longriba fault zone in eastern tibet an important tectonic boundary marking the westernmost edge of the yangtze block global positioning system gps measurements across eastern tibet reveal a sharp velocity gradient zone located about 150 km west of the longmen shan frontal thrust zone where eastward block motion of tibet decreases from 12 mm yr to 3 mm yr over a distance of less than 10 km in order to investigate the tectonic cause for this rapid change in gps velocity together with systematic review on the available geological and geophysical data in easternmost tibet we provide new constraints on the tectonic feature of the longriba fault zone from advanced land observing satellite phased array type l band synthetic aperture radar data we propose that the ne striking longriba fault zone is the key structure responsible for the observed sharp gradient in gps velocities in addition the evidence indicates that the longriba fault zone instead of the longmen shan fault zone marks the westernmost edge of the yangtze crustal block given the irregular western margin of the yangtze block the longriba fault zone represents part of the actual tectonic boundary between the songpan ganzi terrane and the yangtze block the newly identified western edge of the yangtze block implies a paleocontinent ocean boundary at depth this boundary was a potential weak zone and may have been exploited during the formation of the longriba fault zone the results of this paper should advance our understanding of the tectonic relationship between the songpan ganzi terrane and yangtze block and provide additional constraints for studies of the geodynamic response of eastern tibet to the ongoing india eurasia collision

structural and geochronological constraints on the early mesozoic north longmen shan thrust belt foreland fold thrust propagation of the sw qinling orogenic belt northeastern tibetan plateau

proximal provenance of the western songpan ganzi turbidite complex late triassic eastern tibetan plateau implications for the tectonic amalgamation of china abstract the late triassic songpan ganzi turbidite complex on the eastern tibetan plateau which covers an area of 2 2 10 5 km 2 is one of the largest flysch turbiditic basins on earth it is juxtaposed with major chinese continental blocks across several outstanding tethyan sutures and is critical to elucidating the tectonic amalgamation of china however the provenance of the turbidites remains the subject of intense debate detrital modes and heavy mineral spectra of sandstone samples from three turbidite profiles in the western songpan ganzi complex were determined in an attempt to elucidate their provenance and the type of tectonic setting in which they were deposited upper triassic turbidites in the western songpan ganzi complex have an overwhelming derivation from an orogen source as shown by the average framework compositions of the sandstones q 57 f 21 l 22 qm 52 f 21 lt 27 qp 23 lvm 0 lsm 77 the compositional and textural immaturity of the sandstones suggests limited transport and nearby sources both light and heavy mineral and lithic fractions indicate dominant metamorphic source rocks and subordinate ophiolitic and sedimentary source rocks the occurrence of c type garnet omphacite rutile and si rutile and the high silica content of phengites reveal that the source rocks underwent ultrahigh pressure conditions therefore we advocate that the western songpan ganzi late triassic turbidites were derived from nearby central qiangtang triassic collisional orogen sources rather than distant dabie qinling sources eroded after north china south china collision as previously proposed the analogy of the songpan ganzi turbidites to the bengal indus fans is not favored the central qiangtang metamorphic belt is unlikely to have occurred as an early mesozoic melange underthrust from the jinsa suture and is more likely to have been an in situ triassic ultrahigh pressure orogen our provenance interpretation implies that the paleotethys represented by the present jinsa and kunlun sutures was not yet closed when central qiangtang was being exhumed to supply the sediments of the songpan ganzi basin this challenges the conventional model for sequential amalgamation of china during the phanerozoic

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

granulites in the tongbai area qinling belt china geochemistry petrology single zircon geochronology and implications for the tectonic evolution of eastern asia the tongbai area of the eastern qinling belt in china includes granulite grade metamorphic assemblages qinling complex which were previously regarded as archean to early proterozoic in age and belonging to the southern margin of the north china plate craton our petrological and geochemical data characterize these rocks as two pyroxene granulites and garnet granulites which formed at temperatures of 757 840 c and pressures of about 9 5 kbar and are now found as xenoliths in granodioritic gneisses the protoliths of these rocks were granodiorites and tholeiitic basalt or gabbro the 207pb 206pb ratios derived from evaporation of single zircons yield ages of 470 20 and 470 14 ma respectively for the basic granulites which we interpret to reflect the time of protolith emplacement these are intruded by a 435 14 ma granodioritic gneiss post dating granulite formation a metaquartzite sample contains detrital zircons as old as 2555 8 ma two samples of granitoid gneiss from the tongbai complex s of the qinling granulites have single zircon 207pb 206pb evaporation ages of 776 8 and 746 10 ma respectively and document late proterozoic igneous activity we suggest that the qinling granulites document an important and hitherto unknown phase of early silurian crustal thickening following subduction and continental collision and that both the qinling and tongbai complexes were part of the southern margin of the north china craton prior to this event and record late proterozoic igneous activity

detrital zircon reference for the north china block abstract u pb analyses of 250 single detrital zircons from upper proterozoic to ordovician strata collected from the zhuozi shan in north central china provide a detrital zircon reference for the north china block a major crustal entity in the asian tectonic collage the results which range in age from 1 72 to 2 97 ga shed new light on the age of the crystalline basement in north china much of which is covered by younger sedimentary units in addition this detrital zircon reference can be used to help determine the provenance of clastic sedimentary units and for assessing validity of paleogeographic and regional tectonic models that include the complex history of asian continental amalgamation terrane accretion and subsequent translation that is ongoing today

nd and pb isotope variability in the indus river system implications for sediment provenance and crustal heterogeneity in the western himalaya abstract the indus river system is the only major drainage system in the western himalaya and erodes not only the high himalaya but also topographically high regions within and north of the indus suture zone most notably the karakoram ion microprobe analysis of pb isotopes in detrital k feldspar grains taken from the tributaries of the indus together with bulk nd isotope analysis of those same sediments is here used to identify distinct sediment source regions these span the very radiogenic nanga parbat and associated lesser himalaya the relatively radiogenic intermediate high himalaya the unradiogenic ladakh and kohistan batholiths and intermediate values in the hindu kush karakoram and lhasa block the range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis k feldspars from the ladakh and kohistan batholiths are less radiogenic than the laterally equivalent gangdese granite of tibet interpreted to reflect the preferential recycling of accreted oceanic arc units within the western transhimalaya prior to india asia collision similarly the zanskar high himalaya are less radiogenic than their equivalents in nepal isotope values from pleistocene indus fan sediment are compatible with a dominant source in the karakoram with additional important contributions from the arc batholiths and high himalaya reflecting both the area and modern rates of tectonic uplift within the drainage basin in contrast radiogenic grains are common in the lower reaches of the modern indus river possibly as a result of the damming of the main river channel where it reaches the foreland

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

north and south china collision along the eastern and southern north china margins abstract lithofacies distribution and petrography and intracontinental deformation in the north china block ncb and the south china block scb show an active continental margin flanked by the eastern ncb and a passive continental margin was present along the west side of the scb both margins initially trending n ne the tanlu fault possibly initiated as part of the subduction zone during paleozoic time along the eastern margin on the ncb the ncb and the scb were divided along the eastern southern north china margin by the qinling dabie tanlu sulu imjingang yanji zone from southwest to northeast these two continental blocks made contact first in the northeast during late early permian time finally in the southeast at late triassic time and the clockwise collision probably lasted to middle jurassic time the eastern suture the yanji imjingang sulu tanlu zone was dominated by contractional deformation the southern suture the qinling dabie zone was a transpression belt dominated by right lateral strike slip

detrital zircon provenance of the late triassic songpan ganzi complex sedimentary record of collision of the north and south china blocks the majority of the songpan ganzi triassic flysch sequence is believed to have derived from denudation of the dabie and sulu ultrahigh pressure uhp metamorphic belt in eastern china e g nie et al 1994 1 zhou and graham 1996 2 however intense debate still exists on the sources of

discovery of middle late devonian and early permian magmatic events in east asia and their implication for the indosinian orogeny in south china insights from the sedimentary record

the delimitation between the mature and juvenile crustal provinces in se asia insights from detrital zircon u pb and hf isotopic data for the salween drainage myanmar abstract to understand the geological control and tectonic forcing on the development of a major river system in se asia new detrital zircon u pb and hf isotopic data from the salween drainage myanmar is reported three samples with a range of deposition ages corresponding to different tectonic periods of the sibumasu terrane reveal a dramatic change in the drainage system differing from the detrital compositions of modern sediments from the salween river mouth a late triassic sandstone sample shows zircon age distribution implying that the salween drainage may have been connected at that time to the northeastern part of the songpan ganzi terrane and western part of the south china block u pb ages and hf t isotopic data of detrital zircons from other major rivers in se asia including the yangtze red and mekong rivers in the east and the irrawaddy river and the yalu tsangpo in the west are further synthesized a marked discrepancy in zircons younger than jurassic ages is identified similar to results from the salween samples these young zircons from the eastern rivers are overwhelmed by an old recycled crustal component exhibiting negative hf t values in contrast those from the western rivers are dominated by juvenile components that are characterized by high and positive hf t values the salween drainage therefore lies in the frontier with its western outline broadly depicting the boundary between mature and juvenile crustal provinces in se asia

large southward motion and clockwise rotation of indochina throughout the mesozoic paleomagnetic and detrital zircon u pb geochronological constraints abstract we report a combined paleomagnetic and u pb geochronologic study of sedimentary rocks from the huai hin lat and nam phong formations of mesozoic age in ne thailand in order to provide independent constraints on the tectonic movement of the indochina block during convergence of the major blocks now comprising east asia the maximum allowable depositional age of the two formations is estimated to be 227 ma and 215 ma respectively from detrital zircon u pb geochronologic analysis which also indicates a sediment source transition in the khorat plateau basin during the middle late jurassic a formation mean paleomagnetic direction of d g i g 21 4 38 1 k g 19 5 95 9 6 before and d s i s 43 0 48 0 k s 47 4 95 6 1 n 13 after tilt correction is derived from samples with different lithologies bedding attitudes magnetic carriers and polarities and yields a positive fold test hence the magnetization is likely primary the revised mesozoic apwp of the indochina block yields paleolatitudes for a reference site of 22 n 102 e of 33 4 7 2 n during the norian late triassic 25 9 5 9 n during the late triassic to early jurassic 23 9 8 n during the late jurassic to early cretaceous 27 5 3 2 n during the early cretaceous and 24 5 4 9 n by the late cretaceous corresponding declinations are 45 2 8 6 38 0 6 6 36 3 8 8 29 6 3 6 and 24 9 5 4 respectively these data indicate a significantly southward displacement accompanied by clockwise rotation during the mesozoic a reconstruction of the indochina block within the now well studied merging process of south china and north china indicates that the indochina block was located at a higher latitude than the south china block during the norian stage of late triassic times whilst no significant relative poleward displacement apparently occurred during the early jurassic to early cretaceous interval our study supports a post cretaceous tectonic extrusion model with a southeastward displacement of indochina with respect to the south china block estimated to be 1000 850 km since the late cretaceous

eclogites from central qiangtang northern tibet china and tectonic implications abstract eclogites in central qiangtang northern tibet china are characterized by the garnet omphacite rutile phengite quartz assemblage hornblende plagioclase and sphene occur as retrograde amphibolite facies phases in the eclogites pressure temperature estimates for the primary eclogite assemblage are consistent with minimum pressures of 20 25 kbar at 482 to 625 c the retrograde amphibolite facies assemblage suggests conditions of 10 12 kbar and 460 600 c consequently the eclogites from central qiangtang have undergone unambiguous ultrahigh pressure uhp metamorphism the presence of uhp metamorphic rocks implies a likely deep seated continental subduction along the shuanghu suture within the qiangtang terrain the denudation of these uhp metamorphic rocks correlates well with the main interval that the songpan ganzi turbidites accumulated and could have provided a significant source for these sedimentary rocks

environmental signal propagation in sedimentary systems across timescales abstract earth surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales the geomorphic and stratigraphic products of this source to sink sediment transfer record signals of external environmental forcings as well as internal or autogenic dynamics of the sedimentary system here we evaluate environmental signal propagation across sediment routing systems with emphasis on sediment supply qs as the carrier of up system forcings we review experimental numerical and natural examples of source to sink sediment routing and signal propagation during three timescales 1 historic which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries 2 centuries to several millions of years referred to as intermediate timescale and 3 deep time we discuss issues related to autogenic dynamics of sediment transport transient storage and release that can introduce noise lags and or completely mask signals of external environmental forcings we provide a set of conceptual and practical tools for evaluating sediment supply within a source to sink context which can inform interpretations of signals from the sedimentary record these tools include stratigraphic and sediment routing system characterization sediment budgets geochronology detrital mineral analysis e g thermochronology comparative analog approaches and modeling techniques to measure calculate or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment routing systems

assessing effective provenance methods for fluvial sediment in the south china sea sediment is delivered by the rivers of se asia to the south china sea where it provides an archive of continental environmental conditions since the eocene interpreting this archive is complicated because sediment may be derived from a number of unique sources and the rivers themselves have experienced headwater capture that also affects their composition a number of methods exist to constrain provenance but not all work well in this area anthropogenic impacts most notably agriculture mean that the modern rivers contain more weathered materials than they did up until about 3000 years ago the rivers have also changed their bulk chemistry and clay mineralogy in response to climate change so that these proxies as well as sr isotopes are generally unreliable provenance indicators nd isotopes resolve influx from luzon but many other sources in se asia have similar values and clear resolution of end members can be difficult instead thermochronology methods are best suited especially apatite fission track which shows more diversity in the sources than either u pb zircon or ar ar muscovite dating nonetheless even fission track is best used as part of a multiproxy approach if a robust quantitative budget is desired

exhumation of the dabie shan ultra high pressure rocks and accumulation of the songpan ganzi flysch sequence central china the presence of coesite and diamond bearing ultra high pressure uhp metamorphic rocks in the dabie and sulu regions central china suggests that a 100 km thick crustal section 4 x 106 km6 in volume has been denuded this volume is comparable to that represented by the 10 15 km thick middle to upper triassic flysch rocks in the songpan ganzi region regional geology and radiometric dates are compatible with an interpretation that the majority of these sedimentary rocks were derived from denudation of the orogenic belt between north and south china blocks following their latest paleozoic to triassic collision this correlation implies a high denudation rate of 4 mm yr that may have been in part promoted by tropical precipitation and extreme topographic relief for as long as 25 m y

u pb dating on single detrital zircon grains from the triassic songpan ganze flysch central china provenance and tectonic correlations the songpan ganze flysch belt central china covers a huge triangular area of more than 200 000 km and is bounded by the continental blocks of south china north china and the tibetan plateau detrital zircons extracted from three flysch samples collected in the central part of the belt were analyzed grain by grain using the u pb method two samples of middle triassic sandstones collected at different locations in the belt provide identical results which suggests similar source regions the detrital zircons yield a wide range of ages and indicate their principal derivation from mid proterozoic 1 8 2 0 ga source rocks with minor contribution from late archean ca 2 5 2 6 ga material the discordance and pb loss patterns from low u zircons indicate disturbances during a subsequent event which may be of caledonian age as suggested by concordant zircon grains at ca 420 and 450 ma one sample collected within the palang shan pass zone provides concordant zircon grains at around 230 ma 231 1 ma and 233 1 ma these triassic ages are synchronous to flysch deposition and suggest intense geological activity calc alkaline volcanism at that time in the area close to the basin the data support an origin of the clastic material mainly from a northeastern landmass corresponding to the southern margin of the sino korean craton to a lesser degree inputs from the yangtze craton and possibly from the northern margin of the basin kunlun arc are also detected the age spectrum from the upper triassic sandstone is significantly different and shows predominance of sinian ca 760 ma grains probably derived from the yangtze craton this change in the source region is interpreted as reflecting the tectonic evolution of this area and in particular as being linked to the late triassic collision between south china and north china in the middle triassic while subduction of the songpan sea northward beneath the north china plate was still taking place continental subduction of south china in the dabie region was responsible for uplift of the overriding plate i e the sino korean craton which supplied large volumes of sediments during the late triassic clockwise rotation of the south china block uplifted the indo sinian part of the qinling belt and closed the basin as the accretionary wedge was thickening along the southern margin of north china detritus derived from this source region were unable to reach the flysch basin the age spectrum presented by detrital zircons indicates

multiple sources of the upper triassic flysch in the eastern himalaya orogen tibet china implications to palaeogeography and palaeotectonic evolution abstract the upper triassic flysch langjiexue group tentatively named the shannan terrane of the eastern himalaya orogen has been tectonically assigned either to the tethys himalaya or the yarlung zangbo suture zone yzsz in this work geochronology of detrital zircon u pb isotope shows that the shannan terrane is characterized by the population of 260 200 ma peak ca 240 ma strongly supporting the view of no affinity to the tethys himalaya the detrital zircons dated as 400 290 ma display relatively positive ehf t values of 5 0 to 15 0 with t dm c ages of 2 6 1 3 ga for the shannan terrane whereas highly negative are of 20 0 to 5 0 for the lhasa terrane indicating that the two terranes have different devonian carboniferous sources numerous cr spinels found in the shannan terrane but not in the lhasa terrane exhibit contents in cr 2 o 3 and cr of mainly 44 100 and 48 95 in tio 2 of 0 01 1 0 and in al 2 o 3 of 5 257 respectively denoting several parent lithologies these differences suggested that the shannan terrane has multiple sources not only from the lhasa terrane but also from oceanic island arc seamount and mid ocean ridge areas as well as likely from greater india and australia considering the early cretaceous diabase dykes within the upper triassic flysch defined to the comei bunbury large igneous province we propose that the langjiexue group could have been deposited on the ocean between india and australia and would have not stopped till the lhasa terrane was separated from australia during the terminal triassic according to the cenozoic deformation and metamorphic history and palaeogeography of the langjiexue group we postulate that the shannan terrane could have been loaded onto the greater india during the middle early cretaceous and subsequently drifted northward to the collision zone of india and asia implying that it does not represent an accretionary prism within the yzsz

controls on hydrocarbon accumulation by facies and fluid potential in large scale lacustrine petroliferous basins in compressional settings a case study of the mesozoic ordos basin china abstract large scale lacustrine basins in compressional settings are an important type of petroliferous basin and the study of the characteristics of hydrocarbon accumulation in such basins is of great significance this synthesis paper takes the mesozoic ordos basin central china as a case study to establish lateral and vertical hydrocarbon accumulation patterns in this basin type and highlights how facies and fluid potential control hydrocarbon accumulation in such basins based on systematic analyses of the mesozoic source rocks sedimentary facies migration and accumulation patterns and characteristics of the oil reservoirs the hydrocarbon accumulation characteristics in the mesozoic ordos basin are discussed the analysis indicates that sedimentary facies controlled the characteristics and distribution of hydrocarbon source rocks and reservoirs while diagenetic facies controlled the quality and distribution of the reservoirs excess pressure and fluid potential controlled hydrocarbon migration directions and paths whereas facies and potential controlled the locations of oil accumulations and traps it is concluded that source rocks controlled oil bearing regions sedimentary facies controlled oil bearing plays and fluid potential controlled the locations of accumulations for shallow intervals because fluid migration is mainly controlled by buoyancy paleotopographic highs played an important role in controlling hydrocarbon accumulations for deep layers chang 7 to chang 10 members since buoyancy is less than the capillary pressure excess pressure caused by the undercompaction of mudstone and hydrocarbon generation at depth provides the driving force for lateral and vertical migration of oil and becomes the main migration force the reservoir accumulation characteristics differ laterally between regions of the basin at the periphery of the basin reservoir units are stacked in a step wise manner whereas at the center of the basin multiple reservoir intervals are vertically stacked in the form of multistorey accumulations vertically layers with different burial depths have different accumulation characteristics the paleotopography controlled hydrocarbon accumulation in shallow intervals instead excess pressure fluid potential and paleotopography controlled accumulation in deep intervals this understanding could be used to inform prospecting in other large scale lacustrine petroliferous basins in compressional settings such as the eocene green river basin in the u s a and the middle triassic gunnedah basin in australia

was late triassic tanggula granitoid central tibet western china a product of melting of underthrust songpan ganzi flysch sediments geochronological laser ablation inductively coupled plasma mass spectrometry la icp ms mineral chemistry major and trace element and sr nd hf isotopic data are presented for the tanggula granitoid the largest granitic pluton in the northern tibetan plateau the tanggula pluton yields a late triassic emplacement age 228 223 ma and is magnesian mg 29 10 49 81 high k calc alkaline k2o na2o 0 76 3 51 mostly 1 and strongly peraluminous molar al2o3 cao na2o k2o a cnk 1 06 1 42 mostly 1 1 high initial 87sr 86sr ratios 0 716849 to 0 730577 and low nd t 10 95 to 9 60 and hf t values 16 to 5 1 along with an abundance of aluminosilicate minerals e g biotite enrichments in light rare earth and large ion lithophile elements negative eu anomalies and depletion in high field strength elements suggest that the tanggula granitoid is an s type granite derived mainly from the anatexis of metasedimentary source rocks geochemical fingerprinting using sr nd hf isotopes and detrital zircon u pb age spectra shows that triassic flysch sediments from the songpan ganzi paleo tethyan ocean to the north of the pluton are the most likely source of the tanggula granitic magmas the tanggula granitoid could thus have been formed by the partial melting of the flysch sediments from the songpan ganzi complex as they were underthrust beneath the qiangtang terrane along the jinsha subduction zone during the late triassic

detrital zircon u pb ages of paleogene deposits in the southwestern sichuan foreland basin china constraints on basin mountain evolution along the southeastern margin of the tibetan plateau

signatures of mountain building detrital zircon u pb ages from northeastern tibet although detrital zircon has proven to be a powerful tool for determining provenance past work has focused primarily on delimiting regional source terranes here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance and we demonstrate its ability to detect source changes for terranes separated by only a few tens of kilometers for such an analysis to succeed for a given mountain discrete intrarange source terranes must have unique u pb zircon age signatures and sediments eroded from the range must have well defi ned depositional ages here we use 1400 single grain u pb zircon ages from northeastern tibet to identify and analyze an area that satisfi es these conditions this analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete punctuated changes in local source terranes by tracking eroding rock units chronologically through the stratigraphic record this sensitivity permits the detection of the differential rock uplift and progressive erosion that began ca 8 ma in the laji shan a 10 25 km wide range in northeastern tibet with a unique u pb age signature

detrital zircon provenance comparison between the paleocene eocene nangqian xialaxiu and gongjue basins new insights for cenozoic paleogeographic evolution of the eastern tibetan plateau abstract paleogeographic reconstructions of terranes can greatly benefit from the provenance analysis of sediments a series of cenozoic basins provide key sedimentary archives for investigating the growth of the tibetan plateau yet the provenance of the sediments in these basins has never been constrained robustly here we report sedimentary petrological and detrital zircon geochronological data from the paleocene eocene nangqian xialaxiu and gongjue basins sandstone detrital modes and zircon morphology suggest that the samples collected in these two basins were sourced from recycled orogen detrital zircon geochronology indicates that sediments in the nangqian xialaxiu basin are characterized by two distinct age populations at 220 280 ma and 405 445 ma in contrast three predominant age populations of 207 256 ma 423 445 ma and 1851 1868 ma and two subordinate age populations of 50 ma and 2500 ma are recognized in the gongjue basin comparison with detrital zircon ages from the surrounding terranes suggests that sediments in the nangqian xialaxiu basin come from the neighboring thrust belts whereas sediments from the gongjue basin are predominantly derived from the distant songpan ganzi terrane with minor contribution from the surrounding areas a three stage cenozoic evolution of the eastern tibetan plateau is proposed during the paleocene the nangqian xialaxiu basin appeared as a set of small intermontane sub basins and received plentiful sediments from the neighboring mountain belts during the eocene the gongjue basin kept a relatively low altitude and was a depression at the edge of a proto plateau since the oligocene the tibetan plateau further uplifted and the marginal gongjue basin was involved in the tibetan interior orogeny indicating the eastward propagation of the tibetan plateau

mesozoic source rocks and petroleum systems of the northeastern qaidam basin northwest china the qaidam basin is a continental petroliferous basin located in northwest china its northern sector is an important hydrocarbon province where one of the earliest oil discoveries in china was made although mesozoic source rocks are understood to be important parts of qaidam petroleum systems the identification and distribution of mesozoic source rocks in the subsurface are poorly understood middle jurassic coal measures and associated shales have long been considered to be the primary mesozoic source rocks for the northeastern qaidam basin without any support from subsurface geochemical and geological data however new data have been gathered from earlier mesozoic sediments that were penetrated by the lengke 1 well a deep scientific well with a total depth of 5200 m 17 060 ft the well was drilled on the lenghu structural belt in 1997 and documented other effective source rocks geochemical analyses indicate that lower jurassic mudstones are good to excellent source rocks for the commercial oil wells in the lenghu area the upper middle jurassic shales are very good source rocks for the commercial oil wells in the yuka area two source rock intervals in the northeastern qaidam basin allow for two petroleum systems to be distinguished the lower jurassic lower jurassic tertiary and middle jurassic upper jurassic the lower jurassic lower jurassic tertiary petroleum system with a geographical extent of 15 000 km2 5800 mi2 and a cumulative amount of source rocks between 200 and 700 m 650 and 2300 ft represents a favorable target for future exploration the middle jurassic upper jurassic petroleum system however may have a lower exploration potential because of a smaller area 1500 km2 580 mi2 and a thinner cumulative amount of source rocks 100 200 m 330 650 ft

insights into the early tibetan plateau from u th he thermochronology the central songpan ganzi belt located on the eastern margin of the tibetan plateau has a similar high elevation and low relief to parts of central tibet thermochronological studies from the central tibetan plateau reveal a history of slow exhumation rates 1 since 45ma however the exhumation history of the central songpan ganzi belt is unknown to address this we conducted an apatite and zircon u th he thermochronology study of bedrock samples collected across the central songpan ganzi belt and into central parts of the tibetan plateau zircon u th he ages range from 54 2 7 5 to 146 5 10 0ma and the majority of apatite u th he ages fall between 74 7 19 0 and 35 7 9 4ma thermal history models of these data show rapid cooling in the late mesozoic and much slower cooling diagnostic of low rates of erosion throughout most of the cenozoic the late mesozoic rapid cooling is consistent with the existence of significant topography and relief at least in some parts of the songpan ganzi belt at that time we find no evidence for a regional miocene acceleration in erosion although three samples from the headwaters of the salween and mekong rivers gave younger ahe ages between 15 and 16ma that reflect an acceleration in river incision supplementary material laser ablation inductively coupled plasma mass spectrometry zircon u pb data from central and eastern tibet are available at www geolsoc org uk sup18647

early mesozoic magmatism within the tibetan plateau implications for the paleo tethyan tectonic evolution and continental amalgamation

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

numerical investigation of the geodynamic mechanism for the late jurassic deformation of the ordos block and surrounding orogenic belts abstract orogenic belts have developed along the edges of the stable ordos block in northern china three main geodynamic models have been proposed to explain the formation of these orogenic belts they have included the collision between the north china and south china blocks subduction of the pacific plate and stresses transmitted over long distances from the closure of the mongolia okhotsk ocean however these explanations are still controversial and not universally accepted leaving the mechanisms that formed the orogenic belts poorly understood to address these fundamental questions we developed a 3d numerical model using the finite element method to explore the geodynamic mechanism for the late jurassic deformation of the ordos block and its surrounding orogenic belts we investigated the effect of different dynamic regimes on the late jurassic deformation of this region our primary results suggest that strong and stable ordos block remains undeformed despite its location at the center of a region of deformation east west trending fold and thrust belts would have developed along the north and south edges of the ordos block during the closure of the mongolia okhotsk ocean or the collision between the north china and south china blocks north south trending fold and thrust belts would have developed along the east and west edges of the ordos block due to subduction of the pacific plate however the paleo stress field in the late jurassic indicates that the orientations of the maximum compressive principle stress were nearly perpendicular to the edge of the ordos block and the compressive deformation around it was coeval it is difficult to explain the distribution of belts of deformation with a single stress regime our numerical model reveals that multi direction convergence pattern with time during the transformation of these three regimes can be used to interpret the formation and deformation styles of ringed mountains around the ordos block during the late jurassic this proposed mechanism results in many insights into the mesozoic tectonic deformation and mountain building of this region

formation of the jinchuan ultramafic intrusion and the world s third largest ni cu sulfide deposit associated with the 825 ma south china mantle plume we report here shrimp u pb geochronological geochemical and nd isotopic data for the jinchuan ultramafic intrusion gansu province china which hosts the world s third largest magmatic ni cu sulfide deposits u pb baddeleyite analyses yield an age of 812 26 ma for the ultramafic intrusion this age is indistinguishable within analytical uncertainties from the u pb zircon ages of 827 8 ma and 828 3 ma for the sulfide bearing ultramafic rocks and the dolerite dykes that cut the ultramafic intrusion respectively these u pb dating results show beyond doubt that the jinchuan ultramafic intrusion and associated ni cu sulfide deposit were formed at 825 ma rather than 1500 ma as has been widely believed the ultramafic rocks exhibit large negative nd t values 8 9 to 12 0 that decrease with increasing la sm suggesting that their parental magmas were derived from a long term enriched lithospheric mantle and experienced crustal contamination mineralogical petrological and geochemical data all indicate that the jinchuan intrusion was generated by melting of the enriched lithospheric mantle heated by an anomalously hot plume the u pb ages of 825 ma for igneous baddeleyites and zircons and 900 880 ma for inherited zircons in the jinchuan mafic ultramafic rocks are comparable with those in the qaidam block and qilian belt the western extension of the qinling belt that was likely derived from northern yangtze craton the jinchuan ni cu sulfide bearing intrusion along with coeval regional plume related mafic dykes and tholeiites and mafic ultramafic complexes with associated v ti and ni cu pge mineralization is interpreted to be genetically related to the 825 ma south china mantle plume

geochemical characteristics of the triassic tethys turbidites in northwestern sichuan china implications for provenance and interpretation of the tectonic setting the triassic tethys graywacke slate turbidites in the northwestern sichuan china have been analysed for major and trace elements and petrographically studied compared to phanerozoic turbidites the turbidites in this study are quartz intermediate average 55 in composition and are characterized geochemically by their moderate fe2o 3 mgo 9 28 2 84 tio2 0 72 0 17 contents and al2o3 sio2 0 25 0 10 ratios moderate abundances of ferromagnesian trace elements co 15 8 ppm cr 113 72 ppm ni 14 9 ppm sc 12 4 ppm etc and moderate contents of incompatible elements such as th 11 3 ppm u 3 0 7 ppm zr 170 64 ppm hf 4 1 ppm and total rees 159 33 ppm in general the slates show systematically higher fe2o 3 mgo sc co and eueu but lower sollasc and thsc than the associated graywackes suggesting that various provenance components may separate into different grain size fractions during sedimentary sorting processes that is the more mafic materials tended to incorporate into the sedimentary record for the clay size fraction framework modes and geochemical data indicate that the turbidites were mainly derived from a recycled orogenic provenance characterized chiefly by sedimentary metasedimentary rocks and granite gneisses similar to the upper continental crust but with a variable admixture of continental island arc volcanic components flysch deposition took place in a back arc basin situated between an active continental margin the kunlun qinling fold belt and a continental island arc the yidun island arc weathering conditions in the source area significantly influenced the composition and distribution of elements in the sediments with the elapse of time during sedimentation the degree of chemical weathering in the provenance became intense while the tectonic activity decreased gradually

triassic turbidites in the west qinling mountains nw china part of the collisional songpan ganzi basin or an active forearc basin abstract lower to middle triassic clastic rocks in the west qinling mountains along ne margin of the qinghai tibet plateau are generally regarded as part of the songpan ganzi flysch basin however relatively little attention has been paid to the age and provenance of these units new petrological and geochemical results demonstrate that these sediments accumulated along an active continental margin and are dominated by feldspathic litharenite and lithic arkose with low mineral and compositional maturity they were derived primarily from a continental arc source dominated by intermediate to felsic igneous rocks with a minor contribution from older metamorphosed and sedimentary sources turbidite samples yielded two primary detrital zircon u pb age populations of ca 273 ma and ca 435 ma which is different from the early triassic ca 252 ma and middle silurian ca 427 ma age populations that dominate the songpan ganzi basin these data together with paleocurrent results indicate that the south qilian belt was the primary source origin because this belt contains both early paleozoic andean type igneous and magmatic rocks and has a basement of precambrian metamorphosed rocks regionally an andean type arc traverses the south qilian belts and extends into the west qinling mountains and kunlun orogen which formed by north directed subduction of the paleo tethyan ocean during the early to middle triassic voluminous detritus that originated from the qilian and kunlun orogens as they were uplifted and eroded was transported to the south and deposited in the forearc area in front of the a nimaqen mianlue suture

steady state erosion of critical coulomb wedges with applications to taiwan and the himalaya 1 orogenic structure appears to be partially controlled by the addition to and removal of material from the mountain belt by tectonic accretion and geomorphic erosion respectively we developed a coupled erosion deformation model for orogenic wedges that are in erosional steady state and deform at their coulomb failure limit erosional steady state is reached when all material introduced into the wedge is removed by erosion that is limited by the rate at which rivers erode through bedrock we found that the ultimate form of a wedge is controlled by the wedge mechanical properties sole out depth of the basal decollement erosional exponents basin geometry and the ratio of the added material flux to the erosional constant as this latter ratio is increased wedge width and surface slopes increase we applied these models to the taiwan and himalayan orogenic wedges and found that despite a higher flux of material entering the former the inferred ratio was larger for the latter calculated values for the erodibility of each wedge showed at least an order of magnitude lower value for the himalaya relative to taiwan these values are consistent with the lower precipitation regime in the himalaya relative to taiwan and the exposure of crystalline rocks within the himalayan orogenic wedge independently determined rock erodibility estimates are consistent with the accretionary wedge sediments and metasediments and the crystalline and high grade metamorphic rocks exposed within taiwan and the himalaya respectively therefore differences in rock type and climate apparently lead to key differences in the erosion and hence orogenic structure of these two mountain belts

the longmenshan tectonic complex and adjacent tectonic units in the eastern margin of the tibetan plateau a review abstract the longmenshan tectonic complex lstc along the eastern margin of the tibetan plateau the site of devastating earthquakes such as the magnitude 8 0 wenchuan earthquake on 12 may 2008 preserves an exceptionally complete history of the tectonic evolution of the yangtze block and its relations to adjacent tectonic units due to sequential tectonic superposition and tectonic reactivation the tectonic nature of the lstc and in particularly the older history has been profoundly debated and many different tectonic models have been proposed herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex highlighting problems left to be solved by future work including 1 the nature and constraints for at least 6 regional tectonic events i e building of the metamorphic basement art the columbia nuna supercontinent pt1t the rodinia supercontinent pt3t the paleozoic passive continental margin pzt the paleotethys orogeny mzt and the neotethys orogeny kzt 2 metamorphic basement exposures and their tectonic implications including rock types and geochronological constraints for the archean paleoproterozoic and neoproterozoic basements 3 nature of the present lstc and its affinity with adjacent tectonic units 4 consideration of the ne striking longmenshan thrust belt and arcuate shape yanyuan muli thrust belt as parts of a single tectonic feature 5 mountain basin coupled systems recording past tectonic eposides we draw the following conclusions and tectonic models based on published research combined with our own recent studies 1 the well preserved archean yudongzi gneiss group in the lstc has a genetic affinity with the kongling group and thus belongs to the yangtze block 2 the paleoproterozoic hejiayan group juxtaposed adjacent to the archean yudongzi group may represent a 2000 1800 ma orogenic belt which corresponds to the supercontinent nuna columbia amalgamation event 3 a neoproterozoic trench arc basin system which is reconstructed based on identification of a neoproterozoic ophiolite complex arc type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the yangtze block and the lstc may represent the record of eastward subduction of the neoproterozoic mozambique oceanic lithosphere beneath the yangtze block during the assembly of the rodinia supercontinent 4 a complete bidirectional wilson cycle was reconstructed by the formation of the late permian to the middle late triassic back arc ganze litang rift and ocean following the early paleozoic mianlue continental rift and ocean and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision this relatively uncommon bidirectional wilson cycle might be attributed to the formation of the three armed rift system in the eastern paleotethys associated with the late permian eemeishan large igneous province in the lstc 5 a three stage tectonic sequence of in sequence imbricate thrust in the lstc during india eurasian collisional orogeny at 55 15 ma extrusion from 15 to 5 ma and the plateau uplift since 5 ma resulting from lower crustal channel flow is proposed for the formation of the present lstc

tectonic affinity of the west qinling terrane central china north china or yangtze 1 our ignorance about the tectonic affinity of the western qinling songpan ganzi tectonic region which is strategically located between the northeastern corner of the tibetan plateau the northwestern corner of the yangtze block and the southwestern corner of the north china block limits our understanding of the tectonic evolution of east asia basaltic volcanic rocks in the duofutun area within the west qinling terrane in qinghai province china the northernmost part of the songpan ganzi region contain coeval magmatic zircons that constrain the eruption age of the host basalts to 14 ma more significantly the basalts have entrained zircon xenocrysts from the deep crust that record the presence of unexposed neoarchean 2 7 2 5 ga basement u pb and hf isotope data from the xenocrysts reveal that this basement has undergone a complex evolution that includes the addition of new mantle derived material at 2 7 2 4 and 1 1 0 8 ga and crustal reworking events at 1 8 and 1 4 ga phanerozoic thermal events at 320 300 230 and 160 ma have also modified reworked the basement using these data we interpret at least the western part of the west qinling orogenic terrane as a microcontinental block that originally separated from the north china block closed with the northern yangtze block during the meso neoproterozoic and then redocked with the southern part of the north china block in the phanerozoic i e early paleozoic the west qinling terrane was then affected by the northward subduction and collision of the yangtze block in the paleozoic and early mesozoic and underwent lithospheric extension in jurassic time

palaeodrainage evolution of the large rivers of east asia and himalayan tibet tectonics understanding the tectonics that gave rise to the formation of tibet is critical to our understanding of crustal deformation processes the unusual geomorphology of the drainage basins of east asia s major rivers has been proposed to be the result of either 1 distortion and attenuation of antecedent drainages as india indents into asia which can therefore be used as passive strain markers of horizontal shear or 2 due to fragmentation by river captures and flow reversals of an originally continental scale drainage in which the major east asian rivers once flowed into the palaeo red river if the latter hypothesis is correct then it has been proposed that dating the drainage fragmentation constrains the timing of uplift of tibet a number of sedimentary provenance studies have been undertaken in order to determine whether the palaeo red river was once a river of continental proportions into which the upper reaches of the yangtze salween mekong irrawaddy and yarlung drained we have assessed the evidence that the yarlung originally flowed into the palaeo red river and then sequentially into the irrawaddy and brahmaputra connecting to the latter first via the lohit and then the siang for this river system we have integrated our new data from the paleogene recent irrawaddy drainage basin detrital zircon u pb with hf and fission track rutile u pb mica ar ar bulk rock sr nd and petrography with previously published data to produce a palaeodrainage model that is consistent with all datasets in our model the yarlung never flowed into the irrawaddy drainage during the paleogene the yarlung suture zone was an internally drained basin and from neogene times onwards the yarlung drained into the brahmaputra in the bengal basin the central myanmar basin through which the irrawaddy river flows today received predominantly locally derived detritus until the middle eocene the irrawaddy initiated as a through going river draining the mogok metamorphic belt and bomi chayu granites to the north sometime in the late eocene to early oligocene and the river was dominated by a stable mmb dominated drainage throughout the neogene to present day existing evidence does not support any connection between the yarlung and the red river in the past but there is a paucity of suitable palaeo red river deposits with which to make a robust comparison we argue that this limitation also precludes a robust assessment of a palaeo connection between the yangtze salween mekong and the red river it is difficult to unequivocally interpret the recorded provenance changes as the result of specific drainage reorganisations we highlight the palaeo red river deposits of the hanoi basin as a potential location for future research focus in view of the near complete cenozoic record of palaeo red river deposits at this location a majority of previous studies consider that if a major continental scale drainage ever existed at all it fragmented early in the cenozoic such a viewpoint would agree with the growing body of evidence from palaeoaltitude studies that large parts of se tibet were uplifted by this period this then leads towards the intriguing question as to the mechanisms which caused the major period of river incision in the miocene in this region

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

geological controls on prediction of coalbed methane of no 3 coal seam in southern qinshui basin north china article i nfo in order to better understand the geological controls on coalbed methane cbm in southern qinshui basin sqb north china geological surveys and laboratory experiments including coal petrology analysis proximate analysis and methane adsorption desorption were conducted results show that the coals from the sqb contain 0 59 3 54 moisture 3 5 15 54 ash yield 73 62 88 92 fixed carbon and 2 14 4 04 hydrogen with c h ratios in the range of 19 96 36 25 the vitrinite reflectance ro m ranges from 1 95 to 3 49 the coals are composed of 18 5 97 4 vitrinite and 2 4 81 4 inertinite the geologic structures coal bearing strata and coal depositional environment were studied by both field geological research and laboratory tests a positive relationship is found between cbm content and basin hydrodynamics in which cbm easily concentrates in the groundwater stagnant zone because of the water pressure furthermore integrated geographical information system gis and analytical hierarchy fuzzy prediction method ahp were used to evaluate the cbm resources in the sqb the results show that the amount of cbm associated with the no 3 coal seam in the sqb is 3 62 10 11 m 3 t he cbm resource concentration gas in place per square kilometer in the sqb is in the range of 0 72 2 88 10 8 m 3 km 2 with an average of 1 21 10 8

lead isotope variability of fine grained river sediments in tibetan plateau water catchments implications for geochemical provinces and crustal evolution abstract the crustal structure of the tibetan plateau records the dynamic processes of several terranes that underwent disaggregation aggregation and amalgamation the dynamic evolution of continental crusts is best understood from these three processes however the detailed geochemical province division of the tibetan plateau and the palaeo tectonic affinity or evolution of terranes remains unclear in this paper the acid insoluble fraction of fine grained river sediments from catchments in the whole tibetan plateau was measured for lead isotopes and trace elements this study aims to reveal lead isotopic characteristics to delineate different lead isotope geochemical provinces and to trace and uncover the tectonic affinities of various terranes in the tibetan plateau results show that by weak acid chemical treatment the characteristics of the pb isotopes of fine grained river sediments can be utilized to represent and discriminate geochemical provinces the characteristics of pb isotopes enable the identification of different geochemical provinces and the palaeo affinity of various tectonic units constrained by tectonic evolution the tibetan plateau tectonic units can be divided into the following five pb isotope geochemical provinces 1 qilian terrane 2 northern tibetan plateau geochemical province including eastern kunlun qaidam songpan ganzi and eastern qiangtang terrane 3 northern lhasa terrane 4 southern lhasa terrane and 5 himalaya terrane in relation to the controversy concerning the palaeo affinity of the qilian and songpan ganzi terranes the pb isotopic compositions of fine grained river sediments suggest that they were much more likely separated from the yangtze craton than from the north china craton the characteristics of pb isotopes and trace elements of the eastern kunlun qaidam and eastern qiangtang terrane show some similarities with the songpan ganzi terrane which indicate that they also possibly originated from the disaggregation of the yangtze craton the various partial melting and contamination of the old himalaya continental crust from radiogenic pb isotopes and tethys mantle materials with low radiogenic pb isotopes caused different pb isotopes and trace elemental associations in the southern and northern lhasa terranes these factors also led to the evolution of the two different geochemical provinces

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

triassic granitoids in the eastern songpan ganzi fold belt sw china magmatic response to geodynamics of the deep lithosphere the songpan ganzi fold belt sgfb sw china was developed from a passive continental margin into an orogenic belt with the consumption of the paleo tethys during the evolution of the sgfb numerous late triassic granitic plutons formed and exhibited a progressive development from adakite i type granite high ba sr granite a type granite and monzonite representative late triassic plutons were studied to unravel the bewildering evolution of the eastern sgfb the menggu pluton 224 3 ma consists of granites with high alkali k2o na2o 7 85 10 4 wt and adakitic characteristics sr y 19 38 the endt values 2 77 to 5 03 initial 87sr 86sr ratios 0 7050 0 7063 and low nb ta ratios 8 10 are indicative of an origin by partial melting of amphibolitic lower crust rocks from the niuxingou pluton 215 3 ma are richer in k than na k2o na2o 1 1 1 5 and contain high sr 1006 1662 ppm and ba 1277 2009 ppm typical of shoshonite and high ba sr granite they have less enriched endt values 0 08 to 2 04 and less radiogenic 87sr 86sri ratios 0 7047 0 7048 and formed from a mixed melt derived from upwelling asthenosphere and the overlying metasomatised lithospheric mantle the taiyanghe pluton 205 3 ma consists of monzonites with high al2o3 20 wt but low mgo 0 94 1 39 wt the rocks are richer in na than k k2o na2o 0 7 contain high large ion lithophile element lile 681 834 ppm sr and 2142 9453 ppm ba and display strongly fractionated ree patterns la yb n 35 63 these features together with their enriched nd sr isotopic compositions endt 4 78 to 6 50 87sr 86sri 0 7074 0 7090 suggest that the monzonite probably formed from low degrees of partial melting of metasomatised lithospheric mantle although a continuous compressional regime during the mid and late triassic has been invoked for the sgfb the generation of crustally derived adakitic and shoshonitic plutons reflect thickening in response to an arc continental collision accompanied by fracturing of the lithosphere and an extensional regime in the deep lithosphere in the late triassic the 205 ma taiyanghe pluton was emplaced simultaneously with a rapid uplift of the lithosphere when surface deposits changed from deep water turbidite to tidal flat sediments it was therefore generated during decompression probably related to the rapid removal of the overthickened lithospheric mantle the triassic magmatism in the eastern sgfb is therefore important for probing geodynamic processes in the deep lithosphere

slowing extrusion tectonics lowered estimate of post early miocene slip rate for the altyn tagh fault abstract determination of long term slip rate for the altyn tagh fault is essential for testing whether asian tectonics is dominated by lateral extrusion or distributed crustal shortening previous slip history studies focused on either quaternary slip rate measurements or pre early miocene total offset estimates and do not allow a clear distinction between rates based on the two the magmatic and metamorphic history revealed by shrimp zircon dating of clasts from miocene conglomerate in the xorkol basin north of the altyn tagh fault strikingly matches that of basement in the southern qilian shan and northern qaidam regions south of the fault this match requires that the post early miocene long term slip rate along the altyn tagh fault cannot exceed 10 mm year supporting the hypothesis of distributed crustal thickening for post early miocene times this low long term slip rate and recently documented large pre early miocene cumulative offset across the fault support a two stage evolution wherein asian tectonics was dominated by lateral extrusion before the end of early miocene and since then has been dominated by distributed crustal thickening and rapid plateau uplift

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

petrogenesis and tectonic setting of the early mesozoic xitian granitic pluton in the middle qin hang belt south china constraints from zircon u pb ages and bulk rock trace element and sr nd pb isotopic compositions abstract the xitian pluton in southeast hunan province is one of the early mesozoic indosinian granitic plutons in the south china block it is composed of biotite adamellite with k feldspar megacrysts biotite adamellite and biotite granite that have u pb zircon ages of 229 9 1 4 ma 223 6 1 3 ma and 224 0 1 4 ma respectively the indosinian granitoids in the xitian pluton belong to s type granites with highly radiogenic initial 87sr 86sr ratios 0 71397 0 71910 negative end t values ranging from 10 1 to 9 4 and old nd model ages 1858 1764 ma they are enriched in radiogenic pb isotopes with 206pb 204pb t ranging from 18 130 to 18 903 207pb 204pb t from 15 652 to 15 722 and 208pb 204pb t from 38 436 to 39 037 respectively these features indicate that the granitoidswithin the xitian pluton were formed from magmas generated by remelting of metapelite and metapsammite of the paleoproterozoic metamorphic basement at temperatures of ca 800 c with low oxygen fugacity the sr nd isotopic compositions of the rocks from xitian pluton indicate that the granitic magmas were mixed with less than 10 mantle derived magmas we suggest that the xitian pluton was emplaced in an extensional tectonic setting related to release of compressional stresses within the thickened crust during the early mesozoic

carboniferous and triassic eclogites in the western dabie mountains east central china evidence for protracted convergence of the north and south china blocks shrimp u pb dating and laser ablation icp ms trace element analyses of zircon from four eclogite samples from the north western dabie mountains central china provide evidence for two eclogite facies metamorphic events three samples from the huwan shear zone yield indistinguishable late carboniferous metamorphic ages of 312 5 307 4 and 311 17 ma with a mean age of 309 3 ma one sample from the hong an group 1 km south of the shear zone yields a late triassic age of 232 10 ma similar to the age of ultra high pressure uhp metamorphism in the east qinling dabie orogenic belt ree and other trace element compositions of the zircon from two of the huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase namely in the eclogite facies an interpretation supported by the presence of garnet omphacite and phengite inclusions zircon also grew during later retrogression zircon cores from the huwan shear zone have ordovician to devonian 440 350 ma ages flat to steep heavy ree patterns negative eu anomalies and in some cases plagioclase inclusions indicative of derivation from north china block igneous and low pressure metamorphic source rocks cores from hong an group zircon are neoproterozoic 780 610 ma consistent with derivation from the south china block in the western dabie mountains the first stage of the collision between the north and south china blocks took place in the carboniferous along a suture north of the huwan shear zone the major triassic continent continent collision occurred along a suture at the southern boundary of the shear zone the first collision produced local eclogite facies metamorphism in the huwan shear zone the second produced widespread eclogite facies metamorphism throughout the dabie mountains sulu terrane and a lower grade overprint in the shear zone

upper triassic turbidites of the northern tethyan himalaya langjiexue group the terminal of a sediment routing system sourced in the gondwanide orogen abstract the upper triassic langjiexue group exposed south of the yarlung zangbo suture zone in south tibet shows sedimentary features different from typical tethyan himalayan successions and its origin is controversial in this article we combine field observations with paleocurrent petrologic geochronological and isotopic data to determine the provenance of langjiexue sandstones these middle to distal deep sea fan turbidites are crosscut by lower cretaceous diabase sills and dikes generated during rifting of india from gondwana indicating that the langjiexue group was originally deposited along or adjacent to the northern passive continental margin of india flute casts at the base of turbidite beds indicate mostly wnw ward paleocurrents pointing to provenance from a source located east of the depositional area common volcanic fragments and plagioclase grains together with a cluster of 400 200 ma aged magmatic zircons with uniform e hf t values from 5 to 10 are incompatible with any nearby sources including the qiantang block the lhasa block or the india subcontinent and indicate instead supply from a long lived magmatic arc terrane considering what is known about late triassic paleogeography a plausible source for langjiexue sediments is represented by the gondwanide orogen generated during subduction of the pan pacific oceanic lithosphere beneath southeastern gondwana this scenario is supported by the age range and hf isotopic signatures of late paleozoic early mesozoic zircons contained in langjiexue turbidites as in coeval turbidites exposed in western myanmar new data are needed to confirm falsify the existence of a thousand km long sediment routing system similar to the modern amazon which sourced in a cordillera type orogen rising along the southeastern margin of gondwana crossed an entire continent to feed turbiditic fans now exposed from western myanmar to the northern tethys himalaya

triassic sedimentary filling and closure of the eastern paleo tethys ocean new insights from detrital zircon geochronology of songpan ganzi yidun and west qinling flysch in eastern tibet

detrital zircon geochronology of the northeastern tibetan plateau u pb geochronologic analyses have been conducted on 413 detrital zircon grains collected from 16 samples in the altun shan nan shan and qilian shan the samples come primarily from quartz arenites and metaturbidites of middle to late proterozoic age and from feldspathic and volcanic clast rich sandstones of early paleozoic age zircon grains in proterozoic strata resting on tarim basement yielded mainly 2 0 1 9 ga ages whereas proterozoic strata of the qaidam and qilian terranes yielded mainly ca 930 820 ma and ca 1 9 1 1 ga ages the younger grains were apparently shed from local igneous rocks whereas the grains older than 1 1 ga were shed from an undetermined continental source grains in the lower paleozoic strata are mainly ca 500 430 ma and were shed from nearby plutonic and possibly volcanic rocks that formed in a magmatic arc setting our detrital zircon ages are consistent with a model first proposed by e r sobel and n arnaud in which early paleozoic magmatism occurred within a single northeast facing magmatic arc that was constructed across an assemblage of middle to late proterozoic accretionary complexes remnants of magmatic arcs and shallow marine strata this arc system was accreted to the tarim and sino korean cratons during silurian devonian time the resulting suture has been reactivated as tertiary thrust faults that currently define the structural and topographic margin of the tibetan plateau our data also provide two new estimates for the offset along the eastern altyn tagh fault a belt of middle proterozoic shallow marine strata is offset by 400 km whereas a belt of 490 480 ma magmatic arc rocks is offset by 370 km these values are generally similar to the 350 400 km offset reported in most previous studies

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

structural and geochronological constraints on the mesozoic cenozoic tectonic evolution of the longmen shan thrust belt eastern tibetan plateau 1 the longmen shan thrust belt in the eastern margin of the tibetan plateau underwent deformation of d1 associated with the late triassic collision between the north and south china blocks followed by deformation of d2 and d3 related to the eastward growth of the tibetan plateau the d1 is marked by moderately tight folds f1 spaced cleavage s1 mineral lineation l1 multistage reactivated faults and top to the south thrusting this deformation initiated before 237 ma and ended at 208 ma the 193 159 ma d2 deformation is top to the southeast directed and normal ductile in nature and was associated with the formation of half graben basins the mesozoic deformation of the longmen shan belt was related to the subduction of the paleo tethys oceanic lithosphere followed by the south china block underneath the songpan ganze terrane the d1 was produced in the pro side of the overriding songpan ganze plate most probably driven by slab corner flow above the retreating south china block the d2 and extensional songpan ganze turbidite basin were produced by roll back and migration of the overriding plate above the retreating subduction zone this model for the deformation from d1 to d2 is similar to a mediterranean style model the d3 is characterized by se ward thrusting with stepwise migration of rapid denudation and dextral strike slip faulting during the late cretaceous to present therefore the longmen shan thrust belt involved mesozoic compressional and extensional events that were overprinted by the late cretaceous to cenozoic compressional event

influence of a tectonically active mountain belt on its foreland basin evidence from detrital zircon dating of bedrocks and sediments from the eastern tibetan plateau and sichuan basin sw china abstract the tectonically active eastern tibetan plateau tp impacts the populous sichuan basin in the form of dust and exhumed detrital materials to better understand a detailed transport process of detrital material from the eastern tp to the sichuan basin eight samples were collected from the upper reaches of the min river in the eastern tp to the sichuan basin for zircon u pb chronological and grain size analysis the results are compared with those of previously studies zircon grains are comparatively coarse in three bedrock samples one fluvial sand sample and one dust sample but are distinctly fine in three lacustrine samples intriguingly the zircon grain size parameters from the fluvial sand and dust samples are similar to each other consistent with previous studies of this area the analysis of our u pb zircon ages indicates five major age populations at 180 350 ma 350 550 ma 700 1000 ma 1600 2000 ma and 2200 2600 ma which broadly correspond to five known granitoid magmatic events within the yangtze block the min river links lacustrine sediments from lixian fluvial sands from wenchuan leshan yibin and from the dadu river and the dayi conglomerate implying the dayi conglomerate was transported by fluvial rather than glacial processes the denuded detrital material mainly generated by seismic events in the eastern tp was transported by water flow into the western sichuan basin where two thick sedimentary depocenters developed and the relatively fine grains were then transported by wind to the northern sichuan basin thus the thick sediments in the western sichuan basin mainly transported by the min river probably exerted a major influence on dust deposition in the northern sichuan basin in contrast the jialing and dadu rivers made a minor contribution

early cretaceous palaeogeographic evolution of the coqen basin in the lhasa terrane southern tibetan plateau abstract the lower cretaceous sedimentary strata in the lhasa terrane record the palaeogeographic and tectonic history of the tibetan plateau prior to the india asia collision the lower cretaceous strata in the coqen basin of the northern lhasa subterrane include the duoni and langshan formations the duoni formation is composed of conglomerates sandstones siltstones and mudstones in the south deposited in a fluvial environment and quartzose lithic sandstones siltstones and mudstones in the north deposited in a shelf coastal environment the overlying langshan formation is characterized by abundant orbitolina and rudist bearing wackestones and packstones which were deposited on a low energy carbonate ramp the langshan formation in the coqen basin was deposited between 119 115 ma and 98 ma based on its large benthic foraminiferal assemblages age constraints based on the interbedded tuff and conformably overlying langshan formation indicate that the duoni formation was deposited between 123 and 115 ma sandstone detrital modal compositions further indicate that the duoni formation was primarily derived from magmatic arc and recycled orogen sources detrital zircons from the duoni formation yield a primary age population of 160 110 ma peaking at 130 ma with negative e hf t values 18 7 to 2 7 and additional age ranges of 550 500 1200 900 and 1600 1500 ma thereby indicating that the zenong volcanic rocks and palaeozoic sedimentary bedrocks in the northern lhasa subterrane are the most likely sources the palaeogeography of the northern lhasa subterrane can be approximately described in two stages during the aptian 123 115 ma with the eruption of the zenong volcanic rocks the duoni formation accumulated in fluvial and shelf coastal environments and was sourced from the zenong volcanic rocks and basement rocks from the southern region of the northern lhasa subterrane the enhanced magmatic activities in the northern lhasa subterrane may have influenced the duoni formation deposition during the late aptian early cenomanian 115 98 ma a north south transgression occurred causing the majority of the northern lhasa region to be dominated by shallow marine limestones of the langshan formation