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

zircon hf isotopic constraints on the sources of the indus molasse ladakh himalaya india 1 india asia collision has resulted in the largest orogenic event on earth since at least 500 ma and this has had a profound influence on the drainage patterns of asia on the asian monsoon climate on global oceanography as well as on faunal extinctions despite this importance understanding of the paleogene evolution of this system is limited u pb and lu hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the indus molasse located within the indus suture of the ladakh himalaya india show that most have mesozoic cenozoic ages and juvenile hf isotopic compositions this suggests that the main source of these sediments is the transhimalayan batholith with minor flux from the lhasa karakoram terrane and indian plate the lower indus molasse chogdo formation is inferred to have been deposited at 60 49 ma whereas the upper choksti formation was deposited later than 45 41 ma and contains a greater contribution from the lhasa terrane the transhimalayan batholith was eroded throughout indus molasse sedimentation but increasing exhumation of lhasa karakoram terrane indicates its progressive uplift after initial collision and requires formation of apaleo indus river shortly after collision

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

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

flexural subsidence by 29 ma on the ne edge of tibet from the magnetostratigraphy of linxia basin china abstract this study provides a detailed magnetostratigraphic record of subsidence in the linxia basin documenting a 27 myr long sedimentary record from the northeastern edge of the tibetan plateau deposition in the linxia basin began at 29 ma and continued nearly uninterruptedly until 1 7 ma increasing rates of subsidence between 29 and 6 ma in the linxia basin suggest deposition in the foredeep portion of a flexural basin and constrain the timing of shortening in the northeastern margin of the plateau to late oligocene late miocene time by late miocene early pliocene time a decrease in subsidence rates in the linxia basin associated with thrust faulting and a 10 clockwise rotation in the basin indicates that the deformation front of the tibetan plateau had propagated into the currently deforming region northeast of the plateau

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

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

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

late pleistocene slip rate of the northern qilian shan frontal thrust western hexi corridor china we derive a slip rate for a frontal thrust in the western hexi corridor along the northern qilian shan by combining topographic profiling and 10be exposure dating the active yumen beidahe thrust fault offsets late pleistocene alluvial fan deposits and a prominent north facing scarp is well preserved to quantify the slip rate we surveyed the uplifted terraces and sampled quartz rich pebbles on terrace surfaces and river channels to determine surface exposure ages and pre depositional inheritance the minimum vertical slip rate of the fault is 0 73 0 09 mm a 1 this represents a horizontal shortening rate of 1 26 0 31 mm a 1 for a fault dip of 30 5 this estimated slip rate supports the inference made from previous geological and gps constraints that nne directed shortening across the western qilian shan and the hexi corridor is distributed on several active faults with a total shortening rate of 4 10 mm a 1 this article is protected by copyright all rights reserved

late cretaceous to early eocene deformation in the northern tibetan plateau detrital apatite fission track evidence from northern qaidam basin abstract unraveling the growth of northern tibet is crucial to understanding the geodynamic processes of the india eurasia collision evaluating plateau uplift models and reconstructing associated paleoclimate history however pre middle miocene deformation history of northern tibet remains poorly understood we use detrital apatite fission track detrital aft thermochronology of mesozoic and cenozoic sedimentary rocks from northern qaidam basin to constrain the early growth of northern tibet detrital aft ages of the mesozoic samples are younger than their depositional ages indicating that the mesozoic succession underwent two stages of exhumation after deep burial during 80 61 ma and 54 47 ma detrital aft ages of the cenozoic samples are older than their depositional ages and reveal that their source region experienced two periods of exhumation peak ages in 86 59 ma and 54 36 ma these results suggest that the northern tibet successively experienced late cretaceous early paleocene and early middle eocene deformation the late cretaceous early paleocene deformation implies that the extent of pre collisional india eurasia deformation region in the plateau were much larger than previously known the static detrital aft peak ages 54 51 ma based on lag time analysis for the paleogene samples demonstrate the early eocene deformation was a rapid and short lived event which was a far field response to the india eurasia collision hence we advocate synchronous deformation throughout the northern plateau at the collision time lag time analysis results also demonstrate absence of oligocene to early miocene cooling ages and post eocene decreasing exhumation rates in the cenozoic source regions this suggests relatively quiescent tectonic settings in the qilian mountains during the oligocene early miocene and agrees that the lateral strike slip movement of the altyn tagh fault was accommodated out of the plateau by the end of the early miocene

the distribution of active rock uplift in the interior of the western qilian shan ne tibetan plateau inference from bedrock channel profiles abstract the distribution of rock uplift rates in the interior of the western qilian shan is not yet fully resolved which limits our knowledge about the uplift pattern and landscape evolution in the northeastern tibetan plateau the stream power incision model suggests that the spatially differential rock uplift rate usually can exert a primary control on channel gradient thus providing a powerful approach to map the rock uplift pattern of active orogens here we analysed the river longitudinal profiles in the western qilian shan and found a spatially differential pattern with higher steepness indices along the parallel ranges e g the danghe nanshan daxue shan tuolai shan and the northern qilian shan but lower values in the intramontane basins comparison of steepness indices to variations in lithology and annual precipitation revealed limited correlation of channel gradient with lithologic resistance and climate in this landscape we also observed no systematic relationship between steepness indices with drainage area sediment flux or channel concavities we argued that the systematic changes in channel steepness indices are tectonically controlled rather than the consequence of variable sediment flux climate or lithology thus the normalized channel steepness pattern of the western qilian shan could reflect that the rock uplift is largely restricted to mountain ranges bounded by active thrust faults and imply distributed cenozoic crustal shortening by comparing the nne ssw directed elevation swath profiles and the channel steepness pattern we concluded that tectonic uplift rate should be higher in the northern qilian shan than in the internal ranges thus our study provides geomorphic evidence to favor both distributed crustal shortening and asian mantle lithosphere underthrusting as the primary mechanisms to explain the landscape evolution in the ne tibetan plateau

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

dissipation of fast strike slip faulting within and beyond northeastern tibet structural patterns global positioning system gps velocities and quaternary fault slip rates in northeastern tibet indicate a transfer of left lateral slip from the kunlun fault northeast to the haiyuan fault and minor crustal shortening and rotation within a 200 km wide stepover zone related deformation also continues at least a few hundred kilometers north of the haiyuan fault into a region of diffuse extensional shear or rotation underlain by average thickness crust fast localized slip along the central kunlun fault transforms into distributed deformation across a 500 km wide zone where the lower crust is weak the distribution of fault parallel gps velocities across this region suggests a decrease in fault slip toward eastern fault tips and progressive dissipation of slip to the north rather than east of the tibetan plateau as previously suggested

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

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

sources and mechanisms of formation of gaseous hydrocarbons in sedimentary rocks abstract accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in west siberia u s s r such as for example urengoy which comprise 30 of the proven gas reserves of the world a new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions the model allows the calculation of isotope values for different types of organic matter and their dependence on maturity application of the model to west siberia suggests that the supergiant gas accumulations in urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep overmature or bacteriogenic processes the new mathematical model suggests that humic organic matter in general has a high methane generating capacity at comparably low maturities of organic matter equivalent to 0 5 0 7 on the vitrinite reflectance scale

impacts of uplift of northern tibetan plateau and formation of asian inland deserts on regional climate and environment abstract based on the geological evidence that the northern tibetan plateau ntp had an uplift of a finite magnitude since the miocene and the major asian inland deserts formed in the early pliocene a regional climate model regcm4 1 with a horizontal resolution of 50 km was used to explore the effects of the ntp uplift and the related aridification of inland asia on regional climate we designed three numerical experiments including the control experiment representing the present day condition the high mountain experiment representing the early pliocene condition with uplifted ntp but absence of the asian inland deserts and the low mountain experiment representing the mid miocene condition with reduced topography in the ntp by as much as 2400 m and also absence of the deserts our simulation results indicated that the ntp uplift caused significant reductions in annual precipitation in a broad region of inland asia north of the tibetan plateau tp mainly due to the enhanced rain shadow effect of the mountains and changes in the regional circulations however four mountainous regions located in the uplift showed significant increases in precipitation stretching from the pamir plateau in the west to the qilian mountains in the east these mountainous areas also experienced different changes in the rainfall seasonality with the greatest increases occurring during the respective rainy seasons predominantly resulted from the enhanced orographically forced upwind ascents the appearance of the major deserts in the inland asia further reduced precipitation in the region and led to increased dust emission and deposition fluxes while the spatial patterns of dust deposition were also changed not only in the regions of uplift impacted topography but also in the downwind regions one major contribution from this study is the comparison of the simulation results with 11 existing geological records representing the moisture conditions from miocene to pliocene the comparisons revealed good matches between the simulation results and the published geological records therefore we conclude that the ntp uplift and the related formation of the major deserts played a controlling role in the evolution of regional climatic conditions in a broad region in inland asia since the miocene

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

cenozoic deformation history of the qilian shan northeastern tibetan plateau constrained by detrital apatite fission track thermochronology in the northeastern qaidam basin abstract the cenozoic deformation history of the qilian shan which is a reactivated fold thrust belt in the northeastern region of the tibetan plateau is poorly understood but features prominently in the geodynamic mechanism of the evolution of the plateau the northeastern qaidam basin which is located on the south flank of the qilian shan provides a valuable record of the timing and pattern of the cenozoic deformation of the qilian shan in its synorogenic sediments this study analyzes the apatite fission track aft thermochronological signatures of the middle miocene quaternary detrital sediments in the northeastern qaidam basin and modern stream sands draining the qilian shan as a proxy for the timing of tectonic deformation in the qilian shan our detrital aft ages indicate that a cenozoic initial rapid exhumation event occurred in the qilian shan in the late paleocene early eocene 60 54 ma followed by another rapid exhumation event during the middle late eocene 42 38 ma and some exhumation during the oligocene middle miocene 33 14 ma distinct changes in detrital aft ages at depositional ages of 12 ma and 2 1 ma suggest that further tectonic deformation affected the qilian shan at these times our results along with those of previous studies suggest that tectonic deformation propagated into the northeastern edge of the tibetan plateau almost simultaneously with the india asia collision the spatial evolution of cenozoic deformation in the qilian shan is likely based on the distribution of weak structures in the upper crust

fold and thrust deformation of the hinterland of qilian shan northeastern tibetan plateau since mesozoic with implications for the plateau growth abstract the northeastern margin of the tibetan plateau netp represents an ideal site to probe the far field effects and plateau growth in response to the collisions of eurasia continent with india plate and intervening terranes here we investigate the fold and thrust deformation of the shule river region in the hinterland of qilian shan netp since mesozoic based on geological mapping and structural analysis to evaluate the role of multiple phase deformation in plateau rise and growth the structural style of the shule river region is dominated by the foreland verging liuhuang shan fold and thrust belt lhtb to the southwest and the hinterland verging tuolai nan shan fold and thrust belt tltb to the northeast separated by the cenozoic shule river intermontane basin integrated with published thermochronological sedimentological and structural data our study reveals four significant deformation phases in the netp since the mesozoic during the late triassic to early jurassic time the regional deformation spread in the netp and produced the jura type folds and related thrusts of the lhtb in the study area under the ne sw directed compression and was likely driven by the collision between the qiangtang and kunlun terranes during the late early cretaceous the continuous lhasa qiangtang collision induced reactivation of the lhtb and an extensive exhumation event in the netp since the early eocene the upper crustal shortening and initial uplift of the netp have accommodated the far field stress of india eurasian collision given the widespread miocene uplift event in the netp revealed by previous studies we attribute the southwestward thrusting of the tltb and tight isoclinal syncline of the oligocene miocene baiyanghe formation to the significant crustal shortening and topographical growth of netp during the early middle miocene the reactivation of tltb and newly generated low angle reverse faults represent gently tilted deformation and plateau growth in response to surface uplift of netp as a whole since the late miocene our results imply that the multiple phase deformation in the netp since the late triassic should have been a first order control on plateau growth

magnetostratigraphy of cenozoic sediments from the xining basin tectonic implications for the northeastern tibetan plateau 1 the xining subbasin of the longzhong basin holds the longest continuous cenozoic stratigraphic record at the margin of the northeastern tibetan plateau despite a rich biostratigraphic content including the xiejia mammal fauna the tectonic evolution of the basin is largely unconstrained in this study we present stratigraphic biostratigraphic and magnetostratigraphic results that provide a basis for reconstructing the cenozoic tectonic evolution of the xining basin with respect to adjacent regions of the northeastern tibetan plateau magnetostratigraphic analysis from three red bed sections in the xining basin indicates continuous deposition at low and nearly constant accumulation rates average 2 2 cm kyr from 52 0 to 17 0 ma we interpret this result to indicate that no major regional tectonic event implying large sediment accumulation variations has affected the xining basin deposition during this considerable time window in detail accumulation rate variations outline a three stage evolution with 1 8 cm kyr from 52 0 ma to 34 5 ma 4 1 cm kyr from 34 5 to 31 0 ma and 2 3 cm kyr from 31 0 to 17 0 ma the second order increase between 34 5 and 31 0 ma can be interpreted to result from either a distal tectonic event or to be of climatic origin although the region was tectonically quiescent for much of the cenozoic tectonic activity occurred during basin initiation or reactivation at circa 55 0 52 5 ma and during intense basin deformation after 17 0 ma

geologic correlation of the himalayan orogen and indian craton part 2 structural geology geochronology and tectonic evolution of the eastern himalaya despite being the largest active collisional orogen on earth the growth mechanism of the himalaya remains uncertain current debate has focused on the role of dynamic interaction between tectonics and climate and mass exchanges between the himalayan and tibetan crust during cenozoic india asia collision a major uncertainty in the debate comes from the lack of geologic information on the eastern segment of the himalayas from 91 e to 97 e which makes up about one quarter of the mountain belt to address this issue we conducted detailed field mapping u pb zircon age dating and 40ar 39ar thermochronology along two geologic traverses at longitudes of 92 e and 94 e across the eastern himalaya our dating indicates the region experienced magmatic events at 1745 1760 ma 825 878 ma 480 520 ma and 28 20 ma the first three events also occurred in the northeastern indian craton while the last is unique to the himalaya correlation of magmatic events and age equivalent lithologic units suggests that the eastern segment of the himalaya was constructed in situ by basement involved thrusting which is inconsistent with the hypothesis of high grade himalaya rocks derived from tibet via channel flow the main central thrust in the eastern himalaya forms the roof of a major thrust duplex its northern part was initiated at ca 13 ma while the southern part was initiated at ca 10 ma as indicated by 40ar 39ar thermochronometry crustal thickening of the main central thrust hanging wall was expressed by discrete ductile thrusting between 12 ma and 7 ma overlapping in time with motion on the main central thrust below restoration of two possible geologic cross sections from one of our geologic traverses where one assumes the existence of pre cenozoic deformation below the himalaya and the other assumes flat lying strata prior to the india asia collision leads to estimated shortening of 775 km 76 strain and 515 km 70 strain respectively we favor the presence of significant basement topography below the eastern himalaya based on projections of early paleozoic structures from the shillong plateau i e the central shillong thrust located 50 km south of our study area since northeastern india and possibly the eastern himalaya both experienced early paleozoic contraction the estimated shortening from this study may have resulted from a combined effect of early paleozoic and cenozoic deformation

observations of auroral substorms occurring together with preexisting quiet time auroral patterns although horse collar configurations are commonly associated with relatively quiescent magnetospheric conditions observations made with the viking uv imager are presented which clearly demonstrate that classical auroral substorms can coexist with such patterns thus the magnetospheric conditions that lead to the production of these quiet time auroral patterns are not necessarily stable to the growth of the instability that leads to substorm onset as well the horse collar patterns provide useful natural indicators of the underlying magnetospheric topology and can be used to determine in a relative sense the source location of the substorm activity we conclude that the horse collar patterns have a distant tail source location and that the substorm onsets have a source location on closed field lines with much lower l values the observations are therefore inconsistent with the onset mechanisms proposed in either the thermal catastrophe model or the boundary layer dynamics model in addition we have shown that substorm related plasma sheet dropouts are not always produced by a neutral line induced thinning of the plasma sheet but could also be caused by the large scale motion of the open field line region plasma data from dmsp f6 dmsp f7 isee 1 and viking are consistent with the interpretation that the regions between the horse collar arcs are threaded by open lobe field lines and that open field lines can also partially intrude into the space between the transpolar arcs and the lower latitude main oval the significance of these results for substorm activity which occurs together with quiet time auroral patterns is discussed in terms of the flux rope plasmoid version of the near earth neutral line model depending upon the location and extent of the open field line regions relative to the developing plasmoid it is suggested that several possibilities exist for the subsequent evolution of the substorm activity in the tail and that these different scenarios can be related to specific types of auroral morphologies in the ionosphere

middle miocene reorganization of deformation along the northeastern tibetan plateau temporal variations in the orientation of cenozoic range growth in northeastern tibet define two modes by which india asia convergence was accommodated thermochronological age elevation transects from the hanging walls of two major thrust fault systems reveal diachronous miocene exhumation of the laji jishi shan in northeastern tibet whereas accelerated growth of the wnw trending eastern laji shan began ca 22 ma rapid growth of the adjacent north trending jishi shan did not commence until ca 13 ma this change in thrust fault orientation refl ects a middle miocene change in the kinematic style of plateau growth from long standing nne ssw contraction that mimicked the plate convergence direction to the inclusion of new structures accommodating east west motion this kinematic shift in northeastern tibet coincides with expansion of the plateau margin in southeastern tibet the onset of normal faulting in central tibet and accelerated shortening in northern tibet together these phenomena suggest a plateau wide reorganization of deformation

cenozoic tectonic evolution of the qaidam basin and its surrounding regions part 3 structural geology sedimentation and regional tectonic reconstruction the qaidam basin is the largest topographic depression inside the tibetan plateau because of its central position understanding the tectonic origin of the qaidam basin has important implications for unraveling the formation mechanism and growth history of the tibetan plateau in order to achieve this goal we analyzed regional seismic reflection profiles across the basin and a series of thickness distribution patterns of cenozoic strata at different time slices the first order structure of the basin is a broad cenozoic synclinorium which has an amplitude ranging from 16 km in the west to 48 in the west to 15 s 1 to 1 3 10 17 s 1 the eastward decrease in upper crustal shortening requires a progressive shift in crustal thickening mechanisms across qaidam basin from dominantly upper crustal shortening in the west to dominantly lower crustal shortening in the east although sedimentation began synchronously at 65 50 ma across the entire basin the initiation ages of the southern and northern basin bounding structures are significantly different deformation started at 65 50 ma in the north and at 29 24 ma in the south this information and the existing inference that the uplift of the eastern kunlun range south of qaidam basin began after 30 20 ma imply that the paleogene 65 24 ma qaidam and hoh xil basins on both sides of the eastern kunlun range may have been parts of a single topographic depression 500 km wide in the north south direction between the qilian shan and fenghuo shan thrust belts in the north and south the development of this large paleogene basin in central tibet and its subsequent destruction and partitioning by the neogene uplift of the eastern kunlun range requires a highly irregular sequence of deformation possibly controlled by preexist ing weakness in the tibetan lithosphere

northeastward growth of the tibet plateau deduced from balanced reconstruction of two depositional areas the qaidam and hexi corridor basins china we address the problem of late cenozoic uplift erosion and growth of northeastern tibet by reconstructing from isopach maps and drill holes the volumes and masses of sediments deposited in the qaidam and hexi corridor basins since 35 myr ago the mass budget is based on simple geometrical assumptions such as regional similarity of the thickness ratios between strata of different ages in the qaidam where our record extends back to the oligocene the budget shows a huge rise of the accumulation rates after the beginning of the pliocene 5 3 ma the early pliocene seems to be the period of maximum deposition with accumulation rates in excess of 1 mm yr 1 2 7 kg m 2 yr 1 of compacted rocks throughout the basin there also seems to be a southeastward shift of the largest depocenters between the upper pliocene 3 4 1 6 ma and the quaternary in the hexi corridor sedimentation is confined to small foreland flexural depressions associated with the frontal thrusts of the qilian shan and occurs at an average rate one order of magnitude smaller than in the qaidam basin the accumulation rate is maximum in the quaternary the sedimentation history appears to support a plateau building mechanism resulting from the combination of two geologicallly common processes crustal scale thrusting and sedimentary basin infilling the time needed to completely fill the qaidam basin and make its catchment a plateau closely resembling that of the highest part of tibet qangtang is of the order of 9 myr the mechanism now at work north of the kunlun which involves rapid infilling of broad flat areas separated by relatively narrow mountain ranges has thus probably been important in producing the high smooth topography that characterizes much of central tibet

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

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

impacts of the uplift of four mountain ranges on the arid climate and dust cycle of inland asia abstract although some studies have shown that the uplift of the northern tibetan plateau ntp has an important influence on the climate of inland asia the respective roles played by different parts of the ntp in controlling regional aridification and dust cycling remains unclear in this study based on the geological facts that the ntp and its surrounding mountains have uplifted to a certain altitude since the miocene we used the dust coupled regional climate model regcm4 1 to explore the different impacts of the uplift of four mountain ranges the altai mountains mongolian plateau the tian shan mountains the pamir mountains and the qilian mountains on the arid climate and dust cycle of inland asia the results showed distinct contributions of these different mountain ranges with respect to aridity the uplift of the pamirs played a leading role in the aridification of inland asia causing the annual mean precipitation to decrease by 200 across a wide area of northwest china owing to the rain shadow effect a rain shadow is a dry area on the leeward side of a mountainous area in terms of dust cycling dust emissions and deposition increased in the taklimakan desert mainly due to the uplift of the tian shan mountains and the pamirs the increase in magnitude of which was 10 20 times larger than that induced by the uplift of the altai mountains mongolian plateau or qilian mountains besides a narrow passage formed between the uplifted altai mountains mongolian plateau and tian shan mountains that accelerated the northwesterly air flow between them thus increasing dust emissions in northern xinjiang and the gobi desert the increase in dust emissions in these two regions induced by the uplift of the altai mountains mongolian plateau was 7 20 times greater than that induced by the uplift of the three other mountain ranges results also showed that the uplift of the qilian mountains not only controlled the dust emissions and deposition on the loess plateau but also blocked the transportation of dust from northwest china to the middle and lower reaches of the yangtze river leading to the dust loading being reduced by 10 20 in south china the findings of this study improve our understanding of the influence of ntp tectonic uplift on change in the arid climate and dust cycle of inland asia

how a stationary knickpoint is sustained new insights into the formation of the deep yarlung tsangpo gorge abstract in order to test the hypothesis that the stationary nature of the yarlung tsangpo gorge is tectonically controlled the rock uplift pattern in the southeast tibetan plateau and the critical condition to sustain a stable knickpoint must be derived via slope area analysis and the integral approach we first quantify the pattern of channel steepness in southeast tibet and find that the steepness index shows higher values around the gorge but lower values toward the inner land and the mountain front such a pattern of channel steepness indicates that the active rock uplift is restricted in the zone just around the yarlung tsangpo gorge then we derive a general knickpoint migration model that accounts for spatially variant rock uplift rates from the model a critical condition for maintaining a stable knickpoint is concluded that the difference of incision rates in the downstream and upstream reaches of the knickpoint should match that of rock uplift employing a stream power river incision model we calculate the incision rate in the gorge and find a higher correspondence with differential rock uplift rates in the downstream and upstream reaches of the knickpoint therefore we favor tectonic control as the primary mechanism to explain the stability of the knickpoint within the yarlung tsangpo gorge

high resolution magnetostratigraphy of the neogene huaitoutala section in the eastern qaidam basin on the ne tibetan plateau qinghai province china and its implication on tectonic uplift of the ne tibetan plateau abstract the closed inland qaidam basin in the ne tibetan plateau contains possibly the world s thickest 12 000 m continuous sequence of cenozoic fluviolacustrine sedimentary rocks this sequence contains considerable information on the history of tibetan uplift and associated climatic change however work within qaidam basin has been held back by a paucity of precise time constraints on this sequence here we report on a detailed paleomagnetic study of the well exposed 4570 m huaitoutala section along the keluke anticline in the northeastern qaidam basin where three distinct faunas were recovered and identified from the middle miocene through pliocene constrained by these faunal ages the observed thirty three pairs of normal and reversed polarity zones can be readily correlated with chrons 2n 5br of the gpts this study assigns the age of the section to the interval between ca 15 7 ma to 1 8 ma in addition the widely used stratigraphic units the xia youshashan shang youshashan the shizigou and qigequan formations were formed at 15 3 ma 15 3 8 1 ma 8 1 2 5 ma and

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

ionospheric convection response to slow strong variations in a northward interplanetary magnetic field a case study for january 14 1988 we analyze ionospheric convection patterns over the polar regions during the passage of an interplanetary magnetic cloud on january 14 1988 when the interplanetary magnetic field imf rotated slowly in direction and had a large amplitude using the assimilative mapping of ionospheric electrodynamics amie procedure we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high latitude electrodynamics focusing on the period of northward imf by combining satellite data with ground based observations we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres we present evidence that a lobe convection cell was embedded within normal merging convection during a period when the imf by and bz components were large and positive as the imf became predominantly northward a strong reversed convection pattern afternoon to morning potential drop of around 100 kv appeared in the southern summer polar cap while convection in the northern winter hemisphere became weak and disordered with a dawn to dusk potential drop of the order of 30 kv these patterns persisted for about 3 hours until the imf rotated significantly toward the west we interpret this behavior in terms of a recently proposed merging model for northward imf under solstice conditions for which lobe field lines from the hemisphere tilted toward the sun summer hemisphere drape over the dayside magnetosphere producing reverse convection in the summer hemisphere and impeding direct contact between the solar wind and field lines connected to the winter polar cap the positive imf bx component present at this time could have contributed to the observed hemispheric asymmetry reverse convection in the summer hemisphere broke down rapidly after the ratio by bz exceeded unity while convection in the winter hemisphere strengthened a dominant dawn to dusk potential drop was established in both hemispheres when the magnitude of by exceeded that of bz with potential drops of the order of 100 kv even while bz remained northward the later transition to southward bz produced a gradual intensification of the convection but a greater qualitative change occurred at the transition through by bz 1 than at the transition through bz 0 the various convection patterns we derive under northward imf conditions illustrate all possibilities previously discussed in the literature nearly single cell and multicell distorted and symmetric ordered and unordered and sunward and antisunward

tectono magmatic rejuvenation of the qaidam craton northern tibet abstract ascertaining the enigmatic characteristics of the crystalline basement of the qaidam basin the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust has broad implications for the cenozoic basin evolution in particular and intracontinental tectonics of asia in general we carried out a comprehensive investigation on the ages and geochemical isotopic characteristics of the qaidam and suganhu basement rocks obtained from drill cores petrological observations and u pb zircon dating la icp ms of granitoid samples from drill cores indicate that early neoproterozoic early paleozoic and late paleozoic mesozoic intrusions are largely represented suggesting that the qaidam and suganhu blocks were involved into three tectono magmatic episodes similar whole rock geochemistry and sr nd isotopic characteristics between the early neoproterozoic granitoids beneath the qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive early neoproterozoic metamorphism and magmatism along the present day northern tibetan plateau by comparing the trace and rare earth elements patterns as well as the sr nd compositions of the ordovician arc related granitoids and silurian devonian post collisional granitoids beneath the qaidam and suganhu basins with the corresponding granitoids from the surrounding orogenic belts we assert that the proto tethys subduction events that were recorded within the eastern kunlun altyn tagh and the qilian shan orogenic belts were different they generated distinctive subduction related arc magmas whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post collisional magmatism within the qaidam block the widespread permian and triassic granitoids beneath the northwestern northern qaidam basin mainly involved a lower crust or a crust mantle source including mesoproterozoic crust they demonstrate that the influence of the paleo tethys evolution penetrated the qaidam block northwards reaching to the northern edges of the block we conclude that the qaidam block is not a craton as typical as the rigid tarim block but pertains to a tectono magmatic rejuvenated craton which is not mechanically stronger than its surrounding regions however trapped between the lithospheric left lateral strike slip altyn tagh fault system to the northwest and the qilian shan transpressional system to the northeast the qaidam block forms a relatively stable domain that escaped from significant cenozoic deformation

late cenozoic deformation and uplift of the ne tibetan plateau evidence from high resolution magnetostratigraphy of the guide basin qinghai province china the cenozoic intramontane gonghe guide basin in qinghai province china is tectonically controlled by the sinistral strike slip framework of the kunlun and altyn tagh south qilian faults in the northeastern tibetan plateau the basin is filled with thick cenozoic clastic sedimentary formations which provide important evidence of the deformation of this part of the plateau although they have long lacked good age constraints detailed magnetostratigraphic and paleontologic investigations of five sections in the guide basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit the guide group into six formations where ages are now magnetostratigraphically well established they are given in parentheses the amigang 1 8 2 6 ma ganjia 2 6 3 6 ma and herjia formations 3 6 to ca 7 0 7 8 ma and the older miocene ashigong garang and guidemen formations these rocks document a generally upward coarsening sequence characterized by increasing accumulation rates increasing gravel content and sizes of its components changes of bedding dips and source rock types and marginal growth faults collectively reflect accelerated deformation and uplift of the ne tibetan plateau after 8 ma punctuated by a sharp increase in sedimentation rate at ca 3 2 ma that reflects the boulder conglomerates of the ganjia formation interestingly much of the vergence of the compressional deformation in the basin is to the south accommodated by a sequence of six thrusts f1 f6 which become active one by one progressively later toward the south undoubtedly contributing to the uplift of this part of the plateau f1 likely initiated the guide basin due to crustal flexure in the oligocene f2 was active in the early miocene f4 and f5 at ca 3 6 ma and f6 was active in the early pleistocene the detailed late miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and hence uplift of northeastern tibet which when compared with ages for events on other parts of the plateau provides important boundary conditions for the geodynamical evolution of tibet

extrapolation of the kinetics of oil and gas formation from laboratory experiments to sedimentary basins it is generally accepted that the formation of oil and gas from sedimentary organic matter or kerogen is adequately described by kinetic models based on first order kinetics with rate constants obeying an arrhenius equation these models which are extensively used in oil exploration to assess the petroleum potential of sedimentary basins are based on geological observations1 2 3 4 5 6 but are formally quite similar to models designed to simulate oil shale pyrolysis7 8 9 or coal processing10 11 12 the idea of blending these two approaches is not new see for example ref 2 but until now the most sophisticated attempts reproduced only the gross features of kerogen cracking on a geological timescale5 or were uncontrolled by geochemical measurements13 14 here we show that the kinetic parameters determined from the laboratory pyrolysis of an immature kerogen sample apply to the conditions of sedimentary basins altough the time and temperature scale are completely different

distorted drainage basins as markers of crustal strain east of the himalaya extensive lithospheric deformation on the eastern margin of the india eurasia collision has brought three major rivers into exceptionally close proximity for over 300 km the salween mekong and yangtze rivers are only tens of kilometers apart 10 times closer than rivers of comparable length elsewhere in the world we view deeply incised river valleys as displacement markers that move with the underlying crust over time scales of at least tens of millions of years accordingly the close spacing of these major rivers and their nearly parallel trends reflect the large crustal strains near the eastern himalayan syntaxis these river characteristics are consistent with two primary phases of deformation in this tectonic setting ne sw shortening of 0 5 oriented radially from the eastern syntaxis followed by dextral shear strain of 6 1 along a north trending zone pervasive shearing of this magnitude throughout the 150 km wide region of anomalous drainage would account for 1000 km of northward motion of india relative to southern china directly east of this region another 1000 km of northward motion is likely to have been accommodated by pervasive shearing through a zone hundreds of kilometers wide finally we draw attention to the remarkable accord between the arcuate paths of each of the three great rivers in the broader southeastern tibet region and small circles that curve around the eastern himalayan syntaxis

viking observations of a reverse convection cell developing in response to a northward turning of the interplanetary magnetic field observations of a developing reverse convection cell on september 23 1986 are examined using auroral images acquired with the uv imager on board the viking spacecraft the cell possesses a counter clockwise rotational sense and evolves on the duskside of the northern auroral distribution between the duskside oval and a complex duskside transpolar arc system as the structure evolves it grows and appears to displace the transpolar arc toward the dawn we interpret these observations in terms of a model proposed by burch et al 1992 in which open field lines produced by merging on the high latitude magnetopause produce reverse convection cells between the oval and the transpolar arcs associated with horse collar or teardrop auroral patterns

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

cenozoic shortening budget for the northeastern edge of the tibetan plateau is lower crustal flow necessary 1 two of the most popular mechanisms for thickening the crust beneath the tibetan plateau are 1 pure shear with faulting and folding in the upper crust and horizontal shortening below and 2 flow of lower or middle crust without significant shortening of the upper crust to help discriminate between the relative contributions of these two mechanisms well constrained estimates of upper crustal shortening are needed here we document the cenozoic shortening budget across the northeastern tibetan plateau margin with several balanced cross sections that exploit thermochronological and magnetostratigraphic constraints these sections indicate 11 2 1 east west shortening since middle miocene time and 9 2 3 nne ssw shortening between middle eocene and middle miocene times with little subsequent shortening of this orientation shortening rates accelerate fivefold after middle miocene time given the present day crustal thickness of 56 4 km in northeastern tibet crustal restorations that remove cenozoic shortening suggest that the northeastern tibetan crust was 45 5 km thick prior to the india asia continental collision this precollision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the tibetan plateau 44 4 km and globally 41 6 km and suggests that pure shear alone may account for cenozoic crustal thickening in northeastern tibet in contrast to eastern tibet where in the absence of significant shortening structures crustal flow has been invoked to explain the addition of crustal material since middle miocene time our results may obviate lower crustal flow as a necessary crustal thickening agent in northeastern tibet

reaction kinetics of gas generation in selected source rocks of the west siberian basin implications for the mass balance of early thermogenic methane abstract about one third of the actual global recoverable natural gas reserves is accumulated in the west siberian basin in several super giant and mega giant as well as numerous smaller gas fields the elucidation of the nature of this gas its mechanisms of formation and accumulation are still a matter of discussion for instance it is still not yet clear whether the enormous dry gas accumulations in cenomanian reservoirs are of microbial early thermogenic or catagenetic metagenetic origin or if they represent a mixture of these possible formation mechanisms the present contribution provides new results on the thermal gas generation properties of selected source rocks of the cretaceous pokur formation in the west siberian basin eight selected source rock core samples of the pokur formation and a recent peat sample of the same area were submitted to open system programmed temperature pyrolysis in order to quantify the formation of individual gas compounds i e methane as well as c2 and c3 hydrocarbons the rock samples were selected according to geological age and maturity i e from the aptian albian and cenomanian with the most immature samples from the latter organic carbon contents comprise the whole range from 3 to more than 60 the elevated values representing typical lignites a reaction kinetic model system was applied to the generation curves of the gases resulting in activation energy distributions and the corresponding pre exponential arrhenius factors the kinetic data were combined with the temperature history of two selected wells of the urengoy area obtained from basin modelling in order to calculate the gas generation on the geological time scale it was found that even for the low temperatures occurring in the pokur formation early gas generation could have taken place to a certain yet small degree under the assumption of a respective catchment area and the accumulation of this gas in the reservoirs however methane quantities are in the order of magnitude of the urengoy gas accumulation thus early thermogenic methane could at least partially contribute to the gas accumulated in the reservoirs

magmatic history of the northeastern tibetan plateau 1 the northeastern margin of the tibetan plateau is underlain by the qaidam and qilian terranes which consist primarily of mid proterozoic through lower paleozoic oceanic and arc type assemblages that have been accreted to the southern margin of the tarim sino korean craton most previous models suggest that these assemblages formed along a northeast dipping subduction system constructed along the margin of the tarim sino korean craton during early paleozoic time the main components are interpreted to have formed either as an archipelago of volcanic arcs and back arc basins or as a broad expanse of accretionary complexes our geochronologic data support a model suggested by sobel and arnaud 1999 in which the qaidam and qilian terranes are separated from the tarim sino korean craton by a mid paleozoic suture that closed along a southwest dipping subduction zone the basement to these terranes consists of oceanic assemblages that were amalgamated into a coherent crustal fragment prior to emplacement of 920 930 ma granitoids early paleozoic arc type magmatism occurred between 480 and 425 ma apparently sweeping southwestward across much of the qilian and qaidam terranes accretion related magmatism along the inboard margin of the qilian terrane occurred between 423 ma and 406 ma following silurian devonian accretion the region has experienced late paleozoic and mesozoic uplift and erosion and has been severely overprinted by tertiary thrusting uplift and strike slip motion along the altyn tagh fault correlation of geologic features and magmatic histories between the altun shan and the nan shan suggests that the eastern altyn tagh fault has a total left lateral offset of 375 km

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

the aksay segment of the northern altyn tagh fault tectonic geomorphology landscape evolution and holocene slip rate 1 millennial slip rates have been determined for the altyn tagh fault atf at three sites near aksay 94 e in northeastern tibet by dating fluvial channels and terrace riser offsets with radiocarbon and 10be 26al surface exposure dating up to nine main surfaces are defined on the basis of morphology elevation and dating the abandonment age of some surfaces is constrained by radiocarbon dating which typically coincides with the youngest cosmogenic ages for a particular surface older surface exposure ages are taken to represent the duration of terrace emplacement cumulative offsets range from 20 to 260 m and fall in distinct groups indicative of climatically modulated regional landscape formation most samples are younger than 14 ka and postdate the last glacial maximum the end of the early holocene optimum marks the boundary between the ages of the two main terrace levels at 5 6 ka at this longitude the atf is divided into a northern and southern branch the northern atf should thus yield a minimum rate for the atf system slip rate estimates using the abandonment age of the overlying level for fill terraces or channels and the emplacement of the underlying level for strath terraces give 30 consistent results yielding an average holocene rate of 17 8 3 6 mm yr it is 9 mm yr less than the long term rate obtained near tura at 87 e 26 9 6 9 mm yr in keeping with the inference of an eastward decreasing rate on the atf due to increased thrusting to the south however it remains twice the rate determined by gps studies

stable isotopic constraints on the tectonic topographic and climatic evolution of the northern margin of the tibetan plateau abstract this study presents oxygen and carbon isotopic records from lacustrine paleosol alluvial and fluvial carbonate sampled in thirteen cenozoic sedimentary sections that span the northern margin of the tibetan plateau isotopic analyses of 1475 carbonate samples yield 18 o values that range from 13 1 to 38 9 smow and 13 c values range from 11 5 to 3 7 pdb based on these analyses we see two isotopic trends regionally we interpret a paleogene decrease in average oxygen isotope values to result from an increase in the mean elevation of the study region s drainages as they tapped waters from a growing tibetan plateau to the south of the study area we interpret a neogene increase in both carbon and oxygen isotope values to result from the initiation of local mountain building in the study area and the withdrawal of marine waters which increased basin isolation aridity and temperatures the timing of inferred initiation of uplift in this region is consistent with structural thermochronological and sedimentological evidence for a tectonic transition in the early and middle miocene from accommodation of india eurasia convergence through extrusion along the altyn tagh fault to accommodation of convergence through active shortening and mountain building in this region this study also supports tectonic models for the differential uplift of the tibetan plateau in that mountain building in this study region significantly postdates estimates for the attainment of high elevation from isotopic studies of the central tibetan plateau

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

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

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

high latitude ionospheric convection pattern during steady northward interplanetary magnetic field the dmsp f8 satellite s coverage of earth s polar regions provides horizontal ion drift velocities along the dawn dusk meridian at approximately 835 km altitude in each hemisphere during the 100 min orbital period we examine the ionospheric convection signatures observed by this spacecraft in the summer and winter hemispheres during periods when the interplanetary magnetic field imf is directed northward for at least 45 min prior to the satellite entering the polar region and remains northward throughout the polar pass these convection signatures can be readily categorized by the number of sunward and antisunward flow regions and by their potential distributions here we describe the most frequently identifiable and reproducible features of the convection pattern that exist during steady northward imf conditions in addition to imf bz the influences on the convection pattern of the imf bz by ratio season latitude and solar wind velocity are all considered the ratio bz by provides a first order organization of the signatures that occur on the dayside of the dawn dusk meridian sunward flow at highest latitudes on the dayside of the dawn dusk meridian is the dominant feature seen in the large scale convection signature during steady northward imf however sunward flow at highest latitudes does not imply the existence of a particular number of convection cells

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

transforming the miocene altyn tagh fault slip into shortening of the north western qilian shan insights from the drainage basin geometry although it has long been proposed that active crustal shortening within the qilian shan accommodates slip along the altyn tagh fault questions regarding the temporal and spatial amount of slip transfer remain debated traditional shortening calculations cannot yet be made accurately because the geology is not known well enough following the view that long linear drainage basins in the north western qilian shan developed in response to internal shortening associated with slip transfer along the altyn tagh fault we targeted this special irregular drainage basin geometry to develop an alternative way to estimate shortening we infer a total of 66 km of shortening in the western qilian shan with a north eastward decrease in the magnitude of shortening this 39 shortening strain is comparable to previous estimates estimates of dates of initiation support the view that significant shortening and topographical growth within the north western qilian shan occurred in post middle miocene time

direct dating of eocene reverse faulting in northeastern tibet using ar dating of fault clays and low temperature thermochronometry abstract paired together fault gouge dating and low temperature thermochronometry overcome the limitations and assumptions inherent in each independent technique here we establish timing of brittle faulting along the west qinling fault of northeastern tibet by dating several size fractions of fault gouge clay that represent variable populations of illite polytypes results show that the authigenic or fault generated component of illite formed at 50 8 ma and that the detrital component formed at 236 7 ma indicating a middle eocene age of faulting and a middle triassic age of the wall rocks comparing this dataset with published thermochronology from hanging wall rocks supports the interpretation that the west qinling fault initiated at 50 ma and continued until at least middle miocene time and that authigenic clay growth occurred at ambient temperatures of 110 c lack of overprinting of younger clay ages at this site may indicate that rocks were out of the thermal window for authigenic clay formation during later faulting episodes the potential for temperature to control illite growth has implications for interpretation of authigenic illite ages and their relationship to deformation episodes within fault zones

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

cenozoic multi phase deformation in the qilian shan and out of sequence development of the northern tibetan plateau abstract uplift of the tibetan plateau and the distribution of deformation across it are the result of india asia collision which bring an opportunity of understanding intracontinental tectonics in the context of continent continent collision the tibetan plateau is bound on the northern margin by the qilian shan thrust belt and the strike slip haiyuan fault these cenozoic fault systems play a critical role in accommodating continental convergence yet the initiation age deformation sequence and mechanisms of deformation are debated in this study integrated geologic mapping field observations and apatite fission track thermochronology were conducted to constrain the initiation ages of the localized thrust faults and the exhumation history of the central and northern qilian shan northern tibet our analyses reveal the central and northern qilian shan underwent rapid cooling during the cretaceous as a result of a far field tectonic event in the eocene oligocene a period of thrust related cooling occurred along the shule nan shan tuolai nan shan and tuolai shan faults reactivation of the proximal thrust faults and initiation of the western segment of the haiyuan fault occurred at ca 16 ma and drove final accelerated miocene cooling and denudation to the surface we argue that the qilian shan thrust belt has persisted as the stationary and internally deformed northern boundary of the himalayan tibetan orogen since the early cenozoic involved overprinting out of sequence development starting by eocene related to initiation of india asia collision and the basins and ranges across the northern tibetan plateau have since experienced multi phase of growth

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

spatial and temporal distribution of earthquake ruptures in the eastern segment of the altyn tagh fault china abstract we performed field investigations to reconstruct the paleoearthquake history of eastern segment of the altyn tagh fault nw china investigation at the saohu spring trench and shibaocheng west trench sites result in the identification three well resolved earthquakes designated as events e1 e2 and e3 within the last 7000 years radiocarbon dates of detrital charcoal provide constraints on the timing of faulting events the most recent surface rupturing earthquake event e1 dated between 2720 and 2800 years a before present bp had a rupture length of 83 km extending from hongliuxia to bagexia with a coseismic displacement of about 4 5 m the penultimate event e2 occurred between 4180 and 4970 a bp and may have ruptured from subei to bagexia with a coseismic displacement of 7 m the third youngest event e3 occurred approximately 6440 7180 a bp and may have ruptured the whole segment from subei to kuantan mountain with a coseismic displacement of 10 m holocene earthquake recurrence behavior on the eastern segment of the altyn tagh fault conforms to a variable slip earthquake model together with previous studies of slip rate the huge displacement deficit along the eastern segment indicates a high earthquake risk for the surrounding region the fault has the potential to trigger earthquakes of greater than m7 8 or a period of clustered earthquake activity the displacement deficit could also indicate that sub faults in the western qilian mountains have absorbed more lateral extrusion of the plateau during the holocene which would result in a decreasing fault slip rate and weakening of the eastern extension or outward expansion of the altyn tagh fault

determining the petroleum generating potential of coal using organic geochemistry and organic petrology abstract the ardjuna basin of northwest java is typical of many tertiary basins in that it contains high wax crude oil pyrolysis gas chromatography revealed that potential precursors of long chain waxy paraffins are present in coals of the talang akar formation and are most abundant in those that are rich in matrix liptinite conversely it was not possible to estimate waxy oil generating potential using rock eval because pyrolysates from talang akar coal are mainly comprised of naphthenic and aromatic compounds these being derived from resinite and fluorescing vitrinite because of a controlling influence by the abundance of these macerals changes in hydrogen index could not be used to assess maturity resinite and related macerals might play an especially important role in petroleum expulsion as evidenced by their high genetic potential and hence inherent capability of saturating the source rock pore system it is speculated that their maturation products while not constituting typical crude oil might pervade the coal fabric deactivate adsorptive sites and hence facilitate the expulsion of waxy oil that is generated from matrix liptinite

faulted terrace risers place new constraints on the late quaternary slip rate for the central altyn tagh fault northwest tibet the active left lateral altyn tagh fault defines the northwestern margin of the tibetan plateau in western china to clarify late quaternary temporal and spatial variations in slip rate along the central portion of this fault system 85 90 e we have more than doubled the number of dated offset markers along the central altyn tagh fault in particular we determined offset age relations for seven left laterally faulted terrace risers at three sites kelutelage yukuang and keke qiapu spanning a 140 km long fault reach by integrating surficial geologic mapping topographic surveys total station and tripod light detection and ranging t lidar and geochronology radiocarbon dating of organic samples 230 th u dating of pedogenic carbonate coatings on buried clasts and terrestrial cosmogenic radionuclide exposure age dating applied to quartz rich gravels at kelutelage which is the westernmost site 37 72 n 86 67 e two faulted terrace risers are offset 58 3 m and 48 4 m and formed at 6 2 6 1 ka and 5 9 3 7 ka respectively at the yukuang site 38 00 n 87 87 e four faulted terrace risers are offset 92 12 m 68 6 m 55 13 m and 59 9 m and formed at 24 2 9 5 ka 6 4 5 0 ka 5 1 3 9 ka and 24 2 6 4 ka respectively at the easternmost site keke qiapu 38 08 n 88 12 e a faulted terrace riser is offset 33 6 m and has an age of 17 1 2 2 ka the displacement age relationships derived from these markers can be satisfied by an approximately uniform slip rate of 8 12 mm yr however additional analysis is required to test how much temporal variability in slip rate is permitted by this data set

generation of nitrogen and methane from sedimentary organic matter implications on the dynamics of natural gas accumulations nitrogen n2 contents of natural gases in rotliegend and buntsandstein reservoirs of the north german basin regionally approach 100 a review is given of the various hypotheses primordial origin volcanic or magmatic origin radiogenic origin atmospheric origin organic origin inorganic nitrogen in sedimentary rocks presented to account for nitrogen anomalies in this area and other parts of the world the objective of the present study was to investigate sedimentary organic matter in particular coals as a potential source of molecular nitrogen in the subsurface comparison of reservoir sizes and gas generation potentials indicates that carboniferous coal measures which are considered as the source of the natural gas in the north german basin can readily account for the nitrogen quantities found in present day reservoirs laboratory pyrolysis experiments were carried out to investigate the kinetics of generation of methane and molecular nitrogen from coals of different type and rank under experimental conditions nitrogen is formed at higher temperatures than methane supporting the concept of a fractional generation of methane and nitrogen in natural systems based on the kinetic parameters derived from laboratory experiments methane and nitrogen generation rates from coals were calculated for geologic heating rates gas containing more than 50 nitrogen is generated under these conditions at temperatures in excess of 300 c nitrogen rich gases are thus formed only in the final stage of gas generation after methane generation has practically ceased it is concluded that the amounts of gas encountered in nitrogen rich gas accumulations represent only a small fraction possibly 1 of the total gas generation potential of this area while the bulk of the generated gas has escaped to the atmosphere the present day composition of the reservoir gases reflects the composition of only the most recently generated gas on a geologic time scale

lateral extrusion along the altyn tagh fault qilian shan ne tibet insight from a 3d crustal budget the lithospheric strike slip altyn tagh fault has accommodated hundreds of kilometers of displacement between the qaidam and tarim blocks since its eocene reactivation however the way the deformation is accommodated in the qilian shan and further east remains uncertain based on 360 km of northeastward migration of the relatively rigid qaidam block along the altyn tagh fault and 3d isovolumetric balancing of the crustal deformation within the altyn tagh fault qilian shan system we demonstrate that 250 28 km 43 8 49 4 of n20e directed crustal shortening and an additional 250 to 370 km of eastward motion of the qilian shan crust must be accounted for by strike slip faulting in the qilian shan and crustal thickening in the qinling area as well as by extension in the adjoining north china block graben systems

stable isotope evidence for topographic growth and basin segmentation implications for the evolution of the ne tibetan plateau lithologic magnetostratigraphic and stable isotope records from the neogene xunhua and linxia basins along the tibetan plateau9s northeastern margin suggest that topography in the intervening jishi shan mountain range began to develop between 16 and 11 ma perturbations to local climate patterns resulting from the evolution of local topography are tracked through comparison of stable isotope compositions of calcareous basin fill materials across the jishi shan similarity of isotopic compositions is interpreted to reflect the presence of integrated basins whereas distinct isotopic compositions reflect unique basin hydrologies divergent isotope trends develop between ca 16 and 11 ma and are indicative of hydrologic separation in the adjacent xunhua and linxia basins and increased aridity in the leeward xunhua basin the development of aridity in the lee of the growing topography along the plateau9s northeast margin highlights the importance of evaporative enrichment in this extremely continental setting and explains the presence of anomalously positive 18 o values in modern rainfall our findings add to a growing body of evidence for deformation along the plateau9s north and northeastern margins in the middle to late miocene

rapid active thrusting along the northwestern range front of the tanghe nan shan western gansu china the western part of the tanghe nan shan range southwest of subei western gansu china is presently growing on thrust ramps splaying from the left lateral altyn tagh fault late cenozoic thrusting has folded and sliced oligocene miocence red beds into an imbricate wedge capped by warped and uplifted quaternary terraces that form a 2 to 5 km wide ledge north of the steeply faceted range front seismic scarps 1 5 to 4 5 m high cut young fans along the outer thrusts carbon 14 dating of organic remains collected on strath terraces constrains the chronology of deposition and incision by the streams most of the fans and terraces in the southern part of the subei basin appear to have been emplaced after the last glacial maximum particularly during the early holocene optimum 9 5 ka measurements of the shapes of the warped terraces constrain minimum and maximum throws on the outer thrusts the minimum vertical throw of 34 2 m of a surface dated at 8411 530 years b p at one site provides a minimum vertical uplift rate of 4 1 0 5 mm yr the maximum possible uplift 115 15 m of the oldest terrace surface whose probable age is 15 to 18 ka places an upper bound on the uplift rate of 7 2 mm yr the thrust geometry at depth and the cumulative shortening 10 20 km deduced from balancing sections logged across the imbricate thrust wedge are consistent with a shortening rate of about 5 mm yr and an onset of thrusting at about 4 2 ma such a shortening rate implies a significant northward decrease in slip rate along the altyn tagh fault the recent growth of the western qilian mountain ranges thus appears to be intimately coupled with sinistral motion on the altyn tagh fault and the extrusion of tibet

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

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

transformation of displacement between strike slip and crustal shortening in the northern margin of the tibetan plateau evidence from decadal gps measurements and late quaternary slip rates on faults abstract studies of late quaternary geological slip rates and the gps decadal slip rates along the major strike slip faults in the northern margin of the tibetan plateau show that slip rates remain relatively constant along the middle sections of each fault and decrease rapidly toward the ends our recent studies suggest that the slip rates are low

cenozoic tectonic evolution of qaidam basin and its surrounding regions part 1 the southern qilian shan nan shan thrust belt and northern qaidam basin cenozoic qaidam basin the largest active intermountain basin inside tibet figures importantly in the debates on the history and mechanism of tibetan plateau formation during the cenozoic indo asian collision to determine when and how the basin was developed we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern qilian shan nan shan thrust belt and northern qaidam basin our geologic observations provide new constraints on the timing and magnitude of cenozoic crustal thickening in northern tibet specifically our work shows that the southernmost part of the qilian shan nan shan thrust belt and contractional structures along the northern margin of qaidam basin were initiated in the paleocene early eocene 65 50 ma during or immediately after the onset of the indo asian collision this finding implies that stress was transferred rapidly through tibetan lithosphere to northern tibet from the indo asian convergent front located 1000 km to the south the development of the thrust system in northern qaidam basin was driven by motion on the altyn tagh fault as indicated by its eastward propagation away from the altyn tagh fault the eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of qaidam basin suggesting thrust loading was the main control on the basin formation and evolution the dominant structure in northern qaidam basin is a southwest tapering triangle zone which started to develop since the paleocene and early eocene 65 50 ma and was associated with deposition of an overlying southwest thickening growth strata sequence recognition of the triangle zone and its longevity in northern qaidam basin explains a long puzzling observation that cenozoic depocenters have been located consistently along the central axis of the basin this basin configuration is opposite to the prediction of classic foreland basin models that require the thickest part of foreland sediments deposited along basin edges against basin bounding thrusts restoration of balanced cross sections across the southern qilian shan nan shan thrust belt and northern qaidam basin suggests that cenozoic shortening strain is highly inhomogeneous varying from 20 to 60 both vertically in a single section and from section to section across the thrust belt the spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of cenozoic rotations in different parts of qaidam basin the observed crustal shortening strain also implies that no lower crustal injection or thermal events in the mantle are needed to explain the current elevation 3000 3500 m and crustal thickness 45 50 km of northern qaidam basin and the southern qilian shan nan shan thrust belt instead thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern qaidam basin and the southern qilian shan nan shan region

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

low quaternary slip rate reconciles geodetic and geologic rates along the altyn tagh fault northwestern tibet for more than two decades the slip rate along the active left slip altyn tagh fault of northwestern tibet has been disputed with millennial rates reported to be as much as three times faster than those determined geodetically this problem is significant because the total offset plate boundary length and age of the altyn tagh fault make it the most important single structure accommodating india asia convergence north of the himalayas here we show that the central altyn tagh fault slipped at only 14 9 mm a over the past 4 6 ka by tightly bracketing the age of a displaced fluvial terrace riser at yuemake 88 51 e 38 19 n this result contradicts previous latest quaternary rates and is consistent with those derived from geodetic paleoseismic and geologic measurements and thus resolves the long standing dispute over the latest quaternary slip rate along the longest active strike slip fault in tibet

along strike topographic variation of qinghai nanshan and its significance for landscape evolution in the northeastern tibetan plateau abstract cenozoic basins and ranges constitute the high topography of the northeastern tibetan plateau which is derived from the indo asian collision the geomorphological characteristics of the ranges provide direct insight into the uplift processes which are responsible for the patterns of the ranges and the growth of the northeastern tibetan plateau this study analyzed the geomorphological features of qinghai nanshan one of the youngest ranges within the northeastern tibetan plateau including elevation slope distribution and the channel steepness index topographic analysis revealed that elevations and slopes in western and central portions of qinghai nanshan were higher than those in the eastern portion whereas the channel steepness index revealed a step growth mode from west to east considering the topographic features the lateral gradient of precipitation increasing from west to east and the lithology distribution it is concluded that the geomorphological features of qinghai nanshan are influenced mainly by tectonic activities and reflect the growth pattern and or the tectonic setting of the range comparing with previous studies it is shown that the formation mechanism of qinghai nanshan follows a middle to sides growth pattern furthermore the degree of inclination of the erosion surface distributed on the northern flank of the range suggests that qinghai nanshan is controlled jointly by the listric qinghai nanshan thrust fault and the influences from the elashan and riyueshan dextral strike slip faults in addition the northeastern tibetan plateau exhibits an outside in growth process which might reflect the northeastward growth of the entire northeastern tibetan plateau