active deformation to the north of the altyn tagh fault constraints on the northward growth of the northern tibetan plateau abstract sinistral transpressive deformation occurs in the region north of the altyn tagh fault due to the indo eurasian collision in this region several late cenozoic faults have developed and the sanweishan fault is the key feature with clear landforms in this study slip rate measurements combined with several dating methods imply that the sanweishan fault has been active with sinistral strike slip rates of 0 33 0 04 mm a since 14 ka bp and 0 28 0 03 mm a since 20 ka bp which are more than an order of magnitude smaller than that of the atf to the south the horizontal displacements are 1 7 5 5 m in the eastern segment and 25 0 76 0 m in the middle and western segments of the sanweishan fault the increment of horizontal displacement along the main sanweishan fault is 3 0 4 0 m between paleoearthquakes and the magnitude of the latest paleoearthquake on the middle and eastern segments of the fault is up to m 7 2 7 5 the whole length of the sanweishan fault is 360 km or longer which include active faults in the yangguan and danghe reservoirs in the west more components of thrusting occur on the western and eastern segments of the sanweishan fault the growth of the sanweishan fault is similar to that of the atf but the former fault is younger and its slip rate is much smaller the differential slip rates on the sanweishan fault and atf may result in the clockwise rotation and eastward movement of the intervening block which compresses regions to the northeast

late cenozoic river system reorganization and its origin within the qilian shan ne tibet abstract the northward growth of the tibetan plateau has reshaped the qilian shan orogen with prolonged history along two large strike slip faults the altyn tagh fault on the west and the haiyuan fault on the east this orogen with its high elevation is referred to as the water tower of the northeastern margin of the tibetan plateau shedding many rivers into the surrounding arid areas in a way different from all other orogens within the plateau the factors that control the evolution of these rivers in this highly active region particularly their relative contribution through time are not well known our study presents evidence that the left lateral movement of the haiyuan fault one of the largest active strike slip faults within the tibetan plateau since 13 8 ma created a series of nw trending linear thrust fold belts aligned in an en echelon pattern along the trace of the fault this completely reconfigured the flow direction of the rivers within the qilian shan range from n s rivers that flowed into the hexi corridor and qaidam basin to today s w e rivers flowing into the tarim basin and longxi basin along a series of nw trending linear thrust folds belt aligned in an en echelon pattern along the trace of the haiyuan fault on the north and south this river system reorganization event is corroborated by sedimentary and geochronologic evidence within the intermountain basins where these rivers flow the longxi basin the largest intermountain basin surrounding the qilian shan on the east was drained by rivers flowing east which were dammed by the uplift of the liupan shan since 10 8 ma to form a large lake the second river system reorganization again occurred through climate change in 1 8 ma it included the incision of the yellow river capturing major rivers and halting their flow to the southeast it is concluded that the haiyuan fault plays a crucial role not only in the lateral growth of the tibetan plateau but also in the uplift of the qilian shan which led to the river system reorganization

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault 1 zircons and monazites from 6 samples of the north ayilari dextral shear zone nasz part of the karakorum fault zone kfz have been dated with the u th pb method using both id tims and sims techniques the ages reveal 1 inheritance from several events spanning a long period between the late archean and the jurassic 2 an eocene oligocene magmatic event similar to 35 32 ma 3 an oligo miocene magmatic event similar to 25 22 ma at least partly synkinematic to the right lateral deformation and 4 a period of metamorphism metasomatism similar to 22 14 ma interpreted as thermal and fluid advection in the shear zone the labhar kangri granite located similar to 375 km farther southeast along the kfz is dated at 21 1 0 3 ma such occurrence of several oligo miocene granites along the kfz some of which show evidence for synkinematic emplacement suggests that the fault zone played an important role in the genesis and or collection of crustal melts we discuss several scenarios for the onset and propagation of the kfz and offset estimates based on the main sutures zones our preferred scenario is an oligo miocene initiation of the fault close to the na range and propagation along most of its length prior to similar to 19 ma in its southern half the averaged long term fault rate of the kfz is greater than 8 to 10 mm a in good agreement with some shorter term estimates based on the indus river course or quaternary moraines and geodesy our results show the kfz cannot be considered as a small transient fault but played a major role in the collision history

provenance analysis reveals mountain uplift in the midsection of the altyn tagh fault during the middle miocene the altyn tagh fault atf defines the northern margin of the tibetan plateau therefore its tectonic history is key to understanding the plateau s northward growth however our understanding of atf tectonics is incomplete owing in part to a lack of constraints in detailed basin evolution studies of this region approximately 1700 m of middle miocene pliocene clastic strata extracted from a section of the yitunbulake basin adjacent to the midsection of the atf records the uplift of the altyn tagh range this paper reports 490 concordant detrital zircon u pb ages derived from this set of strata in addition paleocurrents and conglomerate clastic compositions were measured to determine the provenance of the basin the dominant detrital zircon age populations within these sedimentary rocks are 260 240 500 400 and 950 900 ma the 260 240 ma component decreases sharply above the lower xia youshashan xyss formation moreover we performed u th he dating on 260 240 ma detrital zircons from the xyss

evidence for northeastern tibetan plateau uplift between 25 and 20 ma in the sedimentary archive of the xining basin northwestern china the growth history of the tibetan plateau provides a valuable natural laboratory to understand tectonic processes of the india asia collision and their impact on and interactions with asian and global climate change however both tibetan plateau growth and asian paleoenvironments are generally poorly documented in pre pliocene times and reflect limited temporal coverage for different parts of the plateau here we present magnetostratigraphic results from the xining basin at the ne margin of the tibetan plateau precisely dating the record between the earliest oligocene 33 ma to the middle miocene 16 ma the pattern of observed paleomagnetic polarity zones is unequivocally correlated to the geomagnetic polarity time scale gpts indicating relatively constant and low sediment accumulation rates 32 m myr except for a peculiar period of unstable accumulation between 25 3 and 19 7ma at the beginning of this interval a marked permanent increase in magnetite content of the sediments is observed and likely relates to a change in provenance we directly relate this unstable period of sediment accumulation and provenance change to the coeval exhumation recently reported by low temperature thermochronology from the laji shan range which subsequently formed the southernmargin of the xining basin evidence for ne tibet tectonismat 25 20 ma can be associated with widespread deformation over the entire himalayan tibetan orogen at this time which may be linked to the coeval appearance of monsoon climate in eastern asia and the onset of central asian desertification

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

early cenozoic exhumation in the qilian shan northeastern margin of the tibetan plateau insights from detrital apatite fission track thermochronology

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

upper oligocene lacustrine source rocks and petroleum systems of the northern qaidam basin northwest china our organic geochemical study of oils from the northern qaidam basin defines a family of genetically related oils that contain biomarkers indicative of source rocks deposited in tertiary hypersaline anoxic lacustrine settings although cenozoic outcrop samples from northern qaidam are too organic lean to be of source quality dark laminated upper oligocene mudstones containing gypsum crystals and pyrite from the shi 28 well yield total organic carbon toc and rock eval data indicative of fair to good source rocks organic matter is derived from algae and bacteria and there apparently was little contribution from terrestrial material biomarker data provide a good correlation between the produced oils and the upper oligocene shi 28 core samples hydrocarbons derived from these source rocks are contained in upper oligocene miocene and pliocene reservoirs although eight of the oil samples are from the northwest corner of the basin one sample in this genetic family of hypersaline oils comes from northeast qaidam an area previously believed to only produce oils derived from jurassic freshwater lacustrine source rocks this sample thus indicates the presence of an unidentified and undocumented source rock in the northeast part of the basin hypersaline oils and the associated source rocks have low biomarker maturity parameters thermal modeling indicates that hydrocarbon generation probably occurred in northwestern qaidam within the last 3 million years

detrital apatite fission track evidence for provenance change in the subei basin and implications for the tectonic uplift of the danghe nan shan nw china since the mid miocene abstract the subei basin is located at the intersection of the northeastern end of the altyn tagh fault atf and the western end of the danghe nan shan in the northeastern tibetan plateau the basin contains up to 4000 m thick cenozoic terrestrial clastic sediments which contain information on the uplift of the danghe nan shan in order to estimate the detrital apatite thermochronology with fission track dating we collected eight sandstone samples from the tiejianggou section of the subei basin which has an established depositional age range from 22 8 to 9 ma we found that a distinct change in slope of the peak age and lag time of the detrital apatite fission track occurred at 14 ma which we interpret as a provenance change caused by the uplift of the western end of the danghe nan shan combined with previous studies in adjacent areas this work implies that the initiation of successive episodes of surface uplift in the northeastern margin of the tibetan plateau took place in the mid miocene

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

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

the evolution of the complex anticlinal belt with crosscutting strike slip faults in the central tarim basin nw china integrated 2 d and 3 d seismic data sets reveal that a wnw trending complex anticlinal belt the tazhong uplift was cut roughly perpendicularly by a series of nne oriented strike slip faults in the central tarim basin nw china through detailed interpretation of the internal architecture of the tazhong uplift and the structural characteristics of the strike slip faults the timing of their movements was determined based upon their geometric relationship and coeval movement we propose an integrated model for the evolution of both the tazhong uplift and the strike slip fault system initially the tazhong uplift formed perpendicular to the nne oriented compression that responded to the collision between the tarim block and the western kunlun terrane in the latest middle ordovician meanwhile regional joints formed parallel to the maximum compression that is perpendicular to the tazhong uplift in the latest ordovician northward compression caused the uplifting climax of the tazhong uplift in response to the collision between the tarim block and the coherent eastern kunlun altyn tagh qaidam qilian terrane under such a northward compression the resolved shear stress on the nne trending joints formed the transpressional strike slip faults afterward the tazhong uplift tilted northward during the ongoing subduction from the kunlun ocean which lasted until the latest middle devonian the negative flower structures formed along the preexisting transpressional strike slip faults due to the dragging of the overlying covers in the latest middle devonian the data and evolution model not only unveil the formation mechanism of the tazhong uplift and the associated strike slip faults but also provide further constraints on the evolutionary age of the proto tethys ocean

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

oligocene and miocene paleogeography of central california and displacement along the san andreas fault recently completed sedimentologic and petrologic studies of oligocene and miocene strata in the temblor range san joaquin basin and santa cruz mountains la honda basin permit detailed reconstructions of paleogeography as well as new estimates of displacement along the san andreas fault during the oligocene and miocene the san joaquin and la honda basins were contiguous the southwestern margin of the san joaquin la honda basin was tectonically unstable and paleogeographically complex with several small deep sea fans fed by sediment derived from nearby subaerial uplifts of franciscan and granitic basement one of these deep sea fans represented by the temblor formation of the southern temblor range and the vaqueros sandstone of the central santa cruz mountains apparently has been displaced about 315 to 320 km by post early miocene post zemorrian about 23 ma right lateral slip along the san andreas fault this new estimate of displacement places an additional constraint on interpretations of san andreas slip history but ambiguities remain the time of initiation of san andreas displacement is poorly known and available data do not permit discrimination between a history of relatively continuous slip versus a history of episodic slip

late cenozoic tectonic activity of the altyn tagh range constraints from sedimentary records from the western qaidam basin ne tibetan plateau the altyn tagh range atr is the northern geological boundary of the tibetan plateau and plays a key role in accommodating its cenozoic lithospheric deformation however knowledge of the structural style and age of uplift of the atr is limited and controversial the qaidam basin in the southeast side of the atr provides an outstanding field laboratory for understanding the history and mechanisms of atr growth this study presents a detailed sedimentological analysis of a 1040 m thick late cenozoic similar to 17 5 0 ma sedimentary sequence from the western qaidam basin together with the analysis of sedimentological data from nearby boreholes and sections our aims were to determine the spatiotemporal evolution of the sedimentary sequences in the study area and to explore their response to late cenozoic tectonic activity in the atr the results show three major intervals of the sedimentary characteristics in the study area similar to 17 16 ma 10 ma and 17 16 ma similar to 16 10 ma and similar to 10 ma during which the atr respectively experienced tectonic uplift fast strike slip motion and intense uplift

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

two stage evolution model for the altyn tagh fault china the northeastern extension of the altyn tagh fault china beyond the apparently truncated qilian shan has been controversial since the recognition of this large left slip fault we propose that the altyn tagh fault may have been contiguous with the east northeast to northeast trending currently inactive but apparently active during the cenozoic alxa east mongolia fault the latter truncated the beishan orogen to the northwest and the inner mongolia orogen to the southeast the beishan orogen can be correlated with the inner mongolia orogen on the basis of the recognition of three offset petrotectonic units and two offset sutures this correlation requires 400 50 km of left lateral offset along the alxa east mongolia fault identical to the slip along the northern segment of the altyn tagh fault inferred by p molnar and p tapponnier we suggest a two stage model for fault evolution during the first stage 400 km of displacement separated the inner mongolia orogen from the originally contiguous beishan orogen along a continuous altyn tagh alxa east mongolia fault during the second stage the alxa east mongolia fault became inactive and additional offset along the altyn tagh fault has been mainly accommodated by shortening of the qilian shan and the qaidam basin we infer that the first stage of movement along the altyn tagh alxa east mongolia fault system may have begun around oligocene time the region transformed to the second stage of fault movement ca 13 16 ma probably because of thinning of the lithospheric mantle beneath northern tibet the proposed model suggests that the derbur fault in northernmost china and beyond is an extension of the alxa east mongolia fault and has a history of strike slip movement the nearly 400 km of offset on the alxa east mongolia fault may have been accommodated mainly by subduction in the sea of okhotsk

lower middle jurassic nonmarine source rocks and petroleum systems of the northern qaidam basin northwest china the qaidam basin is a nonmarine petroliferous basin on the northeastern margin of the tibet plateau potential source rocks are reported from tertiary saline lacustrine deposits and jurassic freshwater lacustrine or terrestrial strata the jurassic source rock is similar in terms of depositional system lithology age and organic geochemistry to nonmarine jurassic rocks that are thought to be potentially significant hydrocarbon sources in many basins of central asia including the tarim junggar and other important petroleum producing basins these jurassic source rocks were deposited in freshwater lacustrine systems in intracontinental foreland style basins during the early and middle jurassic these lacustrine strata are associated with coals and coaly mudstones with possible secondary importance as hydrocarbon source rocks oils from the northern qaidam basin can be divided into two groups based on molecular indicators of depositional environment and age diagnostic biomarkers those derived from this jurassic freshwater lacustrine source rock and those derived from a tertiary hypersaline lacustrine source rock the correlation of some qaidam oils to a jurassic source establishes a petroleum system involving these nonmarine jurassic source rocks oils of this petroleum system have been produced from tertiary and mesozoic reservoirs in anticlinal and thrust related traps in northeastern qaidam maturation modeling of the jurassic source rock indicates that these oils were generated and expelled during the miocene pliocene in much of northern qaidam the geological context of the basin suggests that drainage within the basin primarily was vertical probably mainly along faults until evaporite or overpressured shale seals were encountered in the overlying cenozoic section documentation of this petroleum system suggests other exploration targets remain underevaluated in northern and southwestern qaidam furthermore the northern qaidam petroleum system is a useful analog to interpret the role of similar jurassic source rocks in other sparsely documented basins of central asia

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

continental collision slowing due to viscous mantle lithosphere rather than topography the rate of india s convergence with eurasia has decreased exponentially since their collision which suggests that the deforming continental lithosphere creates a type of viscous resistance that affects plate motion irrespective of how topography evolved the forces that control plate motion are fundamental to plate tectonic theory it has generally been thought that deforming and thickening continental crust is responsible for slowing down the convergence between two continental plates marin clark now shows however that the rate of penetration of the indian subcontinent into eurasia has decreased exponentially since the plates collided which suggests that contractional strain across tibet has been constant throughout the collision she infers that this reflects deformation of the mantle lithosphere and that under conditions of constant stress and strength the deforming continental lithosphere creates viscous resistance that affects plate motion irrespective of how topography evolved because the inertia of tectonic plates is negligible plate velocities result from the balance of forces acting at plate margins and along their base1 observations of past plate motion derived from marine magnetic anomalies provide evidence of how continental deformation may contribute to plate driving forces2 3 4 5 6 7 8 a decrease in convergence rate at the inception of continental collision is expected because of the greater buoyancy of continental than oceanic lithosphere2 3 but post collisional rates are less well understood slowing of convergence has generally been attributed to the development of high topography that further resists convergent motion7 8 9 10 however the role of deforming continental mantle lithosphere on plate motions has not previously been considered here i show that the rate of india s penetration into eurasia has decreased exponentially since their collision the exponential decrease in convergence rate suggests that contractional strain across tibet has been constant throughout the collision at a rate of 7 03 10 16 s 1 which matches the current rate a constant bulk strain rate of the orogen suggests that convergent motion is resisted by constant average stress constant force applied to a relatively uniform layer or interface at depth this finding follows new evidence that the mantle lithosphere beneath tibet is intact11 which supports the interpretation that the long term strain history of tibet reflects deformation of the mantle lithosphere under conditions of constant stress and strength the deforming continental lithosphere creates a type of viscous resistance that affects plate motion irrespective of how topography evolved

the interplay between climate and tectonics during the upward and outward growth of the qilian shan orogenic wedge northern tibetan plateau abstract mountains grow upward and outward when the accretion of material outpaces its removal mountain building is synergistically influenced by geodynamics internal structures crustal and lithospheric and climate the northward growth of the qilian shan which occupies a transition zone between the 4500 m high central tibetan plateau and the adjacent

early pleistocene uplift of the northeastern tibetan plateau evidence from the dunhuang basin nw china abstract the cenozoic uplift of the tibetan plateau plays an important role in global climate change basin mountain geomorphology formation and desertification in western china as an important component the early pleistocene uplift process and its influence on the northeastern tibetan plateau has been controversial for many years quaternary synorogenic sediments within the dunhuang basin on the northeastern tibetan plateau record the details of plateau uplift detailed grain size analysis rock magnetic properties mudstone 36cl dating and 40ar 39ar detrital mica dating were conducted on the quaternary alluvial fluvial lacustrine aeolian sediments of the dunhuang basin the aksay section in the southern dunhuang basin is dominated by conglomerate sandstone siltstone and mudstone detrital mica 40ar 39ar ages show major age populations of 200 160 ma 400 200 ma and 510 430 ma from the northeastern altyn mountains the results of 36cl ages and rock magnetic properties show that the altyn mountains rapidly uplifted at 1 16 ma from 1 16 to 0 80 ma the sedimentary environment was stable with two small scale uplift pulses at ca 1 03 ma and 0 98 ma after 0 80 ma the climate became arid and the kumtag desert formed in the dunhuang basin these multistage uplifts are also widely found in the northeastern tibetan plateau the early pleistocene uplift of the altyn mountains corresponding to the kunhuang movement resulted in the northeastern margin of the tibetan plateau reaching its present height and climate changeing towards drought in this region

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

intensified aridity of the asian interior recorded by the magnetism of red clay in altun shan ne tibetan plateau abstract the aridity history of monsoon dominated areas has previously been traced by high resolution studies of the well known loess and red clay sequences on the chinese loess plateau however the aridity process further west in china and the differences from the monsoon regime are unclear because no continuous aeolian sequences have been found in those areas here we describe and interpret an 88 4 m thick neogene aeolian sequence containing 40 visually defined brownish red clay and gray caliche nodule layers in the eastern xorhol basin northeast of the tibetan plateau magnetostratigraphic results show that the sequence was deposited between 13 and 2 6 ma the sequence can be divided into two parts with different climate conditions according to magnetic susceptibility ms the lower part 13 11 5 ma indicates a more changeable climate with higher ms values average 15 10 8 m3 kg 1 dominated by magnetite the upper part 10 3 2 6 ma reflects a drier climate with lower stable ms values average 9 5 10 8 m3 kg 1 mainly arising from hematite our results indicate that the intensified aridity of the asian interior started between 11 5 ma and 10 3 ma when ms decreased significantly due to outward growth of the tibetan plateau at around 12 ma together with ongoing global cooling and regression of the neotethys ocean during the cenozoic

miocene cooling in the northern qilian shan northeastern margin of the tibetan plateau revealed by apatite fission track and vitrinite reflectance analysis apatite fission track and vitrinite reflectance data from phanerozoic rocks of the northern qilian shan and jiuxi basin at the northeastern margin of the tibetan plateau show a complex thermal history with multiple paleothermal events peak paleotemperatures reached in the middle cretaceous suggest that hydrocarbon generation occurred in the basin at that time paleozoic mesozoic samples show evidence of a middle tertiary cooling episode between 20 and 10 ma this thermal fingerprint is significant because stratigraphic evidence for miocene exhumation is overwhelmed by spectacular pliocene pleistocene deformation and erosion we interpret the miocene cooling as recording initial exhumation of the northern qilian shan earlier than other models have proposed i e after 6 5 ma miocene cooling is broadly coincident with cenozoic uplift and exhumation recorded elsewhere in the tibetan tarim region

late cretaceous to middle tertiary basin evolution in the central tibetan plateau changing environments in response to tectonic partitioning aridification and regional elevation gain located in the bangong suture zone between the lhasa and qiangtang terranes of central tibet the nima basin records cretaceous late miocene sediment accumulation during a period of drastically changing paleogeography and paleoelevation the bangong suture zone originally formed during late jurassic early cretaceous time as the lhasa terrane collided with the qiang tang terrane during early to middle cretaceous time the region lay at northern near equatorial paleolatitudes near sea level by aptian time the nima basin was above sea level and was strongly influenced by nearby volcanic activity and crustal shortening in the reactivated bangong suture zone in the southern nima basin an 50 m y late cretaceous eocene depositional hiatus correlates with major crustal shortening and ensuing voluminous ignimbrite eruptions in the lhasa terrane in the northern nima basin deposition continued during latest cretaceous time recording arid paleoclimate in evaporitic lacustrine and eolian dunefield deposits by oligocene time the nima basin comprised two independent depocenters that accumulated coarse grained alluvial fluvial lacustrine evaporitic and fan delta deposits in close association with reactivated thrusts in the bangong suture zone carbon and oxygen isotope data from oligocene paleosol carbonate reported elsewhere indicate that regional paleoelevation during the late oligocene was 4 6 km as it is today overall the depositional record of the nima basin combined with ongoing structural and geochronologic studies demonstrates that the bangong suture zone was reactivated during middle cretaceous and middle tertiary time that the intervening 50 m y interval was a time of regional upper crustal shortening in the lhasa terrane followed by regional ignimbrite eruptions and that arid paleoclimate and high paleoelevation were established by the late cretaceous and late oligocene respectively within the context of other data sets from the lhasa terrane the record of deposition in the nima basin is consistent with low angle subduction of neotethyan oceanic lithosphere and reactivation of the bangong suture zone during the early cretaceous followed by shortening within the gangdese retroarc and northern lhasa terrane thrust belts during the late cretaceous lithospheric delamination dripping and regional magmatic flare up during latest cretaceous through early tertiary time and underthrusting of indian lower crust and lithosphere as far north as the bangong suture zone during late oligocene time

crustal lithospheric structure and continental extrusion of tibet crustal shortening and thickening to c 70 85 km in the tibetan plateau occurred both before and mainly after the c 50 ma india asia collision potassic ultrapotassic shoshonitic and adakitic lavas erupted across the qiangtang c 50 29 ma and lhasa blocks c 30 10 ma indicate a hot mantle thick crust and eclogitic root during that period the progressive northward underthrusting of cold indian mantle lithosphere since collision shut off the source in the lhasa block at c 10 ma late miocene pleistocene shoshonitic volcanic rocks in northern tibet require hot mantle we review the major tectonic processes proposed for tibet including rigid block continuum and crustal flow as well as the geological history of the major strike slip faults we examine controversies concerning the cumulative geological offsets and the discrepancies between geological quaternary and geodetic slip rates low present day slip rates measured from global positioning system and insar along the karakoram and altyn tagh faults in addition to slow long term geological rates can only account for limited eastward extrusion of tibet since mid miocene time we conclude that despite being prominent geomorphological features sometimes with wide mylonite zones the faults cut earlier formed metamorphic and igneous rocks and show limited offsets concentrated strain at the surface is dissipated deeper into wide ductile shear zones

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

contributions of triassic tectonism to build the northern tibetan plateau insights from tectonic evolution of the jinhongshan range central altyn tagh fault system

sedimentary evidence against large strike slip translation on the northern altyn tagh fault nw china abstract whether the oblique left reverse northern altyn tagh fault has large cumulative offset 120 km is one of the most controversial issues concerning the deformation mechanics for the northern tibetan plateau in order to obtain material constraints on its total displacement sedimentologic and bedrock provenance analysis of oligocene pleistocene strata on the northern side of the fault was conducted lithofacies analysis and 970 paleocurrent measurements show that these strata were products of fluvial systems originating from south of the fault making it possible to constrain the fault s slip history by establishing cross fault sediment source linkages identification of 5217 conglomerate clasts in the field indicates that major clast types are quartzite 30 50 schist gneiss increasing upsection from 10 to 40 50 and marble decreasing upsection from 20 30 to 30 km strike slip translation on the northern altyn tagh fault and support the model that strain induced by indian indentation has been partitioned into left slip on the altyn tagh fault and reverse dip slip on the northern altyn tagh fault

late miocene thrust fault related folding in the northern tibetan plateau insight from paleomagnetic and structural analyses of the kumkol basin abstract constraints on the timing and style of the tibetan plateau growth help spur new understanding of the tectonic evolution of the northern tibetan plateau and its relation to the india asia continental collision in this regard records of tectonic deformation with accurate ages are urgently needed especially in regions without relevant studies the kumkol basin located between two major intermontane basins the hoh xil and qaidam basins may hold clues to how these major basins evolve during the cenozoic however little has been known about the exact ages of the strata and tectonic deformation of the basin herein detailed paleomagnetic and structural studies are conducted on the southern baiquanhe section in the central kumkol basin northern tibetan plateau the magnetostratigraphic study indicates that the southern baiquanhe section spans a time interval of 8 2 4 2 ma well preserved growth strata date to 7 5 ma providing evidence for a significant thrust fault related folding this thrust related folding has also been identified in the tian shan foreland and in the northern tibetan plateau most likely implying a pulsed basinward deformation during the late miocene

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

petrology and geochronology of eclogites from the western segment of the altyn tagh northwestern china abstract the eclogites from the western segment of the altyn tagh occur as lens or boundins within quartzofeldspathic gneisses or pelitic gneisses characterized by amphibolite facies parageneses the petrographic features and reaction textures testify to three main metamorphic stages 1 the peak eclogite facies stage p 15 kbar t 665 880 c 2 the granulitic facies stage p 11 14 kbar t 670 800 c and 3 the amphibolite facies stage p 6 3 9 5 kbar t 619 738 c during decompression the trace element rare earth element and sm nd isotopic data suggest that most of the eclogites have protolith features resembling transitional type t type mid ocean ridge basalt morb the well preserved eclogite was selected for sm nd and u pb isotopic dating the sm nd isotopic data yield a whole rock garnet omphacite isochron of 500 10 ma age the u pb isotopic measurement of zircons from the same eclogite shows that the four grain populations are near concordant and are well plotted on concordia giving a weighted mean age of 503 9 5 3 ma the two different geochronological methods yield a similar age which is interpreted as the peak metamorphic age of eclogites and reflects the existence of a mountain root related to continental subduction during early paleozoic moreover based on the comparison with similar rocks in the northern margin of the qaidam basin a displacement of 350 400 km for the altyn tagh fault have been estimated

cenozoic multiple phase tectonic evolution of the northern tibetan plateau constraints from sedimentary records from qaidam basin hexi corridor and subei basin northwest china an integrated research of sedimentology stratigraphy and provenance analysis on eleven sedimentary sections from the qaidam basin hexi corridor and subei basin representing 36 km cenozoic strata provides a detailed record of the northern tibetan plateau growth since the early eocene sections are divided into three groups based on age geological similarities and geographical locations group one includes three early eocene late miocene sections from the northern qaidam basin group two contains four sections along the altyn tagh fault atf which preserve a complete stratigraphic record from the oligocene to late miocene group three contains the four youngest sections investigated from the northeastern qaidam basin and hexi corridor which preserve a record since the middle miocene to quaternary together the sections reveal a multiple phase tectonic history of the northern tibetan plateau the punctuated history can be divided into four phases 1 the eocene lulehe formation from the northern qaidam basin is interpreted as a synorogenic conglomerate deposited by high gradient depositional systems strong unimodal paleocurrent towards the southwest coarse lithology and distinct recognizable clast types constrain the sediment source within the north qaidam and south qilian terranes indicating activity on inferred thrust faults within the north qaidam and south qilian terranes in response to the initial india eurasia collision the activity on these thrust faults continued through the late eocene 2 the early oligocene conglomerate from group two formed in response to the sinistral transpression related to motion on the atf suggesting inception of substantial slip on the atf in the early oligocene in order to accommodate the continuing indentation of india into eurasia 3 oligocene early miocene fine grained fluvio lacustrine sediments from groups one and two formed as the result of development of internal drainage systems in the qaidam basin in response to the large amplitude slip motion on the atf paleocurrents collected from the oligocene early miocene strata of group one are northwest directed pointing towards the atf consistent with the pre existing subsurface data showing the shift of depocenter from along north qaidam and south qilian terranes toward the atf 4 all eleven sections preserve a post early miocene upward coarsening sequence consistent with the extensive crustal shortening and topographic growth across the northern tibetan plateau

cenozoic vertical axis rotation of the altyn tagh fault system paleomagnetic declination data were collected from cenozoic strata of the southern rim of the tarim basin to address whether the altyn tagh fault has undergone significant rotation during the indian asian collision results from the eastern and central altyn tagh fault zone suggest that it has undergone no significant rotation since the oligocene this implies that the boundary between the tarim and tibet has remained relatively stationary during most of the cenozoic in contrast declination data from the western kunlun shan on the eastern limb of the pamir orocline where the karakax segment of the altyn tagh fault system terminates suggest that the range has undergone clockwise rotations of between 19 3 8 6 and 27 8 5 8 such rotation is in mirror image with the documented counterclockwise rotation of 20 50 in the western pamir orocline and implies relatively small displacements on the karakorum fault our results also suggest that the karakax fault may have formed as an accommodation zone between the western kunlun shan and the karakorum mountains

40ar 39ar ages of detrital white mica constrain the cenozoic development of the intracontinental qaidam basin china ar 39 ar dating of detrital white mica from cenozoic sediments from the nonmarine qaidam basin in western china yields several age groups these include 1 ca 350 450 ma 2 220 280 ma subordinate clusters with 3 122 140 ma and 4 a minor group ca 500 ma ages between 350 and 450 ma are the most common and dominating in the analyzed samples detrital mica in the western qaidam basin can be of a northern altyn mountains and or a southern qimantagh kunlun mountains provenance the main age group of 350 450 ma is well known from intrusions in the altyn mountains whereas the young ages 120 126 ma have been found within shear zones along the central kunlun and altyn tagh faults however hinterland sectors beyond the altyn tagh and central kunlun faults must be considered as potential source areas because the imbalance between the amount of basin fi ll to eroded basement material requires additional sources early paleozoic ages ca 500 ma have been documented so far only in the hongliugou suture zone north of the altyn tagh fault this suggests late or slow continuous uplift of the southern altyn range and because of sinistral slip along the altyn tagh fault further units of the same age are now exposed farther westward the age group of 220 280 ma has been documented only from the northern basin margin this age group may indicate recycling from triassic jurassic cover sequences of the altyn mountains or provenance from permian triassic granite bodies that possibly originated in the qilian mountains

mesozoic and cenozoic tectonics of the northeastern edge of the tibetan plateau evidence from modern river detrital apatite fission track age constraints abstract thermochronometry of modern river sands exploits the natural sampling of detritus in a river catchment to infer plausible regional exhumation patterns when combined with available bedrock thermochronometric information apatite fission track age distributions for six detrital samples are reported in this study to resolve the exhumation history of the upper reaches of the heihe river draining north qilian shan and tuole shan the northeastern margin of the tibetan plateau the apatite fission track aft ages include four major populations late paleozoic 300 55 293 43 ma early mesozoic 223 15 205 17 ma late jurassic cretaceous 112 6 2 84 8 5 6 ma and cenozoic 63 8 5 9 19 3 1 7 ma the ages of these populations correspond well with the deformation and cooling history of the study area the late paleozoic and early mesozoic aft age populations record cooling events resulting from continental collision between the qiantang and kunlun blocks the late jurassic cretaceous aft age populations are interpreted to record cooling events associated with exhumation of north qilian shan and tuole shan due to the collision of the lhasa block with asian continent the cenozoic aft age populations record several cooling events a cooling event is recorded corresponding to exhumation of north qilian shan and tuole shan due to late stress from the lhasa asia collision causing deformation nearly synchronous with the india asia collision another cooling event is recorded corresponding to uplift and exhumation in oligocene time due to ongoing india asia convergence north qilian shan and tuole shan were constructed as a distal effect of india asia convergence in the early miocene while approaching their present mountain river basin distributions thermochronometry applied to heihe river sediments provide convinced evidence of multi stage exhumation of most northeastern margin of the tibetan plateau in the late paleozoic cenozoic

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

displacement and timing along the northern strand of the altyn tagh fault zone northern tibet abstract the northern strand of the altyn tagh fault has a late cenozoic left slip offset of 69 90 km near its northeastern end deformation began in this area as early as the oligocene but left slip displacement may be mainly of middle miocene to recent age because the altyn tagh fault zone transfers strike slip displacement into shortening in the qilian shan the total offset changes along the fault but the magnitude of displacement along this part of the fault zone suggests that only small scale eastward movement of crustal rocks occurred in this part of the tibetan plateau during the late cenozoic

magnetostratigraphy of cenozoic deposits in the western qaidam basin and its implication for the surface uplift of the northeastern margin of the tibetan plateau abstract thick cenozoic deposits in the northwestern qaidam basin record erosion of the altyn tagh and high terrain west of that basin and presumably the concurrent growth of the northeastern tibetan plateau a detailed magnetostratigraphic study of the huatugou section northwestern qaidam basin reveals that this section spans the period from 30 to 11 ma magnetostratigraphic and sedimentological studies indicate that the accumulation rate abruptly increased near 15 ma the acceleration in sedimentation rate suggests enhanced tectonic deformation in the qaidam basin since 15 ma that may have begun simultaneously with accelerated deformation along the altyn tagh kunlun and haiyuan faults which contributed to the growth history of the qaidam basin and its surroundings since 15 ma

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

cenozoic evolution of the pamir plateau based on stratigraphy zircon provenance and stable isotopes of foreland basin sediments at oytag wuyitake in the tarim basin west china abstract the pamir salient is the western expression of mountain growth related to indo eurasian convergence though a rough framework has emerged describing the tectonic evolution of the pamir detailed knowledge of the spatial and temporal evolution of cenozoic deformation is necessary to determine how strain progressed through the orogenic belt here we present new stratigraphic zircon provenance and stable isotope data from jurassic to miocene strata along the pamir s northeastern margin near the town of oytag wuyitake in the tarim basin west china prominent 40 ma peaks in oligocene to early miocene detrital zircon grains record the erosion of an eocene belt of shoshonitic rocks in the central to southeastern pamir this is roughly coincident with an 4 shift in the oxygen isotopic composition 18o of carbonates during the eocene and or oligocene from an average of 8 7 to 12 6 suggesting a reorganization of atmospheric circulation during that time this could have been caused by uplift of tarim basin bounding ranges and or retreat of the paratethys sea a subsequent change from eocene to jurassic aged detrital zircon grains in the early to middle miocene indicates provenance shifted from source rocks in the central and or se pamir to the hanging wall of the main pamir thrust mpt coincident with prograding facies at that time this suggests deformation progressed outward toward the northeast margin of the pamir plateau in the early to middle miocene our results corroborate outward advancement of himalayan deformation affecting all margins of the tarim basin by the middle miocene

in situ oxygen isotope records of crustal self cannibalization selectively captured by zircon crystals from high δ26mg granitoids zircon oxygen hafnium and biotite magnesium isotopic compositions of late cretaceous to oligocene 88 27 ma granitoids from the gyeongsang continental arc southeastern korea collectively provide a new insight into shallow magma petrogenesis zircon crystals extracted from eight calc alkaline or alkaline plutons commonly contain xenocrystic cores and typically show magmatic cathodoluminescence zonings and sharp raman spectra most zircons have positive ehf values plotting below the mid ocean ridge basalt evolution path indicating that the arc magmatism was dominated by the recycling of juvenile crustal materials zircon 18o values shifted upward or downward from the mantle range attest to the o isotopic exchange of crustal protoliths with surface waters at various temperature conditions small 1 but discernable core to rim decreases of 18o values are recognized selectively in magmatic zircon grains from four plutons possessing biotite 26mg values 0 07 to 2 32 distinctly higher than the mantle range such a concomitant o mg isotopic variation provides compelling evidence for a series of self induced hydrothermal alteration and assimilation processes i e crustal self cannibalization this study shows that the supracrustal input to magmas in a young and juvenile orogen can be traced effectively by the combination of stable isotope records from the plutonic root

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

paleomagnetism indicates no neogene rotation of the qaidam basin in northern tibet during indo asian collision paleomagnetic data were obtained from tertiary red sedimentary rocks at two locations separated by several hundred kilometers within the qaidam basin in the east central part of the basin 30 sites from the lower pliocene youshashan formation yielded characteristic remanent magnetization chrm directions with intermediate unblocking temperatures 100 600 8c chrm with high unblocking temperatures to 680 8c was isolated from 14 sites in the same area chrm directions were obtained from six sites within the oligocene lower gancaigou formation characteristic magnetization was also determined from 16 sites within the lower gancaigou formation exposed in the e bo liang range of the north central qaidam basin when compared with equivalentage expected directions for eurasia the mean paleomagnetic directions indicate no neogene vertical axis rotation of the qaidam basin or the altyn tagh fault the qaidam basin may act as an indentor translating without rotation toward the north china block and driving clockwise vertical axis rotations by differential shortening within the nan shan fold and thrust belt

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

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

new paleomagnetic constraints on middle miocene strike slip faulting along the middle altyn tagh fault knowledge of the evolution of the altyn tagh fault atf has significant implications for our understanding of the tectonic deformation of the tibetan plateau controversy exists regarding the formation of the orocline like arcuate structures or curved thrust faults south of the atf in this paper we conducted a paleomagnetic rotation study of the akatengnengshan ak and youshashan yss anticlines to determine whether the changes in the anticlines axes were caused by frictional drag associated with sinistral strike slip faulting along the atf no significant paleomagnetic rotations during the last 20ma were observed at the xichagou and laomangai localities which are situated along the yss anticline whereas significant counterclockwise ccw rotations of similar to 50 degrees that occurred between similar to 16 2 and 11 1ma were noted at the yitunbulake locality which lies along the western edge of the ak anticline this amount of ccw rotation is consistent with the difference in axes between the ak and yss anticlines combined with other geological evidence we believe that the middle atf was active between similar to 16 and 11ma frictional drag associated with sinistral strike slip motion likely resulted in the similar to 50 degrees ccw rotation of the ak anticline which was originally straight or parallel to the yss anticline there was concentrated or insignificant strike slip faulting along the middle atf before similar to 16ma but rapid and distributed 40km strike slip faulting occurred between similar to 16 and 11ma at a rate of 10mm yr and the minimum displacement was similar to 50km

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

jurassic early cenozoic tectonic inversion in the qilian shan and qaidam basin north tibet new insight from seismic reflection isopach mapping and drill core data

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

far field lithospheric deformation in tibet during continental collision 1 crustal deformation along the present day northern margin of the tibetan plateau has occurred since mid to late eocene time soon after india collided with eurasia assuming that on these distance and time scales the lithosphere can be approximated using a thin viscous sheet we show that far field lithospheric deformation caused by an indenting boundary is expected to start shortly after collision begins when a strong region analogous to cratonic lithosphere like that of the tarim basin is included in the calculations shear and vertical strain rates concentrate along the southern edge of the strong region resulting in enhanced deformation there in calculations scaled to the dimensions of india and the tibetan plateau shear and vertical strain rates on the northern edge of the plateau increase soon after collision begins crustal thickening accelerates later in the calculations we propose that the apparent increased exhumation and perhaps surface uplift around 10 ma may signal the arrival of the thickening front

from sea level to high elevation in 15 million years uplift history of the northern tibetan plateau margin in the altun shan approximately 1300 in of oligocene miocene clastic strata are exposed along the miran river in the southeastern tarim basin where the adjacent altun shan form the topographic escarpment of the northern tibetan plateau the sedimentary section is faulted against proterozoic rocks of the altun shan in the footwall of the south dipping oblique reverse northern altyn tagh fault oligocene lower miocene strata consist of fine grained rocks that record low gradient depositional systems mid miocene and younger rocks consist of coarse conglomerate derived from the altun shan and deposited by high gradient depositional systems the change to coarse high gradient depositional systems with detrital source areas coincident with the modern miran river drainage is interpreted to mark the onset of uplift of the altun shan on the northern altyn tagh fault and its erosional exhumation the age of the change from pre orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes early middle miocene planktonic foraminifera this interpretation is also supported by apatite fission track and u th he ages and thermal models that indicate rapid miocene cooling and hence rapid exhumation of the altun shan in addition to defining the age of the synorogenic section the foraminifera assemblage contains planktonic taxa indicating a connection to open marine waters and benthic assemblages typical of brackish to near sea level paleobathymetry thus micropaleontologic evidence demonstrates that the miran river locality now at 1400 in elevation was at sea level approximately 15 million years ago thus in addition to constraining the age of surface uplift and exhumation of the altun shan the principal mountain range of the tibetan plateau in this region as 15 to 16 ma the foraminifera assemblage indicates that the se tarim basin off the northern edge of the plateau had an average surface uplift rate of nearly 100 m m y for the past 15 million years these results suggest that shortening in the altun shan and uplift of the range significantly post dated the initiation of large scale strike slip on the altyn tagh fault and that regional surface uplift mechanisms operated in the tarim basin beyond the margins of the tibetan plateau

evidence of miocene crustal shortening in the north qilian shan from cenozoic stratigraphy of the western hexi corridor gansu province china new sedimentologic stratigraphie and compositional data from the paleogene neogene stratigraphie succession exposed in the northwest hexi corridor and within the north qilian shan provide evidence to suggest that crustal shortening in the north qilian shan fold thrust belt initiated during die miocene the section is composed of four lithostratigraphic units oligocene miocene fine to coarse grained unit 1 miocene conglomeratic unit 2 and pliocene pleistocene conglomeratic units 3 and 4 unit 3 lies in angular unconformity over both units 1 and 2 and unit 4 contains a progressive unconformity the onset of conglomerate deposition at the base of unit 2 suggests an increase in depositional energy which we interpret as me result of proximal orogenesis in the north qilian shan fold and tiirust belt supporting evidence includes the appearance of strongly northeast trending paleocurrents indicat ing paleoflow away from the qilian shan clast lidiologies that match sources in the north qilian shan and sandstone with detrital framework modes that indicate a recycled orogen source in contrast unit 1 contains paleocurrent indicators that are variable but generally trend northward and sandstone and clast compositions which are more diagnostic of a continental block source detrital zircon age determinations from unit 1 are also not consistent with a source in the north qilian shan rather they suggest a provenance in hinterland regions within the south qilian shan and north qaidam terranes in sum these results are all consistent with initiation of proximal uplift of the north qilian shan during deposition of the gradational transition from unit 1 to unit 2 demonstrating shortening in the qilian shan before die late miocene this comprehensive study tightens our understanding of when far field stress related to the india eurasia continent continent collision reached the northeastern edge of the tibetan plateau

oligocene miocene tectonics and sedimentation along the altyn tagh fault northern tibetan plateau analysis of the xorkol subei and aksay basins abstract tertiary basins adjacent to the northern edge of the tibetan plateau include both giant intracontinental sedimentary basins such as tarim and qaidam and smaller basins directly related to the evolution of the altyn tagh strike slip fault system and nearby fold thrust belts three examples of these smaller basins that formed during early evolution of the altyn tagh fault system are the xorkol aksay and subei basins the xorkol basin was the site of nonmarine siliciclastic sedimentation in alluvial fan playa and fluvial environments from at least the mid oligocene through the miocene sediment was delivered to the basin from source areas uplifted by basin bounding thrust faults and from the opposite side of the altyn tagh fault the age of the aksay basin is more poorly constrained but it also contains oligocene miocene nonmarine clastic strata that were derived from the southern side of the altyn tagh fault and adjacent thrust fault bounded uplifts the subei basin is characterized by s

localization of shear along a lithospheric strength discontinuity application of a continuous deformation model to the boundary between tibet and the tarim basin 1 a marked contrast in strength or viscosity within a continuously deforming zone can lead to concentration of shear strain in the weaker material adjacent to the boundary between them but localization comparable to the width of the altyn tagh shear zone requires an additional weakening process during numerical experiments on a thin viscous sheet indented by a rigid object a shear zone develops adjacent to a strong region mimicking the tarim basin when the boundary between the weak and strong regions is oblique to the orientation of convergence the width of this shear zone narrows with increased strain and for comparable penetration by the indenter the strain is more concentrated for larger values of n the exponent that relates strain rate to a power of stress and for smaller values of the argand number ar a measure of buoyancy induced stress relative to viscous stress increasing concentration of shear occurs as the indentation develops without weakening because of a change in material properties additional localization develops with the inclusion of strain dependent weakening associated with for instance a temperature increase due to shear heating for such localization to scale to the width of the altyn tagh fault zone of tibet the initial temperature near the moho must be relatively low 600 c and a large value of n 10 is required this suggests that deformation there is described by a high strength flow law such as that proposed by evans and goetze 1979 in which the lithosphere would deform approximately plastically

the cenozoic growth of the qilian shan in the northeastern tibetan plateau a sedimentary archive from the jiuxi basin sedimentary deposits in tibetan basins archive the spatial temporal patterns of the deformation and surface uplift processes that created the area s high topography during the cenozoic india asia collision in this study new stratigraphic investigation of the caogou section from the jiuxi basin in the northeasternmost part of tibetan plateau provides chronologic constraints on the deformation and northward growth of the plateau magnetostratigraphic analysis results suggest that the age of the studied 1000 m thick section spans from 24 2 ma to 2 8 ma detailed sedimentology and apatite fission track aft analyses reveal that variations in the clast provenance lithofacies sediment accumulation rates and aft lag times occurred at 13 5 10 5 ma we interpret these changes as in response to the initial uplift of the north qilian shan in addition paleomagnetic declination results from the section indicate a clockwise rotation of the jiuxi basin before 13 5 ma which was followed by a subsequent counterclockwise rotation during 13 5 9 ma this reversal in rotation direction may be directly related to left lateral strike slip activity along the easternmost segment of the altyn tagh fault combined with previous studies we suggest that movement on the western part of the altyn tagh fault was probably initiated during the oligocene 30 ma and that fault propagation to its eastern tip occurred during the middle late miocene

evolution of the ne qinghai tibetan plateau constrained by the apatite fission track ages of the mountain ranges around the xining basin in nw china abstract the laji shan and daban shan which are located along the southern and northern margins of the xining basin in the northeastern qinghai tibetan plateau experienced important multi stage exhumations during the cenozoic the apatite fission track aft dating of 19 samples along four north south sections in the laji shan and daban shan showed that the aft ages of the laji shan from 88 ma to 12 ma and the ages of the daban shan are between 60 and 32 ma all these aft ages are significantly younger than their host rock formation or sediment deposition ages thermal modeling of the aft data indicated that the laji shan had undergone important exhumation events in the late cretaceous ca 50 30 ma and 17 8 ma whereas the only significant thermal event in the daban shan occurred at ca 50 30 ma the exhumation of the laji shan during the late cretaceous may result from the lhasa qiangtang collision during 50 30 ma the central qilian block rotated clockwise relative to the south qilian block which led to the formation of the xining basin the slow uplift of the laji shan and daban shan in this period was the isostatic adjustment of the footwalls of normal faults along the two margins of the xining basin the exhumation of the laji shan during 17 8 ma resulted from compression due to the clockwise rotation of the south qilian block relative to the central qilian block causing the inversion of the xining basin a marked change in the sedimentary environments and a rapid increase in sedimentation rates

intracrustal detachment within zones of continental deformation geologic mapping of active to recently active geologic structures in panamint valley western united states and in the haiyuan region and northern tibetan plateau china suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres detachment occurs similarly in predominantly extensional panamint valley and in predominantly compressional china environments it involves structures with displacements of more than 10 km and displacement rates of more than 3 mm yr perhaps more than 10 mm yr the steeply dipping strike slip faults present in all three areas hunter mountain fault haiyuan fault and altyn tagh fault zone terminate in zones of extension or compression and geometric relations indicate that all structures including strike slip faults are thin skinned and restricted to the upper crust in panamint valley and in the haiyuan region deformation within these systems can be reconstructed in three dimensions displacement on the strike slip faults is absorbed by extension or compression occurring at the termination of the faults so strike slip displacement is roughly equal to and in the same direction as shortening or extension we propose that left slip on the altyn tagh fault zone in northern tibet is similarly absorbed by shortening southeast of the fault zone within the qaidam basin and the nan shan

danghe area western gansu china biostratigraphy and implications for depositional history and tectonics of northern tibetan plateau the danghe area in western gansu province is at the focal point of interaction of the northeastern end of the left lateral altyn tagh fault and growing ramp thrusts of the danghe nanshan mountains along the northern rim of the qinghai tibetan plateau with a thick sequence of tertiary sediments and associated fossil records the danghe area is one of few places on the tibetan plateau that can offer integrated studies of its tectonic history depositional environment and biological records including vertebrate and plant fossils past studies however have not been able to capitalize on the paleontological data or were often misguided by an outdated notion of regional chronology incorrect age estimates in these studies often have profound effects on tectonic interpretations we present new stratigraphic and paleontologic evidence from the danghe area and demonstrate a new chronologic scheme that indicates a much younger age for the majority of the sediments we recognize three packages of sediments in the danghe area 1 oligocene paoniuquan new name formation basal predominantly fine grained dark purple mudstones and siltstones that include the classic yindirte fauna which forms the basis of the tabenbulukian mammal age 2 early miocene to early late miocene tiejianggou new name formation that contains a new platybelodont proboscidean in a coarsening upward sequence terminating in a massive conglomerate and 3 an unnamed late neogene formation that contains another coarsening upward sequence in light of our new stratigraphic framework we reinterpret a previously published magnetic column for the middle sequence in xishuigou as representing chrons c6n through c4ar corresponding to a span of about 20 9 3 ma much younger than has been realized so far this new chronological framework suggests a depositional history of the danghe nanshan that spans at least the early oligocene through late miocene to possibly pliocene early depositions during the oligocene through middle miocene are dominated by fine grained sediments indicating a distant source of sedimentation paleontological data suggest a relatively dry environment as is typical of northern china today by late miocene around 9 12 ma the danghe area began to receive coarse sediments and was much closer to the mountain front the new stratigraphic framework indicates an earlier onset of sedimentation than has generally been assumed but also suggests the presence of sediments much younger than many have realized c 2003 elsevier science b v all rights reserved

late quaternary and present day rates of slip along the altyn tagh fault northern margin of the tibetan plateau 1 both global positioning system gps measurements and studies of late quaternary faulting are consistent with a slip rate of 10 mm yr along the central segment of the altyn tagh fault and a systematic decrease in that rate toward the eastern end of the fault dates of terraces above and below laterally offset terrace risers yield bounds on quaternary slip rates that range from those that agree with gps measurements to values as much as three times faster we argue that offset terrace risers that are protected by topography upstream of them are more closely dated by the age of the upper terrace than by that of the lower terrace in some cases valleys upstream of the fault have been incised into bedrock and few if any terrace risers can be seen within the valleys such streams debouch onto alluviated floodplains or fans that become incised presumably during climate changes to create terrace risers the terrace risers are then displaced so that they lie downslope from bedrock ridges on the upstream side of the fault and thus the risers become protected from further incision in such cases dates of upper terraces should more closely approximate the ages of the risers than those of lower terraces such dates yield slip rates of 10 mm yr in the central segment of the fault and decreasing rates eastward although we cannot with certainty rule out the higher slip rates along the altyn tagh fault our analysis does show that viable interpretations consistent with gps measurements are more likely at least along some segments of the fault not only do these rates support the view that the tibetan plateau deforms internally by slip on a distributed network of faults in the shallow brittle crust and hence behaves as a continuum at depth but the gradual decrease toward the east also shows that the altyn tagh fault does not separate two effectively rigid lithospheric plates correspondingly the relatively low slip rate and the eastward decrease in slip rate suggest that the altyn tagh fault does not transfer a significant portion of the convergence between india and asia into northeastward extrusion of the tibetan plateau thus large scale extrusion of crustal material in india s path into eurasia seems to be limited largely to the confines of the tibetan plateau