215 Geologische Rundschau 74/2 i 215-228 I Stuttgart 1985

The Permo-Triassic ,,Paleotethys,, in mainland Southeast-Asia and adjacent parts of China B y DIETRICH HELMCKE, C/O M a r b u r g " ' )

With 9 figures

Zusammenfassung Aspekte der geodynamischen Entwicklung des s~idostasiatischen Subkontinentes und Chinas werden unter besonderer Beriickslchtigung des Problems der permotriadischen ~,Pal~iotethys,~diskutiert. Es wird gezeigt, daf~ alle Suturen in Thailand, Vietnam und Yiinnan bereits im Pal~ozoikum geschlossen wurden und der ganze Bereich den Nordkontinenten zugerechnet werden mull Die permotriadische ,,Pal;iotethys,( mug sfidlich yon Tibet (siidlich des Kangdese Orogens) und in Burma gesucht werden.

Abstract Aspects of the geodynamic evolution of mainland Southeast Asia and China are discussed in consideration of the Permo-Triassic ,)Paleotethys(, problem. It is shown that all sutures in Thailand, Vietnam and Yunnan already closed during the Paleozoic era and that the entire region must be regarded as part of the northern continents. The PermoTriassic ,~Paleotethys~must be expected south of Tibet and in Burma.

R~sum~ Le d&eioppement gSodynamique du Sud-Est asiatique continental et de la Chine est discutS, en particulier par rapport au probl~me de la ~,PalSot&hys,, permotriassique. Toutes les sutures en Thailande, au Vietnam et au Yunnan &aient dSj~tfermSes pendant le PalSozoique, de sorte que la r~gion enti~re dolt &re consid&6e comme une partle des continents du nor& On dolt chercher la ),PalSot&hys,, permotriassique susdite au sud du Thibet (au sud de la r& gion orog6nique du Kangdese) et en Birmanie. KpaTKOe coaep~KaHHe 0 6 c y ) I ( j l a r o T c ~ H e K o T o p b m npo6YleM~,I r e o / I ~ H a M ~ q e c KOFO pa3B~ITPI~ rOFO-BOCTOqHOH qaCTH a3I/IaTCKOFO c y ~ KOHTHHeHTa, a Tax)Ke KUTaSI, npl/IqeM npleIHrtMalOT BO BHHMaHHe HCTOpHIO pa3B]4THfl FeOCHHKY[HHa.rIH "I~[aYleO T e T H c a " B IlepMO-TpHaccOBOM n e p l I o R e . CqHTarOT, qTO Bce LLIBbIB Wa~IYlaH~e, BbeTHaMe H tOHbH~IHe 3aKpblYU4Cb eme B nayleo3oe t4 HO3TOMy BClO O~YlaCTb c.rle~yeT

*) Author's address: Prof. Dr. D. HELMCKE, c/o Institut for Geologie u. Pal~iontologie der Philipps-Universit~t, Lahnberge, D~3550 Marburg.

rlpFlqHC.rl~TbKceBepHOMyMaTepHKy.Ce~uac nb~TaroTca HaiTI4 cYteAl,~ nepMo-TpHaccoBoro ~Ylaneoyewnca)> B TH6eTe rO)KHeeoporeHa Kangdese H B EHpMe.

Introduction At the dawn of the Mesozoic era (pre-Upper Permian) a plate-tectonic cycle, which started in the Upper Proterozoic and which is characterized by the Panafrican - Baikalian, the Taconian - Caledonian, and the Akadian - Variscan orogenies, came to a close with the folding of the Urals and the Appalachians. The product of this cycle was Pangaea (TR~MVY, 1982:713). The configuration of Pangaea is quite well known (SMI~, 1981). Pangaea was surrounded by the huge Panthalassa ocean. Two bays branched off from the Panthalassa ocean: the Arctic gulf and the Tethys ocean. The Tethys ocean, which was closed to the west, divided the eastern realms of Pangaea into a northern (Laurasia or Paleoeurasia) and a southern (Gondwana) region. The position of all major continents within Pangaea is quite well known (SMIT~, 1981). Much less understood is the paleogeographic position of many smaller crustal fragments during Permian - Triassic times. It has been said that fragments which are now linked to major continents as *Displaced Terranes~, might have occupied positions with different paleomagnetic latitudes somewhere in the realms of the Panthalassa and the Tethys during this time (Toz~R, 1982). ,Displaced Terranes,< are best known from the western parts of North America where their nature is rather well documented. Many authors suspect that >,Displaced Terranes<< also play an important part in a huge belt which traverses Asia from the Black Sea via Tibet to mainland Southeast Asia (~>Cimmerian Continent<< of ~EN6OR, 1979). There have been speculations that these ,Displaced Terranes<~ rifted off Gondwana during the Paleozoic - Triassic and drifted northwards. During their drift they closed the Permian - Triassic ,Paleote-

216

D . HELMCKE

thys<, which was situated in their front while the new ,,Neotethys<, opened in their back. These ,,Displaced Terranes,~ finally collided with Paleoeurasia during the ,,Indosinian, (Triassic-Lower Jurassic) orogeny thus forming one or more suture(s) marked by ophiolites.

the drift the ,,Cimmerian Continent<, closed the Permian-Triassic ,,Paleotethys,, which was situated in its front, while the new ,,Neotethys,< opened in its back. The ,,Displaced Terranes,< of the ,,Cimmerian Continent~, finally collided with Paleoeurasia during the ,,Indosinian,< (Triassic-Lower Jurassic) orogeny - thus forming one or more suture(s) marked by ophiolites (Fig. 1-4). T h e ,~Paleotethys<< c o n c e p t East of the Pamirs these (or this) suture(s) are (is) The attractive ,,Paleotethys<< concept emerged du- located north of the Indus-Tsangpo-Suture in central ring the past decade. It was designed to explain the Asia. According to LI CHUNYU(1980) two sutures are following seemingly contradictionary points: situated north of the Indus-Tsangpo-Suture which - The paleogeographic reconstructions of Pangaea are belived to have been formed during the Mesozo(SMn~-t, 1981) show a wedge shaped ocean opening to ic. The northern one is situated between the Kuen the east (Tethys, >,Tethys I<, DEWEYet al., 1973 ; ,,Pa- Lun and the Tanggula fold-system. According to leotethys,, LAUBSC~iER& BERNOULLI, 1977). ,,The him this suture was formed most probably during the central domains of this wedge-shaped ocean should Triassic. It's continuation to the east and southeast is have been underlain by an oceanic crust. Permo- situated in Yunnan and northern Vietnam. The soutTriassic ophiolites are the evidence we seek to con- hern one is situated between the Tanggula fold-sysfirm the plate-tectonic postulate<, (Hs~ & BERNOUL~ tem and the Kangdese fold-system of Tibet. This suLI, 1978:943 p.). ture was formed during the Jurassic. It's continua-- True witnesses of this ,,Paleotethys,, Permotion to the east and southeast is situated in Yunnan, Triassic ophiolites, have not been found in the Te- northern Thailand and in the Malay Peninsula. The thyan mountain belt. ,,A zone of ophiolite melange interpretation given by STOCKLIN(1980) that the suextended from Cyprus to southern Turkey, to Za- ture found in Thailand branches off from the suture gros in Iran, to Oman and thence to Afghan (GANs- between the Kuen Lun and the Tanggula fold belt SER, 1974). Yet like the Alpine ophiolites, the melan- somewhere in Yunnan would demand a somewhat ges include only rocks of Jurassic and Cretaceous different parallelization between the Tibetian sysage, but no Permo-Triassic ocean-floor fragments,, tems and the plates in mainland Southeast Asia (Hsr3 & BERNOULLI,1978:944). (comp. Fig. 7-9). This interpretation (continuation This dilemma has had to be explained: ,,We believe of the suture found in Thailand is north of the Tangthat the oceanic crust and much of the continental gula) is favoured in recent Chinese papers dealing crust of the Permo-Triassic Ocean were carried with this question (HUANG JIQING, 1984; CHANG down to the mantle by plate-subduction under the CHENGFA~X~PAN YUSHENG, 1984; XIAO XUCHANG~X~ southern margin of the southeastern European Plat- GAO YANLIN, 1984). In the context of this paper it is form. The existence of the Paleotethys can only be not necessary to give an answer to the question which identified in a consuming plate-margin south of the of the interpretations might be the more correct one. Permo-Triassic Eurasian continent<, (Hsr3 & BERDoes the attractive concept of a Permo-Triassic NOULLI, 1978:944). Therefore it was proposed ,>Paleotethys<< really solve the delemma? During the (comp. DEWEY et al., 1973; Hsr3 & BERNOULLI, last years a new problem arose: field-data from cen1978 :Fig. 2) that the tract of Old Cimmerian (in Eu- tral Thailand (HELMCKE& KRAIKHONG,1982) do not rope) and of Indosinian (in Asia) mountain belts fit into this attractive scenario. The aim of this conmight host the suture caused by the elimination of tribution is to critically review the geodynamic evothe Permo-Triassic ,Paleotethys,,. According to Hsu lution of parts of this belt based on the new results & BERNOULLI(1978 : 944 ) ,>there is no alternative if we from central Thailand. Only areas east of the Pamirs will be discussed; no attempt will be made to enter are to accept the concept of a Triassic Pangea,< Seemingly there was great progress in the solution the discussion on the complex geodynamic evolution of this dilemma during the last years. ~ENGOR(1979) of the areas west of the Pamirs. Data on the sediproposed the existence of the ,,Cimmerian Conti- ments of Upper Permian to Triassic age will be used nent<, or - more likely - the existence of a number of as a test of the validity of the >,Paleotethys<, concept. microcontinents which are thought to be ,,Displaced It must be stressed that only the results from ThaiTerranes<,. According to this speculation the ,Cim- land are based on own field-observations, while the merian Continent,, rifted off Gondwana during the remarks on the other regions are based exclusively on Paleozoic - Triassic and drifted northwards. During information from selected papers and maps.

The Permo-Triassic ,,Paleotethys~, The situation in the central parts of mainland Southeast-Asia During the last decade it was widely accepted that the geodynamic evolution of the central parts of mainland Southeast-Asia was governed by a continent/continent-collision which occured during the Upper Triassic (Indosinian orogeny). The two microplates involved - ~dndosinia~ in the east, ,,ShanThai Craton,, (BuNoPAs & VELLA, 1978) in the w e s t were regarded as ,,Displaced Terranes~ by most authors. RIDD (1971) was the first to suggest that the western microplate rifted off Gondwana. Supposed remnants of the oceanic terrane (,,Paleotethys,, or one branch of ~,Paleotethys,,) which formerly possibly divided these two ,,Displaced Terranes~, were

217

described from the region of Nan and Uttaradit in northern Thailand. Recent investigations (HELMCKE & KRAIKHONG, 1982; HELMCKE & LINDENBERG, 1983; HELMCKE, 1983) in the Petchabun fold-belt (this region is situated east of the southern, unexposed continuation of the ~Nan-Uttaradit-Suture,,) revealed a Permian succession clearly indicative of a Late Variscan (Permian) orogeny (comp. WIELCHOWSKY& YOUNG, 1983). According to the new data a pelagic facies prevailed here until Kubergandian times (WINKEL et al., 1983). During Murgabian times a thick flysch-sequence was deposited, it is followed by molassestrata. The molasse can be dated Upper Murgabian Lower Midian (ALTERMANNet al., 1983).

Fig. 1-4. Possible extension of suspect displaced terranes of Gondwana origin in mainland Southeast Asia and China which collided during the M e s o z o i c (~,Indosinian~ and ,,Yenshanian~ orogenies) with Paleoeurasia as discussed during the last years. Fig. 1. mainly based on ~ENGOR(1979); Fig. 2. based on STC)CKLIN(1980); Fig. 3. based on L1 CHUNYr3et al. (1982); Fig. 4. as discussed in this paper.

218

D. HELMGKE

Since the molasse strata are well developed, this region must be regarded as part of an external zone of a much larger orogen. In view of the fact that the folds and faults in the strongly deformed strata of the pelagic facies and the flysch dip mostly westwards, the internal zones of this Late Variscan orogen must be located farther to the west. These internal zones are situated in the mountain ranges of northwestern Thailand and eastern Burma (HEL~CKE, 1983). They are characterized by Precambrian basement and shallow marine strata of Lower Paleozoic age. Since the ,,ophiolites<< (BavM et al., 1970) of the Nan-Uttaradit area are located within the realms of this huge orogen (between the eastern external zone and the internal zone), it must be postulated that the oceanic terrane (if there ever was a real huge oceanic terrane) closed not later than Middle Permian (HELMCKE& LINDENBERG,1983). But there are preliminary indications that the main orogenic event which is accompanied by metamorphism already occurred much earlier in this more internal zone. If these preliminary indications can be substantiated by further data, then we have to expect that the closure of this oceanic terrane probably already occured during the Lower Carboniferous (comp. also HAHN, in print). Studies on the ,ophiolites<< (DAMM et al., in preparation) point in this direction: first K/Ar-ages (courtesy of D. Mr~LLeR-SOHNIUSand P. HORN, Min. Petr. Inst. Univ. Miinchen) we obtained from amphiboles from a metamorphosed ,,ophiolite~<-sample from the Sir• area (Uttaradit) indicate the interval Upper Devonian- Lower Carboniferous (comp. Tab. 1). We interpret these data as the age of the metamorphic event respectively as the age of the post-metamorphic ,,uplift<~.

Sample

B 5/83/1

The result that the main orogenic event which is accompanied by tow grade metamorphism occured in the Uttaradit region already during the Upper Devonian - Lower Carboniferous is compatible with important fossil-finds in a region north of Uttaradit (comp. HAHN, in print) and also with the find of Lower Carboniferous fossils in the Chon Daen area (FONTAINEet al., 1983; CHONCLAKMANIet al., 1983). In this case the whole orogen would be the result of a long-ranging and complex geodynamic process with main acts of contractional deformation during the Precambrian, the Carboniferous, and the Permian: in the internal zones west of Chiang Main (comp. BAUM et al., 1970) during the Precambrian and the Carboniferous, in the zones from Chiang Mai to east of Uttaradit during the Carboniferous, and in the eastern external zone (Petchabun area) during Permian times. Since no evidence of an ,,oceanic basement<< was found until now in the region of the Petchabun fold an thrust belt, it might be speculated that this region was completely underlain by thinned continental-crust, i.e., the oceanic terrane of the ,,Paleotethy,, might have closed on Thai territory as early as Carboniferous. The Middle Triassic ,,ftysch-like<, sediments (Hong Hoi Formation of the Lampang Group), which were used by some authors as an argument for a Triassic closure of the ,,Paleotethys<~ on Thai territory, are also located within the confines of the Late Variscan orogen described. It can be demonstrated that the Triassic strata of the Lampang area in northern Thailand contain neither pelagic sediments nor real flysch-sequences (Ht~LMCKE, in print). Moreover, the geological maps 1:250.000 (sheet Lampang, sheet Uttaradit) of this region clearly show an uncon-

Weight [mg]

4~ rad Ix 10-7cc/g STP]

% Air-Ar

16.14

5.03

63.9 5.11

7.26

5.19

65.25

Weight [mg]

K %

12.35

.0329

T Ma

T Ma mean value

361•

66.6 344•

B 5/83/3

13.14

60.6

7.484

7.25 4.81

7.013

61.5

11.3

.0529

327•

62.4

Tab. 1. K/Ar-age of post-metamorphic ,,uplift(, in the Uttaradit area. Obtained from amphiboles from metamorphosed ,,ophiolite~,-sample from Sir•

The Permo-Triassic ,,Paleotethys, formable overlap of Middle Triassic marine strata (Hong Hoi Formation) over folded Paleozoic strata in many areas. A more or less continuous sequence from the Upper Paleozoic to the Lower Triassic (CHoN6LAKMANI, 1984) seems to be restricted to other areas in this zone. These strata were sedimented under epicontinental conditions in rather rapidly subsiding areas (intramontaneous basins)- much like the Saar-Selke trough of the European Variscides where subsidence also started at different times. The deformation of these strata during the Upper Triassic (,,Indosinian orogeny<<) is therefore strictly intracontinental (HELMCKE& LINDENBERG,1983) and the importance of this orogeny for the geodynamic evolution of the central parts of mainland Southeast Asia was highly overestimated in previous publications. Since the new data from Thailand exclude the existence of any oceanic terrane (,~Paleotethys<< or a branch of the ,,Paleotethys,) within the confines of central mainland Southeast Asia after the Middle Permian (more likely even after the Carboniferous) the question arises whether the real Permo-Triassic ,,Paleotethys~, might have been situated somewhere else: the most likely candidate is the so-called ,Red River Suture~, in the northern parts of Vietnam and its continuation towards N W in Yunnan. If remnants of the Permo-Triassic ~,Paleotethys,< cannot be found here, then we have to search for the ,,Paleotethys<< somewhere else: possibly north of the Yangtze Platform in China or elsewhere. The situation in the northern parts of Vietnam For the description of the geodynamic evolution of the northern parts of Vietnam it is advisable to distinguish strictly the very young deformations affecting this area and the processes linked to the real orogenic evolution of this region. The Red River Fault, which is sometimes interpreted as the ,,suture~ between the Indosinia Plate and the South China Plate, is a young fracture caused by the collision between India and Eurasia (MOLNAR& TAVPON~R,1975). This fracture has nothing to do with a possible suture between two plates during the Triassic: N W of Hanoi this fault cuts through metamorphic terranes which are apparently older than Upper Paleozoic (comp. geol. map 1:500.000, sheet ,,Cao Bang@ To the SW of this young fracture there are two areas composed of basic to ultra-basic suites which might be considered ,,ophiolites~,. Approx. 120 km SW of the Red River Fault ,,ophiolites, are situated i[n the region of the Song Ma (Ma River) in a metamorphic terrane. This metamorphic terrane is unconformably overlain by marine Triassic sediments

219

(Virglorien to Carnien; comp. geol. map 1:500.000, sheet ,,Hanoi ouest,,). The metamorphic event in this region is therefore older than Virglorien (Virglorien = approx. Anisian). In other regions shown on sheet ,,Hanoi ouest,, this metamorphic event is pre-dated by overlaying Paleozoic strata. In any case, these ,,ophiolites,, can hardly substantiate an Upper Triassic closure of a Permo-Triassic ,,Paleotethys,. The second area composed of basic to ultrabasic suites is located in the region of the Son Da (mainly to the N and E of the Song Ma ,ophiolites@ these rocks are Upper Triassic (roughly the Carnian-Norian boundary according to FONTAINE& WORKMAN, 1978:578) since they are underlain by fossiliferous Triassic sediments. These Triassic sediments reach a thickness of as much as 6000 m (FONTAINE& WORKMAN, 1978:578); they were interpreted in some papers as geosynclinal. This sequence starts with Scythian strata which rest unconformably on Permian ,,with a basal conglomerate in some places. Several bauxite horizons in the upper part of the Permian indicate some degree of emergence, but without any important disturbances. The earliest Triassic sedi~ ments were deposited on an irregular surface of deeply eroded limestones, and in places fill large cavities in the latter,, (FONTAINE& WORKMAN,1978:555). The Triassic sequence is composed predominantly of shales, sandstones and limestones which are often rich in fossils (comp. FONTAINe & WORKMAN, 1978:555). Such a setting is not a convincing argument for an Upper Triassic closure of a Permo-Triassic oceanic terrane: A continent/continent-collision should be accompanied by metamorphism. This very short discussion revealed that it is hardly possible to find remnants of a huge Permo-Triassic ,,Paleotethys,, within the defines of these regions of Viemam. STARITSKIYet al. (1973) recognized already more than ten years ago that the true geosynclinal history of northern Vietnam ended in a main phase of folding which occured at the threshold between the Early and Middle Carboniferous. According to these authors only a residual geosynclinal basin continued in the Dien Bien Phu Zone and in parts of Laos into the Lower Triassic. About the Triassic sediments of northern Vietnam STARITSKIYet al. (1973:1387) note in general: ,,There is really no need to show that the slightly deformed, predom!nantly terrigenous deposits developed in the isometric structures are not geosynclinal<<. They concluded that the Mesozoic epoch was a time of activation (Diwa) over the whole area of northern Vietnam: i.e., widespread intensive folded-block movements which may reach geosynclinal proportions and occur on a rigid basement with a continen-

220

D. HELMCKE

tal crust within regions that have ended their geosynclinal development (regions of completed folding and platforms). The view that the collision between the Indosinia Craton and the South China Plate already happened during the Paleozoic is shared, for example, by LE TrtAC X I ~ (1981:633) who stated: ~,Since the Lower Paleozoic period, old Indochina plate had completely joined the South-China plate by Truongson continental collision zone,, (Truongson continental collision zone equals the above mentioned Song Ma ,,ophiolites~,). According to MORGt3NOV (1970) the Truongson zone terminated its geosynclinal development in the Late Devonian to Early Carboniferous and, was intensively folded during this interval. LE THAC X I ~ (1981) interpreted the mafic to ultramafic rocks of the Song Da region as products of continental rifting during Triassic times (comp. Fig. 5). GA~NSKY & HUTCHISON (1984:12) also share this view: ~Cathaysia . . . had Indosinia sutured onto it along the Truongson- Song Ma mobile belt by Early Carboniferous times,,. Descriptions of the stratigraphic columnes of Vietnam (FoNTAINE & WORKMAN,1978; PHAN CF TIEN, 1981) show clearly that a major geological event happened during the Lower Carboniferous. According to P~AN Cu TEN (1981:377)this event can be dated as about Early or Middle Tournaisian. According to FONTAINE & WORKMAN (1978:546) the Famennian has still not been identified in northern Vietnam. About the Carboniferous of Vietnam, Laos and Cambodia FONTAIN~ & WORKMAN (1978:547) note in general: ,,The Carboniferous is only locally concordant with the Devonian; the division between the two systems is generally marked by a stratigraphic gap representing widespread marine regression and emergence. Also, there are clear angular unconformities within the Lower Carboniferous of certain areas,,.

The situation in Yunnan

We failed to find either remnants of the PermoTriassic ~Paleotethys,, or one branch of it in the central parts of mainland Southeast Asia (Uttaradit-Nan Suture) as well as in the northern parts of Vietnam (Song Ma Suture) but we found ample evidence that both sutures already closed during the Paleozoic era. The northern continuations of both sutures are situated in Yunnan where they are found close together in the ~Three River,, region. Obviously based on the age of ,,surroundings, country rocks, it is believed that both sutures closed here during the Mesozoic era (comp. HUANG CHI-C~NG, 1978; LI CHUN k , 1980; Z~. M. ZHANC et al., 1984). This is not compatible with the data provided in this paper for Thailand and Vietnam, since it seems unlikely that these sutures closed in mainland Southeast Asia during the Paleozoic while their northern continuations in Yunnan closed during the Mesozoic. The question arises as to whether the closure of these sutures is dated correctly in Yunnan- in mainland Southeast Asia the closure of these sutures was also often incorrectly dated as Triassic. Since we know from Thailand that Triassic ~flysch-like~ sequences turned out to be thick clastic sequences deposited in intramontaneous basins, and since STAR~TSKIVet al. (1973) did not hesitate to state that the Triassic sequences of northern Vietnam are not geosynclinal, it seems challenging to examine the nature of the Triassic sequences in Yunnan on the basis of published data. In papers dealing with the plate-tectonics of China the Triassic of the region under discussion is labelled ,flysch,, or ,,flyschoid,~. For the Kekexili-Jinsha-Ailao Accretionary Fold Belt (= northwestern continuation of the suture found in northern Vietnam) ZH. M. ZHANGet al. (1984:305) provide, for example, the following information: ,,Olistostromal m~-

SW

NE Sam Neua M.Son Rift

Rift

Da R i v e r Rift

Tam Dao

Hiem River Rift

Fig. 5. Cartoon showing the rifting in North Vietnam during Late Paleozoic - Early Mesozoic (C3-T2) according to L~ THAC XINH (1981).

The Permo-Triassic ,,Paleotethys~, lange characterized by exotic blocks containing Silurian to Early Permian fossils was mapped in Triassic flysch. In the back-arc basin of the fold belt, thick piles of Triassic flysch accumulated. The back-arc basin is connected with the Triassic foredeep in the southern part of the Kunlun-Qinling accretionary fold belt, forming the largest flysch basin in the world,,. Emplacement and folding of this belt is described as late Triassic (>>Indosinian<,) by ZH. M. Z~tANC et al. (1984:Fig. 5). For the North Tibet-West Yunnan Accretionary Fold Belt (= northern continuation of the suture found in Thailand) ZH. M. ZHANC et al. (1984:305) note: >>Tothe east of the microcontinent, Triassic Jurassic flysch was accumulated and folded prior to deposition of Cretaceous terrestrial sediments . . . This accretionary fold belt therefore was formed at the end of the Jurassic and is called the early Yanshanian fold belt<~. The geological situation of western Yunnan and southern Szechwan as shown on the geological map 1:4.000.000 of China (1976) is very different. This map reveals a feature which favours an interpretation of the Triassic strata quite contrary to flysch. It clearly shows that the Triassic (mainly T~) overlaps in

"~

221

many regions (between Pai-yu and Chung-tien east of the Jinshajiang River) sequences of Ordovician, Devonian and Carboniferous age. Such a setting usually indicates a transgression. Is it possible that there is a >>transgressive flysch,, in Yunnan? The short description of the Triassic of this region in ~>An outline of the marine Triassic of China,, (WA~6 Y~-GA~o et al., 1981:3) supports scepticism: ~>Triassic strata on the Tanggula (5), Qamdo (6), Yidun (7) and Western Yunnan (8) districts are very similar. Generally the Lower and Middle Triassic record is incomplete except in parts of districts 5, 6 and 7, where the Triassic is well developed and includes marine clastics and carbonates, as well as continental sediments interbedded with marine strata and coals in the upper part. The whole Triassic sequence is more than 6000-7000 m thick. Intermediate and basic volcanic rocks are interbedded~,. This is hardly a description of a flysch-sequence. The data provided by WAnG Y~-GA~G et al. (1981:9 and Tab. 1) for Western Yunnan rule out the possibility that there are flysch strata of Triassic age in this region (Fig. 6). These data show that there is a gap in the stratigraphic record in Yunnan from Griesbachian to Ladinian (the >>Shanglan Formation~ mentioned on page

~u

. . ~r ~. ;. 9 - ~ .;.-..7., ,;...~.;.....; .

w

?

.... > _ . . . . . . . . . . . . , ~}=i=~<~Z~:'i='{.-Ti}'=fi11'@.!

0

...::... [ . . . [

U

PERMIAN

U

......

PERMIAN

PERMIAN

Fig. 6. Marine Triassic sequences of the Tanggula Shan, the Qamdo, the Yidun, and the Western Yunnan districts of China (for location ref. to Fig. 9) according to WANGYI-GANGet al. (1981, Tab. 1 and p. 3).

222

D. HELMCKE

9 of the WANe YI-GANc et al. paper is not included in their Table 1). The description of the Lower Triassic ,,Zigan Formation, by FAN JIASONG(1980:1138) from the area between the east bank of the Jinshajiang River (Yangtze River) and the line joining Ganzi, Xinlong, Litang and Mull countries is also definitely not the description of a typical flysch sequence: ,,[Zigan Formation] is composed of grey banded slates and sandstones intercalated with light-grey limestones, oolitic limestones and algal limestones, containing abundant bivalves and ammonites,. This is the description of the Lower Triassic of exactly the area which is believed to host a Triassic eugeosyncline (,,and a eugeosyncline (the Y i d u n - Zhongdian area) in which melange and ophiolite set occur,.; L1 ZISHUN, 1980:1152). The result of this comparison can be summarized as follows: there are definatly contradictions in the literature. If the descriptions of the stratigraphy and facies of the Triassic strata are more-or-less correct then the two sutures could not have closed in Yunnan during the Mesozoic era. In this case it is most probable that they already closed during the Paleozoic era and that the Triassic strata are sequences developed on continental crust. This interpretation is supported by LI CHUNYrdet al. (1982:15) who stated: ,,Thus, the plate collision zone on the eastern side of the Shan State massif should have merged with the Lancang River and it is suggested the particular plate should have been sutured and welded during Permian - Triassic times, being a bit older than its northern segment, with reference to the metamorphic age of phengite ranging from 240 m.y. to 260 m.y. dated by Rb-Sr method, as well as to the time of the formation of the ophiolites,. (Shan State massif = Shan-Thai Craton, Lancang River = Mekong River). According to HUANGJIQING(1984, Fig. 5) the suture which he traced from north of the Tanggula via Yunnan into northern Thailand and which he interpreted as the remnant of the ,,Great Paleotethys Ocean, closed at the end of the Permian (and reopened again in the Triassic). Is it possible to find the Permo-Triassic

,,Paleotethys- in Southeast Asia? Since we failed to find any convincing arguments which can prove the existence of a Permo-Triassic ,,Paleotethys. in Thailand, Vietnam or Yunnan, it might be advisable to look farther north. The next candidate would be a ,,suture. north of the South China Plate. But this suture already closed during

Late Paleozoic times (ZH. M. ZHANC et al., 1984). Does this mean that we have to cancel the concept of the Permo-Triassic Pangaea, as Hsu & BERNOULLI (1978:944) stated, since we failed to find remnants of the Permo-Triassic ,,Paleotethys,? There is still the possibility that we looked at the wrong places and that the ,,Paleotethys, is actually situated somewhere where we did not investigate. Starting from Thailand we looked to the east and the north - we did not search for the ,>Paleotethys, west or south of Thailand. If we accept that all described sutures in Thailand, Vietnam and mainland China already closed during the Paleozoic, then there is only one possible interpretation: these areas were part of the Northern Continents at the time during which Pangaea was finally assembled. In this case the Permo-Triassic ,,Paleotethys, must be searched for south of these regions. If we take the Cenozoic rotation of mainland Southeast Asia into consideration then we have to expect the ,,Paleotethys,< at present west of these regions. Are there any indications in these regions which may serve as hints for the former existence of an oceanic terrane (,,Paleotethys,) ? West of the ,,Shan-Thai Craton, (BuNOVAS& V~LLA, 1978) there is, caught between two sets of young strike-slip faults, a triangle shaped terrane made up of the Tenasserim region of Burma and parts of Peninsula Thailand with a geology unlike that of the Shan-Thai Craton. This region is composed mainly of Upper Paleozoic clastic sediments (Phuket Group, Mergui Series). Sequences of Lower Paleozoic age or even Precambrian basement have not been found in this region. In 1970 MITCHELLet al. (1970:411) already described the Phuket Group, which they divided into a very thick (exceeding 3 km) Lower Formation and a quite thin (100-200 m) Upper Formation as follows: ,,Facies analysis shows that the Lower Formation consists of mass flow deposits and sandstones comparable to the deposits of modern continental rises and continental slopes. The Upper Formation was deposited in a shallow marine and probably deltaic environment . . . The sediments, which are rich in quartz, were derived from a continental area and deposited on its margin. In contrast to previous interpretations of the Paleozoic history of Peninsular Thailand, it is considered that the continental source lay to the east. The continental margin resembled modern margins of either Atlantic or Japan Sea type,. If we accept this view, then we have found already the continental margin bordering an oceanic terrane during the time the Phuket Group was deposited. In this case, however, it will be necessary to reject the

The Permo-Triassic ,~Paleotethys,, interpretation that the ,~pebbly mudstones~ of the Phuket Group are of glacial origin (comp. e.g. STAUFFER,1983). We do have to accept these strata as sediments typical for a continental margin (comp. REINECK& SINGH,1975:388) if we still like to maintain the concept of a huge Permo-Triassic ,,Paleotethys~,. A thorough sedimentological re-investigation of these strata is urgently needed. H o w old is the oceanic terrane off this continental margin ? It is likely that it opened prior to the onset of the sedimentation of the Phuket Group, i.e. it must have been already in existence in the Carboniferous. BURRE~ & STAIT(1984:3) claim that the CambroOrdovician fauna of Thailand and Malaysia have a very close relationship to those of Australia. They propose, therefore, that the Shan-Thai Craton was placed close to northwest Australia during this time. If this interpretation is correct then it is likely that this oceanic terrane opened after the Ordovician. H o w long did this oceanic terrane last? The answer to this question is difficult and highly speculative. The on-shore geology of the Thai Peninsula and the Tenasserim region of Burma does not give much information: During Permian times the depositional environment shallows and the Upper Formation of the Phuket Group is topped by limestones (Ratburi Limestones) of Kungurian age (WATERHOUSE,1981). After the deposition of these limestones the sea withdrew from this area; sandstones and shales containing brackish water molluscs found in the Tenasserim region (Martaban Beds) were placed in the Upper Permian to? lowermost Triassic (comp. BENDER et al., 1983:75). Today the Andaman Sea is located west of this region. This is a young structure which opened only during the Tertiary. West of the Andaman Sea the Bay of Bengal, again a rather young structure, developed after the northward flight of Greater India (comp. JOHNSONet al., 1976). Therefore, we can not expect any information on the problematic (Mesozoic) further evolution of the oceanic terrane (~Paleotethys?,,) from these regions. A scenario based on few assumptions may help us to unravel the possible story. The assumptions: - we assume that Greater India is the only Gondwana-derived continent in the region under discussion which was welded to the Eurasian continent after the Late Permian; - we assume that the collision between India and Paleoeurasia triggered a clockwise rotation of Southeast Asia. Fig. 7-9 shows three cartoons which illustrate this scenario. N o w we can see how this oceanic terrane was possibly destroyed. The younger Mesozoic gra-

223

nitoids of Southeast Asia may be regarded as possible witnesses for this process: contrary to the granites of Triassic age they have geochemically, at least in part, I-type affinities (comp. BECKINSALEet al., 1979). It shall be stressed that the scenario illustrated in the cartoons (Fig. 7-9) might be based on an erroneous parallelization between the single Tibetian and the single Southeast Asian plates: If we follow STOCK~IN's (1980) interpretation then we should search the western continuation of the Petchabun )~geosynclinal,, zone not to the north of the Kangdese fold belt but to the north of the Tanggula fold belt. In this case both - the Kangdese and the Tanggula would be the Tibetian equivalents of the Shan-Thai Craton. If the assumptions given above and the scenario illustrated in the cartoons (Fig. 7-9) turn out to be without fundamental error, then it should be possible to outline the following concept: - within the defines of mainland Southeast Asia we have to search for the Permo-Triassic ,,Paleotethys~ west of the Shan-Thai Craton, i.e. the only region in mainland Southeast Asia in which we can find obducted oceanic material of the ~Paleotethys~, is in Burma; - prior to the rotation of mainland Southeast Asia the connection between mainland Southeast Asia and Tibet was much clearer: mainland Southeast Asia and Tibet are built up by the same Paleozoic orogens. The suture of the ~Paleotethys~, therefore has to be searched for south of Tibet - in the same region in which we expect the suture of the ,~Neotethys,,. East of the Pamirs and the Hindukush the ~,Paleotethys~ and the ~Neotethys~ finally turn out to be the same oceanic terrane: the longstanding ~)Tethys,, (comp. TR~3MPY, 1982:715 p.). West of this region the situation may be quite different since microplates- like the Lud Block- may be involved. The

situation

in

Burma

The geodynamic evolution of Burma during Paleozoic and Mesozoic times is still little understood (comp. BENDERet al., 1983). Nevertheless, it can be stated that the eastern parts of Burma are part of the Shan-Thai Craton (BANNERT& HELMCKE,1981), i.e. part of the internal zone of the Variscan fold belt of central mainland Southeast Asia. Late Paleozoic stratigraphic units which can be interpreted as equivalents of the Phuket Group have been found along the western margin of the Shan Plateau from the South at least up to the area east of Ya-

224

D. HELMCKE

methin (S of Mandalay) (comp. BENDER et al., 1983:72). According to STAUFfeR(1983 :Fig. 10) they also contain pebbly mudstones (,tilloid~) facies (comp. also MITCI~ELS,1981:113). This facies may be an indication that continental margin facies of Upper Paleozoic age could be developed to the north at least up to S of Mandalay. The question as to whether this continental margin was of the Atlantic-type or the Pacific-type should be left open for the time being.

Possibly positive evidence for the oceanic terrane which we are searching for may be found in Upper Burma: in the poorly investigated regions of Upper Burma huge areas are build up by basic and ultrabasic sequences (comp. geol. map of Burma 1:1.000.000, 1977, or geol. map. of Burma 1:2.000.000 in BZNDER et al., 1983). In the Jade Mine District jade and glaucophane occur together with basic and ultrabasic rocks. This setting may indicate a high pressure/low

The Permo-Tfiassic ,~Paleotethys,,

225

Fig. 7-9. Possible evolution of mainland Southeast Asia and adjacent parts of China during Middle Permian, Tertiary and recent times. The parallelizatiou of the single Tibetian elements with the single Southeast Asian elements is highly speculative. It is equaly possible that both Tibetian zones have to be regarded as the western continuation of the Shah-Thai Craton (comp. STOCKHN,1980). These cartoons demonstrate a possibility to destroy the Tethys: north of Greater India the Tethys is destroyed by continent/continent-collision,east of Greater India the Tethys is destroyed by the rotation of Southeast Asia (and the opening of the Andaman Sea). Only to the east of the Andaman Sea a relatively small area containing Paleozoic continental slope sediments (Phuket area, Tenasserim) is preserved. Fig. 7 shows the situation during the lower Middle Permian: The Petchabun basin is still open, closure by contractional deformation starts approx at the Kubergandian- Murgabian boundary. South of the Shan-Thai Craton and the Kangdese fold belt occured sedimentation of continental slope sediments till lower Middle Permian (in Phuket area). Fig. 8 shows the situation prior to the impact of Greater India. The Tertiary flysch basin is indicated. Fig. 9 shows the present situation. The continental slope sediments (Phuket Group, Mergui Series) are preserved east of the Andaman Sea. Abbreviations: AY = Arakan Yoma, B = basic and ultrabasic sequences in Upper Burma, IBTB = Inner Burma Tertiary Basin, P = Phuket, Pa = Pamirs, Pe = Petchabun fold and thrust belt, Q = Quamdo, T = Tenasserim, U = Uttaradit-Nan ,,ophiolites~,, WY = Western Yunnan, Y = Yidun.

temperature metamorphic regime (comp. BENDER et at., 1983:211). Though these sequences are usually belived to be of Cretaceous to Eocene age (comp. BENDER et al., 1983:139) we should not totally rule out the possibility that a part of these sequences is older. If this speculation is not fundamentally erroneous, then we should be able to find a slice of the Permo-Triassic oceanic terrane we are searching for. In this case this sequence may even indicate the subduction (B-subduction) zone.

The situation in Tibet Prior to the impact of Greater India and prior to the rotation of mainland Southeast Asia, the connection between Tibet and mainland Southeast Asia was much less disturbed than today. Since we failed to find any suture in Thailand, Vietnam and in Y u n n a n which might have been caused by an U p p e r Triassic (or even younger) closure of a Permo-Triassic ~,Paleotethys% it is evident that the whole of Tibet must

226

D. HELMCKE

also be regarded to have been part of the Paleoeurasian Plate at the time Pangaea was finally assembled. The Permo-Triassic Tethys must have been situated south of the Kangdese fold-system (Lhasa Block). In this connection, the Upper Paleozoic strata in the regions north of the Indus-Tsangpo-Suture deserve special attention. Published statements on the paleogeographic position of this area are still contradictory:

Regions to the north of the metamorphic complex (Lhasa Block) are expected to be equally interesting: by transfering what we have learned from the Petchabun and Uttaradit areas of Thailand to Tibet, it seems possible to date the orogenic events which affected the Kangdese - and the Tanggula-fold-systerns: these fold-belts may finally emerge as being essentially Paleozoic and - in respect to the Permian Pangaea - therefore as parts of the Northern Continents. - TAPPONIERet al. (1981) mentioned that, north According to CHANG C~eN-FA et al. (1977:13) and west of Linzhu, the probably Precambrian flysch of Devonian age is found north of the suture metamorphic basement is covered by Carboni- dividing these two fold-belts. In this connection it is ferous tillites with Gondwanian affinities interesting to note that CHiN GUOMIN6 et al. (comp. also LI CHu>:Y~3et al., 1982:7 and 30); (1980:58) refer to the basement of the Tanggula- and - According to MITCHELL(1981) Upper Carboni- the Kangdese-fold-systems as being Variscan and say ferous pebbly slates in the Southern Tibet Pla- that this area appeared in the middle of the Triassic teau support the postulated continuity of the ,,to be a southward dipping continental slope to the Southern Tibet - western SE Asia block. north of the ,main, Tethys<<. - According to JA~GERet al. (1982) the metamorRecent investigations by ALLECREet al. (1984) and phics are unconformably overlain by fossilife- Gn~ARDeAU(1984) point to a somewhat different sorous Carboniferous and Permian slates, quartz lution for the suture north of the Lhasa Block. Acschists, conglomerates, and Carbonates of Ca- cording to their data this suture was formed by the thaysian affinities; closure of a small oceanic basin (back arc or interarc - JACKSON(1980) reported that according to Chi- basin) around 140 m.y. ago. From this region they nese authorities a paleontological boundary was describe ophiolites and metasediments of ?Paleozoic developed along the Tsangpo valley. ,tin the age which from nappes thrusted over Middle to UpHimalaya, fossils of Glossopteris and cold wa- per Jurassic flysch. The lithological description of ter biota were found in late Paleozoic beds, the Jurassic flysch series seems to be a little peculiar, while north of the Tsangpo fossils of Giganto- for instance they mention besides ,,rhythmics internoclea and warm water biota were uncovered in calations of dark shales, slates and yellow sandstones the Permian formation ..... (JACKSON, with scarce bio-detritic limestones forming lenses se1980:486). veral meters thick<, (GIRARDEAUet al., 1984:28) also ophiolites ,,reworked in a grey neritic limestones of Recently ALLi~GREet al. (1984:18) stated: ,,SoUpper Jurassic age,< (ALLEGR~et al., 1984:19). mewhat surprisingly, there seems to be no unambiguous paleontological proof of the Gondwanian origin of the Lhasa block as doubts can be cast on the siConclusions gnificance of the Danxung-Linzhu tillites. ExaminaThe results from Thailand and the information tion of these ,tillites< is not sufficiant to demonstrate that they are a glacial sediment or alternatively rift in- from published papers and maps discussed in this fill. If they are indeed late Carboniferous glacial tilli- contribution indicate clearly that no oceanic terrane tes, they imply a climate and latitude in striking con- of the Permo-Triassic ~)Paleotethys,, can be expected trast with the early Permian climate and latitude im- in any of the regions discussed which are north of the plied by the Cathaysian flora which has been disco- Indus-Tsangpo-Suture or east of Burma at any time vered in the Lhasa block and which does not contain after the final assembly of Pangaea in the Middle a single Gondwanian element,<. They conclude that Permian. This also implies that the Triassic ,,Flysch,, ,,the Lhasa block for instance is a Cathaysian block of the Sungpan-Kantze area in China was definitely and not necessarily of Gondwanian origins< (ALLI~CRe deposited neither on Triassic oceanic crust nor in a et al., 1984:22). If we consider these sediments as an back arc basin position (comp. ZH. M. ZHANCet al., equivalent of the Phuket Group and if we accept the 1984). Recently STOCKLIN (1984:76) informed us on interpretation given by MITCHetL et al. (1970:411) also for this sequence then we have found the conti- Middle East Asia that ~the geological evidence nental slope bordering a Carboniferous/Permian against the existence of a Permo-Scythian Tethys Ocean has become too persistent, too alarming to be oceanic terrane to the north also in Tibet.

The Permo-Triassic ,,Paleotethys~, disregarded any longer, or to be explained away by subduction< Well, it seems to me that we still have the chance to find a Permo-Triassic ,,Paleotethys, in mainland Southeast Asia if we search west of the Shah-Thai Craton: the Tenasserim region of southern Burma and Peninsula Thailand may be a positive indication - if the interpretation of the U p p e r Paleozoic sequences as being continental slope deposits (MITCHELL et al., 1970) is correct.

227 Acknowledgements

The work carried out in Thailand was supported by the Royal Thai Department of Mineral Resources (DMR), Bangkok, with financial aid by the German Research Foundation (DFG) and the Free University of Berlin which is gratefully acknowledged. Special thanks go to Mrs. Rucha Ingavat (DMR, Bangkok) for her careful determination of the foraminifera found in the Petchabun area and to W. Altermann, S. Grammel, C. Strobel and R. Winkel for their effective assistance. Discussions with many friends and colleagues were extremely fruitful and are noted with thanks.

References Fifth Regional Congress on Geology, Mineral and ALLI2GRE,C. J. et al. (1984): Structure and evolution of the Energy Resources of Southeast Asia, April, 1984, 1 p., Himalaya - Tibet orogenic belt. - Nature, 307, 17-22. Kuala Lumpur. ALTERMANN,W., GRAMMEL,S., INGAVAT,R., NAKORNSCHONGLAKMANI, C., FONTAINE, H. & VACHARD, D. RI, N. & HELMCKE,D. (1983): On the Evolution of the (1983): A Carboniferous-Lower Permian (?) section in Paleozoic Terrains bordering the Northwestern Khorat Chon Daen area, central Thailand. - Preprint from the Plateau. - Conference on Geology and Mineral ReSymposium on Stratigraphy of Thailand, Nov. 1983, sources of Thailand, November, 1983, Bangkok, 5 p., Bangkok, 1-5. preprint. CHUNY~, L. (C. Y. LEE) (1980): A preliminary study of BANNERT, D. & HELMCKE, D. (1981): The Evolution of Plate Tectonics of China. - Bull. Chinese Acad. Geol. the Asian Plate in Burma. - Geol. Rdsch., 70, 446458, Sci., Series I, 2, 19-22. Stuttgart. CHUNYr.3, L., QUAN, W., XUEYA, L. & YAOQING, T. BAUM, F., v. BRAUN, E., HAHN, L., HESS, A., KOCH, (1982): Explanatory notes to the tectonic map of Asia. K.-E., KRUSE, G., QUARCH, H. & SIEBENHr3NER,M. Cartographic Publishing House, 49 p. (1970): On the Geology of Northern Thailand. - Beih. DAMM, K.-W., HELMCKE, D. & TODT, W. (in preparageol. Jb., 102, 3-24. tion): Geochronology and geochemistry of ,mphiolites~, from Thailand. BECKINSALE, R. D., SUENSILPONG, S., NAKAPANDUNGRAT, S. & WALSH, J. N. (1979): Geochronology and DEWEY,J. F., PITMAN,W. C., RYAN, W. B. F. & BONNIN, J. (1973): Plate Tectonics and the Evolution of the AlGeochemistry of Granite Magmatism in Thailand in pine System. - Geol. Soc. Amer. Bull., 84, 3137-3150. Relation to a Plate Tectonic Model. - J. geol. Soc. LonFONTAINE, H., LOVACHALASUPAPORN,S., TIEN, N. D. & don, 136, 529-540. VACHARD,D. (1983) : New data on the Lower CarboniBENDER, F. with contributions by BANNERT,D., BRINCKferous in Thailand. - CCOP Newsletter, 10/1-2, MANN, J., GRAMANN,F. & HELMCKE,D. (1983): Geo13-18. logy of Burma. - Beitr. Reg. Geol., 16, 293 p., BornFONTAINE, H. & WORKMAN,D. R. (1978): Review of the traeger, Berlin. Geology and Mineral Resources of Kampuchea, Laos BUNOPAS, S. & VELLA, P. (1978): Late Paleozoic and Meand Vietnam. - In: NUTALAYA,I3. (Edit.): Proceedings sozoic Structural Evolution of Northern Thailand a of the Third Regional Conference on Geology and MiPlate Tectonic Model. - In: NUTALAYA, P. (Edit.): neral Resources of Southeast Asia, 739-762, Bangkok. Proceedings of the Third Regional Conference on Geology and Mineral Resources of Southeast Asia, Bang- GANSSER, A. (1974): The Ophiolitic M61ange, a worldwide problem on Tethyan Examples. - Eclog. Geol. kok, 133-140. Helv., 67, 479-507 BURRETT, C. & STAIT,B. (1984): South East Asia as a Part of an Early Paleozoic Gondwanaland. - Abstract of Pa- GATINSKY,Y. O. & HUTCHISON, C. S. (1984): Cathaysia, Gondwanaland and the Paleotethys in the Evolution of per of the Fifth Regional Congress on Geology, MineContinental Southeast Asia. - Abstract of Paper of the ral and Energy Resources of Southeast Asia, April, Fifth Regional Congress on Geology, Mineral and 1984, 1 p. Kuala Lumpur. Energy Resources of Southeast Asia, April, 1984, 2 p., CFLENGFA,C. & YUSHENG,P. (1984): A preliminary synKuala Lumpur. thesis of the tectonic evolution of the Qinghai-Xizang GIRARDEAU,J., MARCOUX,J., ALLEGRE,C. J., BASSOUL(Tibet) Plateau. - Reports 27th Intern. Geol. congr., 5, 190-206. LET, J. P., YOUKING, T., XUCHANG, X., YOUGONG, Z. & XIBIN, W. (1984) : Tectonic environment and geoCHI-CHING, H. (T. K. HUANG) (1978): An Outline of the tectonic characteristics of China. - Eclogae geol. Helv., dynamic significance of the Neo-Cimmerian Donqiao ophiolite, Bangong-Nujiang suture zone, Tibet. - Na71, 611-635. ture, 307, 27-31. CHONGLAKMANI, C. (1984): Upper Permian and Lower Triassic Sequence in Amphoe Ngao, Changwat Lam- GUOMING, C., TUNGLIN, H. & ZHIZHI, Z. (1980): Prelipang, Northern Thailand. - Abstract of Paper of the minary analysis of the tectonic framework of Eastern

228

D.

HELMCKE

Yizang (Tibet). -Bull. Chinese Acad. Geol. Sci., Series I, 2, 57-58. HAHN L. (in print): The Indosinian Orogeny in Thailand and Adjacent Areas. - Bull. Soc. Geol. France. HELMCKE, D., KRAIKHONG, C. with a contribution by LINDENBERG, H.-G. (1982): On the GeosynclinaI and Orogenic Evolution of Central and Northeastern Thail a n d . - J. geol. Soc. Thailand, 5, 52-74. & LINDENBERG, H.-G. (1983): New Data on the ,,Indosinian,< Orogeny from Central Thailand. - Geol. Rdsch., 72, 317-328, Stuttgart. (1983) : On the Variscan Evolution of Central Mainland Southeast Asia. - Earth EvoIution Sciences, 4/1982, 309-319. (in print) : The Orogenic Evolution (Permian- Triassic) of Central Thailand. Implications on Paleogeographic Models for Mainland SE-Asia. - Bull. Soc. Geol. France. Hsu, K. J. & BERNOULLI, D. (1978): Genesis of the Tethys and the Mediterranean. - In: Hso, K. J., MONTADERT, L. et al.: Initial Reports of the Deep Sea Drilling Project, 42/1, 943-949. JACKSON, P. (1980): On the Tibetian Plateau. - Nature, 287, 486-487. JAEGER, J. J., ADLOFF, C., DOUBINGER, J., PONS, D., VOZENIN-SERRA, C. & WANG, N. W. (1982): The contribution of fossils to paleogeography of the Lhasa block (Tibet). - E.O.S., 63/45, 1093-1094. JIASONG, F. (1980): The main features of marine Triassic sedimentary facies in Southern China. - Riv. ltal. Paleont., 85, 1125-1146. JIQING, H. (T. K. HUANG) (1984): New researches on the tectonic characteristics of China. - Reports 27th Intern. Geol. Congr., 5, 13-28. JOHNSON, B. D., POWELL, C. McA. & VEEVERS, J. J. (1976): Spreading history of the eastern Indian Ocean and Greater India's northward flight from Antarctica and Australia. - Geol. Soc. Amer. Bull., 87, 1560-1566. LAUBSCHER, H. & BERNOULLI, D. (1977): Mediterranean and Tethys. - In: NAIRN, A. E. M., STEHLI, F. G. & KANES, W, (Edit.): The Ocean Basins and Margins. IV Mediterranean, 1-28. LE THAC XINH (1981): Mineralization of the Continental Rifting Epoch in North Vietnam. - Proceedings, Fourth Regional Conference on the Geology of Southeast Asia, Manila, 633-638. MITCHELL, A. H. G. ( 1981): Phanerozoic plate boundaries in mainland SE Asia, the Himalayas and Tibet. - Jour. Geol. Soc. London, 138, 109-122. - , YOUNG, B. & JANTARANIPA, W.: The Phuket Group, Peninsular Thailand; a Palaeozoic? geosynclinal deposit. - Geol. Mag., 107, 411-428. MOLNAR, P. & TAPPONIER, P. (1975): Cenozoic tectonics o f Asia: Effects of a Continental Collision. - Science, 189, 419-426. MORGUNOV, Y. G. (1970): Basic features of Tectonics of North Vietnam. - Int. Geol. Rev., 12, 1333-1345.

PHAN CU TIEN (1981): The limits of the natural division in the Late Paleozoic in North Vietnam. - Proceedings, Fourth Regional Conference on the Geology of Southeast Asia, Manila, 377-381. REINECK, H.-E. & SINGH, I. B. (1975): Depositional Sedimentary Environments. - Springer, Berlin, 439 p. RIDI), M. F. (1971): Southeast Asia as a part of Gondwanaland. - N a t u r e , 234, 531-533. ~ENGOR, A. M. C. (1979): Mid-Mesozoic closure of Permo-Triassic Tethys and its implications. - Nature, 279, 590-593. SMITH, A. G. (1981): Phanerozoic Equal-Area Maps. Geol. Rdsch., 70, 91-127, Stuttgart. STARITSKIY, Y. G., MAYMIN, Y. S. & TROFIMOV, V. A. (1973): Tectonic development of North Vietnam. - Int. Geol. Rev., 15, 1381-1390. STAUFFER, P. H. (1983): Unraveling the mosaic of Paleozoic crustal blocks in Southeast Asia. - Geol. Rdsch., 72, 1061-1080, Stuttgart. STOCI~LIN, J. (1980): Geology of Nepal and its regional f r a m e . - J. geol. Soc. London, 137, 1-34. (1984): Orogeny and Tethys Evolution in the Middle East an appraisal of current concepts. - Reports 27th Intern. Geol. Congr., 5, 65-84. TAPPONIER, P. et ai. (1981): The Tibetian side of the IndiaEurasia collision. - Nature, 294, 405-410. TOZER, E. T. (1982): Marine Triassic Faunas of North Americas: Their Significance for Assessing Plate and Terrane M o v e m e n t s . - Geol. Rdsch., 71, 1077-1104, Stuttgart. TRUMPY, R. (1982): Das PhSnomen Trias. - Geol. Rdsch., 71, 711-723, Stuttgart. WATERHOUSE, J. B. (1981): Age of the Rat Buri Limestone of Southern Thailand. - In: WATERHOUSE, J. B., P> TAKPAIVAN, K. & MANTAJIT, N.: The Permian Stratigraphy and Palaeontoiogy of Southern Thailand., Geol. Surv. MEN., 4, 1-42. WIELCHOWSKY, C. C. & YOUNG, J. D. (1983): Regional facies variations in Permian rocks of the Phetchabun fold and thrust belt, Thailand. - Abstract from the Conf. on Geol. and Min. Resources of Thailand, November 1983, Bangkok (manuscript in print). WINKEL, R., INGAVAT,R. & HELMCKE, D. (1983): Facies and stratigraphy of the Lower - lower Middle Permian strata of the Petchabun fold-belt in Central Thailand. Proc. Workshop Strat. Corr. Thailand and Malaysia, 1, 293-306. XUCHANG, X. & YANLIN, G. (t984) : Tectonic evolution of the Tethys-Himalayas of China. - Reports 27th Intern. Geol. Congr., 5, 181-189. YI-GANG, W., CHU-CHEN, C., Guo-XIONG, H. & JINHUA, C. (1981): An outline of the marine Triassic in China. - I. U. G. S. Publ., 7, 21 p. ZHANG, Z. M., LIOU. J. G. & COLEMAN, R. G. (1984): An outline of the plate tectonics of China. - Geol. Soc. Amer. Bull., 95, 295-312. ZI-SHUN, L. (1980): The stratigraphic regionalization of the Triassic in China. - Riv. Itai. Paleont., 85, 1147-1156.