apatite fission track evidence for the cretaceous cenozoic cooling history of the qilian shan nw china and for stepwise northeastward growth of the northeastern tibetan plateau since early eocene abstract apatite fission track aft data from hinterland of the qilian shan at the northeastern margin of the tibetan plateau suggest this range has experienced northeastward propagation of surface uplift since early eocene and that crustal shortening occurred in the qilian shan before the late miocene thermochronometry data indicate that the qilian shan experienced a three stage cooling history including 1 rapid initial cooling during cretaceous 2 a stage of slow cooling during late cretaceous early eocene and 3 rapid stepwise cooling in a southwestern northeastern orientation since early eocene cretaceous rapid cooling may be a record of the lhasa block and eurasian collision early cretaceous denudation was followed by tectonic and quasi isothermal quiescence that continued until early eocene early eocene rapid cooling in the south qilian shan may be the first far field response in the qilian shan to the collision and convergence of the indian and eurasian continents from late eocene to middle miocene crustal shortening propagated into the central qilian shan and north qilian shan and produced surface uplift of the entire qilian shan region before the late miocene this study provides a better understanding of the tectonic evolution of the qilian shan and when the far field stress from the india eurasia collision into the northeastern tibetan plateau began

intraplate extension prior to continental extrusion along the ailao shan red river shear zone left lateral movement of the ailao shan red river shear zone lends support to the hypothesis of continental extrusion resulting from the collision of india with asia our new observations from northwestern yunnan china and northwestern vietnam on different sides of the shear zone demonstrate that the sinistral offset was 600 km according to correlations of permian triassic flood basalt successions and late paleogene highly potassic mafic magmas we conclude that the shear was propagating on the south china continental margin and does not correspond to a suture between south china and indochina furthermore the highly potassic magmas were emplaced from ca 40 to 30 ma before the shear movement which was caused by the late oligocene to early miocene ca 27 22 ma extrusion activity this suggests that a late eocene to early oligocene intraplate extension possibly induced by delamination of thickened continental lithosphere took place in northwestern yunnan or eastern tibet as a response to the india asia collision this extension and sea floor spreading of the south china sea that began ca 30 ma could have accounted for the initiation of the ailao shan red river shear zone

platinum in earth surface environments platinum pt is a rare precious metal that is a strategic commodity for industries in many countries the demand for pt has more than doubled in the last 30years due to its role in the catalytic conversion of co hydrocarbons and nox in modern automobiles to explore for new pt deposits process ores and deal with ecotoxicological effects of pt mining and usage the fundamental processes and pathways of pt dispersion and re concentration in surface environments need to be understood hence the aim of this review is to develop a synergistic model for the cycling of pt in earth surface environments this is achieved by integrating the geological biogeo chemical literature which focuses on naturally occurring pt mobility around ore deposits with the environmental ecotoxicological literature dealing with anthropogenic pt dispersion in pt deposits pt occurs as sulfide telluride and arsenide native metal and alloyed to other pges and iron fe increased mining and utilization of pt combined with the burning of fossil fuels have led to the dispersion of pt containing nano and micro particles hence soils and sediments in industrialized areas urban environments and along major roads are now commonly pt enriched platinum minerals nuggets and anthropogenic particles are transformed by physical and bio geochemical processes complexation of pt ions with chloride thiosulfate ammonium cyanide low and high molecular weight organic acids lmwoas and hmwoas and siderophores can facilitate pt mobilization iron oxides clays organic matter and micro biota are known to sequester pt complexes and particles microbes and plants are capable of bioaccumulating and reductively precipitating mobile pt complexes bioaccumulation can lead to toxic effects on plants and animals including humans bio mineralization in organic matter rich sediments can lead to the formation of secondary pt particles and grains ultimately pt is enriched in oceanic sediments where pt is commonly concentrated in manganese mn oxides when these sediments are subducted pt re enters the magmatic cycle in conclusion this review demonstrates that geological geochemical as well as biological and most recently anthropological processes are strongly interlinked in driving the cycling of pt in surface environments

geochronological and geochemical constraints on mesozoic suturing in east central tibet 1 this paper reports isotopic major and minor element geochemistry of igneous and metamorphic rocks from the kokoxili and yushu regions of central and eastern tibet the first region lies along the kunlun suture which separates the bayan har songpan ganze songpan terrane from the tarim and qaidam blocks two kokoxili granitoids yield u pb zircon dates of 217 10 and 207 3 ma late triassic which represent the time of emplacement and rb sr isochron dates of 195 3 and 190 3 ma early jurassic which are interpreted as cooling ages the geochemical signatures of these granitoids suggest that they are related to subduction continuing into the late triassic in the yushu area three samples help constrain the age of the jinsha suture which separates the songpan terranes from the qiangtang blocks a leucocratic granite and an orthogneiss in the suture zone yield u pb zircon dates of 206 7 and 204 1 ma respectively and a paragneiss south of it a u pb monazite date of 244 4 ma the existence of coeval magmatism in both the jinsha and kunlun sutures suggests that the two subduction zones were simultaneously active combining isotopic dating with structural evidence on subduction polarity and paleomagnetic reconstructions we propose that the kunlun and qinling block boundaries which were distinct in the permian subsequently formed a continuous late triassic northward subducting plate margin our data suggest that the jinsha suture correlates with the benzilan and nan uttaradit sutures which together belong to a major late triassic subduction zone

cenozoic exhumation in the qilian shan northeastern tibetan plateau evidence from detrital fission track thermochronology in the jiuquan basin the india asia collision resulted in the cenozoic framework of faults ranges and tectonic basins and the high topography of the northeastern tibetan plateau but how and when these features formed remains poorly understood leading to conflicting tectonic models however information on the tectonic evolution of these active orogenic belts is well preserved in synorogenic basin sediments in this study we carefully analyze the detrital apatite fission track aft ages of cenozoic synorogenic sediments from the jiuquan basin to decipher the entire exhumation process of the adjacent qilian shan throughout the cenozoic our data indicate that initially rapid cenozoic exhumation occurred in the qilian shan during the late paleocene early eocene 60 50 ma almost synchronous with the india asia collision the qilian shan subsequently experienced long lived exhumation that continued until at least the middle miocene 45 10 ma during this period of exhumation in the qilian shan tectonic deformation occurred throughout the northeastern tibetan plateau the early cenozoic deformation in the northeastern tibetan plateau may have been caused by the transfer of tectonic stress from the distant india asia collision boundary through the complex lithospheric environment of the tibetan plateau the present tectonic configuration and topography of the qilian shan and the northeastern tibetan plateau likely became established since the middle miocene and after the long lived deformation began in the early cenozoic

paleogene clockwise tectonic rotation of the xining lanzhou region northeastern tibetan plateau 1 to help understand the deformational history of the northeastern tibetan plateau paleomagnetic samples were collected from 177 sites and two magnetostratigraphic sections at 16 localities distributed among upper jurassic lower cretaceous to pliocene sedimentary and subordinate volcanic rocks within the xining lanzhou region 34 37 n 101 105 e a total of 127 sites at 12 localities yielded primary magnetizations confirmed by fold reversal and conglomerate tests age control on sedimentary rocks is provided by regional synthesis of chronostratigraphic data and our own biostratigraphic and magnetostratigraphic analysis presented in the companion paper by horton et al 2004 analysis of paleomagnetic declination combined with results from previous studies yield a remarkably consistent trend of vertical axis tectonic rotations across the studied region whereas 19 0 7 2 to 37 8 10 6 clockwise rotations are recorded consistently in all paleomagnetic localities in lower cretaceous to eocene rocks all paleomagnetic localities in oligocene to pliocene rocks have recorded minor to insignificant rotations indicating that the xining lanzhou region has undergone a wholesale regional clockwise rotation during late paleogene time consistent with regional chronostratigraphic and thermochronologic results this late paleogene tectonic rotation confirms that deformation reached regions of the northern tibetan plateau shortly after the initial collision of india with asia when compared to rotational paleomagnetic results from adjacent regions several mechanisms can be proposed to explain the clockwise rotation on the basis of consistency with geologic data we prefer a model involving clockwise rotation of the xining lanzhou region through right lateral shear and associated shortening related to northward indentation of the qaidam basin index terms 1525 geomagnetism and paleomagnetism paleomagnetism applied to tectonics regional global 8102 tectonophysics continental contractional orogenic belts 9320 information related to geographic region asia 9604 information related to geologic time cenozoic keywords tectonics paleomagnetism tibetan plateau

cooling history and tectonic exhumation stages of the south central tibetan plateau china constrained by 40ar 39ar and apatite fission track thermochronology between the qiangtang block and yalung zangpo suture zone in the south central tibetan plateau the following geological units and suture zones have been identified from south to north the gangdese granitic belt the lhasa block the nyainqentanghla shear zone the dangxiong sangxiong tectono granitic belt and the bangong nujiang suture zone to better constrain the tectonic evolution and cooling histories of these units 40 ar 39 ar muscovite biotite and k feldspar as well as apatite fission track dating and thermochronological analysis have been carried out the analytical results indicate that the south central tibetan plateau with the exception of the nyainqentanghla shear zone provides a record of three cooling stages at 165 150 130 110 and 45 35 ma fission track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks very different cooling phases occurred in the south central tibetan plateau compared with southern tibet as well as along the yalung zangpo suture zone there is no thermochronological evidence to indicate that the south central part of tibetan plateau was influenced by the underthrusting of indian plate the three stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the bangong nujiang suture zone along its eastern segment during middle late jurassic 165 150 ma and its western segment in the early late cretaceous 130 110 ma as well as by the collision between the indian and asian plates in the paleogene 45 35 ma 2005 elsevier ltd all rights reserved

miocene range growth along the altyn tagh fault insights from apatite fission track and u th he thermochronometry in the western danghenan shan china the left lateral strike slip altyn tagh fault that defines the northern margin of the tibetan plateau plays a crucial role in accommodating the cenozoic deformation related to the growth of plateau however the slip history along the fault remains highly debated here we report new 14 16 ma apatite fission track aft and 9 11 ma apatite u th he ahe data in the western danghenan shan north tibet age elevation relationships and aft ahe age differences suggest a period of rapid exhumation with an average rate of 0 1 0 3 km ma from 16 to 9 ma for this area thermal history modeling indicates that this was preceded by accelerated exhumation between the late oligocene and middle miocene 15 ma a northward increase in aft ages and asymmetric topography across the western danghenan shan indicate that the uplift and exhumation are mainly controlled by the thrust fault along the southern flank of the western danghenan shan as the thrust fault is a branch of the altyn tagh fault the rapid exhumation probably represents onset of the transition along the altyn tagh fault from left slip motion to crustal shortening in the dangnenan shan region our findings show that the middle miocene deformation is not only recorded in the middle and northern qilian shan but also in the southwestern portion of the qilian shan which favors a synchronous middle miocene deformation model for the entire qilian shan

an early unroofing in northeastern tibet constraints from 40ar 39ar thermochronology on granitoids from the eastern kunlun range qianghai nw china abstract in order to better constrain the mechanisms accommodating the india asia collision along the whole kunlun range northern tibet which is essential to better understand the evolution of the entire deformations area a 40 ar 39 ar thermochronological study has been carried out on a suite of granitoids collected in the vicinity of golmud eastern kunlun range biotite and k feldspar have been analysed and the cooling histories of the latter have been modelled the ranges of 40 ar 39 ar data bt 128 257 ma kf 102 228 ma are similar to previous rb sr and k ar data indicating both a middle paleozoic unit and a mesozoic unit including a triassic series and a jurassic cretaceous series this suggests that the two geological units previously reported in the western kunlun are also present in the eastern part of the range suggesting that eastern and western kunlun ranges might have been left laterally offset by as much as 500 km along a strike slip fault presently parallel to the altyn tagh fault the cooling histories based upon k feldspar modelling show that samples from the southern part of the range recorded an important cooling event 9 15 myr around 30 ma which is thought to reflect an increasing rate of denudation related to the tectonic activity in this area minimum denudation rates of 0 2 0 3 km ma have been estimated in contrast samples from the northern part of the range did not record any variation in their cooling history this heterogeneous denudation across the range is thought to be related to ramp stacking and normal faulting with associated uplift mainly affecting the southern part of the range suggesting that the eastern kunlun underwent an important crustal thickening period 30 ma ago this crustal thickening event is suggested to be related to the motion along the great asian strike slip faults in a way which remains problematic but possibly associated to the cenozoic propagation of the altyn tagh fault finally unroofing in the eastern kunlun range appears to predate that in the western kunlun range where it is suggested to have started around 20 ma ago this diachronous denudation could be related to a higher denudation rate in western kunlun range and it is thus highly probable that the important unroofing event outlined around 20 ma ago in the western kunlun has also affected the eastern part of the range even though the signature is not available at the moment

early middle miocene topographic growth of the northern tibetan plateau stable isotope and sedimentation evidence from the southwestern qaidam basin abstract this study presents facies analysis and carbonate stable isotopic records of a 4435 m thick oligocene middle miocene 30 to 11 ma stratigraphic section from the southwestern qaidam basin which place constraints on the interplay between topographic growth and climatic hydrologic changes in the northern tibetan plateau three types of carbonate including marl limestone pedogenic carbonate and carbonate cement were collected and went through detailed screening for diagenesis carbonate cements are primary early diagenetic carbonates formed in shallow ground water setting the majority of marls limestones and pedogenic carbonates are primary micritic carbonates whereas a few of them showing alterations were sub sampled to avoid diagenetic phases a negative shift in the 18o values of marls limestones and depositional environment change from palustrine to shallow lacustrine associated with paleohydrological change at 20 ma are likely caused by tectonic activity in adjacent ranges around 15 14 ma a decrease of 1 5 in the most negative 18o values of carbonate cements is interpreted to reflect the topographic growth of surrounding mountain ranges i e altun shan east kunlun range this inference is supported by the sedimentary facies change from marginal lacustrine to fluvial that was accompanied by an abrupt increase in sedimentation rate finally a 1 5 positive shift in the most negative 18o values of carbonate cements and pedogenic carbonates enriched 13c values of pedogenic carbonates as well as sedimentary environment change from fluvial to braided river alluvial fan at 13 12 ma most likely reflect a regional aridification event observed over a large area of the central asia this aridification event may have been associated with continued topographic growth of the northern tibetan plateau to a critical elevation to block moisture e g westerlies from penetrating the interior of central asia

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

cenozoic cooling history and fluvial terrace development of the western domain of the eastern kunlun range northern tibet abstract the growth of the tibetan plateau resulted primarily from cenozoic india asia collision and continued convergence and thus the deformation timing and geomorphic evolution of northern tibet are critical to understanding the dynamics of orogenic plateau growth although previous studies have suggested that the altyn tagh shan and the eastern kunlun range of northern tibet have experienced differential faulting and exhumation history our knowledge of the temporal and spatial distribution of the growth of the northwestern tibetan plateau is still lacking in this study we integrate new geologic mapping low temperature themochronometry 18 apatite fission track ages and optically stimulated luminescence osl dating to provide constraints on the cenozoic cooling history of northwestern tibet and late quaternary fluvial terrace development we focus on where altyn tagh shan structures are juxtaposed against eastern kunlun range structures new fission track cooling ages from one traverse along the aksu river yielded three cooling age domains paleocene miocene and early pliocene with this new knowledge of 12 10 ma initiation of jianxiashan thrusting and exhumation we suggest a refined n s shortening rate of this thrust system of 2 0 2 4 mm yr and strain rates of 8 9 10 16 s 1 thermal history modeling suggests that the study area experienced two broad events including slow cooling through the aft paz since the early eocene and rapid cooling during the late miocene our osl dating results from the aksu drainage reflect two separate processes of aggradation and incision that occurred during the late pleistocene and holocene respectively which are interpreted to result from long term forcing of incision by a constant rate of tectonic uplift modulated by late quaternary climatic variations we interpret that this incision occurred at a rate of 1 mm yr which is faster than exhumation rates inferred from the aft data 0 3 0 5 mm yr these quaternary exhumation rates may reflect faster recent exhumation or uplift associated with the proximal altyn tagh fault in accordance with previous studies we present a refined cenozoic tectonic model for the evolution history of northern tibet the deformation pattern of northern tibet results from clockwise rotation of preexisting weaknesses and transpressional deformation along the kunlun fault and the haiyuan fault

crustal and upper mantle structure of northern tibet imaged with magnetotelluric data 1 magnetotelluric mt data were collected in northern tibet along the amdo to golmud highway during the 1995 and 1999 project indepth international deep profiling of tibet and the himalaya surveys broadband and long period mt data were collected and the te mode tm mode and vertical magnetic field data were inverted to yield a minimum structure two dimensional resistivity model the model obtained from inverting all responses simultaneously shows that a pervasive midcrustal conductor extends from the kunlun shan to the bangong nuijiang suture the vertically integrated conductivity conductance of this crustal layer is greatest in the northern qiangtang terrane at latitude 34 n the electrical resistivity of the upper mantle is constrained by the mt data to be in the range of 10 30 m across the songpan ganze and qiangtang terranes this is lower than would be expected if asian lithosphere underthrusts northern tibet as far as the qiangtang terrane the mt responses are more consistent with a model in which asian lithosphere extends as far south as the kunlun shan and the upper mantle beneath the songpan ganze and qiangtang terranes is sufficiently hot to contain a small fraction of interconnected partial melt

cenozoic structural inversion from transtension to transpression in yingxiong range western qaidam basin new insights into strike slip superimposition controlled by altyn tagh and eastern kunlun faults abstract a cenozoic structural inversion event from transtension to transpression involving salt tectonics has been uncovered in the yingxiong range the western qaidam basin seismic reflection data show that there are two common structural styles in the yingxiong range 1 the positive flower structure 2 the thrust controlled fold at shallow depth and the positive inverted flower structure at deep levels which are separated by a salt layer in the upper xiaganchaigou formation the yingxiong range experienced a first stage of transtension in the eocene induced by the altyn tagh fault and a second stage of transpression from the early miocene to present jointly controlled by the altyn tagh and eastern kunlun faults the eocene transtension produced numerous nw striking right stepping en echelon transtensional normal faults or fractures in the yingxiong range at the same time evaporites and mudstone were deposited in the vicinity of these faults in the early miocene the eocene transtensional normal faults were reactivated in a reverse sense and the thrust controlled folds at shallow depth started to form simultaneously with transpression enhanced in the late cenozoic positive flower structures directly formed in places without evaporites the cenozoic transtension to transpression inversion of the yingxiong range is the result of strike slip superimposition controlled by the altyn tagh and eastern kunlun faults in time and space

uniform permian 40ar 39ar detrital mica ages in the eastern qaidam basin nw china where is the source new single grain 40ar 39ar detrital white mica ages from the lulehe section at the eastern qaidam basin yield uniform permian ages between 250 3 and 279 3 ma throughout the whole cenozoic sequence this is inconsistent with the present hinterland which is composed of early palaeozoic metamorphic units with subordinate early palaeozoic and few permian granites the new data indicate that permian tectonic units are likely more widespread at the north eastern margin of the tibetan plateau as known at present particularly within the qilian mountains the preferred explanation is that the qaidam block represents a rigid indenter which indented during late tertiary times into early palaeozoic orogenic units this is consistent with recent findings of a nw trending sinistral permian ductile shear zone and a dextral nw trending tertiary fault system close to the north eastern margin of the qaidam basin

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

diachronous uplift in intra continental orogeny 2d thermo mechanical modeling of the india asia collision abstract the cenozoic india asia collision reactivated several ancient thrust belts in the interior of the asian continent including the west and east kunlun ranges in central tibet and the tian shan and qilian shan further north both basin sedimentary records and thermochronological data show that the uplift of the south tian shan and qilian shan at the north occurred earlier than that of the west and east kunlun ranges at the south diachronous continental deformation and initiation of uplift during orogeny are contrary to the general notion that the stress transfer in response to the india asia collision should propagate sequentially from south to north here we systematically conducted 2d thermo mechanical simulations to investigate possible factors for this diachronous deformation pattern the results show that a hotter tian shan lithosphere with moho temperature 100 c hotter than that of the proto southern asia leads to an earlier and higher uplift of the tian shan additionally a faster convergence rate of the india asia collision results in a more efficient transfer of boundary force into the upper plate s interior giving rise to a larger amount of uplift in the tian shan we conclude that intra continental ranges with weaker lithosphere such as the tian shan or qilian shan uplift earlier than stronger regions such as the west and east kunlun ranges faster convergence rates amplify this situation our results imply that the unique diachronous growth of the tibetan plateau arises from its complex pre collisional history which includes collided arc continent terranes with hotter and weaker lithosphere that respond to the effects of far field stress transfer

indian plate motion and shape constraints on the geometry of the himalayan orogen abstract sea floor palaeomagnetic data that reflect variations in rate and vector of indian plate movement and rotation suggest that initial collision between india and asia occurred at about 50 55 ma ago as the pre collisional indian plate was diamond shaped with the northern margin comprised of two oblique boundaries collision was earliest where these boundaries meet or in what is now the northwest himalaya oblique convergence along each of these two boundaries would generate rotation of thrust sheets as they climb on to the indian plate the oroclinal shape of the main himalayan chain to the east of the northwest himalayan syntaxes reflects a combination of the effects of oblique convergence post collisional anticlockwise rotation of the indian plate and the pinning of the main thrusts at their northwestern terminations by crust thickened during the earliest collisional stage the indian plate rotation enhances a strike slip component of movement along the western oblique margin with the transpressively sinistral chaman fault zone now acting as a continental escape structure

quaternary and active faulting observed on the 1985 academia sinica royal society geotraverse of tibet active and recent faulting along the main north south road in tibet is dominated by normal faulting occurring on northerly trending planes and by strike slip faulting both of which reflect an east west extension of the plateau normal faulting is prevalent in the southern half of the plateau but we saw no evidence for any major graben in the northern half strike slip faulting on roughly easterly trending structures is m ore prevalent in the northern half but conjugate faulting with right lateral slip on northwesterly trending planes and left lateral slip on northeasterly trending planes is common in the southern half in two areas we also observed components of thrust faulting apparently in association with young strikeslip faulting our most important results are bounds on the rates of slip on the two main strands of the kunlun strike slip fault system which trends east w est through the kunlun range ground moraine containing boulders of pyroxenite is separated by 30 km from the nearest outcrop of such rock implying that amount of displacement in the last 1 5 to 3 m a therefore the average rate of slip during the quaternary period has been between 10 and 20 mm a with a likely value of 13 mm a abundant fresh tension cracks and mole tracks imply continued slip on the main strand the xidatan tuosuohu maqu fault and the likely occurrence of a major earthquake in the last few hundred years consistent offsets of gullies and dry stream channels of about 10 m may reflect slip of that amount during such an earthquake and possible multiple offsets at one site suggest that slip may occur by large displacements of 10 m during infrequent great earthquakes along the other strand the kunlun pass fault offsets of roughly 50 to 150 m of apparently post glacial valleys and of one glacier and its terminal moraine suggest a holocene rate of slip between 5 and 20 mm a and most likely about 10 mm a on this fault these rapid rates of displacement imply that tibet is being extruded rapidly eastward at a rate com parable to the rate at which india is penetrating into eurasia and therefore that at present a substantial fraction of this penetration is being absorbed by the eastward extrusion of tibet

sedimentary characteristics of cenozoic strata in central southern ningxia nw china implications for the evolution of the ne qinghai tibetan plateau abstract cenozoic sedimentary deposits in central southern ningxia province nw china are an important record of tertiary tectonic events along the evolving qinghai tibetan plateau s northeast margin shortly after the onset of the indo eurasia collision to the south a thrust belt and adjoining foreland basin began to form during 40 30 ma the eocene sikouzi formation developed in a distal setting to this basin in normal fault bound basins that may have formed in a forebulge setting subsequent deposition of the oligocene qingshuiying formation occurred during a phase of apparently less intense tectonism and the previous underfilled foreland basin became overfilled during the early miocene contractional deformation was mainly distributed to the west of the liupan shan this resulted in deformation of the qingshuiying formation as indicated by an unconformity with the overlying miocene hongliugou formation the unconformity occurs proximal to the haiyuan fault suggesting that the haiyuan fault may have begun movement in the early miocene in the late miocene thrusting occurred west of the southern helan shan and an unconformity developed between the hongliugou and qingshuiying formations proximal to the the cha gu fault relationships between the miocene stratigraphy and major faults in the region imply that during the late miocene the deformation front of the qinghai tibetan plateau had migrated to the cha gu fault along the western ordos margin and the xiang shan was uplifted central southern ningxia was then incorporated into the northeast propagating thrust wedge the driving force for ne propagation of the thrust wedge was most likely pronounced uplift of the northeastern plateau at the same time analysis of the sedimentary record coupled with consideration of the topographic evolution of the region suggests that the evolving fold and thrust belt experienced both forward breaking fold and thrust belt development and out of sequence fault displacements as the thrust wedge evolved and the foreland basin became compartmentalised the documented sedimentary facies and structural relationship also place constraints on the miocene recent evolution of the yellow river and its tributaries

mesozoic cenozoic evolution of the xining minhe and dangchang basins northeastern tibetan plateau magnetostratigraphic and biostratigraphic results 1 accurate stratigraphic ages are crucial to understanding the deformation history of the tibetan plateau prior to and during the indo asian collision efforts to quantify mesozoiccenozoic ages are hindered by limited fossils and a paucity of volcanic horizons and regionally correlative strata magnetostratigraphic and biostratigraphic results from the xining minhe longzhong basin complex and dangchang basin provide an improved chronology of nonmarine basin development over a large region of the northeastern tibetan plateau 34 37 n 101 105 e analyses of 171 magnetostratigraphic levels and 24 palynological assemblages 120 species indicate late jurassic early cretaceous to mid tertiary deposition although magnetic polarity zonation is incomplete independent palynological age control partially restricts possible correlations to the geomagnetic polarity timescale the sediment accumulation record basin provenance structural geology and published thermochronological data support a history of jurassic exhumation late jurassic early cretaceous fault related basin initiation and cretaceous paleogene reduced accumulation these patterns which are compatible with late jurassic early cretaceous extension and cretaceous paleogene postrift thermal subsidence were disrupted at about 40 30 ma when shortening related to the indo asian collision induced localized range uplift vertical axis rotation and amplified subsidence indexterms 1520 geomagnetism and paleomagnetism magnetostratigraphy 8102 tectonophysics continental contractional orogenic belts 9320 information related to geographic region asia 9604 information related to geologic time cenozoic 9609 information related to geologic time mesozoic keywords tectonics magnetostratigraphy tibetan plateau cenozoic mesozoic sedimentary basins

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

structural deformation pattern within the nw qaidam basin in the cenozoic era and its tectonic implications abstract the qaidam basin is located in the northeastern tibetan plateau and provides an excellent field laboratory in understanding the history and mechanism of the plateau growth it deformed widely over the northwest during the cenozoic but with little thrust loading along the margins where no foreland depression is observed based on satellite images seismic and borehole data we investigated the structural deformation pattern including the structural style and timing of deformation and its formation mechanism within the northwestern qaidam basin during the cenozoic era mapping of surface geology shows that the modern qaidam basin is characterized by five se trending anticlinal belts each belt consists of several right step en echelon anticlines with plenty of normal and strike slip faults crossing the crests those anticlines are generally dominated by double fault systems at different depths an upper thrust fault system controlling the anticlines identified on the surface and a lower dextral transpressional fault system characterized by typical flower structures they are separated by weak layers in the upper xiaganchaigou or the shangganchaigou formations the upper system yields shortening strain 2 5 times larger than that of the lower system and the additional strain is interpreted to be accommodated by hinge parallel elongation in the upper system growth strata indicate that deformation within the qaidam basin initiated in the middle miocene 15 ma and accelerated in the late miocene 8 ma a simple riedel p shear model is used to explain the deformation mechanism within the northwestern qaidam basin

quartz arenites of the cambro ordovician kamouraska formation quebec appalachians canada i deep water depositional processes in a continental slope environment the kamouraska formation is an uppermost cambrian lowermost ordovician quartz arenite dominated unit of controversial origin deposited on the southeastern slope of laurentia bordering the iapetus ocean it is exposed in the quebec appalachians on the south shore of the st lawrence estuary the formation consists of basal polymictic conglomerate and overlying massive sheet like quartz arenite the conglomerate beds are reversely and reversely to normally graded the quartz arenite beds are generally massive although they may show coarse tail grading beds containing full or partial bouma sequences are rare paleoflow directions from ripple cross lamination ripple marks on bed surfaces and sole marks point towards southeast south and southwest the clastic sediments of the kamouraska were transported into the deep sea by sediment gravity flows that evolved from hyperconcentrated to concentrated density flows and then to turbidity currents the depositional environment is interpreted to have been a

cenozoic pulsed deformation history of northeastern tibetan plateau reconstructed from fission track thermochronology abstract the synorogenic basin deposits and bedrocks of their source terranes within and along the tibetan plateau contain fundamental information regarding the spatiotemporal evolution of the largest orogenic plateau on earth the guide xining region is located on the northeastern portion of the tibet and its eocene early pleistocene basin succession is well preserved by integrating apatite fission track thermochronology from sedimentary and basement samples with heavy minerals and paleocurrent data we decipher an almost complete sequence of exhumation and depositional events during the cenozoic our data indicates that the initial deformation along the guide xining region occurred since the eocene with the reorganization of the regional tectonomorphology and the formation of a broad basin thereafter this single large basin was disrupted by multiple episodes of exhumation and deformation our study illuminate that the multiple stage active processes occurred at 49 42 36 32 23 19 16 13 and 8 4 ma work together to produce the current ne tibetan plateau

a late neogene framework and transpressional system within the yingxiongling range western qaidam basin northeast tibetan plateau insights from seismic reflection profiles and active tectonics abstract the yingxiongling range is a topographically unique and active tectonic belt in the western qaidam basin that has recorded the structural evolution and interactions between itself and surrounding ranges throughout the late cenozoic although a large scale fault fold system within this region accommodates transpressive deformation the overall kinematic pattern remains highly debated regional seismic reflection profiles earthquake distributions focal mechanisms and displacement vector results are used in this study to rebuild a northern verging thrust and wedge tectonic system in a perpendicular direction interpretations of newly acquired three dimensional seismic data the timing of growth strata and the kinematics of active structures strongly support lateral structural deformation propagation and evolution of the southern yingxiongling range in the late neogene a novel analysis of active tectonic and seismic profiles enables us to rebuild the framework kinematics and evolutionary pattern of the yingxiongling range we also provide a new interpretation of lateral differentia along the yingxiongling range based on critical taper theory and suggest that this overall structure is an integrated part of the qimen tagh wedge since the late neogene rapid uplift in this area occurred in response to northward propagation of the qimen tagh wedge

thermochronology of the yidun arc central eastern tibetan plateau constraints from 40ar 39ar k feldspar and apatite fission track data abstract four k feldspar samples from the yidun arc eastern tibetan plateau were analysed by the 40ar 39ar method with the aim of recovering information on their thermal history using multiple diffusion domain mdd theory arrhenius plots for each of the samples reveal low retentivity early in the heating experiments a property that is attributed to their recrystallised nature this low argon retentivity appears to violate the mdd assumption that volume diffusion is the only mechanism for argon transport within the crystals thus the thermal histories derived from these analyses are considered suspect nevertheless the age spectra themselves suggest that the majority of samples had cooled below 200 c prior to the eocene collision of india with asia thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the cenozoic in samples from the high elevation low relief areas of the yidun arc while samples from the major jinsha river valley show rapid cooling through the partial annealing zone beginning in the miocene these results suggest that significant cenozoic denudation has been localised and that most parts of the yidun arc have experienced very little denudation during the cenozoic

stratigraphic and paleomagnetic evidence of mid pleistocene rapid deformation and uplift of the ne tibetan plateau abstract the ne tibetan plateau has become an important region for deciphering the cenozoic uplift of the plateau previous studies have verified that the quaternary uplift in this region had a multi stage character however geologists have not established which event constituted the main tectonic phase fortunately stratigraphic and paleomagnetic evidence from the jiuquan basin gansu province china now confirm that the laojunmiao movement represented as an angular unconformity occurred between 0 9 and 0 8 ma and an almost synchronous tectonic event has been well recorded within and around the plateau moreover many proxies indicate that the global climate changed more rapidly after 0 9 ma these proxies include eolian loess and vermiculated red soils caused by the asian monsoon the eolian sedimentation rate the stilostomella extinction changes in the global thermohaline circulation and the increased 13 c values recorded in the marine sediments based on the uplift driven climate change the mid pleistocene transition mpt could be the result of the laojunmiao movement certainly the laojunmiao movement and mpt had the significant impact on the quaternary earth we conclude that the laojunmiao movement was likely the main tectonic phase of the quaternary plateau uplift

isotopic preservation of himalayan tibetan uplift denudation and climatic histories of two molasse deposits two distinctive molasse deposits within the indo asian collision zone have been investigated to help understand the post oligocene evolution of the himalaya and southern tibetan plateau the siwalik group predominantly fluvial sandstones and siltstones is widespread throughout the foothills of the himalaya from pakistan to eastern india paleomagnetic analysis of a measured section in the bakiya khola southeastern nepal constrains depositional ages t dep to between 10 8 and 4 9 ma the average accumulation rate during this interval was 0 4 0 5 mm yr 40 ar 39 ar dating of 126 detrital k feldspars from nine horizons in the bakiya khola section t dep 8 25 to 2 2 ma provide snapshots in time of the cooling ages exposed at the earth s surface in this drainage basin the minimum age in the spectra from seven of the nine horizons averages only 3 m y older than t dep indicating exceptionally rapid unroofing in the himalaya throughout that interval half of the grains fro

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

oligocene miocene 28 13 ma climato tectonic evolution of the northeastern qinghai tibetan plateau evidenced by mineralogical and geochemical records of the xunhua basin abstract changes in sediment composition in the xunhua basin provide insights into the climatic and tectonic evolution of the northeastern qinghai tibetan plateau during the oligocene and miocene here we analyzed the clay mineralogy i e the proportions of smectite illite and chlorite and clay indicators bulk mineral composition i e the amounts of calcite quartz gypsum k feldspar plagioclase dolomite and halite and trace element indicators i e rb sr and ba sr ratios of sediments deposited from 28 to 13 ma in the xunhua basin to reveal the climate and or provenance changes the results suggest that significant changes in sediment provenance occurred at 25 1 ma and 21 6 ma caused respectively by initial uplift and accelerated uplift of the laji shan the xunhua basin experienced warm and humid conditions at 28 0 25 1 ma cool and dry conditions at 25 1 21 6 ma and somewhat warmer and wetter conditions at 21 6 19 2 ma followed by aridification in two steps at 19 2 ma and 13 9 ma the climate cooling event at 25 1 ma corresponds temporally to a major phase of uplift of central tibet relatively warmer and wetter conditions during the early miocene 21 6 19 2 ma are considered to record the influence of the asian summer monsoon and accelerated uplift of the laji shan the shift toward more arid conditions on the northeastern qinghai tibetan plateau at 19 2 13 9 ma was probably driven by uplift of the tibetan plateau and further aridification since 13 9 ma may reflect a weakening of the east asian summer monsoon and global climatic cooling

kongur shan normal fault type example of mountain building assisted by extension karakoram fault eastern pamir the northernmost segment of the karakoram fault is an active normal dextral wrench fault that bounds the muji tashgurgan pliocene quaternary basin eastern pamir the kongurshan 7719 m and mustaghata 7546 m mountains are interpreted as twin crustal ramp anticlines formed en echelon on the eastern side of the karakoram fault by subduction of the tarim lithosphere under the pamir west dipping s c mylonitic gneisses that have downdip stretching lineations form the western flank of kongur mountain kinematic criteria consistently indicate a top to the west sense of shear the mylonitic foliation is cut by a steeper active normal fault which is marked by prominent triangular facets on west facing spurs the ductile normal shearing deformation occurred during the interval 5 1 ma therefore like the himalayas the pamir mountain range shows the coeval development of frontal thrusting and rear normal faulting the kongur fault thus appears to be an excellent example of synorogenic extension where normal faulting contributes to relief

timing and magnitude of displacement on the altyn tagh fault constraints from stratigraphic correlation of adjoining tarim and qaidam basins nw china the altyn tagh fault plays an important role in growth of the north western tibetan plateau but the timing of its inception and magnitude of left lateral displacement are not well constrained this study provides new independent constraints by correlating stratigraphic development and spatial distribution of the neighbouring tarim and qaidam basins it is shown that the tarim and qaidam basins experienced quite similar stratigraphic and sedimentary evolution from late sinian to early palaeogene times this fact indicates that the tarim and qaidam basins were a single block at least until oligocene time which was then offset by the altyn tagh fault early palaeozoic and late triassic suture zones within the east and west kunlun and pinch outs of mesozoic strata are chosen as piercing lines restoration of these lines gives total offset estimates of 350 400 km across the south western and central segments of the altyn tagh fault

high cooling and denudation rates at kongur shan eastern pamir xinjiang china revealed by 40ar 39ar alkali feldspar thermochronology orthogneiss samples taken from the kongur antiform show ages varying from 2 ma to 1 ma for 40ar 39ar ages of biotites and muscovites and fission tracks on apatites leading to cooling rates of 150 c m y modeling of k feldspars highlights the effect of a range of diffusion domains with contrasting diffusion characteristics yielding closure temperatures from 400 to 150 c the feldspar data document the cooling history since 5 ma and indicate a sudden change in cooling rates of the antiform at 2 ma at that time cooling increases by a factor of 5 from an average of 20 c m y to a minimum of 150 c m y consideration of the regional thermal history ongoing uplift and erosional history of the antiform during the quaternary suggests that denudation rates have been of the order of 5 7 km m y since 2 m y ago and could be associated with significant upward surface movement triggered by major normal faulting the antiform is interpreted to have formed during thrusting at the pamir front as a result of the development of thrust ramps and normal faulting at the crustal scale ramp stacking is an important process of mountain building and normal faulting in this context must be regarded as a very efficient way of building high relief

tectonic activities in dongshangen polymetallic ore district eastern kunlun mountains qinghai tibet plateau evidences from fission track thermochronology abstract the dongshangen polymetallic ore district is located in east section of the eastern kunlun mountains the south eastern margin of the qaidam basin and is one of the most important polymetallic mining regions however there is a relatively lower research degree on the district especially lack of thermochronology data using zircon and apatite fission track thermochronology this article reveals the tectonic activities experienced in dongshangen polymetallic ore district it is shown that the 6 age groups of geological thermal events i e 197 ma 182 170 ma 160 110 ma 110 80 ma 80 23 ma and 23 0 ma combining with the geological characteristics we consider that the 6 age groups belong to 6 periods of tectonic activities in the dongshangen ore district the first age group of 197 ma mainly resulted from the south kunlun fault strike slip and the qiangtang block collided with the kunlun block the second age group of 182 170 ma was related to the songpan ganzi bayan har basin closure the third age group of 160 110 ma was bound up with the left lateral strike slip took place in the north kunlun fault and the squeezing and collaging activities of both the qiangtang block and the lhasa block toward the eurasian plate the event during the 110 80 ma responded to northward subduction of the neo tethys ocean and strong strike slip in the altyn tagh fault zone the late cretaceous to miocene 80 23 ma was affected by the northward napping of the central kunlun terrane and the northward subduction of neo tethys ocean continued from 23 ma to present the collision of the indian plate toward the eurasian plate occurred leading to the qinghai tibet plateau uplifting as a whole synthesizing the geological characteristics and the tectonothermal events we discriminate 4 metallogenic periods of 197 ma 182 170 ma 155 112 ma and 109 88 ma in the district better reflecting the characteristics of multi stage metallogenic events

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

early cenozoic faulting of the northern tibetan plateau margin from apatite u th he ages models to explain the distributed nature of continental deformation predict the propagation of strain and high topography away from the plate boundary yet a growing body of evidence in the tibetan orogen suggests that deformation occurred at the far northern extent of the modern plateau early in the orogen s history and thus our current mechanical understanding of orogenic plateau development is incomplete new apatite u th he ages from four elevation transects document periods of rapid exhumation related to erosion pulses in hanging wall rocks of major thrust structures accelerated erosion is used as a proxy of fault timing and is interpreted in a larger context of structural data and sediment accumulation in adjacent foreland basins helium results are synthesized with published geologic thermochronometric and sedimentologic data from which a growing picture of regional compressional deformation in middle to late eocene time in northern tibet emerges we relate the early cenozoic period of deformation to the initiation of collision between india and eurasia despite the fact that the plate boundary was located 3000 km to the south regardless of whether or not high topography was built simultaneously as a result of this deformation early cenozoic strain signifies that the modern limit of the orogen has been relatively stationary since continental collision began and that deformation has not significantly propagated farther away from the plate boundary in time

a possible middle paleozoic suture in the altyn tagh nw china preliminary 40ar 39ar thermochronologic results from two transects across the altyn tagh at range allow new interpretations for the genesis of the range and provide constraints for its subsequent displacement recent reports of middle to upper ordovician pillow lavas in the ne portion of the range as well as the first reports of high pressure metamorphic rocks within the range are interpreted as the remnants of a lower paleozoic ocean subducted within the at muscovite and biotite ages from schist gneiss and granodiorite document a significant metamorphic and intrusive event throughout the range at 435 20 ma this fabric is crosscut by undeformed postorogenic microgranite plutons dated at 383 7 ma by muscovite these data suggest that an ocean basin closed after the early silurian and prior to the middle devonian forming the herein named lapeiquan suture the lack of similary aged plutons to the north and the suggestion of a synchronous arc to the south implies that subduction was south dipping present geography if the altyn tagh contains a middle paleozoic suture lateral continuations should be identifiable possibilities to the west include the kudi suture in the western kunlun shan comparisons of lithologies and radiometric data reveal significant similarities between the kudi suture and the altyn tagh suggesting that the at originated as part of the same middle paleozoic orogenic belt reconstruction of the paleozoic structure of northern tibet is complicated by cenozoic deformation particularly along the altyn tagh fault although this could be used as a measure of the finite post devonian deformation a more thorough understanding of paleozoic geodynamics is a prerequisite to unraveling subsequent displacements

holocene left slip rate determined by cosmogenic surface dating on the xidatan segment of the kunlun fault qinghai china cosmogenic dating using in situ sup 26 al and sup 10 be in quartz pebbles from alluvial terrace surfaces constrains the late holocene slip rate on the xidatan segment of the kunlun fault in northeastern tibet two terrace risers offset by 24 3 and 33 4 m having respective ages of 1799 388 and 2914 471 yr imply a slip rate of 12 1 2 6 mm yr the full range of ages obtained le 22 8 k y most of them between 6 7 and 1 4 k y confirm that terrace deposition and incision hence landform evolution are modulated by post glacial climate change coupled with minimum offsets of 9 12 m this slip rate implies that great earthquakes m approximately 8 with a recurrence time of 800 1000 yr rupture the kunlun fault near 94 e

a prolonged cenozoic erosional period in east kunlun western china constraints of detrital apatite u th he ages on the onset of mountain building along the northern margin of the tibetan plateau abstract the timing of the development of the highland topography along the northern margin of the tibetan plateau is the key to understanding the manner of tibetan growth and the far field effects of the collision between india and eurasia although various studies have investigated the exhumation and uplift of the basement rocks thermochronological studies on the detritus from a continuous depositional sequence inan intermontane basin are lacking but might shed light on this issue in this study a set of detrital apatites from an upper eocene to pliocene depositional sequence in the kumukol basin the largest intermontane basin in the east kunlun were dated by using the u th he technique the detrital apatites had consistent ages of 40 ma for all deposit formations from bottom to top which were older than the depositional ages the ages and their consistency suggested that these detrital apatites were not reset and that the ages represented the original ages in the provenance region these detrital apatite ages from the upper eocene to pliocene formations strongly suggested that the high mountains surrounding the kumukol basin formed at or before 40 ma and have remained high since then the process of mountain building resulted in a prolonged period of erosion from 40 to 2 6 ma the coupling of mountain and basin at 40 ma was widespread along the east kunlun our present results constrain the time of onset of the mountain building along the northern margin of the tibetan plateau which may represent a rapid response to the india eurasian collision

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

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

eocene to pliocene exhumation history of the tianshui huicheng region determined by apatite fission track thermochronology implications for evolution of the northeastern tibetan plateau margin abstract this study presents new apatite fission track aft data from the tianshui huicheng region which is situated in the northeastern margin of the tibetan plateau aft results including 19 detrital and 13 bedrock samples show that deposition in the tianshui huicheng basin range from early eocene to late miocene pliocene and most of the apatites derived from the western qinling orogenic belt reflecting one rapid exhumation episode at 34 29 ma and two phases of volcanism at 23 18 ma and ca 13 ma the exhumation history of the tianshui huicheng region is likely related to episodic tectonic activity and directly linked to the kinematics of active deformation of the tibetan plateau active processes deciphered from the detritus indicate that deformation reached the northeastern tibetan plateau margin as early as ca 49 ma which is manifested by the initiation of the tianshui huicheng basin the 23 18 ma event linked to the lithosphere deformation of the western qinling and the neogene basin formation along the tianshui huicheng region by modeling the bedrock samples an 8 4 ma event was revealed which resulted from the intense deformation of the tianshui huicheng region

formation and re orientation of the suerkuli basin within the altyn tagh in northeastern tibetan plateau since late miocene abstract the altyn tagh fault atf had formed in eocene time however the temporal evolution of slip along the fault remains elusive despite its important role in governing growth of the tibetan plateau tp and evaluating models of continental lithosphere deformation here we perform a high resolution magnetostratigraphic study on neogene sediments from the suerkuli basin a small basin located between two active strands of the atf results show that both depositional environment and the sedimentation rate changed at about 5 4 and 6 ma respectively lithofacies shift from conglomerates and sandstones with parallel and cross beddings to mudstones with horizontal bedding suggesting a sedimentary fluvial to lacustrine depositional environment shift even aridification increased over northern china from the tarim basin to the qaidam basin during late miocene to early pliocene times lacustrine deposition had started in the suerkuli basin still we argue that an increase in slip rate along the atf triggered concurrently forming of the intermontane basin the inferred timing of increased slip rate on the atf coincides with a variation in movement of the indian plate relative to eurasian plate since late miocene early pliocene time our work suggests that a re orientation of crustal shortening and deformation in the northern tp began since late miocene and supports the idea that the modern boundary of the tp orogen had rejuvenated to adjust deformation in plate boundary conditions

northward growth of the qimen tagh range a new model accounting for the late neogene strike slip deformation of the sw qaidam basin abstract situated along the western termination of the eastern kunlun mountains the qimen tagh range represents a key area to understand the cenozoic basin range interactions between the northeastern tibetan plateau and the qaidam basin within that region several huge bow like fault systems such as the kunbei and qimen tagh fault systems accommodate the transpressive deformation but their kinematic evolution is still highly debated newly acquired seismic profiles and isopach maps of the late eocene sediments strongly suggest that the kunbei fault system consisting of the kunbei arlar and hongliuquan faults in the southwestern qadaim basin was initially a left lateral strike slip fault system rather than a thrusting system growth strata indicate an early miocene onset age for this strike slip deformation however earthquake focal mechanisms show that the present day tectonic pattern of this fault system is dominated by ne sw transpression as for the qimen tagh fault system numerous linear geomorphic features and fault scarps indicate that it was again a strike slip fault system deformed sediments within the adatan valley prove that strike slip motion prevailed during the pleistocene yet the present day deformation is marked by ne sw transpression collectively the kunbei and qimen tagh fault systems were initially left lateral strike slip fault systems that formed during early miocene and pleistocene respectively colligating with these southward younging left lateral strike slip faulting ages and the fact that these convex northward structures converge to the center segment of active kunlun fault in the east we thus considered the kunbei and qimen tagh fault systems as former western segments of the kunlun fault once located further south in the present day location of that fault these faults gradually migrated northward since the early miocene while their kinematics changed from left lateral strike slip motion to ne sw transpression

relief history and denudation evolution of the northern tibet margin constraints from 40ar 39ar and u th he dating and implications for far field effect of rising plateau abstract how does the rising tibetan plateau affect its peripheral region the current understanding of the mechanism of orogenic plateau development is incomplete and thus no consensus yet exists in this regard however our new 40ar 39ar and u th he dataset presented in this study may shed some light on this issue 40ar 39ar dating on two vertical transects from the massif between nuomuhong and golmud indicates that the eastern kunlun range was built up and exhumated during the later triassic initially and a minimum overburden of 11 7 14 0 km has been eroded since 220 ma u th he age elevation relationships aers indicate a rapid exhumation event at 40 ma following a long period of slow exhumation phase from late mesozoic to early eocene time in this study two scenarios one assuming a single stage and the other assuming multiple stages of evolution history are modeled modeling of a multiple stage scenario is reasonable and is able to reflect the actual situation which reveals the entire denudation and relief history of the northern tibet from late mesozoic to the present time after prolonged denudation before 50 ma a low topography 0 17 times the relief of the present developed by 50 ma with an erosion rate of 0 013 0 013 0 025 mm yr the highest relief 1 82 times the relief of the present of the cenozoic time came into being at 40 ma with an erosion rate of 0 052 0 025 mm yr which was possibly a result of the collision between india and eurasia subsequently the relief steadily decreased to the present level due to continued denudation this suggests that deformation propagation from the continued convergence boundary between india and eurasia was insignificant after the construction of the highest relief this observation is broadly consistent with published accounts on the stratigraphic cooling and faulting histories of the northern tibet margin

preservation and exhumation history of the harizha halongxiuma mining area in the east kunlun range northeastern tibetan plateau china abstract the extent to which ore bodies are preserved in orogenic belts remains a poorly understood area of ore deposit research using zircon and apatite fission track analysis together with apatite u th he dating we constrained the erosion history of the ore bodies in the harizha halongxiuma mining area of the east kunlun range northern tibetan plateau china apatite fission track ages range from 114 8 to 87 6 ma with mean track lengths varying from 11 4 1 9 to 12 9 2 0 m zircon fission track ages vary from 205 14 to 142 7 ma in addition apatite u th he dating yielded ages of 60 56 ma the thermal history of jiapigou was modelled based on the apatite fission track data including ages and track lengths with constraints of zircon fission track ages and u th he ages the exhumation history of the harizha halongxiuma mining area was reconstructed with these age data revealing that since the early mesozoic the area has undergone three cooling stages 1 rapid cooling from 175 30 ma to 100 10 ma with a cooling rate and inferred exhumation of 2 0 0 8 c myr and 4 3 1 7 km respectively 2 a relatively stable stage from 100 10 ma to 40 10 ma with a cooling rate and inferred exhumation of 0 3 0 1 c myr and 0 5 0 2 km respectively and 3 rapid cooling since 40 10 ma with a cooling rate and inferred exhumation of 1 2 0 6 c myr and 1 4 0 4 km respectively this exhumation history is consistent with the subduction process of pacific plate and the strike slip movements of dunmi fault the total exhumation after main mineralization is calculated to be 7 6 3 2 km suggesting that ore bodies in the harizha halongxiuma mining area remain partially preserved

continental deformation accommodated by non rigid passive bookshelf faulting an example from the cenozoic tectonic development of northern tibet abstract collision induced continental deformation commonly involves complex interactions between strike slip faulting and off fault deformation yet this relationship has rarely been quantified in northern tibet cenozoic deformation is expressed by the development of the 1000 km long east striking left slip kunlun qinling and haiyuan faults each have a maximum slip in the central fault segment exceeding 10s to 100 km but a much smaller slip magnitude

39ar 40ar laser probe dating of terrestrial rocks we have shown that for metamorphosed granites as well as for metamorphosed sediments it is possible to obtain a reliable k ar age from a sample as small as 0 2 g samples with ages as young as 40 m y are easily studied there is no reason to believe that the method could not be used for samples considerably younger the main application of the laser will probably be for cases where the same mineral species has been formed during two distinct metamorphic events in the same rock in this case it is difficult if not impossible to make a mineral separate suitable for a 39 ar 40 ar study we have shown that in the case of an old granite the biotite in one sample distinctly shows thermal events at 1600 m y whileits primary cooling age is 2100 m y the thermal release study yields a good plateau age roughly an average age of the two thermal events an other interest of this method is demonstrated by argon dating of two different kinds of glaucophane only one of theseshowing argon in excess

paleogene crustal extension in the eastern segment of the ne tibetan plateau abstract the tibetan plateau experienced lateral growth in response to the india eurasia collision but uncertainties remain about when and how its present day margins were formed it was commonly viewed that crustal shortening in the ne tibetan plateau had commenced since the eocene and led to reverse faulting and compressional basins our recent investigations of some cenozoic intermontane basins reveal that synsedimentary normal faults occur widely in the eastern segment of the ne tibetan plateau normal faulting at basin bases obviously controlled basin sedimentation and presumably resulted in footwall uplift and basement exhumation small scale synsedimentary normal faults are very common in basin fill sequences although they decrease in intensity upwards and eventually vanish in the uppermost paleogene sequences measurement of the attitudes of synsedimentary normal faults indicates that crustal stretching was in nw se direction the nw se extension was consistent with paleogene stress field of the whole north china craton which were thought responsible for the ne sw trending rift basins in the interior of the north china craton such as the yinchuan weihe and bohai bay rift basin systems a broad unconformity separates paleogene and neogene sequences in the eastern segment of the ne tibetan plateau contrasting strikingly with conformable oligocene to middle miocene sequences in the neighboring ningnan and yinchuan rift basins it thus follows that the eastern segment of the ne tibetan plateau had not been formed in paleogene when it was basically dictated by crustal extension possibly as a result of far field effect of subduction of the western pacific plate end oligocene termination of normal faulting and the presence of a regional unconformity indicate that the eastern segment of the ne tibetan plateau began rising at the beginning of the miocene

a mechanism for syn collisional rock exhumation and associated normal faulting results from physical modelling abstract properly scaled physical modelling of the subduction of continental lithosphere is performed with a three layer lithospheric model the model includes a strong upper crust a weak ductile lower crust and a strong mantle part the lithosphere is underlain by a low viscosity asthenosphere subduction is produced by a piston push force and the pull force from the mantle lithospheric layer which is slightly denser than the asthenosphere the results of the modelling are tested on the example of the himalayas in the experiments all lithospheric layers subduct into the mantle to a depth corresponding to 200 300 km in nature until the upper crustal layer fails in front of the subduction zone forming a first major thrust fault the mct in our interpretation of the himalayas underthrusting along this fault increases relief which upon reaching a height corresponding to several kilometres in nature is removed mechanically by a blade the blade is moved horizontally back and forth throughout the experiment this erosional unloading mechanism causes the previously subducted segment of the buoyant upper crust to slide upward over the weak lower crust at a rate comparable to the subduction rate the rise of the crustal slice accelerates displacement along the crustal thrust while producing a normal sense motion and exhumation of the material from great depth up to 40 50 km depending on the model parameters along the upper surface of the slice the rapid uplift of the crust then ceases and the orogenesis occurs further due to continuing underthrusting along the first major thrust at a certain stage the crust fails again producing a new major crustal thrust the mbt in the himalayas

multi stage tectono magmatic events of the eastern kunlun range northern tibet insights from u pb geochronology and u th he thermochronology article i nfo to understand the magmatic and tectonic events in the eastern kunlun range we conducted systematic zircon u pb geochronology and paired zircon zhe and apatite ahe u th he themchronology investigations in the central and eastern segments of this range zircon u pb ages show two stage magmatic events of late silurian and latest permian early jurassic zhe and ahe ages and multi system thermochronometers reveal multi stage rapid cooling events from a combination of these data with previously published geochronological and thermochronological ages and regional geological setting we confirm several important phanerozoic tectono magmaticeventsinthisregion whereasthesiluriangranitesmightberelatedtoasmallpaleo oceansub duction and subsequent collision the latest permian early triassic granitoids were produced by northward sub duction of the songpan ganzi paleo tethyan ocean the late triassic earliest jurassic granitoids and late triassic early jurassic exhumation are interpreted as response to the collision between kunlun qaidam and qiangtang samples close to the kunlun fault show rapid late oligocene early miocene exhumation 1 3 1 6 km ma whereas those from the northern part of central segment display extremely low exhumation rates 0 02 0 05 km ma this heterogeneous denudation during 30 20 ma between northern and southern part of the central segment requires that crustal thickening was completed by lower crustal underthrusting with littleex humation or crustal thickening in pre cenozoic times the activity of the kunlun fault and associated normal faulting component were probably responsible for this stage of rapid exhumation in the southern part the com plex tectono magmatic evolution of the eastern kunlun range is controlled by pre cenozoic paleo ocean subduc tions and subsequent continent collisions and paleogene india asia collision

geometry and kinematics of the arlar strike slip fault sw qaidam basin china new insights from 3 d seismic data abstract the right stepping en echelon kunbei fault system consisting of the hongliuquan arlar xiii and kunbei faults features importantly in the tectonic evolution of the southwest qaidam basin the 3d seismic cross section interpretation and key horizon similarity attribute analysis show that the nww striking arlar fault is composed of two steeply dipping faults f1 and f2 in cross sectional view and branches eastward into two west dipping faults f5 and f6 in map view the fact that the strata above t 2 the base of the early miocene xiayoushashan formation become dramatically thinner toward the high points of the arlar fault suggests an early miocene initiation ca 22 0 ma for this fault as indicated by the windowed amplitude related attribute maps the arlar fault and f5 one branch of the arlar fault have cumulative sinistral offsets of 8 6 8 7 km and 5 2 5 4 km respectively these considerably greater strike slip components in conjunction with the respective maximum true dip slip displacements of