n i t e , s t a u r o l i t e , a mph i bo l e a nd ga r ne t i nd i c a t i ng a mph i bo l i t ef ac ie s m e t a m o r p h i s m i n t h e M a l a y - T h a i b o r d e r r e g i o n . P h a s e 3 - - p o s t -ge osync l i na l , l ow g r a de r e g i ona l me t a mor ph i sm a f f e c t e d t he r oc ks o fe l e me n t s e , f a nd g in t he C a r n i a n t o l a te Ju r a s s i c i n t e r va l , p r ob a b l yd u r i n g N o r i a n t o R h a e t i c t i m e s .3 4 4 - S D e f o r m a t i o n : P h a s e 1 - - d e f o r m a t i o n o f e l e m e n t g in t h e M .D e v o n i a n t o S a k m a r i a n i n t e r v a l , p r o b a b l y d u r i n g N a m u r i a n t i m e s ,i s s t r ong l y suspe c t ed b u t i s no t w h o l l y p r ove n . P ha se 2 - - 1a t e ge o -sync l i na l de f o r ma t i on o f e l e me n t s f a nd g oc c u r r e d i n t he G ua d a l up i a n


13/16

3 12 P E N I N S U L A R T H A I L A N Dt o A n i si a n i n te r v a l , p r o b a b l y d u r i n g O l e n e k i a n t i m e s. T h e o r o g e n w a ss t r o n g ly u p w a r p e d t o p r o d u c e t h e w i d e s p re a d U . P e r m i a n / L . T r i as s ich i a t us , a nd dow nw a r pe d t o ge ne r a t e ka t a z ona l s c h i s t a nd gne i s s i cg r a n i t e a nd t o r e s t o r e ge osync l i na l c ond i t i ons . P ha se 3 - - t he c u l mi na t -i ng ge osync l i na l de f o r m a t i on i nvo l v e d t i gh t f o l d i ng o f t he r oc ks o fe l e me n t s e , f a nd g i n t he Ca r n i a n t o L . Ju r a s s i c i n t e r va l , p r oba b l y i nN or i a n t o Rha e t i c t i me s ; t he r oc ks o f e l e me n t d a r e muc h l es s de f o r m e dt ha n t he unde r l y i ng s t r a t a . P ha se 4 - - pos t - ge osync l i na l de f o r ma t i on ,i nvo l v i ng up l i f t a nd ge n t l e f o l d i ng , a f f e c t e d e l e me n t d du r i ng t heM . Ju r a s s i c t o L . C r e t a c e ous i n t e r va l , p r oba b l y i n U . Ju r a s s i c t i me s .P ha se 5 - - a s e c ond pos t - ge osync l i na l e p i sode , i nvo l v i ng up l i f t a ndt i l t i ng , a f f e c t e d e l e me n t c a nd o l de r e l e me n t s du r i ng t he L . C r e t a c e ousto Ple is tocene inte rva l .35o-5 Fold s tructures: f o lds r e l a t e d t o de f o r ma t i on pha se s 1 a nd 2 a r eno t know n . P ha se 3 fo l ds ha ve w a v e l e ng t hs o f 100 m t o 1 c m a n dt r e nd bo t h e a s t a nd w e s t o f t he N - S r e g i ona l s t r i ke . P ha se 4 f o ldsh a v e w a v e l e n g t h s > 1 k m .3 5 9 - 6 2 Planar and l inear s tructures: de f o r m a t i on pha se 2 p r odu c e d f o l i a t i oni n t he r oc ks o f e l e me n t s f a nd g ( H u t c h i nson 196 1 ; A l e xa nd e r ,M a c D o n a l d & S l a te r 1 9 61 ; M a c D o n a l d 1 9 67 ). P h a s e 3 p r o d u c e df o l i a t ion s t r uc t u r e s i n e l e me n t s e , f a nd g ( K ob a ya sh i et al . 1967).P ha se 4 p r od uc e d j o i n t i ng i n e l e me n t d ( K oop ma n s 196 8).366-73 Faul t ing: s teep, s t r ike- s l ip f aul t s cut e leme nts g an d t r end 065 ,090 a nd c . 110 . D i sp l a c e me n t s po s s i b l y do no t e xc e e d a f e w hun dr e dme t r e s . T h e 06 5 a nd 090 g r oups a l so c u t P e r m i a n s e d i m e n t a r y r oc ksa nd i n T r e n gga nu ( e a s t M a l a ya ) ha ve s e r ve d a s c ondu i t s f o r i n t e r -me d i a t e t o ba s i c dyke s , w h i c h ma y be synge ne t i c w i t h ba sa l t i n t heU . Ju r a s s i c t o L . C r e t a c e ous G a ga u G p ( e qu i va l e n t t o i gne ous e p i sode 6a bove ) . T he c . 110 g r oup c u t s t r a t a t ho ugh t t o be o f P e r m i a n da t e .1VIa p o f some f a u l t s : M a c D o na l d ( 196 7).

3. M I O G E A N T I C L I N A L Z O N E804 Zon e mar g ins a r e b r oa d l y g r a da t i o na l ( > 3 km) . 308- 10 A p p r o x i m a t eareas of t he z one oc c up i e d by t he ou t c r op o f r oc k t ype s : vo l c a n i c 5% ;p l u t o n i c 2 5 % ; s e d i m e n t a r y 7 0 % ( i n c l u d i n g 2 0 % Q u a t e r n a r y a l l u -v i u m ) ; m e t a m o r p h i c r o ck s a r e a b s e n t, a l t h o u g h t h e o l d e r s e d i m e n t a r yr oc ks show s l i gh t r e g i ona l m e t a m or ph i sm a nd c . 10% of t he g r a n i t e i sgneissose.312--16E l e m e n t s : t he ma i n ge osync l i na l ( a nd p r e - ge osync l i na l ) r oc ks o fe l e m e n t g a re s t r on g l y fo l d e d a n d c l e a v e d - - a n d p r o b a b l y h a v e b e e ns t r ong l y fo r e shor t e ne d a nd t h i c ke ne d . Roc k s be l ong i ng t o o t he re l e me n t s a l so p r oba b l y oc c u r i n t h i s z one bu t ha ve no t be e n pos i t i ve l yi de n t i f i e d . E l e me n t g oc c u r s ove r t he w ho l e z one ( l e ng t h 880 km,6 2 5 k m o f w h i c h l ie s b e n e a t h t h e G u l f o f T h a i l a n d ; w i d t h ,< 62 kin) .

T a b l e 6S T R A T I G R A P H Y I N Z O N E 3

319 Unita2o Age and

ev iden ce fo rag e s~ z L i th o l o g y

s 2 s E l e m e n tin which322 Thickn ess these ocks1 ? Z o c c u r

B a n n a n gSa ta gp(T ha i -l a nd) -B a l ingg p ( M a l -aya)

"K roh ? L a te Ordo- B la c k s ha le w i thfm v ic i a n to in t e rc a la t e d da rkE ms ia n , fo ss i ls l ime s tone a nda re n i t e , p lus s omeoph io l i t eGr ik ? Ordov ic i a n , R hy .o l it i c a ndtu f ts s t ra t ig ra ph ic a l rhyo-da c i t i cpos it ion crys ta l tuftsP a p a l u t ? C a m b r i a n t o S u b m a t u r equa r t z - ? Ordov ic i a n , qua r t z i t e s p lusi t e s t ra t ig ra ph ic a l a rg i l l it e spos i t ion

B a s e no t s e e n

2700 g

?1000 g

?1000 g

32e-32 Igne ous activi ty: E pi sode 1 - - r hyo l i t i c vu l c a n i sm i s e v i de nc e d byt he G r i k t u f t s o f ? mi d t o l a te O r do v i c i a n da t e . E p i sode 2 - - sm a l l ,s e r pe n t i n i z e d i n t r us i ons o f u l t r a ba s i c r oc ks ( oph i o l it e s ) f o r me d ,p r o b a b l y i n S i l u r ia n t o G e d i n n i a n t i m es , m o s t l y n e a r t h e e a s t m a r g i no f t he z one . E p i sode 3 - - m e soz o na l g r a n i t i c ba t ho l i t h s w e r e i n t r ud e di n mi d t o l a t e Ca r bon i f e r ous t i me s ( Rb / S r , w ho l e r oc k r a d i ome t r i cda t e s o f 270- 300 m. y . ; S ne l l i ng et al . 1968; Bur ton & Bigne l l 1969) .T he y c a nno t be d i s t i ngu i she d by f i e l d o r pe t r o l og i c a l da t a f r om t hel a t e T r i a s s i c g r a n i t i c s , so t he i r vo l ume i s no t know n , bu t i s pos s i b l ysma l l . E p i sode 4 me soz ona l g r a n i t i c ba t ho l i t h s f o r m e d i n l a t eT r i a s s i c t i m e s ( R b / S r w h o l e r o c k a n d K / A r m i n e r a l r a d i o m e t r i cd a t e s o f c . 2 0 0 m . y . ; S n e l l i n g et al . 196 8) a nd oc c upy a vo l ume o f20 , 000 km 3 ( a s sumi ng a de p t h o f 10 km) .335--48 M e t a m o r p h i s m a n d d e f o r m a t i o n : t w o p h as e s o f m e t a m o r p h i s m a n dde f o r ma t i on , c o r r e spond i ng t o t he mi d t o l a t e Ca r bon i f e r ous a nd l a t eT r i a s s i c o r oge n i c / p l u t on i c e p i sode s , ha ve p r o ba b l y oc c u r r e d bu t ha veno t ye t be e n s e pa r a t e l y d i s t i ngu i she d .350-5 Fold s tructures t yp i c a l l y ha ve a ve r a ge w a ve l e ng t hs i n t he r a nge100 m t o 10 m m a nd a p i c a l a ng l e s o f c . 40 . A x i a l su r f a c e s d i p sou t h -east.366-73 Faul t ing: s t r ike - s l ip f a u l t s , p r oba b l y o f l a t e Ju r a s s i c da t e , t r e n da t 324 ( s i n is t r al ) a nd 030 ( de x t r a l) a nd show d i sp l a c e me n t s o f upt o a f e w k i l ome t r e s . T he se f a u l t s a r e a n e x t e ns i on o f t he w r e nc h f a u l tsys t e m p r e se n t i n z one 4 . T he y c u t l a t e T r i a s s i c g r a n i t e s bu t a r ec ove r e d by T e r t i a r y ( ? P li o - P l ei s t oc e ne) a nd Q u a t e r n a r y s t r a t a i nz one 4 .


14/16

P E N I N S U L A R T H A I L A N D 3134. M I O G E O S Y N C L I N A L Z O N E

304. 306 g o n e m a r g i n s : t h e e a st m a r g i n i s b r o a d l y g r a d a t i o n a l ( > 3 k m )a n d the w e s t m a r g i n l i e s be low se a l e ve l a n d so i s i nde f in i t e . 308- 10 A p -p r o x i m a t e a r e a s o f t h e z o n e o c c u p i e d b y t h e o u t c r o p o f r o c k t y p e s :v o l c a n i c < 1 % ; p l u t o n i c 1 5 % ; s e d i m e n t a r y 8 5 % (i n c l u d e s 3 2 %Q u a t e r n a r y a l l u v ia l c o v e r ); m e t a m o r p h i c r o ck s a r e a b se n t , a l t h o u g h5 to 10% o f t he g r a n i t e i s gne i s sose .312-14 E l e m e n t s : t h e ' O l d e r a l l u v i u m ' ( e l e m e n t a ) h a s b e e n u p l i f t e d a n dg e n t l y f o l d e d a n d i s e i t h e r c o n f o r m a b l e o r d i s c o n f o r m a b l e o n e l e m e n t b .T h e C e n o z o i c b a s i n d e p o s i t s ( e l e m e n t b ) o c c u r i n d o w n f a u l t e dg r a b e n s . T h e U p p e r K h o r a t ( c) h a s b e e n u p l i f t e d a n d t i l t e d a n d r e s tsu n c o n f o r m a b l y o n o l d e r e l e m e n t s . T h e L o w e r K h o r a t ( d ) h a s b e e nu p l i f t e d a n d a f f e c t e d b y b r o a d f o ld s a n d i s s l i g h t l y f o r e s h o r t e n e d ; i ti s u n c o n f o r m a b l e o n o l d e r r o c k s. E l e m e n t e ( s e c o n d g e o s y n c l i n a ls e q u e n c e ) i s fo l d e d a n d h a s b e e n a p p r e c i a b l y f o r e s h o r t e n e d ; i t i s? u n c o n f o r m a b l e o r fa u l t e d a g a i n s t t h e o l d e r e l e m e n t s . E l e m e n t f( P e r m i a n s h e l f o r q u a s i - c r a t o n s e q u e n c e ) h a s b e e n m o d e r a t e l y f o l d e da n d s o m e w h a t f o r e s h o r t e n e d ; i t is u n c o n f o r m a b l e , d i s c o n f o r m a b l e o rr e st s w i t h b e d d i n g p l a n e s l i p o n e l e m e n t g . T h e l a t t e r h a s b e e n s t r o n g l yf o l d e d a n d i s f o r e s h o r t e n e d a n d t h i c k e n e d .315-1e Outcrop areas o f th e e lemen ts: a , > 1 5 x 4 k m ; b , < 3 3 x 3 3 k m ;c, 1 . 3 x 0 . 5 k m ; d , < 3 4 x 5 k m ; e , < 1 3 2 x 6 2 k m ; f , < 9 6 0 x 1 2 3 k m ;g , < 1080 x 74 km .32e-32 I g n e o u s a c t i v i t y : E p i s o d e 1 - - m e s o z o n a l g r a n i t i c b a t h o l i t h s w e r ei n t r u d e d i n t o e l e m e n t g i n m i d t o la t e C a r b o n i f e r o u s t i m e s ( R b / S rw h o l e r o c k r a d i o m e t r i c d a t e s o f 2 8 0 - 3 0 7 m . y . ; S n e l l i n g e t a l . 196 8 ;B u r t o n & B i g n e l l 1 9 69 ) . T h e v o l u m e o f s u c h g r a n i t i c s is p r o b a b l y n o tg r e a t , b u t t h e y a r e n o t s p e c i fi c a ll y i d e n t i fi a b l e b y f i e l d o r p e t r o l o g i c a lc h a r a c t e r s . E p i s o d e 2 - - m e s o z o n a l g r a n i t e b a t h o l i t h s i n t r u d e d e l e m e n t se , f a n d g in l a t e T r i a s s ic t i m e s ( R b / S r w h o l e r o c k a n d s e v e r a l K / A rm i n e r a l d a t e s n e a r 2 0 0 m . y . ) . T h e y h a v e a n e s t i m a te d v o l u m e o f1 0 0 , 00 0 k m 3 ( a s s u m i n g a d e p t h o f 1 0 k m ) a n d c o v e r c . 1 3 % o f t h e z o n e ,b u t t h e y c a n n o t b e d i s t i n g u i s h e d f r o m t h e r o c k s o f e p i s o d e 4 . E p i s o d e3 - - s m a l l e p i z o n a l g r a n i t i c s t o c k s i n t r u d e d e l e m e n t s d t o g p r o b a b l yi n t h e l a t e J u r a s s i c t o e a r l y C r e t a c e o u s i n t e r v a l ( K / A r m i n e r a l r a d i o -m e t r i c d a t e s o f c . 1 35 m . y . ) a n d h a v e a v o l u m e o f 1 5 0 0 k m 3 . E p i s o d e 4- - m e s o z o n a l g r a n i t i c b a t h o l i t h s i n t r u d e d e l e m e n t s d t o g i n 1 V[. C r e t a -c e o u s t im e s ( R b / S r w h o l e r o c k d a t e s o f 1 1 1 a n d 1 13 m . y . ; B u r t o n &B i g n e l l 1 9 6 9 ) . T h e y a r e i n d i s t i n g u i s h a b l e o n f i e l d o r p e t r o g r a p h i ce v i d e n c e f r o m t h e g r a n i t e s o f ep i s o d e 2 .335-42 M e t a m o r p h i s m : t h e r o c k s o f e l e m e n t g w e r e a f f e c t e d b y l o w g r a d er e g i o n a l m e t a m o r p h i s m d u r i n g t h e L u d l o v i a n t o U . C a r b o n i f e ro u si n t e rv a l , p r o b a b l y i n N a m u r i a n t im e s , a l t h o u g h t h e s t r a t i g ra p h i ce v i d e n c e f o r t h o s e d a t e s is d i s p u t e d . G r e e n s c h i s t f a ci e s m e t a m o r p h i s ma f f e c t e d t h e r oc k s o f e l e m e n t s e , f a n d g d u r i n g t h e N o r i a n t o ' T i t h o n -i a n ' i n t e r v a l , p r o b a b l y i n R h a e t i c t i m e s . S t r a t a u p t o N o r i a n a r ea f f e c t e d a n d t h e o t h e r d a t e s a r e t h o s e i n d i c a t e d b y r a d i o m e t r i cd e t e r m i n a t i o n s o n a s s o c i a t e d g r a n i te s ( i g n e o u s e p i s o d e 2 a b o v e ) .

Table 7S T R A T I G R A P H Y I N Z O N E 4

8x9 Unit32 0

3 22 T h i c k n e s s m 8 2 3 ElementAge and in whichevidence or M axi- M ini- Aver - these rocksage 821 Lithology mum mum age occur'Older ?L. Pleistoc, mo r- Sand , gravel 90 + 0 aalluvium' phology & (fluvial-es tuarine)present attitudeKrabi fm Mi oc-P leis toc , Sand, clay, marl, 175 + 0 bfossil plants & limest one, igniteg a s t r o p o d s ( l a c u s t r i n endpart marine)Khorat Gp Jurassic-Greta- Red sandstone, 0 ?400 c, dceous, spo radic siltston e nd shale,molluscs some sandstone,limestone andconglomerate(mainlynon-marine)Nathaw i Ladin-Nor, Black shale, grey- ?1000 efm mar ine fossi ls wack e , ub-mature arenites,bedded chertRat Buri gpSarabur i Sakm-?Gu ad, Pa le l imestone 120 0 600 850 flimesto ne marine fossilsMatsi fm Sak m- Leo nar d, Orthoquartzite, 2600 0 finterdigitates protoquartzite,with Saraburi subarko se,l i m e s t o n e c o n g l o m e r a t e ,limestonePhuket gpPathiu fm ?Namur-Sakm, Mud stone, 0 1640 gbryozoa and protoquartzitebrachiopodsnear topKhlong Ged in-V is6an , Muds tone , 2500 gKaphon fm mar ine fossi ls greyw acke

Satun gpThun g L./M. Ordo- Dark grey 1600 gSong vician-- limestoneLime- U. Silurian,stone marine fossilsNai Tak Probably lowe r- Calcareous 570 + 0 gfm most Ordovician , argillite andstratigraphic san dsto ne, mpureposition limes oneTarutao ?--Camb rian, Mature arenite, 19 80 465 c. gquartzite tr ilob ites argillite + 1500

Base not seen344-8 D e f o r m a t i o n : P h a s e 1 - - D e f o r m a t i o n o f e l e m e n t g i n t h e V is ~ a nt o S a k m a r i a n i n t e r v a l , p r o b a b l y i n N a m u r i a n t i m es , is i n d i c a t e d b y a


15/16

314 P E N I N S U L A R T H A I L A N Dl o c a l h i a t u s i n t h e s e d i m e n t a r y r e c o r d . K o o p m a n s ( 1 9 65 ) r e p o r t e dr e c u m b e n t f o ld s , c l e a va ge f o ld s , f l e xu r e f o ld s , a c c o r d io n f o ld s a ndb o u d i n a g e o f g r a n i t i c s il ls . A l a t e S i l u r i a n t o D e v o n i a n d e f o r m a t i o nw a s s u g g e st e d b y K o o p m a n s b u t w a s c o n s i d e r ed p a r t o f t h e C a r -b o n i f e r o u s p h a s e b y B u r t o n ( 1 9 66 ) . P h a s e 2 - - f o l d i n g o f e l e m e n t s e ,f a n d g o c cu r r e d d u r i n g t h e N o r i a n t o ' T i t h o n i a n ' i n t e r v al , p r o b a b l yi n R h a e t i c t i m e s : s t r a ta a s y o u n g a s u p p e r C a r n i a n o r l o w e r N o r i a na r e a f fe c t e d a n d a r e i n t r u d e d b y g r a n i t i c ro c k s d a t e d a t a r o u n d2 0 0 m . y . a n d u n c o n f o r m a b l y o v e r l ai n b y J u r a ss i c s t r a ta . T h r u s t i n gi n t h e L a n g k a w i I s l a n d s m a y p e r t a i n t o th i s p h a s e . P h a s e 3 - - e l e m e n t se , f a n d g w e r e a f f e c t e d b y u p l i f t , g e n t l e f o l d i n g a n d ? s t ri k e - sl i p f a u l t i n gi n t h e H e t t a n g i a n t o P a l a e o c e n e i n t e r v a l , p r o b a b l y i n m i d J u r a s s i c t oe a r l y C r e t a c e o u s t i m e s . T h e e v i d e n c e f o r t h e s e a g e s c o m e s f r o m aK / A r m i n e r a l r a d i o m e t r i c d a t e o f 1 50 m . y . o n t h e a f f e c t e d g r a n i t e( S n e l l i n g 1 9 6 6 ) a n d t h e s t r a t i g r a p h y i n o t h e r z o n e s .3 ~ o - 5 F o l d s t r u c t u r e s : d e f o r m a t i o n p h a s e 1 f o l ds h a v e w a v e l e n g t h s i n t h er a n g e 1 0 0 m - - 1 0 r a m , a p i c a l a n g l e s o f c . 4 0 a n d a x i a l s u rf a c es i n c l i n e ds o u t h - e a s t. P h a s e 2 f o l ds h a v e w a v e l e n g t h s o f 1 0 0 0 m - - 1 0 0 m , a p i c a la ng le s o r e . 70 a nd a x i a l su r f a c e s i nc l i ne d sou th - e a s t . P ha s e 3 f o ld s ha vew a v e l e n g t h s o f 1 0 0 0 m , a p i c a l a n g l e s o f c . 1 4 0 a n d v e r t i c a l (? ) a x i a lsu r f a c e s .3 5 9 -6 2 P l a n a r a n d l i n ea r s t r u c t u r e s : d e f o r m a t i o n p h a s e 1 p r o d u c e d s l a t ya n d f r a c t u r e c l e a v a g e , a s s o c ia t e d w i t h r e c u m b e n t f o l d s b u t p r e - d a t i n go t h e r f o l d s , a n d c r e n u l a t i o n c l e a v a g e a s s o c i a t e d w i t h a s e c o n d s u b -p h a s e o f f o l d i n g ( K o o p m a n s 1 9 6 5) . D e f o r m a t i o n p h a s e 2 p r o d u c e df r a c t u r e c l e a v a g e , j o i n t i n g a n d p a r a l l e l m i n e r a l l i n e a t i o n , s h e a r i n ga n d k n i c k zo n e s ( K o o p m a n s 1 9 65 ) .8 s n - 7 2 F a u l t i n g : P h a s e 1 - - a s i n g l e , l o w - a n g l e t h r u s t ( ' K i s a p t h r u s t ' )b r i n g s S i l u r i a n o n t o P e r m o - C a r b o n i f e r o u s s t r a t a a n d p r o b a b l yf o r m e d d u r i n g t h e l a te T r i a s s i c o ro g e n i c p h a s e . S e e K o o p m a n s ( 1 9 65 ) .P h a s e 2 - - w r e n c h f a u l ts , t h e p r i n c i p a l m e m b e r s o f w h i c h a r e r e f e r r e dto i n 111, d i s p l a c e la t e T r i a s si c g r a n i t e a n d , i n n o r t h - w e s t M a l a y a ,C a r n i a n ( t o N o r i a n ? ) s t r a t a . T h e y a l so c u t s o m e l a t e g r a n i t i c s t o ck sw h i c h a r e t h o u g h t t o b e l at e J u r a s s i c / e a r l y C r e t a c e o u s ( e p i so d e 3 in326 -32 bu t o t he r s t oc ks o f t he s a m e su i t e e v id e n t l y c r o s s t he f a u l t sw i t h o u t d i s p l a c e m e n t . S e e 1 11 -1 6. P h a s e 3 - - N [ i o c e n e t o P l io c e n e h o r s ta n d g r a b e n f a u l t i n g a l l o w e d a c c u m u l a t i o n o f s t r a ta i n t h e f a u l tt r o u g h s .

4 A . S H E L F S U B - Z O N ET h e U . C a m b r i a n T a r u t a o q u a r t z it e a n d t h e O r d o v i c i a n - S i l u r ia nN a i T a k f m a n d T h u n g S o n g L im e s t o n e t o g e t h e r c o n s t i t u te a no r t h o q u a r t z i t e - c a r b o n a t e o r s h e l f f a c ie s w i t h i n t h e m i o g e o s y n c l i n a lz o n e . T h i s f ac i e s i s e x p o s e d i n t h e co r e o f a m a j o r N - S a n t i c l i n e a n ds inc e t he L . P a l a e o z o ic r oc ks t o t he e a s t a r e o f ba s in f a c ie s i t m a y bet h a t t h e r e e x i s t e d h e r e a n o t h e r p e r s i s t e n t p o s i t i v e t r a c t o r s u b - z o n e .T h e w e s t e r n m a r g i n o f t h i s t r a c t is u n k n o w n , b e i n g c o n c e a l e d b y

y o u n g e r r o ck s . T h e l a t t e r i n c l u d e t h e U . D e v o n i a n t o L . C a r b o n i f e r o u sK h l o n g K a p h o n f ro , s ho w i n g t h a t a t t h a t p e r i o d s h e l f s e d i m e n t a t i o nw a s o v e r w h e l m e d b y f l y sc h . T h e e f fe c t o f t h e p o s t u l a t e d p o s i t i v e t r a c ts e e m s t o f in d f u r t h e r e x p r e s si o n , h o w e v e r , i n t h a t t h e t e r r i g e n o u s f a c i eso f t h e s u c c e ed i n g P e r m i a n s t r a t a ( t h e M a t s i F o r m a t i o n ) i s r e s t r ic t e dt o t h e w e s t e r n s i d e o f t h e o u t c r o p o f t h e L . P a l a e o z o i c s h e l f f a ci e s .I n t h e T h a i l a n d / M a l a y a b o r d e r a r e a t h e s am e t r a c t s aw g e n e r a t i o no f M . t o U . T r i a s s i c i n t r a s p a r i t e l i m e s t o n e ( I s h ii & N o g a m i 1 9 66 ) i nc o n t r a d i s t i n c t i o n t o t h e c o n t e m p o r a r y f l y s c h t o t h e e a s t, p o s s i b l y a g a i ni m p l y i n g s h e l f c o n d i t i o n s . T h e r e i s al s o so m e e v i d e n c e t h a t p a r t o ft h e T r i a s s i c f l y s c h is o f w e s t e r ly p r o v e n a n c e .

D . R E F E R E N C E SALEKSEEV, M . N . & TAKAYA,Y. 1967. An outline of the Up per Cenozoic deposits inthe Chao P hraya b asin, central T hailand. Southe ast Asian Studies Ifyoto Univ.5, 106-24.ALEXANDER, F. E . S. 19 50. Report on the availability o f granite on Singapore and the sur-rounding islands. Singapore (Government Press).ALEXANDER, . B. 1962. A short outline of the g eology of Malaya with special referenceto Mesozoic orogeny. Monogr. Am. geophys. Un . 6 , 81-6.ALEXANDER, J. B., MACDONALD, S. & SEATER, D. 1961 . Th e bas em en t rock s ofMalaya and their palaeogeographic significance in South East Asia.--A dis-cussion. Am. 07. Sci. 259, 801-6.ARANYAKANOND, P. 1955. Diamo nd disco very in Phangng a and Phuket, southThailand. Roy. De pt. Min es, Bangkok, Rept. of Investigation no. 1, 35-6.- - 1963. The ca

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