provenance of xigaze fore arc basin clastic rocks cretaceous south tibet the xigaze group of south tibet was deposited in a fore arc basin produced by northward subduction of the neotethys under eurasia during middle cretaceous time clasts of andesite from the gangdese magmatic belt to the north and limestone clasts from a shelf rimming the basin to the north are the near exclusive detrital components in the xigaze group in the eastern part of the studied region and in older albian deposits in the west younger cenomanian coniacian deposits from western and central parts of the xigaze group show increasing amounts of tonalite pebbles in conglomerates and quartz sand these trends reflect differential arc uplift and erosional dissection with higher rates in the west some arenites show evidence for sediment contribution from an additional source probably from an orogen to the north of the lhasa block the presence of this orogen indicates that crustal thickening of tibet is not restricted to cenozoic times the middle cretaceous gangdese belt apparently lacked acid volcanic rocks this suggests a low degree of crustal contamination and or differentiation of primitive magma probably because the crust beneath the arc area was thin a thin crust is in accordance with a low elevation of the arc deduced from continuous carbonate production on and marine excursions beyond the arc magma eruption rates of the arc estimated from the xigaze basin sediment volume were probably low 7 5 km 3 km arc segment per million years but within the range of modern arcs the varying sediment compositions of the xigaze group may be typical of fore arc basin deposits in front of continental magmatic arcs the lack of a correlation of trends in sediment composition with fining upward sedimentary supercycles in the xigaze group is taken as evidence in favor of a eustatic cycle control

palaeomagnetic re investigation of early permian rift basalts from the baoshan block sw china constraints on the site of origin of the gondwana derived eastern cimmerian terranes a palaeomagnetic investigation was carried out on a series of rift basalts woniusi formation that accumulated on the baoshan block sw china in the early permian the aim being to provide quantitative palaeogeographical information on the eastern cimmerian terrane as it detached from eastern gondwana reliable data were obtained from four locations 28 individual cooling units and when combined with the findings of an earlier study three locations 19 sites indicate that breakup occurred at 41 9 s with errors 34 2 51 2 s using this information we fit baoshan against gondwana within a narrow longitudinal belt close to where northeast greater india and northwest australia were once in close proximity furthermore we suggest that sibumasu simao burma malyasia sumatra the largest of the eastern cimmerian blocks lay directly to the east offshore of australia qiangtang and lhasa almost certainly sat to the west off northern greater india se arabia but we are uncertain as to their exact configuration our findings are compared with several rather different models that have been published in recent years the new palaeomagnetic constraint highlights the flexibility authors currently have in reconstructing the region principally because of the overall lack of similar high quality data from the various blocks we explain how new data could resolve these ambiguities thereby offering more robust explanations for eastern gondwana s late palaeozoic development

permian brachiopods from the baoshan and simao blocks in western yunnan china this paper describes and illustrates four permian brachiopod assemblages assemblages a d from western yunnan southwest china assemblage a occurs in the basal part of the yongde formation in the xiaoxinzhai section in the southern baoshan block and is assignable to the latest artinskian or earliest kungurian assemblage b occurs about 50 m stratigraphically above assemblage a in the same section and is of chihsian kungurian roadian age assemblage c was collected from the yongde formation in the anpaitian section in the southern baoshan block and is most likely roadian to wordian in age assemblage d came from the longtan formation in the simao block and is of late wuchiapingian in age the brachiopod faunas from the yongde formation of the baoshan block as a whole is dominated by species characteristic of the cathaysian province although some links with peri gondwanan faunas are also evident in contrast assemblage d from the simao block is characterised exclusively by taxa of the cathaysian province new taxa described and illustrated are neochonetes huangichonetes inflatus n sp costatumulus minor n sp and celebetus yunnanensis n sp

paleomagnetic study of the eocene quxu pluton of the gangdese belt crustal deformation along the indus zangbo suture zone in southern tibet abstract forty five samples have been collected at nine sites on the 42 5 ma quxu pluton 90 50 e 29 20 n in the gangdese batholith westerly declination d 48 and 83 is observed in primary magnetizations from two sites about 25 km from the indus zangbo suture zone after thermal demagnetization this direction is consistent with the westerly paleomagnetic directions of the crustal blocks in other areas along the indus zangbo suture zone the quxu pluton of the gangdese belt was rotated in a domino style deformation process as a part of a long 840 km and narrow less than 100 km deformed zone between the india eurasia continents associated with the collision of india since 42 5 ma the pluton between 11 km and 14 km from the suture acquired the secondary magnetization d 28 and 39 during a cataclastic metamorphic process at sometime during the domino style deformation the primary magnetization was completely destroyed in the pluton within 11 km of the suture during slow cooling at the uplift stage and was replaced by thermoviscous remanent magnetization parallel to the present axial dipole field

late palaeozoic corals of tibet xizang and west yunnan southwest china successions and palaeobiogeography abstract a dynamic pattern of coral faunal provincialism in the carboniferous to permian sequence is preserved in tibet west yunnan during the early carboniferous an undifferentiated eurasian province was present containing the kueichouphyllum keyserlingophyllum siphonophyllia and cyathaxonia faunas that reflect major environmental differences relative to previous interpretations during the late carboniferous early permian the indoralian province and the cathaysian province can be distinguished the former is recognised by an absence of late carboniferous asselian corals and by the presence of the sakmarian artinskian cyathaxonia fauna the latter contains the late carboniferous and early permian compound corals nephelophyllum and kepingophyllum as many blocks drifted northward beginning in the late early permian the indoralian province had evolved into two discrete provinces the himalayan and cimmerian provinces the himalayan province as a relic of the indoralian province was in the northern margin of gondwanaland the cimmerian province between the himalayan and the cathaysian provinces consists of the present tectonic blocks lhasa qiangtang tengchong and baoshan in tibet and west yunnan it is characterised by roadian non dissepimental solitary corals and wordian capitanian compound waagenophyllidae as well as some endemic cimmerian taxa such as thomasiphyllum and wentzellophyllum persicum the cathaysian province is dominated by szechuanophyllum and ipciphyllum during the late permian the himalayan province and the cathaysian province can be recognised the former contains only small solitary corals referred to as the lytvolasma fauna and the latter is identified by liangshanophyllum a fasciculate waagenophyllid

magmatism and metamorphism in the lhasa block tibet a geochronological study u pb systematics in small fractions of zircon monazite and sphene 5 to 20 grains each have been analyzed in order to decipher the age and origin of magmatism in the lhasa block and to date the tectono metamorphic events additionally we analyzed a few minerals for rb sr the results show that the granites and an ignimbrite were formed essentially through anatexis of continental crust the magma source regions of which consisted of palaeozoic to precambrian materials up to 2 b y in age the following episodes can be distinguished 1 an early tertiary plutonism volcanism in the southern lhasa block yangbajing region strongly related to intracontinental tectono metamorphism 2 a late jurassic to early cretaceous plutonism in the central and northern lhasa block and 3 a middle jurassic low grade metamorphism affecting the basement at the northern margin 171 6 m y ago the early tertiary magmatism and metamorphism in the south are probably a direct result of tethys subduction indian plate

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

cretaceous palaeomagnetic results from hainan island in south china supporting the extrusion model of southeast asia abstract we report the cretaceous palaeomagnetic results from hainan island south china in hainan island we collected the early cretaceous redbeds of the lumuwan formation at eleven sites we also describe the tectonic kinematics for and around hainan island since the cretaceous deduced from our and previous palaeomagnetic results the palaeolatitude of hainan island is 25 9 n 3 4 3 2 implying that hainan island was situated about 7 north from the present position during the cretaceous the palaeopole of hainan island latitude 77 7 n longitude 162 1 e k 65 6 and a95 4 4 suggests 4 0 5 8 counterclockwise rotation and 14 1 5 5 southward translation relative to the suspected coherent part of the south china block scb since the cretaceous the rotation and translation of similar sense 18 8 7 4 and 7 8 6 9 respectively are detected in the existing palaeomagnetic result from the xinlong formation in guangxi which is situated approximately 400 km north northwest from hainan island the southward translation of both areas seems to have been due to the southeastward extrusion of dissected zones within the southwestern part of the scb in a similar pattern to the indochina block which had resulted from the indentation of india into asia this sw part seems to have slightly rotated counterclockwise because its extrusion was probably smaller in scale than the indochina block and therefore it was dragged out by the indochina block this hypothesis is supported by the existence of a northwest southeast trending fault system parallel to the red river fault

palaeomagnetism of cretaceous to tertiary sediments from southern tibet evidence for the extent of the northern margin of india prior to the collision with eurasia abstract palaeomagnetic studies have been carried out on mid cretaceous to latest palaeocene sediments from the tethyan himalaya on the northern margin of the indian plate near the localities of gamba 28 3 n 88 5 e and duela 28 0 n 89 2 e in southern tibet a total of 61 sites more than 700 cores have been sampled mainly from limestones zongshan formation jidula formation member ii zongpu formation sandstones jidula formation member iii and graywackes gamba group member ii with ages well defined from detailed lithological and biostratigraphic analyses carriers of characteristic remanences are magnetite in limestones and graywackes and hematite in sandstones reliable palaeodirections were obtained from 35 sites 356 specimens positive fold tests antiparallel normal and reverse polarities a northward trend of the palaeolatitudes with decreasing age and absence of any metamorphic overprint indicate a primary origin for the characteristic remanences the results have been compared with expected palaeodirections according to available data for the indian subcontinent based on its present day geometry the late maastrichtian sites fourteen sites 156 specimens and the middle late palaeocene sites fourteen sites 113 specimens yield palaeolatitudes of 5 7 s and 4 0 n for the sampling localities in southern tibet respectively these palaeolatitudes are much further north than expected and imply that crustal shortening between the tethyan himalaya and the indian shield since the time of india eurasia collision has occurred on the order of 1500 km at the longitude of gamba duela comparison of our observed palaeolatitudes with palaeolatitudes for the lhasa block during cretaceous and palaeocene times indicate that initial contact of the northern indian margin with the lhasa block was already established at 65 60 ma with suturing completed at about 55 50 ma

vertical axis block rotations in southwestern china since the cretaceous new paleomagnetic results from hainan island a paleomagnetic study of early cretaceous redbeds from hainan island south china reveals a pre folding remanence from six sites with a mean direction of d 4 3 i 41 8 k 51 5 95 9 4 the results suggest that hainan island may have been rotated 10 counterclockwise about a vertical axis since the early cretaceous this rotation is likely to have occurred during the mid tertiary when large scale left lateral motion occurred along the red river fault as a result of the indentation of the indian plate into eurasia causing extrusion of the indochina block and opening of the south china sea a comparison of early cretaceous paleomagnetic results from south china indicates that local rotations are widespread in the western part of the south china block such rotations have to be taken into account when examining pre cenozoic tectonic kinematics of south china and constructing apparent polar wander path s for the region

magnetostratigraphic investigations on an emeishan basalt section in western guizhou province china abstract a magnetostratigraphic investigation has been conducted on a late permian emeishan basalt section at duge in western guizhou province china the characteristic remanent magnetization chrm directions resolved at high temperatures from the basalts pass the fold test with dual polarity and define a normal magnetozone of five sixths of the total thickness in the lower part and a reversed magnetozone of one sixth of the thickness in the top part of the section the chrm directions from the basalt clasts of pyroclastic rocks fail the conglomerate test but the direction and polarity of the chrm of the clasts from the upper reversed zone are consistent with those of the basaltic lavas in the reversed zone and the normal directions also dominate the chrm of the clasts taken from the lower normal zone this suggests that either the original remanence of the clasts was reset by cementing basaltic lavas or the chrm of the basalts was acquired late but not beyond a field reversal the magnetostratigraphic pattern n r observed at duge is as simple as that observed from some major continental flood basalt provinces in the world where very few magnetic polarity zones were observed from volcanic sequences of great thickness the emplacement of the emeishan basalts in western guizhou is estimated to be less than two million years the normal polarity magnetozone observed indicates that the extrusion of the emeishan basalts in western guizhou postdates the permo carboniferous reversed superchron pcrs the apparent shortness of the reversed magnetozone explains why far fewer reverse directions than normal ones have been so far reported from the emeishan basalts

understanding mesozoic accretion in southeast asia significance of triassic thermotectonism indosinian orogeny in vietnam results from a zircon u pb study of the metamorphic basement of vietnam reveal that a large part of the continental crust was affected by a short lived episode of ductile deformation and high temperature metamorphism between 258 6 ma and 243 5 ma although coincident with final stages of north south china collision qinling orogenesis the thermotectonism in vietnam was caused by accretion of sibumasu to indochina south china this accretion event indosinian orogeny has regional significance because it contributed to the final stages of north south china collision an aspect not explicitly recognized in qinling orogenic models

apparent polar wander paths of the major chinese blocks since the late paleozoic toward restoring the amalgamation history of east eurasia abstract high quality paleomagnetic poles a k a paleopoles are essential for quantitative lithospheric plate reconstruction however the current paleomagnetic database of the major chinese blocks including the north china block ncb the south china block scb and the tarim block tb since the late paleozoic era contain outdated and low quality data here we update the database by adding recently published high quality paleopoles and rejecting low quality outdated ones the database includes 288 paleopoles published 1980 2014 90 of them published after 2000 following the van der voo selection criteria 75 paleopoles each with a quality factor q smaller than 4 were rejected in the first round of selection we then removed another 59 paleopoles that have been locally rotated or shallowed since the acquisition of stable remanence eventually 154 paleopoles were selected and adopted to calculate the new apparent polar wander paths apwps for the major chinese blocks we found comparable clastic and igneous paleopoles at intervals when a quantitative comparison was available as such comparison was not possible during most periods epochs our conclusions reflect an unclear extent of inclination errors in chinese clastic paleopoles new models of the chinese apwps with and without inclination error corrections were computed from carefully selected paleopoles version 1 running mean v1rm paths were calculated at the period epoch level version 2 running mean v2rm paths were computed in a set sliding time window of 20 or 30 myr spline paths were calculated with the same time windows along with a smoothing parameter of 50 using a recent global reconstruction model and up to date geological observations new models of the chinese apwps allowed us to re evaluate the coalescence history of east eurasia since the late paleozoic era four major tectonic events were confirmed 1 the tb accreted with the kazakhstan orocline during amalgamation of the west altaids during the middle late permian period ca 265 250 ma 2 the suturing of the ncb and the scb likely occurred in a scissor like pattern and had been accomplished no later than the middle jurassic period ca 180 160 ma 3 the amalgamation between the ncb and the tb along with the microblocks between the two might have been achieved during the late jurassic early cretaceous periods ca 160 140 ma 4 the mongol okhotsk ocean should have been closed no later than the early cretaceous period ca 140 120 ma

paleohydrological processes in siling co lake in the qing zang tibetan plateau based on the physical properties of its bottom sediments bottom sediments in siling co in central tibet reveal that late in the last glacial period the area around the lake was arid water inflow was small and the level of the lake was low in the early postglacial period it became markedly humid and the water level rose rapidly because of large inflows from surrounding basins the climate was humid and the level of the lake high during the hypsithermal at about 2 000 4 000 yr b p it again became arid within a short time and the water level dropped sharply after this short arid interval and low water level it again became humid and the water inflow increased sharply large inflows continued for a time after which it again began to get arid

position of the lhasa block south tibet during the late cretaceous the latitude of the lhasa block xizang south tibet during the late cretaceous early tertiary is of prime importance for understanding the collision of india and eurasia and the mechanism of the formation of the qinghai xizang plateau during the first field expedition of the french chinese collaboration several geological formations have been sampled in southern tibet between lhasa 29 40 n 91 09 e and dingri 28 35 n 86 38 e we present here the first results obtained for middle cretaceous to palaeocene red beds from the lhasa block north of the yarlung zang bo suture zone recognized as the main suture between the indian and the eurasian plates they indicate a palaeolatitude of the lhasa block of 20 n during the late cretaceous while india was situated 30 s

first report of lower permian basalts in south tibet tholeiitic magmatism during break up and incipient opening of neotethys abstract the neo tethys ocean began to form at early permian times when continental flood basalts were emplaced in various areas of the newly formed indian passive margin exposed today in the so called tibetan sedimentary zone of the himalaya lower permian mafic volcanic rocks which have long been known from various himalayan localities from kashmir to arunachal pradesh are here for the first time reported to occur also in south tibet bhote kosi basalts of the gyirong county the basalts unconformably overlie lowermost permian diamictites with locally intervening black shales and debris flow deposits and are followed in turn by chert bearing quartzarenites and silty to phosphatic marls yielding brachiopods of roadian wordian age the age of the lavas can thus be bracketed as late early permian post sakmarian and pre roadian the geochemistry of these subalkalic tholeiites akin to morbs testifies to their similarity not only with the adjacent nar tsum spilites of central nepal but also with the panjal traps and abor volcanics of the western and eastern himalayas respectively the geochemical signature of lower permian volcanic rocks is in fact uniform all along the himalayan range and markedly different from that of basaltic rhyolitic alkalic products sporadically emplaced during the previous rifting stage rift volcanism in the tethys himalaya began in the early carboniferous and came to an end in sakmarian times in the early permian initial submergence of the rift shoulders and sediment starvation were followed by tholeiitic magmatism which is therefore interpreted as following break up and incipient sea floor spreading in the neotethys ocean roughly contemporaneous emplacement of continental flood basalts of similar geochemical signature along a 2000 km long rift axis would in fact suggest extensive mantle melting at the transition from continental rifting to break up and opening of the neotethys between northern gondwana and the peri gondwanian blocks

new insights into the cenozoic lateral extrusion of crustal blocks on the southeastern edge of tibetan plateau evidence from paleomagnetic results from paleogene sedimentary strata of the baoshan terrane in order to characterize the lateral extrusion of crustal material during the cenozoic we conducted a paleomagnetic study of the eocene oligocene zhushan formation and paleocene muguahe formation in the central part of the baoshan terrane bst on the southeastern edge of tibetan plateau a primary magnetic component and a remagentized component with the miocene acquisition age were isolated from the muguahe formation and zhushan formation respectively these data indicate that the bst did not commence clockwise rotation in the period of the paleocene and the oligocene and that the bst experienced 80 clockwise rotation relative to east asia since the miocene combining with the documented history of crustal boundary strike slip faults on the southeastern edge of the tibetan plateau shows that the bst and tengchong terrane tct firstly underwent latitudinal crustal shortening in the oligocene and the eastward extension was the main type of motion of the crustal material during this period which induced the initial strike slip movement of their boundary faults since the miocene the main form of crustal motion of bst tct and simao terrane was gradually transformed into clockwise rotation which possibly indicates that the fold and thrusting fault systems induced crustal shortening and thickening in the southeastern edge of the tibetan plateau have reached extremity and the southeastern part of the tibetan plateau have already been uplifted to the similar elevation with today s elevation in the miocene

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

paleomagnetic results from the triassic of the yangtze platform two widely separated localities have been sampled from triassic formations of the yangtze platforms the first is from the border area between sichuan and guizhou provinces where the early triassic yelang formation was sampled at 15 sites located on both flanks of an anticline characteristic high temperature components were isolated from nine sites the remainder were severely overprinted by a recent field two polarities are present one directed toward the northeast with shallow positive inclinations and the other to the southwest with almost horizontal inclinations the northeast group passes the fold test at the 95 level the second area of study was from the city of nanjing jiangsu province where 19 sites were drilled from three formations ranging in age from the lower to upper triassic the samples are severely overprinted with a component that is almost vertical and whose origin is unclear however in 23 of the samples a high temperature component was isolated directed to the northeast and positive and to the southwest and negative the fold test is indeterminate the pole positions from the two localities are sichuan

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

late triassic paleomagnetic result from the baoshan terrane west yunnan of china implication for orientation of the east paleotethys suture zone and timing of the sibumasu indochina collision abstract in order to better understand the paleogeographic position of the baoshan terrane in the northernmost part of the sibumasu block during formation of the pangea supercontinent a paleomagnetic study has been conducted on late triassic basaltic lavas from the southern part of the baoshan terrane in the west yunnan region of southwest china following detailed rock magnetic investigations and progressive thermal demagnetization stable characteristic remanent magnetizations chrms were successfully isolated from late triassic niuhetang lava flows the chrms are of dual polarity and pass fold and reversal tests with magnetic carriers dominated by magnetite and subordinate oxidation induced hematite we thus interpret them as a primary remanence this new paleomagnetic result indicates that the baoshan terrane was located at low paleolatitudes of 15 n in the northern hemisphere during late triassic times together with available paleomagnetic data from the baoshan terrane and surrounding areas a wider paleomagnetic comparison supports the view that the east paleotethys ocean separated the sibumasu and indochina blocks and closed no later than late triassic times we argue that the currently approximately north to south directed changning menglian suture zone is very likely to have been oriented nearly east to west at the time of the sibumasu indochina collision

ichnology of a subaqueously prograding clastic wedge late pliocene morne l enfer formation fullarton trinidad implications for recognition of autogenic erosional surfaces and delineation of stress factors on irregular echinoids abstract the morne l enfer formation outcrops near fullarton trinidad expose an erosional surface between the shelf deposits below and a prograding clastic wedge of the late pliocene paleo orinoco system above the surface exhibits similarities as well as dissimilarities with examples of regressive surfaces of marine erosion rsmes in wave influenced shelf settings and also with incised valleys inherited from fluvial incision of shelf during a forced regression episode however detailed ichnological studies reveal that the surface is a subaqueous autogenically controlled erosional surface on a shelf dominated by the hyperpycnal and hypopycnal discharges with transient wave influence integration of ichnological and sedimentological characteristics also suggests complicated interrelationships among different stress factors affecting the infauna in different subenvironments especially the irregular echinoids the delta prograded subaqueously through autogenically establishing its lobe on the open shelf without stratigraphically significant erosional removal of sediments in the subaqueously prograding clastic wedge the fluvial influence pertains high stress conditions not only for the adult infauna but also for their larvae within the water column especially in and near the subaqueous distributary channels

triggers of permo triassic boundary mass extinction in south china the siberian traps or paleo tethys ignimbrite flare up abstract assessment of the synchroneity between the siberian traps and the permo triassic boundary ptb mass extinction has led to the proposition that the siberian flood volcanism was responsible for the severest biotic crisis in the phanerozoic however recent studies suggest that the siberian traps may have postdated the main extinction horizon in this paper we demonstrate using stratigraphy a time and intensity coincidence between ptb volcanic ash and the main extinction horizon geochemistry of the ptb volcanic ashes in five sections in south china indicates that they were derived from continental magmatic arc zircons extracted from the ptb volcanic ashes have negative e hf t 12 9 to 2 0 and 18 o 6 8 to 10 9 consistent with an acidic volcanism and a crustal derived origin and therefore exclude a genetic link between the ptb mass extinction and the siberian traps on the basis of spatial variation in the number of the ptb volcanic ash layers and the thickness of the ash layers in south china we propose that the ptb volcanic ash may be related to paleo tethys continental arc magmatism in the kunlun area ignimbrite flare up related to rapid plate subduction during the final assemblage of the pangea super continent may have generated a volcanic winter which eventually triggered the collapse of ecosystem and ultimately mass extinction at the end of the permian the siberian traps may have been responsible for a greenhouse effect and so have been responsible for both a second pulse of the extinction event and early triassic ecological evolution

the indus tsangpo suture zone in ladakh northwest himalaya further palaeomagnetic data and implications abstract a total of 81 samples 244 specimens from upper cretaceous indus molasse and middle to upper cretaceous dras flyschoids of the indus tsangpo suture zone in ladakh northwest himalaya has been studied by thermal demagnetization methods both formations showed a characteristic magnetization component indicative for equatorial to low northern palaeolatitudes of acquisition similar palaeolatitudes have been obtained before from secondary magnetization components of early tertiary age in the ladakh intrusives and in the tibetan sedimentary series of central nepal the present characteristic components are interpreted likewise as secondary magnetizations which stabilized between 50 and 60 m y ago during greater india s collision with asia s southern margin the dras flyschoids show another magnetic component which in case of primary origin indicates acquisition at a low southern palaeolatitude if correct this interpretation supports recent suggestions for late cretaceous obduction of an island arc on greater india s northern margin

discordance of jurassic paleomagnetic data from south china and their tectonic implications abstract we have collected oriented cores in jurassic redbeds from two areas in southern guangxi province stepwise thermal demagnetization of the samples and subsequent statistical analysis show that the stable magnetization from both areas is a near primary chemical remanence that passes the fold test area 1 lies in a shear zone and is rotated 24 12 counterclockwise and insignificantly displaced 4 12 northward with respect to area 2 which lies outside the shear zone 80 km to the northwest of area 1 after adjusting for a post jurassic tectonic rotation identified in a previous paleomagnetic study the pole for area 2 is indistinguishable from an averaged early to middle jurassic reference pole for the yangtze craton suggesting that this area was joined to the yangtze craton by that time and confirming that considerable clockwise rotation of south china relative to north china remained to be accomplished before the present configuration of the two blocks was attained in combination with geological observations these data support a terrane model based on sinistral shear acting parallel to recognized structural trends in this part of southeast china during post triassic time

a preliminary upper triassic paleomagnetic pole for the khorat plateau thailand consequences for the accretion of indochina against eurasia we report new paleomagnetic results from the upper triassic norian huai hin lat formation at the base of the khorat group in central thailand five sites of conglomerate sandstone and limestone reveal a stable component of magnetization d 43 i 43 95 7 5 we argue that this component is of primary origin on the basis of a positive fold test observation of both normal and reversed directions and a reported magnetostratigraphy from middle triassic to cretaceous the new triassic pole yields together with published younger poles a mesozoic apparent polar wander path for indochina this unit is found to have remained at tropical northern latitudes since the upper triassic comparison with eurasian poles reveals 1650 850 km of sw ne convergence and 15 10 of counterclockwise rotation between 205 and 160 ma two mechanisms are discussed to account for this motion the first one implies the closure of an oceanic basin to the north of the south china block the second one involves post welding intracontinental deformation

possible correlation between a mantle plume and the evolution of paleo tethys jinshajiang ocean evidence from a volcanic rifted margin in the xiaru tuoding area yunnan sw china abstract several paleozoic sutures in southwestern china provide a record of the history of the paleo tethys ocean whose birth and final closure are associated with the breakup and assembly of gondwanaland recent studies indicate that there are widespread oib type mafic volcanic rocks within these suture zones and intervening terranes this paper examines the geology and geochemistry of volcanic rocks in the xiaruo tuoding area a remnant passive margin succession of the jinshajiang paleo tethyan ocean the sedimentary and volcanic stratigraphy of this area is interpreted as a seaward dipping margin with a few continentward dipping normal faults the available geochemistry of these volcanic rocks suggest that they are oib like basalts characterised by sio 2 42 78 50 46 wt high tio 2 contents tio 2 2 2 3 55 wt moderate mgo 4 15 6 49 wt mg 0 37 0 50 high ti y ratios mostly 450 large ion lithosphere elements enrichment high strength field elements and rare earth elements with la nb 1 04 1 39 ce yb 18 38 30 sm yb 2 16 3 52 87 sr 86 sr i 0 705350 0 707867 and nd t 1 43 1 90 these geochemical and isotopic signatures are generally similar to those of the emeishan flood basalts which together with stratigraphic constraints demonstrate that these volcanics were formed in a volcanic rifted margin probably associated with a mantle plume a new model is proposed to interpret the evolution of the jinshajiang paleo tethyan ocean and its possible relationship to the emeishan mantle plume in this model we argue that the opening of the jinshajiang paleo tethyan ocean in the carboniferous was caused by a mantle plume the mantle plume was active to the east along the western margin of the yangtze craton between 300 and 260 ma from which the voluminous emeishan flood basalts were erupted at 260 ma the closure of the jinshajiang ocean occurred since the middle permian continuous westward subduction generated the jiangda weixi magmatic arc to the west of the jinshajiang suture this subduction also partly destroyed and or tectonically sliced the volcanic rifted margin some seaward dipping volcanic sedimentary sequences on the east flank of the jinshajiang ocean were preserved but are strongly deformed

sedimentary history of the tethyan basin in the tibetan himalayas after an epicontinental phase the sedimentary rocks in the tibetan himalayas document a complete wilson cycle of the neo tethyan tethys ill evolution between the gondwana supercontinent and its northward drifting margin lhasa block from the late permian to the eocene during the triassic rift stage the basin was filled with a huge clastic dominated sediment wedge with up to 5 000 m of flysch in the northern zone widespread deltaic clastics and shallow water carbonates of late norian to earliest jurassic age in the southern zone mark in conjunction with decreasing tectonic subsidence the transition to the drift stage some 4 500 m of jurassic and early cretaceous shallow water carbonates and siliciclastics accumulated on the tethyan indian passive margin deepening upward sequences with condensed beds at their tops alternate with repeated progradational packages of shelf sediments extensive abyssal sediments with basaltic volcanics in the northern deep water zone reflect continued ocean spreading and thermal subsidence paleomagnetic data gained separately for the northern indian plate and the lhasa block indicate that the neo tethys reached its maximum width about 110 ma ago with a spreading rate of 4 8 cm year before it commenced to close again during the remnant basin stage in the late cretaceous and paleogene a shallowing upward megasequence capped by a carbonate platform developed in the southern inner shelf realm in the northern slope basin plain zone turbidites and chaotic sediments derived from both the acretionary wedge and the steepening slope of the passive margin accumulated the depositional center of the remnant basin shifted southward as a result of flexural subsidence and southward overthrusting the sediments from the triassic to the paleogene are tentatively subdivided into five mega sequences which are controlled mainly by regional tectonics climatic influence e g carbonate deposition due to northward plate motion is partially subdued by terrigenous input and or increased water depth during the oligocene and miocene crustal shortening led to rapid uplift and the deposition of fluvial molasse in limited basins

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

paleomagnetic results from some permian triassic rocks from southwestern china the ailao shan fault zone in west yunnan represents a suture boundary between south china and indosinian cratons preliminary paleomagnetic results from three sites in sichuan guichou and yunnan provinces reveal a 14 northward migration of south china craton between late permian and middle triassic the two cratons were separated by about 20 latitudes during the early triassic the tectonic setting of east asia during the triassic was probably analogous to the present indonesian region

tectonic evolution of the malay peninsula abstract the malay peninsula is characterised by three north south belts the western central and eastern belts based on distinct differences in stratigraphy structure magmatism geophysical signatures and geological evolution the western belt forms part of the sibumasu terrane derived from the nw australian gondwana margin in the late early permian the central and eastern belts represent the sukhothai arc constructed in the late carboniferous early permian on the margin of the indochina block derived from the gondwana margin in the early devonian this arc was then separated from indochina by back arc spreading in the permian the bentong raub suture zone forms the boundary between the sibumasu terrane western belt and sukhothai arc central and eastern belts and preserves remnants of the devonian permian main palaeo tethys ocean basin destroyed by subduction beneath the indochina block sukhothai arc which produced the permian triassic andesitic volcanism and i type granitoids observed in the central and eastern belts of the malay peninsula the collision between sibumasu and the sukhothai arc began in early triassic times and was completed by the late triassic triassic cherts turbidites and conglomerates of the semanggol formation were deposited in a fore deep basin constructed on the leading edge of sibumasu and the uplifted accretionary complex collisional crustal thickening coupled with slab break off and rising hot asthenosphere produced the main range late triassic earliest jurassic s type granitoids that intrude the western belt and bentong raub suture zone the sukhothai back arc basin opened in the early permian and collapsed and closed in the middle late triassic marine sedimentation ceased in the late triassic in the malay peninsula due to tectonic and isostatic uplift and jurassic cretaceous continental red beds form a cover sequence a significant late cretaceous tectono thermal event affected the peninsula with major faulting granitoid intrusion and re setting of palaeomagnetic signatures

permian of west yunnan southwest china a biostratigraphic synthesis recent progress in the study of permian stratigraphy of western yunnan southwest china is reviewed with particular references to the tengchong and baoshan blocks and the changning menglian belt where confusion or controversy exists in stratigraphical nomenclature and or dating we attempt to clarify the situation based on our recent field observations and newly obtained research results the permian within the changning menglian belt embraces different stratigraphic successions suggesting different tectonic settings ranging from passive margin and active margin to oceanic basin and seamounts permo carboniferous faunas in the carbonate sequences of the changning menglian belt are of typical cathaysian affinity as demonstrated by abundant fusulinaceans and compound rugose corals the permian stratigraphy and faunas of the tenchong and baoshan blocks are markedly different from those of the changning menglian belt the baoshan block lacks upper carboniferous deposits and its subsequent lower permian sequence consists predominantly of siliciclastic strata yielding cool water faunas and possibly glaciogene diamictites overlain by thick basaltic lava and volcaniclastics of probably rift origin the upper part of the permian in the baoshan block is characterized by carbonates containing mixed cathaysian and gondwanan faunas the tengchong block has a similar evolutionary history to the baoshan block but completely lacks volcanic rocks

paleomagnetic study of cretaceous rocks from the yangtze block central yunnan china implications for the india asia collision abstract more than 200 samples for this study were collected at 30 sites from the cretaceous matoushan and puchanghe formations around the city of chuxiong 25 n 101 5 e twenty four sites have characteristic directions with a high temperature component above 350 c paleomagnetic directions from 21 sites of the cretaceous formations reveal clockwise deflection in declination d 44 6 i 41 3 and 95 10 7 the reliability of the direction is ascertained through a positive fold test and the presence of normal and reversed polarities comparison with paleomagnetic data from other areas indicates that the chuxiong area was rotated clockwise through26 17 with respect to the eastern part of the yangtze block whereas it was subjected to more than 44 of clockwise rotation with respect to the neighboring blocks of lhasa 56 21 and western sichuan 44 16 since cretaceous time the clockwise rotation of chuxiong is a reflection of rotational motion of the large region including the southeastern qiangtang terrane and the jinsha suture red river fault paleomagnetic data and tectonic features suggest that the rotation occurred prior to the folding in the central yunnan province probably during the paleogene this large rotation is a spectacular example of the deformation in the southeastern part of the asian continent due to the collision of india

tectonic evaluation of the indochina block during jurassic cretaceous from palaeomagnetic results of mesozoic redbeds in central and southern lao pdr rock magnetic and palaeomagnetic studies were performed on mesozoic redbeds collected from the central and southern laos the northeastern and the eastern parts of the khorat plateau on the indochi

tectonic evolution of the qiangtang block northern tibet during the late cisuralian late early permian evidence from fusuline fossil records abstract the tectonic evolution of the qiangtang block in the qinghai tibetan plateau has been a controversial subject for a long time in this paper the discovery of new stratigraphic and fusuline fossil evidence from the permian sequences qudi and lugu formations of the qiangtang block is reported and the palaeogeographical position and tectonic history of this block during the late cisuralian late early permian are discussed the qudi formation is typified by thick turbidite deposits and contains artinskian fusulines such as pseudofusulina and chalaroschwagerina the fusulines were deposited as grains involved in debris flow deposits suggesting a synchronicity with the depositional time of the turbidites the subsequent lugu formation is dominated by seamount type carbonates with an irregular basalt base fusulines cancellina pseudodoliolina and parafusulina in the base of the carbonates confirm its age as middle kungurian the transition from the turbidite qudi formation to the seamount lugu formation is here interpreted to be a continuous depositional process recording the qiangtang block s separation from the indian plate this separation signaled the opening of the neotethys ocean between the qiangtang block and the indian plate palaeogeographically the qiangtang block s separation is comparable with the baoshan block s separation in the east and central pamir s separation in the west by contrast the ultimate opening of the neotethys ocean by the separation of india pakistan and northern oman is apparently much later than this event recorded in the qiangtang block consequently it is interpreted that the opening of the neotethys ocean in the whole northern gondwanan margin is a diachronous series of events

palaeomagnetic estimates of crustal shortening in the himalayan thrusts and zangbo suture this article reports new palaeomagnetic results from precisely dated late palaeocene limestones from the former northern margin of the indian subcontinent now in tibet between the major himalayan thrusts and the india tibet suture zone convergence in the suture and intracontinental thrusting can be estimated separately and are respectively found to be of the order of 550 km 650 km and 400 km 400 km comparison with kinematic models derived from magnetic anomalies constrains the age of the collision at about 50 myr

paleomagnetic results from the upper permian of the eastern qiangtang terrane of tibet and their tectonic implications abstract paleomagnetic samples were collected from red intercalations within the upper permian tuoba formation from the eastern qiangtang terrane of tibet progressive thermal demagnetization has revealed a prefolding possibly primary characteristic remanent magnetization chrm which yields a tilt corrected mean direction ofd i 25 2 6 7 95 8 6 the equatorial paleolatitude for the qiangtang terrane indicated by this result and the similarity of late permian fauna and flora shared by the qiangtang terrane and south china block scb suggest that the two terranes were in close proximity during the late permian a late permian paleogeographic reconstruction involving the major terranes of the present day east asia is constructed in which the songpan garze sea is surrounded by laurasia the north china block ncb the scb and the qiangtang terrane the permian development of the songpan garze sea appears to be related to the rifting of the qiangtang terrane off the scb its triassic evolution may resemble that of the solomon sea today in the southwestern pacific

stratigraphy of volcanic rocks in the changning menglian belt in southwestern yunnan china abstract the changning menglian belt is regarded as an important geosuture of the paleotethyan ocean in southwest china volcanic rocks occur extensively in this belt and are critical for understanding its tectonic evolution however the lithostratigraphic division age and correlation of these volcanic rocks remain contentious in this paper the sequences in two lithostratigraphic units in the manxin area which include volcanic rocks the pingzhang and huoju formations have been determined this is a key area for interpreting the changning menglian belt using systematic biostratigraphy and information from the recently published 1 50 000 geological map the huoju formation is assigned to the middle permian five sections in the pingzhang formation from different parts of the changning menglian belt are correlated on the basis of their biostratigraphy this correlation suggests that the top of the pingzhang formation becomes progressively younger from visean to early late carboniferous from north to south recent progress on the late permian laochang formation is also reviewed it is concluded that most of the volcanic rocks were formed in seamount oceanic island settings and that the changning menglian belt represents a late devonian to late permian paleotethyan ocean basin

long and complex thermal history of the song chay metamorphic dome northern vietnam by multi system geochronology multi system geochronology was used to unravel the long and complex thermal history of the song chay range northern vietnam a high grade granitic and metamorphic dome in the vicinity of the cenozoic ailao shan red river fault zone it was considered to be proterozoic south china basement but its geological history was basically unknown scattered field observations suggest three episodes of high temperature deformation firstly at the time of granite emplacement secondly a decollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages p t estimates suggest that metamorphism coeval with the second deformation phase culminated at 580 ca nd 4 5 kbar 16 km depth multi system geochronology is applied to a two micas granite sample slightly deformed within the decollement u pb dating of zircon yields an age of 428 5m a 2s interpreted as the time of granite crystallization within the south china caledonian belt rb sr on white micas and biotite yields ages of 206 10 ma and 176 5 3 ma respectively 2s whereas 39ar 40 ar ages of the same minerals are 210 9a nd 190 8m a 2s these ages suggest an upper triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the decollement the k feldspar irregular 39ar 40ar age spectrum can to the first order be explained by a cooling history with two episodes of rapid cooling one at 140 ma and a second around 41 to 25 ma apatite fission tracks central age 33 6 3 6 ma 1s confirms a tertiary rapid cooling event interpreted as the final exhumation of the song chay dome 2000 elsevier science b v all rights reserved

stratigraphy and palaeoenvironmental evolution of the mid to upper palaeozoic succession in northwest peninsular malaysia abstract the stratigraphy of the devonian to permian succession in northwest peninsular malaysia is revised the timah tasoh formation consists of black mudstone containing graptolites and tentaculitids indicating a pragian or earliest emsian age the sanai limestone overlies the timah tasoh formation at sanai hill b and contains conodonts indicating a late devonian frasnian to possibly early famennian age in other places late tournaisian chert of the telaga jatoh formation overlies the timah tasoh formation the overlying kubang pasu formation is predominantly composed of mudstone and sandstone and can be divided into 3 subunits from oldest to youngest 1 chepor member 2 undifferentiated kubang pasu formation 3 uppermost kubang pasu formation the ammonoid praedaraelites tuntungensis sp nov is reported and described from the chepor member of bukit tuntung pauh the genus indicates a late visean age for part of the subunit dropstones and diamictites from the chepor member indicate a glacial marine depositional environment the carbo permian undifferentiated kubang pasu formation consists of similar interbedded mudstone and sandstone the uppermost kubang pasu formation of kungurian age consists of coarsening upward cycles of clastics representing a shallow marine wave and storm influenced shoreline the permian chuping limestone also represents shallow marine wave and storm influenced deposits a mid palaeozoic unconformity separating early late devonian rocks from overlying late devonian carboniferous deposits probably marks initiation of rifting on sibumasu which eventually led to the separation of sibumasu from australian gondwana during the late sakmarian early permian

new cretaceous and early tertiary paleomagnetic results from xining lanzhou basin kunlun and qiangtang blocks china implications on the geodynamic evolution of asia we present the results of a paleomagnetic study of 360 cores drilled at three different areas from the tibetan plateau 13 sites from lower cretaceous red beds in the xining lanzhou basin around xining and lanzhou cities southwest of the qilian mountains 36 2 n 103 5 e 13 sites from cretaceous red beds in the kunlun block near maqin 34 5 n 100 1 and 9 sites from paleocene lower eocene red beds in the qiangtang block near fenghuoshan 34 5 n 92 8 e thermal demagnetization of the samples allowed us to isolate a high temperature component which passes both positive reversal and fold tests for all formations the corresponding paleopoles lie at 50 3 n 195 5 e a95 4 6 for xining lanzhou 80 1 n 281 2 e dp 7 8 dm 12 7 for maqin and 62 6 n 210 5 e dp 3 9 dm 6 8 for fenghuoshan we discuss these in the frame of a new paleogeographic reconstruction of the cretaceous paleoposition of the blocks forming the asian mosaic we conclude that the xining lanzhou area could not be part of the north china block but rather was associated with the tarim qaidam assemblage paleomagnetic data argue in favor of a qaidam kunlun tarim junggar assemblage in the cretaceous significantly to the south of its current position with respect to the asian continent siberia mongolia and north china the large n s convergence 800 500 km implied since the cretaceous appears to be far larger than could be absorbed in the altay range to the north and qilian shan to the east of the order of 300 km part of this motion could have occurred along a large left lateral strike slip fault system which may connect with the mongol okhotsk suture to the northeast verifying this hypothesis will require new geologic and paleomagnetic data from these remote regions

paleomagnetic analysis of eastern tibet implications for the collisional and amalgamation history of the three rivers region sw china abstract a comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the south china simao baoshan shan thai indochina qiangtang lhasa and himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the three rivers region western yunnan the results show that 1 the simao block is a south china derived block 2 the baoshan and shan thai blocks were subjected to rapid northward drift during the period from late carboniferous to late permian 3 the baoshan block collided with the simao block in the late permian and continued to drift rapidly northwards together with the south china and shan thai blocks until the late triassic 4 the paleo tethys separating the baoshan and simao blocks was possibly opened in the early silurian 5 the meso tethys ranged in age from early permian time to early cretaceous time and reached its greatest width of about 42 latitude in the late triassic

paleomagnetic constraints on the mesozoic drift of the lhasa terrane tibet from gondwana to eurasia the mesozoic plate tectonic history of gondwana derived crustal blocks of the tibetan plateau is hotly debated but so far paleomagnetic constraints quantifying their paleolatitude drift history remain sparse here we compile existing data published mainly in chinese literature and provide a new high quality well dated paleomagnetic pole from the ca 180 ma sangri group volcanic rocks of the lhasa terrane that yields a paleolatitude of 3 7 s 3 4 this new pole confirms a trend in the data that suggests that lhasa drifted away from gondwana in late triassic time instead of permian time as widely perceived a total northward drift of 4500 km between ca 220 and ca 130 ma yields an average south north plate motion rate of 5 cm yr our results are consistent with either an indian or an australian provenance of lhasa

cenozoic clockwise rotation of the tengchong block southeastern tibetan plateau a paleomagnetic and geochronologic study abstract paleomagnetic data from 50 35 ma likely 40 ma mafic dykes in yunnan southeastern tibetan plateau cutting 115 ma granitoids record the rotation of the tengchong lhasa block around the east himalayan syntaxis ehs ti rich titanomagnetite and magnetite carry a primary magnetic component group1 a magnetic overprint resides in magnetite group2 likely induced by low grade metamorphism between 30 and 10 ma the tilt corrected overall mean directions are d i 89 8 35 1 for group1 and d i 33 3 41 4 for group2 these data imply a clockwise rotation of 87 87 3 12 5 of the tengchong block since remanence acquisition at 40 ma with respect to stable eurasia the average rotation rate of 2 18 0 31 myr is at the upper limit of the present day rotation rates around the ehs obtained from gps velocities and quaternary strain rates the remagnetized group2 indicates a poorly defined rotation of 31 31 2 32 9 our key results the detection of 87 clockwise rotation with high rotation rates following the india asia collision and a decrease in rotation rates during the miocene suggest that first the tengchong block rotated rapidly around the ehs synchronous with eastward tectonic escape of lithospheric blocks the later slower clockwise rotation similar to those recorded geodetically may be related to viscous flow of tibetan crust

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

permo carboniferous sequences of gondwana affinity in southwest china and their paleogeographic implications abstract in southwest china permo carboniferous depositional sequences of gondwana affinity were first discovered in the himalayan region by the expedition team of acadimia sinica in 1975 by 1983 gondwana affinity permo carboniferous sequences had been identified also in the lhasa block the south qiangtang block in tibet and the tengchong and baoshan blocks in yunnan these sequences are characterised by the presence of successions which are interpreted as glacio marine deposits and by the presence of gondwana affinity biota the distribution of gondwana affinity permo carboniferous indicates that basins whose remnants are now represented by the yarlung zangbo suture and the bangong nujiang suture did not exist at that time and the vast area south of the lungmu shuanghu jinshajiang zone in tibet and west of the changning menglian belt in yunnan formed a part of the northern margin of gondwana

paleomagnetism of cretaceous to lower tertiary rocks from southwestern sichuan a revisit abstract a re study has been carried out on the cretaceous to lower tertiary rocks from southwestern sichuan province on the south china block the characteristics remanent magnetization chrm resolved from the paleocene eocene leidashu formation is of dual polarity and very shallow inclination the anomalouslylow paleolatitude 6 9 6 3 n indicated by the inclination is not supported by geological evidence from this region and is probably due to inclination error related to depositional and or post depositional processes a positive fold test as well as the prevalence of normal polarity suggests that the chrm of the mid upper cretaceous xiaoba formation might be acquired during the cretaceous long normal superchron clns the tilt corrected mean direction of the xiaoba formation d i 8 1 38 8 95 6 6 n 18 sites is not significantly different from a preliminary result d i 357 6 31 6 95 8 6 n 12 samples we reported earlier for the collective xiaoba and leidashu formations the resultant paleopole 81 5 n 220 9 e a95 7 1 is coincident with other cretaceous poles for the chinese blocks comparison with the eurasian apparent polar wander path apwp indicates neither significant rotation nor latitudinal translation of the study area relative to eurasia the newly obtained mean direction for the xiaoba formation is believed to be more reliable than our earlier result since it is based on a larger sample size and is apparently free from effects of the shallow inclination observed in the leidashu formation and should supercede our previous preliminary result the paleopole derived from sevenentes of the lower cretaceous feitianshan formation 69 0 n 204 6 e a95 4 3 deviates from the track from the late jurassic to late cretaceous poles the deviation might be reduced by further sampling

paleogeographic and tectonic evolution of southern tibet since middle cretaceous time new paleomagnetic data and synthesis during the second french chinese paleomagnetic campaign in tibet in the summer of 1981 we sampled the middle cretaceous red beds of the takena formation and the cenozoic volcanics of the lingzizong formation a detailed analysis of about 400 specimens of red beds reveals a stable component of normal magnetization n in the north of the lhasa block north of the nyainqentanglha range and two stable components in the south lt ht where the red beds are more strongly folded and are unconformably overlain by the lingzizong volcanics all three components are carried by hematite blocking temperatures range from 400 to 600 c for lt and up to the neel temperature of hematite for both n and ht lt is shown to postdate part of the folding of the takena whereas n and ht both indicate a positive fold test at the 99 probability level in addition a small less than 10 of the natural remanent magnetization antiparallel component is superimposed in most samples and may be consistent with a model of long term acquisition of a chemical remanent magnetization for the red beds analysis of the volcanics reveals a single stable component with mixed polarities carried either by hematite or magnetite the paleomagnetic directions indicate that 1 the lhasa block stood at 12 5 3 n by upper cretaceous and at 13 5 6 5 n in the paleocene eocene thus confirming the limited displacement of the margin of eurasia between albian aptian deposition of the red beds and eocene onset of the india asia collision these values imply crustal shortening by as much as 1900 850 km north of the block since the upper cretaceous and by 1400 1200 km south of the block since the onset of the collision 2 southern tibet formed a single tectonic unit by middle cretaceous time and 3 differential rotations are observed within the block and are related to the collision these rotations are discussed in the frame of a recent propagating extrusion tectonics model this study confirms the close paleogeographic relationship between indochina khorat plateau and southern tibet prior to the india asia collision

tertiary paleomagnetism of north and south china and a reappraisal of late mesozoic paleomagnetic data from eurasia implications for the cenozoic tectonic history of asia abstract to contribute to the understanding of the cenozoic tectonic history of china and eastern eurasia in general we collected paleomagnetic samples from tertiary rocks in both north and south china our miocene paleomagnetic data for northern china are from four widely separated basalt sections in the inner mongolia autonomous region and shandong province both normal and reversed polarities of the characteristic magnetization are present in the stratigraphie sequence and the mean normal and reversed directions are closely antiparallel to each other the fact that the same characteristic direction was carried by both magnetite and hematite suggests that the hematite was probably formed by auto oxidation processes during primary cooling of the basalts the paleomagnetic data from these four areas also pass a regional generalized fold test the corresponding mean miocene paleomagnetic pole for northern china is longitude 261 6 e latitude 88 3 n a 95 6 4 our early tertiary paleomagnetic results for south china are from two sandstone sections around the city of nanning 22 7 n 108 3 e in guangxi zhuang autonomous region high temperature characteristic directions isolated in 31 samples from five sites pass both tilt and reversal tests the paleomagnetic pole position determined from the five sites lies at longitude 228 0 e latitude 83 6 n a 95 8 5 the tertiary paleomagnetic poles for north and south china are statistically indistinguishable from each other and thus confirm that north and south china were fully assembled at least by the tertiary our new tertiary paleomagnetic data are consistent with the hypothesis that the major continental blocks of north and south china were in the same position as today during the tertiary a critical evaluation and selection of paleomagnetic results from the late jurassic onward for siberia europe and north and south china further corroborate this hypothesis most previously existing jurassic and cretaceous paleomagnetic poles from europe siberia are of uncertain reliability and should not be used for tectonic reconstruction using poles derived from transferring reliable data from other continents we show that the previous paleomagnetic inferences of large eastward displacements between these chinese blocks during the cenozoic are no longer warranted the available paleomagnetic data that meet our acceptance criteria are also of interest concerning the boundary conditions of the propagating extrusion model for asian tectonics additional mesozoic and cenozoic paleomagnetic data from siberia and north and south china are still needed to resolve the smaller second order displacements that appear to characterize the cenozoic tectonic history of this part of asia

the zedong window a record of superposed tertiary convergence in southeastern tibet determining the timing magnitude and location of deformation due to the indo asian collision is widely acknowledged as an important step in understanding how the lithosphere responds during continental collision a puzzling result of geological investigations of the lhasa block over the past 2 decades has been the apparent lack of significant tertiary deformation there perhaps the most important structural feature of the lhasa block is the south directed gangdese thrust system which developed along its southern edge the thrust system which separates the andean type batholith of southern asia from rocks of indian affinity is obscured at most locations across southeastern tibet by back thrusts of the younger north directed renbu zedong thrust system the best documented site where both thrusts are exposed occurs near zedong zedong window systematic geochronologic analyses were conducted in this area u pb zircon dating of three samples of a synkinematically to postkinematically deformed hanging wall granitoid the yaja granodiorite cut by the gangdese thrust indicates a crystallization age of 30 4 0 4 ma 2 thus placing an upper bound on the initiation of the thrust u pb zircon dating of granitoid samples structurally higher in the gangdese hanging wall yields emplacement ages of 42 5 1 0 ma and 48 9 0 8 ma 2 similar to other magmatic complexes within the gangdese arc geochemical results are consistent with these plutons forming in the same environment as precollisional intrusions within the gangdese batholith suggesting a significant post collisional input of juvenile heat the 40ar 39ar thermochronology of samples from a vertical section through the hanging wall within the yaja granodiorite coupled with results of a numerical thermal model indicate an average slip rate along the gangdese thrust of 7 mm yr between 30 and 23 ma and a minimum displacement of 50 km farther east in the zedong window thermal effects produced by later north directed thrust sheets of the renbu zedong system appear to have obscured thermal history signatures in the gangdese hanging wall related to earlier south directed thrusting thermochronological results from this region indicate that thermal overprinting related to the north directed thrusting occurred between 25 and 10 ma consistent with previous estimates

cretaceous and tertiary paleomagnetic results from southeast china and their tectonic implications abstract we report cretaceous and tertiary paleomagnetic data from fujian guangxi and guangdong provinces in south china in guangxi province we sampled early cretaceous redbeds of the xinlong formation at eight localities separated by up to 100 km the high temperature component obtained by thermal demagnetization is of dual polarity and passes the fold test and implies 18 8 counterclockwise rotation and insignificant poleward displacement with respect to cratonic localities in sichuan province a tertiary basin lying in a southeast trending fault zone is also rotated counterclockwise by 40 8 both results can be explained very well by a simple block rotation model for the cenozoic tectonic evolution of western guangxi province that is driven by left lateral shear on southeast trending faults the timing and sense of shear are the same as for india asia collision models involving the extrusion of indochina along the red river fault zone which lies several hundred kilometers to the southwest but the magnitude of fault displacement in guangxi is much less in the coastal provinces of fujian and guangdong we find late cretaceous directions that are rotated clockwise with respect to sichuan province combined with similar clockwise rotations found by two other studies of coeval rocks from the same region the mean rotation for the coastal provinces is 12 8 this could indicate a coherent block rotation of the region driven by extrusion tectonics however the limited number of sampling localities also allows the possibility that the directions reflect local rotations due to dextral shearing driven by circum pacific tectonics

magnetic fabric and paleomagnetism of the middle triassic siliciclastic rocks from the nanpanjiang basin south china implications for sediment provenance and tectonic process a combined magnetic fabric and paleomagnetic study has been carried out on the siliciclastic rocks gathered from a stratigraphic cross section through the nanpanjiang basin south china in an attempt to extract the paleoflow information preserved in and thus constrain the possible origins of these clastic rocks the sediments used for this study were formed by sediment gravity flows along the southern margin of the south china block in the middle triassic time ca 245 228 ma the results show a normal distribution of both low field magnetic susceptibility values and natural remanent magnetization intensities which along with the monotonic detrital framework mode mainly comprising quartz and lithic particles may suggest a single provenance involved in deposition of these clastic deposits anisotropy of magnetic susceptibility ams analysis acquires primarily the sedimentary magnetic fabrics which in this study reveal paleoflow directions ranging from nnw to ene with an overall mean orientation of ne demagnetization on a part of samples isolates a characteristic remanent component averaged at d 44 8 degrees i 16 9 degrees k 9 7 alpha 95 6 5 degrees n 55 corresponding to a paleolatitude n8 6 degrees and a clockwise rotation of ca 45 degrees since the middle triassic for the studied cross section this mean direction passes fold tests and is consistent with the reference direction expected from the south china block at the 95 confidence level restoring this similar to 45 degrees declination renders an overall northward paleoflow which combined with other evidence suggests a southern provenance for these sediments during deposition in the middle triassic time in terms of the early mesozoic plate framework of southeastern asia a tectonic scenario is proposed here whereby the nearly n s convergence of the indochina and south china blocks and its related indosinian orogeny in the middle triassic caused the formation of the nanpanjiang foreland basin which was filled by voluminous detritus shed from the uplifted orogenic belt on its southern side c 2013 elsevier ltd all rights reserved

the jinshajiang ailaoshan suture zone china tectonostratigraphy age and evolution abstract the jinshajiang suture zone is important for enhancing our understanding of the evolution of the paleo tethys and its age tectonic setting and relationship to the ailaoshan suture zone have long been controversial based on integrated tectonic biostratigraphic chemostratigraphic and isotope geochronological studies four tectono stratigraphic units can be recognized in the jinshajiang suture zone the eaqing complex the jinshajiang ophiolitic melange the gajinxueshan group and the zhongxinrong group isotope geochronology indicates that the redefined eaqing complex composed of high grade metamorphic rocks might represent the metamorphic basement of the jinshajiang area or a remnant micro continental fragment eaqing complex protolith rocks are pre devonian and probably of early middle proterozoic age and are correlated with those of the ailaoshan complex two zircon u pb ages of 340 3 and 294 3 ma separately dated from the shusong and xuitui plagiogranites within the ophiolitic assemblage indicate that the jinshajiang oceanic lithosphere formed in latest devonian to earliest carboniferous times the oceanic lithosphere was formed in association with the opening and spreading of the jinshajiang oceanic basin and was contiguous and equivalent to the ailaoshan oceanic lithosphere preserved in the shuanggou ophiolitic melange in the ailaoshan suture zone the latter yielded a u pb age of 362 41 ma from plagiogranite the re defined gajinxueshan and zhongxinrong groups are dated as carboniferous to permian and latest permian to middle triassic respectively on the basis of fossils and u pb dating of basic volcanic interbeds the gajinxueshan group formed in bathyal slope to neritic shelf environments and the zhongxinrong group as bathyal to abyssal turbidites in the jinshajiang ailaoshan back arc basin latest permian earliest middle triassic synorogenic granitoids with ages of 238 18 and 227 5 255 8 ma respectively and an upper triassic overlap molasse sequence indicate a middle triassic age for the jinshajiang ailaoshan suture formed by collision of the changdu simao block with south china

internal deformation of the shan thai block inferred from paleomagnetism of jurassic sedimentary rocks in northern thailand abstract paleomagnetic samples of red sandstones were collected at 16 sites from the lower to upper jurassic phu kradung formation and the upper jurassic phra wihan formation around nan city 19 2 n 101 0 e in the southern region of the shan thai block after stepwise thermal demagnetization a high temperature component with an unblocking temperature of about 680 c is isolated from 11 sites we interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95 confidence level the tilt corrected mean paleomagnetic direction from 11 sites is d 32 3 i 33 3 95 12 2 k 15 0 which gives a paleomagnetic pole for this area of 60 1 n 186 5 e with a95 11 7 compared with a jurassic paleopole for the stable part of the yangtze block we observe a clockwise tectonic rotation of 12 8 which is similar to the observed rotation 18 28 of the northern region of the shan thai block this amount contrasts with a large rotation of more than 45 that is estimated from the narrow zone extending from luxi to mengla in the central region of this block this declination aspect suggests that a coherent whole block rotation by about 20 of the shan thai block took place in an earlier phase during indentation of india into asia and that an internal deformation with additional local rotation between 25 and 77 followed within a limited zone in the central part the internal deformation of the shan thai block absorbed the stress on the asian continent induced by indentation of india as well as its coherent whole block motions of clockwise rotation and southward displacement

a comprehensive upb smnd rbsr and 40ar39ar geochronological study on guidong granodiorite southeast china records of multiple tectonothermal events in a single pluton a complicated tectonothermal history of the guidong granodiorite from the huanan fold belt has been revealed by using combined dating techniques u pb single zircon and whole rock nd model ages suggest that the granodiorite was derived from an ancient crustal source which was probably composed of a mixture of 1 2 2 4 ga crustal materials with a nd model age of 1 6 ga the granodiorite emplacement age of 427 3 ma is defined by concordant u pb single zircon analysis plagioclase biotite hornblende apatite sphene and whole rock yield an internal sm nd isochron age of 428 12 ma consistent within the analytical errors with the u pb zircon age due to the presence of inherited zircon however the zircon data point deviates from the sm nd isochron four whole rocks and two mineral separates plagioclase and hornblende yield a rb sr isochron age of 422 14 ma which is coincident with zircon u pb and sm nd isochron ages hornblende 40ar 39ar step heating analysis gives a main plateau age of 371 4 1 3 ma which is considerably younger than the crystallization age this age is interpreted as recording a post crystallization folding event which produced the prominent unconformity between pre devonian and middle devonian strata and resulted in the deformation of all major minerals of the granodiorite since most deformed minerals have remained closed to sm nd and rb sr isotopic migration since emplacement of the granodiorite it can be suggested that this folding event took place without significant fluid circulation and contemporaneous metamorphism a low temperature heating step of hornblende yields an apparent 40ar 39ar age of 208 5 2 0 ma which may or may not have a connection to the minimum age of the huanan indosinian orogeny a biotite 40ar 39ar age spectrum yields much younger apparent ages of 145 and 92 ma which are coincident with two important yanshanian magmatic episodes

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

new mesozoic apparent polar wander path for south china tectonic consequences a new paleomagnetic study in the south sichuan basin south china block has been carried out on sediments of early triassic to middle jurassic age detailed stepwise thermal and alternating field demagnetizations allowed us to isolate two to three components a low temperature component component a falls close to the local present earth field direction a middle temperature component component b is found both in limestone and red beds of early triassic age in limestones of middle triassic age and finally in red beds of jurassic age the component b directions failed the fold test but show a significant increase of the ks kg ratio at 60 when a progressive stepwise unfolding is applied the directions obtained at 60 unfolding are grouped best and yield a pole position at 76 5 n 174 1 e a95 3 7 that is close to the late cretaceous pole of the south china block scb or the early tertiary pole of the eurasian plate characteristic directions are finally obtained component c for early triassic and early to middle jurassic sediments only both with reversal and fold tests they yield pole positions at 44 1 n and 217 2 e a95 4 9 and 79 n and 227 e a95 4 5 respectively the early triassic result well fits other data of the same age from the scb the revised late permian to cretaceous paleopole data provide a new mesozoic apparent polar wander path for south china the successive pole positions from late permian to early triassic indicate motion of the south china block as a whole rather than local rotations linked to important strain within the block the early to middle jurassic pole is statistically indistinguishable from the compiled north china block ncb poles and indicates that final suturation between the two blocks occurred by the end of the triassic which is coherent with the age of ultra high pressure metamorphism in the dabie sulu areas of eastern china the asian plate including the mongol central asian block ncb and scb however was probably separated from siberia by the mongol okhotsk ocean during jurassic time

tectonic deformation of the southwestern part of the yangtze craton inferred from paleomagnetism abstract upper cretaceous red sandstones have been sampled at 21 sites from the jiangdihe formation in yuanmou 25 9 n 101 7 e the northern part of yunnan china characteristic directions with unblocking temperature of 680 c have been isolated from all the sites and provide a positive fold test which is significant at the 99 probability level remanent magnetization of the prefolding origin represents a characteristic direction of the jiangdihe formation d 26 9 i 35 6 and 95 3 6 this paleomagnetic direction confirms the fairly large easterly declination of the cretaceous time for the southern part of the yangtze craton incorporating this result into previous data from the areas along the longitude of 102 e in the southwestern part of yangtze craton the declination value in the cretaceous paleomagnetic direction monotonously decreases from 45 to 2 as latitude increases from 25 0 to 30 1 n the tectonic rotation expected from the apparent polar wander path of eurasia shows that the clockwise rotation decreases gradually from 30 to 10 whilst increasing in latitude the systematically differential rotation along the longitude in the southwestern part of the yangtze craton is a part of the deformation mode of the asian continent due to the collision with india the yangtze craton behaved as a unit continuum material with a ductile nature during deformation

syn subduction crustal shortening produced a magmatic flare up in middle sanjiang orogenic belt southeastern tibet plateau evidence from geochronology geochemistry and structural geology abstract the permo triassic jomda weixi yunxian continental margin arc belt in the southeastern tibetan plateau was formed by the subduction of the main paleotethyan branch underneath the cathaysian affinity blocks along the longmu co shuanghu changning menglian suture this belt consists of three segments with distinctive magmatism history available geochronological data revealed that the northern and southern segments of this belt comprise several volcanic successions intercalated with terrestrial clastics suggesting long lived and pulsed magmatism in contrast the middle segment is made of a single volcanic pile of dacite rhyolite and minor basalt with thickness of 1 6 km numerous granodiorite batholiths and a few diabase dykes intruded the volcanic pile detailed zircon u pb dating indicates that the volcanic rocks and intrusive rocks were formed during a short time period of 7 million years 244 251 ma defining a magmatic flare up petrographic and geochemical data including sr nd isotopics demonstrate that the felsic magmas were derived from ancient crust while the basalt and diabase are sourced from the mantle wedge induced by subduction of the paleo tethys structural studies reveal syn subduction crustal shortening and thickening of the middle segment the thickened crust likely has prevented the subduction induced basaltic magma from eruption they alternatively were accumulated in the bottom of the crust yielding a magma chamber the chamber heated softened and melted the crust forming felsic magmas when the crust was weakened to a critical threshold the felsic magmas rose up and erupted to the surface resulting in the magmatic flare up this study suggests that syn subduction shortening and thickening of the overriding crust seems to have played a significant role in the development of magmatic flare ups along a continental margin arc system other well studied examples include the mesozoic serra nevada and the late miocene to holocene altiplano puna plateau central andes

the changning menglian suture zone a segment of the major cathaysian gondwana divide in southeast asia abstract in southwest china the major cathaysian gondwana divide the palaeo tethyan suture is very well delineated by a narrow north south zone of oceanic siliceous sedimentary rocks and dismembered ophiolite complexes including probable remains of reef capped oceanic islands the location of this zone the changning menglian suture is not well appreciated in the english language literature probably because of the failure to recognise the approximately 600 400 km simao terrane which lies to the east of the suture many analyses mistakenly include the simao element in the sibumasu terrane thus placing a terrane of distinct cathaysian affinities on the gondwana side of the major palaeogeographic divide a measure of the size and time span of palaeo tethys is contained in the changning menglian suture zone sedimentary rocks deep marine cherts are dated between early devonian and middle permian and limestones interpreted as caps to seamounts extend the age range of the ocean to late permian these data agree with recent views of cathaysian elements rifting from gondwana in the silurian or devonian followed by a major rifting event on the north gondwana margin early in the permian subduction created an active continental margin on the western edge of the simao terrane throughout much of the triassic and the closure of this branch of palaeo tethys is marked by the cessation of this activity in the early late triassic

paleomagnetic results from cretaceous and jurassic rocks of south and southwest yunnan evidence for large clockwise rotations in the indochina and shan thai malay terranes abstract cretaceous and jurassic redbeds have been sampled from south and southwest yunnan china for paleomagnetic study the paleomagnetic directions resolved from the cretaceous rocks indicate that the xiaguan area which is located on the red river fault has not been rotated with respect to stable eurasia since at least late cretaceous times and that the jinggu mengla area 200 400 km farther south has been rotated by 46 65 clockwise the jurassic results reveal the same rotation pattern at face value the differences between the observed cretaceous paleolatitudes and those predicted from the eurasian apparent polar wander path apwp indicate a southward extrusion of the region but the amount of extrusion is not large enough to be resolved by paleomagnetic methods comparison with mesozoic paleomagnetic data from central yunnan northern thailand and northwestern borneo suggests that the red river fault is not a demarcation between unrotated and significantly rotated regions and that sundaland did not respond to the india asia collision as a single coherent unit the existing paleomagnetic data from east asia appear to indicate that the crust in central tibet and tien shan north of tarim directly in front of the indian indentor has been substantially shortened and thickened whereas the crust in the syntaxial areas has probably been largely squeezed out to further evaluate the relative importance of crustal thickening and extrusion in the tectonic evolution of the tibetan plateau paleomagnetic investigation should be intensified in the bounding zones to the indian indentor and be expanded into the cenozoic sedimentary rocks in tibet and surrounding regions

paleomagnetism of upper cretaceous rocks from south china paleomagnetic study of upper cretaceous redbeds from two areas in south china was undertaken in an effort to constrain better the history of tectonic movements in southeastern asia from the nanjing area 32 n l19 e high temperature characteristic directions which pass a fold test were obtained from ten sites 43 samples in the upper cretaceous puko and yanzijing formations the paleomagnetic pole position 76 3 n 172 6 e a95 10 3 agrees well with a late cretaceous reference pole for eurasia and thus confirms that this part of south china was fully sutured to eurasia by the end of the cretaceous with no paleomagnetically resolvable subsequent relative rotation in western sichuan 26 5 n 102 3 e high temperature characteristic directions of normal and reverse polarity were obtained from twelve samples 48 specimens in the upper cretaceous to lower paleocene xiaoba and leidashu formations a provisional paleomagnetic pole position 80 9 n 296 8 e a95 7 7 differs significantly from a late cretaceous eurasia reference pole in terms of apparent tectonic movement the difference in paleopole positions would indicate a 13 10 3 northward translation and 22 11 2 counterclockwise rotation of western sichuan relative to eurasia confirmation of this reconnaisance result which would suggest that western sichuan was pushed ahead of an impinging india is needed

devonian paleomagnetism of yunnan province across the shan thai south china suture a paleomagnetic study of devonian sedimentary sequences from western and eastern yunnan china yields contrasting paleolatitudes for these two areas they indicate an equatorial position for eastern yunnan as part of the yangtze paraplatform or south china block and a paleolatitude of about 40 for western yunnan as part of the shan state or shan thai block which probably was part of the gondwana supercontinent the majority of samples is strongly overprinted by a present day field magnetization but thermal demagnetization has been successful in isolating ancient dual polarity characteristic directions of magnetization in rocks from eastern and western yunnan with results from the latter passing the fold test the paleopole from eastern yunnan is located at 8 9 n 10 4 e declination inclination 279 2 2 7 k 13 alpha 95 6 9 n 33 samples from 7 sites the paleopole from western yunnan is located at 66 5 n 133 8 e declination inclination 18 0 62 0 k 21 alpha 95 5 8 n 31 samples from 7 sites yielding a paleolatitude of 42 the two blocks studied are separated by the red yuan river and lancang mekong river fault zones one of which is inferred to be an ancient suture

paleomagnetic results from the silurian of the yangtze paraplatform gpdyke n d huang k xu g zhang w y and kent d v 1987 paleomagnetic results from the silurian of the yangtze paraplatform in d v kent and m km editors laurasian paleoma etism and tectonics teetonophysics 139 123 132 samples have been collected from sites from three localities located in sichuan and in yunnan provinces the samples were taken from limestones and red siltstones covering most of the silurian of the south china block the results from the limestone sites were disappointing and all the sites that yielded successful results were from red siltstones characteristic high temperature components were successfully isolated from fifteen of these sites the sites from xiushan county sichuan 28 48o n 108 99 0 e successfully pass the fold test at the 99 level indicating that the magnetization was acquired before folding in the mesozoic the direction obtained from this locality is directed toward the east with shallow positive inclinations d 85 6 o i 12 1 cuss 5 33 the results obtained from a single red bed locality from qijiang county sichuan 28 58 n 106 85 e yield a similar direction the results from the upper silurian of yunnan 25 5 n 103 73o e were obtained from only two sites and the isolated directions were towards the west with shallow inclinations this direction is opposed to the characteristic directions obtained from sichuan and are interpreted as a reversed silurian direction the paleomagnetic pole position determined from all sites given equal weight n 15 falls at 4 9 n lat 194 7 e long with ass 5 61 o

paleomagnetic results from the upper carboniferous of the shan thai malay block of western yunnan china the upper carboniferous basaltic woniusi formation was sampled at 21 sites from two limbs of a syncline near baoshan city 25 2 n 99 3 e and from a monocline near yongde county 23 9 n 99 2 e for paleomagnetic study the study area is generally thought to be part of the shan thai malay microplate thermal demagnetization reveals a single polarity characteristic remanent magnetization chrm which is carried by both magnetite and hematite with the former being the dominant mineral in basalt and the latter being the principal carrier in associated tuffaceous basalt and sandstone the tilt corrected formation mean from baoshan d 209 2 i 61 0 95 6 7 confirms the results reported by previous workers and a positive fold test constrains the chrm acquisition to be prefolding the paleomagnetic inclinations determined from this study are similar to that derived from the devonian rocks from the same area by other workers indicating a paleolatitude of about 42 for the baoshan area during the devono carboniferous time the paleomagnetic declinations however present a large difference between the two sampling localities for the upper carboniferous as well as between the sampling sites for the devonian and for the upper carboniferous the paleo declination difference can be partly explained by the apparent polar wander of gondwana if the shan thai malay microplate was rigidly attached to gondwanaland during this time interval the large part of it has to be ascribed to tectonic rotations between the sampling sites this fact suggests that extreme caution should be exerted when trying to establish an apparent polar wander path for and to reconstruct the paleo geographic position of the shan thai malay microplate

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

fragmentation of asia in the permian asia is a composite continent formed by the accretion of crustal blocks1 3 a likely sequence of events is that siberia collided with a kazakhstan block which together then collided with europe along the urals in permo triassic times2 this was followed by the sucessive accretion of various blocks of south and east asia to siberia culminating in the collision of india with asia during the cenozoic palaeomagnetic data have already demonstrated that the kolyma and sikhote alin blocks of eastern asia collided with the main continent along the late mesozoic fold belts of verkhoyansk and sikhote alin4 furthermore results from the malay peninsula5 and japan6 suggest that south east asia and japan were situated near the equator in permian times and were therefore separated from the asian continent we report here some palaeomagnetic results from the permian of the sino korean and yangtze blocks of china that show they were also situated near the equator were not in their present relationship to one another and were widely separated from siberia

tectonics and paleomagnetic rotation pattern of yunnan 24 n 25 n china gaoligong fault shear versus megablock drift

paleomagnetic study of western tibet deformation of a narrow zone along the indus zangbo suture between india and asia abstract more than 150 oriented samples were collected along the kaxigal lhasa road in the southwestern part of the tibetan plateau to determine the deformation aspect of the tibetan region from a paleomagnetic point of view the counter clockwise deflection about 60 in declination was revealed at four localities in the narrow zone along the indus zangbo suture zone a north to northeast direction d 9 to 30 was observed at four localities more than 14 km from the suture zone in the western tibetan region significant tectonic deformation has occurred exclusively in a narrow zone whose width is about 40 km spanning the suture zone the crustal blocks of this narrow zone were rotated in a compressive regime accompanied by left lateral shear during the collision of the indo eurasia continents the deformation of the narrow zone behaves as a buffer zone in a tectonically gigantic dimension where the tangential stress is mainly absorbed

age and origin of the tanghu granite southeast china results from u pb single zircon and nd isotopes u pb single zircon and sm nd whole rock isotopic data for the tanghu granite of the zhuguangshan batholith suggest that a basement either composed of or derived from middle proterozoic to late archean rocks underlies southeast china the granite contains two kinds of inherited zircon components whole anhedral zircons and small cores within younger magmatic zircons the u pb data for a single analysis of four magmatic zircons yielded a concordant age of 433 2 ma whereas single zircons yielded two linear arrays with lower intercepts of 435 1 and 434 14 ma and upper intercepts of 1415 3 and 2516 6 ma respectively xenocrystic zircons of archean age had not previously been recognized in any rocks from southeast china two whole rock samples from the granite yielded nd values of 7 1 and 8 3 at 434 ma and nd model ages of 1750 ma relative to a depleted mantle we conclude from this isotope data that the tanghu granite crystallized at 434 1 6 ma weighted average and was derived from a source of unknown age but had an average crustal residence age of 1750 ma and was partially composed of a mixture of continental crustal material of at least two ages 1400 and 2500 ma

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

a long lived indian ocean slab deep dip reversal induced by the african llsvp a slab like high seismic velocity anomaly referred as seis has been inferred beneath the central southern indian ocean in a recent tomographic inversion although subduction has previously been suggested regionally by surface observations the new inversion is consistent with a north dipping slab extending from the upper mantle to the core mantle boundary cmb we propose that seis anomaly originated from an oceanic plate in the paleo tethys that was consumed by a south dipping intra oceanic subduction zone during the triassic and jurassic periods seis challenges traditional concepts of the dynamics of slab descent by its relatively shallow depths and a present day polarity opposite to the geometry of subduction geodynamic models show the upwelling mantle flow exerted by a thermochemical pile can hold and stagnate the descending seis slab at shallow depths for more than 100 myr the spatial distribution of resistance from the upwelling mantle flow can reverse the slab dip producing a structure consistent with seismic inversions as well as with our proposed tectonic scenario and geology constraining the tethyan tectonic domain the results suggest that slabs can descend through the lower mantle at rates substantially lower than 1 cm yr and even reverse their polarity through interactions with background mantle flow

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace

estimation of shortening between the siberian and indian plates since the early cretaceous abstract a comparative study of the amount of latitudinal shift of the siberian plate the lhasa block the himalayan block and the indian plate using palaeomagnetic data shows that the himalayan block belongs to the indian plate the neo tethys ocean which separated the himalayan and lhasa blocks opened to its greatest width of 31 9 in latitude in the early cretaceous the extent of shortening of the latitudinal distance between the siberian and indian plates amounts to 58 2 since the early cretaceous it was found that after the determination of the greatest width of neo tethys ocean the latitudinal shortening of the crust between the indian and siberian plates reached 26 3 or about 2760 km on the basis of the palaeomagnetic data obtained from the qaidam block the latitudinal shortening between the himalayan and qaidam blocks reached 50 2 since the early cretaceous it was concluded that over the past 50 ma since the early cretaceous the latitudinal shift of the southern blocks or plates was larger than that of the northern ones and that shortening between the qaidam and himalayan blocks was greater than the shortening between the qaidam block and the siberian plate this differential latitudinal movement is the main cause of convergence resulting in the compression and uplift of the qinghai tibetan plateau