the nature of the witwatersrand hinterland conjectures on the source area problem although the au and u deposits of the witwatersrand basin are generally regarded as modified placer in origin the nature of the source area and the ultimate origin of au and u still remain a major enigma a number of domal outcrops of the archean basement are exposed in the witwatersrand hinterland revealing the presence of a diverse suite of granitoids and a minor 20 greenstone belt component in addition samples from over 130 boreholes drilled adjacent to the basin have revealed the character of subsurface archean basement beneath early proterozoic sedimentary and volcanic cover the granitic subsurface basement is commonly characterized by pervasive hydrothermal alteration evident as propylitization sericitization carbonation and greisenization as well as a variety of vein related alterations comprising quartz or k feldspar or chlorite or co 3 or sulfide or fluorite parageneses these hydrothermally altered granites appear to have been preserved beneath early proterozoic cover but have largely been eroded from surface outcrops the hydrothermally altered granites which are believed to be or 3 050 ma are significantly enriched in au and u with respect to both surface granitoids from the witwatersrand hinterland and the entire range of granites from the barberton mountain land the presence of enriched hydrothermally altered granites in the witwatersrand hinterland lends support to the view that mineralization processes in the basin were dominated in the first instance by placer processes the remarkable concentrations of au and u that are unique to the central rand group of the witwatersrand basin indicate that the sediments in the upper portions of the sequence tapped a fertile source not present in the hinterland during earlier cycles of sedimentation the erosional remnants of this source area are represented by the hydrothermally altered granites which are considered to have been a suite of high level granitoids the upper portions and roof zones of which were mineralized in au and u and easily accessible to erosion the emplacement of these granites and the development of extensive zones of attendant high level hydrothermal alteration was synchronous with witwatersrand sedimentation the hydrothermally altered granites not only contributed to the au and u rich detritus in the witwatersrand but their emplacement may have been linked causally to the deposition of the upper part of the sedimentary sequence

evidence for enhanced aridity in the tarim basin of china since 5 3 ma abstract thick cenozoic deposits formed from the erosion of the northern evolving edge of the tibetan plateau provide opportunities to study the exhumation history and climatic changes within the region such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the tibetan plateau multi proxy studies indicate that hyperarid climate has prevailed since 5 3 ma ago within the basin this information together with the geometry analysis of syntectonic deposits of the sanju anticline which indicate tectonic deformation at 5 3 ma enable us to better understand the interlay between climatic changes and tectonic uplift our results suggest that the tectonic uplift of the kunlun mountains at 5 3 ma must have been one of the significant regional tectonic events and the uplifted elevation of the kunlun mountains more effectively blocks the penetration of moisture from the indian monsoon into the tarim basin and thus enhances the rain shadow effect this can account for the increasing aridity as well as the formation of the world s second largest active sand desert the taklimakan desert in the tarim basin initiated at 5 3 ma ago

the uplift history of the haiyuan liupan shan region northeast of the present tibetan plateau integrated constraint from stratigraphy and thermochronology abstractthe haiyuan liupan shan delimits the northeastern margin of the tibetan plateau we present the integrated results of new stratigraphic investigations apatite fission track analyses and related thermal history modeling tied to the structural fabric of this region these constraints provide insight into the timing of northward propagation of the plateau with 1 local relief creation and enhanced erosion in the latest jurassic to earliest cretaceous representing the local element of a complex regional far field deformation response to the lhasa qiangtang collision with the south asian margin 2 evidence for likely late cretaceous exhumation but this is uncertain given the regional sedimentary gap that exists across this interval 3 eocene relief generation as a first likely response to far field effects of the india asia collision and related to wider regional events recognized in this part of northwestern china and 4 the latest deformation episode propagating strongly into the haiyuan

microscale evidence of liquefaction and its potential triggers during soft bed deformation within subglacial traction tills published conceptual models argue that much of the forward motion of modern and ancient glaciers is accommodated by deformation of soft sediments within the underlying bed at a microscale this deformation results in the development of a range of ductile and brittle structures in water saturated sediments as they accommodate the stresses being applied by the overriding glacier detailed micromorphological studies of subglacial traction tills reveal that these polydeformed sediments may also contain evidence of having undergone repeated phases of liquefaction followed by solid state shear deformation this spatially and temporally restricted liquefaction of subglacial traction tills lowers the shear strength of the sediment and promotes the formation of transient mobile zones within the bed which accommodate the shear imposed by the overriding ice this process of soft bed sliding alternating with bed deformation facilitates glacier movement by way of stick slip events the various controls on the slip events have previously been identified as i the introduction of pressurised meltwater into the bed a process limited by the porosity and permeability of the till and ii pressurisation of porewater as a result of subglacial deformation to which we include iii episodic liquefaction of water saturated subglacial traction tills in response to glacier seismic activity icequakes which are increasingly being recognized as significant processes in modern glaciers and ice sheets as liquefaction operates only in materials already at very low values of effective stress its process form signatures are likely indicative of glacier sub marginal tills

the origin of a giant downward directed clastic dyke in a kame belchatow mine central poland a kame near czubata gora in the pleistocene overburden of the belchatow open cast browncoal mine in central poland shows several types of deformations a number of diapirs occur but also a structure that shows all characteristics of a diapir but consists of sediments that apparently intruded the underlying rather than the overlying sediments analysis of this structure shows that it consists of material that was originally deposited as a fine grained mainly silty glacilacustrine sediment seismic activity triggered the material to fluidise resulting in a structureless mass part of the fluidised material flowed down into a fissure that had formed in the underlying sediments probably due to tectonics in the active graben thus forming a clastic dyke more of the overlying silty material was later pressed down into a dyke with the shape of a downward directed diapir

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

late neogene loess deposition in southern tarim basin tectonic and palaeoenvironmental implications abstract uplift of the tibetan plateau during the late cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the kunlun and altyn mountains in the southern tarim basin early neogene sediments are characterised by sandstone siltstone and red mudstone representing floodplain to distal alluvial fan environments the early pliocene artux formation consists of medium grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone the late pliocene to early pleistocene xiyu formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits sedimentological investigation together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the xiyu and artux formations point to an aeolian origin suggesting desertic conditions in the tarim basin by the early pliocene the onset of aeolian sedimentation in the southern tarim basin coincided with uplift of the northern tibetan plateau inferred from the lithofacies change from fine grained mudstone and sandstone to coarse clasts tibetan plateau uplift resulted in the shift of sedimentary environments northwards into the southern tarim basin and could well have triggered the onset of full aridity in the taklimakan region as a whole

cenozoic deformation of the tarim basin and surrounding ranges xinjiang china a regional overview abstract with its central position between the tibetan plateau and the tian shan range the tarim basin is a key element of the cenozoic asian orogenic system however a comprehensive regional study and more particularly the quantification of shortening through this basin and its margins are still needed to understand its role in the cenozoic deformation of asia from a compilation of previous works together with an extensive dataset of satellite field seismic and well data we provide a tectonic map of the cenozoic structures and four balanced geological transects of the tarim basin and its surrounding ranges based on this map and these cross sections we characterize the cenozoic deformation of the original proterozoic tarim block from structural restorations and crustal budgets we also quantify the compressive component of this deformation most of the cenozoic compressive deformation from 94 to 100 is concentrated in the ranges along the block margins to the west up to 78 23 km and 54 24 18 km of crustal shortening are accommodated across the compressive western kunlun and southwestern tian shan ranges while to the east up to 38 6 18 km and 15 20 15 km are accommodated across the transpressive altyn tagh and southeastern tian shan ranges a non negligible amount of compressive deformation up to 6 is also accommodated within the tarim basin by large basement cored uplifts with a vergence synthetic to the deformation of the tibetan plateau edge to the west the bachu uplift absorbs 5 km of the total crustal shortening of the western kunlun thrust system while to the south the tanan uplift accumulates 0 6 km of the altyn tagh strike slip system structural inheritance has a major influence on the cenozoic deformation since 33 3 to 100 of the total shortening is accommodated by reactivated basement structures inherited from the protero paleozoic history of the tarim block finally we argue that the basement cored uplifts in the centre of the basin imply a deformation transfer from the tibetan plateau to the tian shan above a deep crustal decollement decoupling the deforming crust from an underlying rigid mantle

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

cenozoic right slip faulting along the eastern margin of the pamir salient northwestern china the pamir salient defines the western end of the himalayan tibetan orogen and has overthrust the tarim tajik basin to the north by 300 km along a late cenozoic south dipping intracontinental subduction zone field mapping structural measurements and analysis of mesoscale structures along a 32 km long reach of the yarkand river document the tectonic evolution of the east flank of this salient between the north pamir to the west and the western kunlun shan to the east the study area is cut by a set of four north northwest striking steeply dipping brittle faults microstructures and asymmetric outcrop to map scale folds indicate right slip along these faults between these structures fault bounded panels of phanerozoic strata are deformed by en echelon folds with axes that trend more westerly than the adjacent faults consistent with dextral transpression the fault system described here extends for 350 km along the eastern flank of the pamir salient transpressional right slip along this set of faults here called the kashgar yecheng transfer system appears to have accommodated late cenozoic separation of the north pamir from the western kunlun shan during south directed intracontinental subduction beneath the leading edge of the pamir salient correlation of major faults suggests total slip along the kashgar yecheng transfer system is likely on the order of 280 km this offset estimate implies long term slip rates of 7 15 mm a along the kashgar yecheng transfer system when combined with previous sedimentologic stratigraphic and thermochronologic data that indicate deformation along the east flank of the pamir started between the late eocene and early miocene these results imply that the first order structures on the western and eastern flanks of the pamir are asymmetric previous work has shown that deformation in the west was accommodated by anticlockwise vertical axis rotation of the pamir over the eastern margin of the tajik basin this rotation is generally interpreted to reflect northwest directed radial thrusting in contrast to the transpressional right slip transfer faulting on the east side reported here

evidence for mesozoic shear along the western kunlun and altyn tagh fault northern tibet china the strike slip faults of north tibet accommodate part of the cenozoic convergence between india and asia along the karakax valley south of yecheng and near the xidatan trough south of golmud the active traces of the altyn tagh and kunlun faults follow narrow belts of metamorphic rocks the deformation recorded in those mylonites is sinistral strike slip rb sr and 40ar 39ar ages of deformation from syntectonic fabrics formed at 350 400 c 120 ma argon loss suggests that deformation was associated to a 250 300 c thermal pulse that lasted 5 20 ma after the onset of movement unroofing occurred much later around 25 ma when sudden cooling suggests a component of thrusting or more likely normal faulting the cretaceous shear may be related to collision between the qiantang and the lhasa blocks the karakax and xidatan shear zones may have formed a unique continuous boundary in the cretaceous which was later reused by the tertiary strike slip faults leading to potentially calculable offsets along the altyn tagh fault

an immediate response to the indian eurasian collision along the northeastern tibetan plateau evidence from apatite fission track analysis in the kuantan shan hei shan abstract the tibetan plateau offers an ideal region for understanding the processes of continental collision and related intracontinental deformation however when the cenozoic deformation was initiated in the present northeastern margin of the plateau 2000 km north to the indian eurasian collision front remains an issue in debate two competing end member models have been proposed involving immediate deformation response and progressive deformation propagation solving this problem partly relies on determining whether there was contemporaneous deformation with initial indian eurasian collision along the northeastern margin of the tibetan plateau in this study we employ apatite fission track aft analysis to shed new light on the exhumation history of the kuantan shan hei shan along the northeastern margin of the tibetan plateau with a motivation to determine whether deformation related exhumation during initial collision stage occurred in the region the 22 granite samples produce aft ages ranging from 22 3 2 6 ma to 175 18 ma and mean track lengths from 11 17 2 26 m to 13 63 1 93 m thermal history modeling indicates five episodes of rapid exhumation related cooling which took place in the early jurassic early cretaceous and late cretaceous during since the eocene and since the middle miocene the exhumation events prior to the cenozoic are attributed to far field responses of successive closure of fossil oceans and assembly of blocks along the southern margin of the eurasian continent the eocene exhumation along the kuantan shan hei shan is speculated to represent an immediate response to the initial indian eurasian collision these results lend support to the immediate deformation response model along the northeastern plateau the episodic exhumation observed in this study combined with previous geophysical findings implies that the kuantan shan hei shan represents the southern margin of the alashan block serving as a significant and long lived lithospheric weak zone susceptible to intracontinental deformation during episodes of far field tectonic event

the alichur dome south pamir western india asia collisional zone detailing the neogene shakhdara alichur syn collisional gneiss dome complex and connection to lithospheric processes neogene syn collisional extensional exhumation of asian lower middle crust produced the shakhdara alichur gneiss dome complex in the south pamir the 1 km thick mylonitic brittle top nne normal sense alichur shear zone asz bounds the 125 25 km alichur dome to the north the shakhdara dome is bounded by the 4 km thick mylonitic brittle top sse south pamir normal sense shear zone spsz to the south and the dextral gunt wrench zone to its north the alichur dome comprises cretaceous granitoids gneisses cut by early miocene leucogranites its hanging wall contains non weakly metamorphosed rocks the 22 17 ma alichur dome injection complex leucogranites transition from foliation parallel centimeter to meter thick sheets within the asz into discordant intrusions that may comprise half the volume of the dome core secondary fluid inclusions in mylonites and mylonitization temperature constraints suggest alichur dome exhumation from 10 15 km depth thermochronologic dates bracket footwall cooling between 410 130 c from 16 4 ma tectonic cooling exhumation rates 42 c myr 1 1 km myr contrast with erosion dominated rates in the hanging wall 2 c myr 0 1 km myr dome scale boudinage oblique divergence of the asz and spsz hanging walls and dextral wrenching reflect minor approximately e w material flow out of the orogen we attribute broadly southward younging extensional exhumation across the central south pamir between 20 4 ma to i mostly northward foreland directed flow of hot crust into a cold foreland during the growth of the pamir orocline and ii contrasting effects of basal shear related to underthrusting indian lithosphere enhancing extension in the underthrust south pamir and inhibiting extension in the non underthrust central pamir

problems and progress in the research on soft sediment deformations abstract the study of soft sediment deformations has gradually evolved from describing them as remarkable features into a structural analysis that should contribute to the reconstruction of the sediments early diagenetic history it appears that most attention has been devoted to this field during a few phases of the development of sedimentology a third phase when interest was renewed started in the eighties but progress is still hampered by inefficient scientific communication due to the absence of an unambiguous terminology specific topics deserving of much more attention in the near future are the interrelationships between the various forces that may effect a sediment simultaneously the development of deformational structures during a number of subsequent stages the preservational potential of the structures and systematic experiments that deal with the influence of the physico chemical and physico mechanical properties of the sediment

oligocene clockwise rotations along the eastern pamir tectonic and paleogeographic implications despite the importance of the pamir range in controlling asian paleoenvironments and land sea paleogeography its tectonic evolution remains poorly constrained in time and space hindering its potential for understanding deep to surface processes we provide here new constraints on vertical axis tectonic rotations from the southwest tarim basin along the eastern flank of the pamir arcuate range based on paleomagnetic results two well dated eocene to oligocene sections previously analyzed using biostratigraphy and magnetostratigraphy yield consistently clockwise rotations of 21 6 4 2 in 41 to 36 ma strata then 17 1 6 5 in 33 to 28 ma strata at the aertashi section and 14 2 11 5 in 41 to 40 ma strata at the kezi section combined with a regional review of existing paleomagnetic studies these results indicate that most of the clockwise rotations along the eastern pamir occurred during oligocene times and did not extend systematically and regionally into the tarim basin in contrast on the western flank of the pamir tectonic rotations in cretaceous to neogene strata are regionally extensive and systematically counterclockwise throughout the afghan tajik basin this timing and pattern of rotations is consistent with paleogeographic reconstructions of the regional sea retreat out of central asia and supports a two stage kinematic model 1 symmetric rotations of either flanks of the pamir arcuate range until oligocene times followed by 2 continued rotations on its western flank associated with radial thrusting and along the eastern flank no further rotations due to decoupled transfer slip starting in the early miocene

geometry and kinematic evolution of the hotan tiklik segment of the western kunlun thrust belt constrained by structural analyses and apatite fission track thermochronology abstractthe western kunlun thrust belt defines the boundary between the stable tarim basin in the north and the intensely deformed cenozoic tibetan plateau in the south because of its important tectonic position understanding its tectonic evolution should have important implications for propagation of deformation from tibet to its neighboring cratonal regions during india eurasia convergence we here present new structural analyses based on field investigations and seismic reflection profiles across the hotan tiklik segment of the western kunlun thrust belt the results indicate that the structural section crosses two major thrust zones the tiklik zone in the hinterland to the south and the hotan zone in the foreland to the north within these the hotan thrust zone is thin skinned with its deformation characterized by fault bend folding and fault slipping along detachment layers whereas the tiklik thrust zone involves basement with its deformation driven by the currently steeply dipping tiklik faul

lithospheric deformation beneath the altyn tagh and west kunlun faults from recent gravity surveys 1 new gravity and topographic elevation data crossing the altyn tagh and west kunlun faults in northern tibet are used to test key features of a recently proposed tectonic model for the northern boundary of the tibetan plateau the observations collected in 1997 and 1998 at 468 stations along three profiles were converted to bouguer gravity anomalies to constrain flexural models for isostatic compensation of the large relief associated with these faults initially we failed to reproduce the main features of the gravity anomalies with any isostatic model that assumes that the main contribution to the observed gravity anomalies is from the flexure of the moho by integrating sedimentary information derived from exploration seismology in the tarim and qaidam basins we obtained satisfactory fits to the data using simple models of isostasy no elastic strength across the altyn tagh is required to fit the gravity data suggesting that the fault breaks the entire lithosphere beneath it and has negligible thrust component currently or in the past this result is consistent with tectonic models that create the thickened crust of northern tibet through thick skinned thrust sheets progressively overriding asia to the northeast as the altyn tagh behaving as a classic transform fault propagates in that direction farther west the gravity observations across the west kunlun are best explained by significant underthrusting of the high topography by an elastic plate with effective thickness between 30 and 40 km in agreement with geologic interpretation and modeling of earlier but very sparse gravity observations

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

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

reconstruction of the altyn tagh fault based on u pb geochronology role of back thrusts mantle sutures and heterogeneous crustal strength in forming the tibetan plateau 1 reconstructing deformation along the northwestern margin of the tibetan plateau is critical for evaluating the relative importance of microplate versus continuum models of the indo asian collision questions regarding this margin s evolution are as follows 1 what is the total offset along the sinistral altyn tagh strike slip system 2 how has that offset been absorbed in the western kunlun shan 3 why does the n s width of the plateau vary along strike ion microprobe u pb zircon apparent ages of 17 plutons from nw tibet together with regional geologic observations define a discrete e w trending boundary between two tectonic belts that has been offset along the altyn tagh system by 475 70 km kinematic arguments indicate that this offset cannot be the result of north directed thrusting in the western kunlun shan therefore we propose that south directed faulting in the tianshuihai thrust belt both offset the tectonic boundary and produced the asymmetry in the plateau shortening appears to have been absorbed in the upper crust by thin skinned thrusting in the middle lower crust by east directed ductile flow and or subduction and in the mantle by north dipping subduction factors controlling the formation of the south directed thrust system appear to be the contrast between the rigid tarim and the weaker songpan ganzi flysch belt and a mantle suture inherited from late paleozoic subduction the evolution of western tibet leads to a view of continental deformation that integrates elements of the microplate model e g plate like mantle and crust mantle decoupling with aspects of the continuum model weak crustal flow beneath the plateau

the age of the taklimakan desert the taklimakan desert is located in the foreland basin of the tibetan plateau we report here the results of stratigraphic investigations of a 1626 meter thick sequence with interbedded wind blown silt from the southern marginal taklimakan desert because the studied section is located downwind of the desert the eolian silt accumulation is closely linked to desert formation our new evidence indicates that shifting sand dunes prevailed in the tarim basin by at least 5 3 million years ago as they do today we attribute this event to late cenozoic climatic deterioration as well as to changes in atmospheric circulation induced by tibetan plateau uplift

cenozoic tectonic rotations in different parts of the ne pamir implications for the evolution of the arcuate orogen the pamir salient defining the nw end of the himalayan tibetan orogen is a prominent curved orogen as a response to the indian eurasian collision its evolution history is essential for understanding intracontinental tectonic processes in the context of continental collision in this study we carry out systematic paleomagnetic studies on four sections in different parts of the ne pamir to unravel the tectonic evolution of the curved orogen our new results from the oytag section suggest that the clockwise cw rotations of the eastern pamir salient mainly occurred in the oligocene 32 26 ma as a response to the northward indentation of the pamir salient and was dominated by large scale dextral strike slip faults since then additionally the final collision between pamir and sw tian shan in the latest miocene reactivated the dextral talas ferghana fault tff thus be responsible for the counter clockwise ccw rotations at ulugqat however the limited tectonic rotations of the keliyang and sanju sections can be explained by the dominant thrust faulting in the foreland of the west kunlun mountains combined with the existing paleomagnetic data around the pamir salient our results support a four stage evolution 1 a roughly linear orogen before the early eocene 2 symmetric rotations on both sides until the latest oligocene followed by 3 asymmetric geometries with continued radial thrusting on the western flank and large scale strike slip fault on the eastern flank and 4 final collision between the pamir salient and sw tian shan in the late miocene

the vistulian aeolian succession in central poland abstract central poland is situated in the centre of the late pleistocene and holocene european aeolian sand belt this area has the highest frequency of round mat grains of all europe due to intense aeolian abrasion aeolian processes were very active during several glaciations but the changes in aeolian activity in the course of an entire glaciation can be studied only for the vistulian weichselian wisconsinan the reason is that a continuous blanket of glacial sediments either covered or partly eroded older aeolian sediments in central poland during the wartanian saalian ii aeolian processes began just after deglaciation and became intense under the periglacial conditions of the late wartanian and the whole vistulian the evolution of these processes is reconstructed especially for the interval of the highest and most effective aeolian activity i e the late plenivistulian oxygen isotope stage 2 the coldest stage of the last glaciation a model of the sequence of periglacial aeolian events during an entire glaciation is presented this model may be used for the reconstruction of older pleistocene cycles of high periglacial aeolian activity

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

along strike and downdip segmentation of the pamir frontal thrust and its association with the 1985 mw 6 9 wuqia earthquake

oceanic style subduction controls late cenozoic deformation of the northern pamir orogen abstract the northern part of the pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent continent collision such zones are the least understood type of plate boundaries because modern examples are few and of limited access and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes in the pamir it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate bounding main pamir thrust mpt which forms the principal northern mountain and deformation front of the pamir however the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the mpt experienced relatively minor amounts of late cenozoic exhumation the pamir orogen as a whole is an integral part of the overriding plate in a subduction system while the remnant basin to the north constitutes the downgoing plate with the bulk of the convergence accommodated by underthrusting herein we demonstrate that the observed deformation of the upper and lower plates within the pamir alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback subduction erosion subduction accretion and marginal slab tear faults we suggest that the curvature of the north pamir is genetically linked to the short width and rollback of the south dipping alai slab northward motion indentation of the pamir is accommodated by crustal processes related to this rollback the onset of south dipping subduction is tentatively linked to intense pamir contraction following break off of the north dipping indian slab beneath the karakoram

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

soft sediment deformations in the kleszczow graben central poland abstract a wide variety of soft sediment deformation structures is found in the quaternary overburden of a giant open cast browncoal mine near belchatow sw of od central poland situated within a graben the deformation structures range in size from tens of meters to only millimeters it is remarkable that their size is often related to a specific type of genesis most large scale deformations appear to result from tectonic activity other structures commonly of intermediate size result from exogenic processes such as glaciotectonism and overburden induced diapirism penecontemporaneous and other early diagenetic deformational processes among which bioturbation and cryoturbation are commonly of small size only they are nevertheless important because their analysis allows a reconstruction of not only the depositional environment but also the deformational history of the sedimentary succession in spite of the different types of genesis many of the soft sediment deformation structures are in one way or another related to the graben activity since the tectonic conditions in the quaternary deposits within the graben are in many respects comparable to those in rift valleys the deformation structures in the graben might be considered as representative for rift valleys as well the analysis of the structures resulting in an improved insight into their genesis may thus contribute to a better understanding of the conditions to which sediments in rift valleys can be exposed

an outline of the pleistocene stratigraphy of the kleszczow graben bechatow outcrop central poland abstract the pleistocene sequence of the kleszczow graben central poland is located in a brown coal quarry 8 km long and 4 km wide it contains ten separate organic horizons in part stacked one above another and in part correlated by reference to associated inorganic units using heavy minerals and gravel petrography three of the organic horizons represent interglacials ferdynandovian mazovian holsteinian and eemian others represent interstadial or periglacial deposits the tertiary quaternary boundary is recorded at the site by reuverian c and prae tiglian biostratigraphy occurring in a single section a major hiatus exists above the prae tiglian and lower pleistocene and cromerian deposits are absent glacial deposits are represented by three elsterian tills five saalian tills and glaciofluvial and glaciolacustrine deposits the czyzow formation lies between the elsterian and saalian deposits and contains at least two interglacials the ferdynandovian and mazovian and several interstadial units without glacial intervening deposits the lower saalian odranian drenthe deposits are separated from the middle saalian wartanian 1 by fluvial sands and organic deposits of the pilica interstadial the middle wartanian 1 and upper saalian wartanian 2 also may be separated by an interstadial palaeosol the evidence from the kleszczow graben supported by other central european quaternary sequences suggest that only four glaciations occurred within the region during the middle pleistocene and that these glaciations were separated by long periods with a complex climate ranging from temperate to periglacial

refuting the evidence for an earlier birth of the taklimakan desert in a recent issue of pnas zheng et al 1 report a late oligocene early miocene age of the taklimakan desert in northwest china their age was based on 40ar 39ar dating of biotites and u pb dating of zircons from layers within the xiyu formation which they interpreted as volcanic ash this chronology effectively extends the formation of the taklimakan desert from 5 ma as recently reported from outcrop 2 and high resolution borehole data 3 to 27 ma 1

late oligocene early miocene initiation of shortening in the southwestern chinese tian shan implications for neogene shortening rate variations abstract the cenozoic tian shan is one of the preeminent examples of an intracontinental orogen however there remains a significant controversy over when deformation related to the india asia collision commenced and therefore how shortening within the mountains has been partitioned over time one approach has been to look at the modern shortening rate as measured by geodetic studies combined with estimates of the total shortening across the range and extrapolate backwards this approach suggests that the onset of range construction was ca 10 ma k y abdrakhmatov s a aldazhanov b h hager m w hamburger t a herring k b kalabaev k b kalabayev v i makarov p molnar s v panasyuk m t prilepin r e reilinger i s sadybakasov b j souter y a trapeznikov v y tsurkov a v zubovich relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates nature 384 6608 1996 450 453 an alternate method is to determine the age of the onset of exhumation using thermochronology we present 19 new apatite fission track aft results from the southwestern chinese portion of the belt this region represents the first area exhumed during the late tertiary along a transect at ca 76 e exhumation commenced at the oligocene miocene boundary 24 ma along the maidan and muziduke thrusts which bound the southern side of the kokshaal range subsequently deformation propagated ca 20 km south to the kashi basin bounding thrust kbt which was exhumed by no earlier than 18 9 3 3 ma three detrital aft samples from plio pleistocene strata deposited ca 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20 9 7 0 5 3 ma to 15 9 5 4 4 0 ma with a fairly constant lag time of 16 to 18 ma these ages combined with structural data suggest that both the hanging wall and the footwall of the kbt experienced a renewed episode of exhumation during the latest cenozoic the discrepancy between the late oligocene miocene initiation of significant exhumation shown herein and the 10 ma initiation estimate from geodesy suggests that the tian shan has undergone a complex late cenozoic shortening history assuming that the present shortening rate could account for the total amount of cenozoic shortening in 10 ma and realizing that shortening initiated at least 15 myr earlier we conclude that the shortening rate must have varied over time possibly in pulsed southward migrating events and that the present rate may not reflect the average rate since initiation of range uplift

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

tectonic evolution of the pamir recorded in the western tarim basin china sedimentologic and magnetostratigraphic analyses of the aertashi section the northward indentation of the pamir salient into the tarim basin at the western syntaxis of the india asia collision zone is the focus of controversial models linking lithospheric to surface and atmospheric processes here we report on tectonic events recorded in the most complete and best dated sedimentary sequences from the western tarim basin flanking the eastern pamir the aertashi section based on sedimentologic provenance and magnetostratigraphic analyses increased tectonic subsidence and a shift from marine to continental fluvio deltaic deposition at 41 ma indicate that far field deformation from the south started to affect the tarim region a sediment accumulation hiatus from 24 3 to 21 6 ma followed by deposition of proximal conglomerates is linked to fault propagation into the tarim basin from 21 6 to 15 0 ma increasing accumulation rates of fining upward clastics is interpreted as the expression of a major dextral transtensional system linking the kunlun to the tian shan ahead of the northward pamir indentation at 15 0 ma the appearance of north pamir sourced conglomerates followed at 11 ma by central pamir sourced volcanics coincides with a shift to e w compression clockwise vertical axis rotations and the onset of growth strata associated with the activation of the local east vergent qimugen thrust wedge together this enables us to interpret that pamir indentation into tarim had started by 24 3 ma reached the study location by 15 0 ma and had passed it by 11 ma providing kinematic constraints on proposed tectonic models involving intracontinental subduction and delamination

cenozoic depositional sequences in the piedmont of the west kunlun and their paleogeographic and tectonic implications abstract the west kunlun forms the northwestern margin of the qinghai tibet plateau well developed cenozoic depositional sequences in the piedmont along the margins of the tarim basin record changes in sedimentary environment and the uplift of the west kunlun during the cenozoic during latest cretaceous to oligocene deposition in the west kunlun occurred in a marine environment the tarim bay during the paleogene gypsum beds bivalve shell limestones and variegated clastics were deposited rapid sedimentation during the late miocene resulted in the deposition of molasse sediments 2000 3000 m thick indicating a relatively high depositional rate the upper miocene sequences show a coarsening up tendency indicating a rapid and accelerated uplift of the west kunlun from late miocene to early pleistocene times molasse deposition was interrupted in the early pleistocene by a tectonic pulse which resulted in tilting of the molasse and underlying sediments at high angle towards the tarim basin undeformed middle to late pleistocene coarse fluvial and pluvial deposits overlie the steeply dipping molasse and older rocks unconformably and represent the resumption of rapid deposition a continual high rate of uplift during the holocene is presumed on the basis of an incised drainage system that flows from west kunlun into the tarim basin and cuts middle to late pleistocene gravels and older sediments to a depth from 50 m to more than 100 m although climatic changes may also have played a part

the influence of syntectonic sedimentation on thrust belt deformation a kinematic model example from the triangle zone within the western kunlun thrust belt although syntectonic sedimentation has been shown to be one of the most important factors involved in thrust belt deformation previous studies have mostly focused on the influence of just one stage in this context two geometric sediment packages that are described as progradation and aggradation are known to lead to different thrust belt deformation subsequences yet the influence of multistage sedimentary strata remains less well understood interpretation of the latest seismic data shows that the western kunlun thrust belt is characterized by classical triangle zone there are two adjacent sections with different geometrical characteristics a prograding monocline and a spaced ramp anticline we restored these two sections and analyzed the potential geological factors leading to their formation in this study the results of this analysis provide new insights into a kinematic model for triangle zones and suggest that these two distinct styles formed because of two stage syntectonic sedimentation we further discuss the kinematic model of tectonic deformation given the presence of two stage syntectonic sediments and propose four distinct sedimentary superposition patterns all of these sequences suggest that deformation is controlled by total syntectonic sediment geometry and imply that early sediment shape exerts the greatest influence the presence of early prograding sediment promotes the development of the spaced thrust belt while an early aggrading package enhances the structure of the restricted thrust adjacent to the hinterland

mesozoic tertiary exhumation history of the altai mountains northern xinjiang china new constraints from apatite fission track data abstract this study uses apatite fission track ft analysis to constrain the exhumation history of bedrock samples collected from the altai mountains in northern xinjiang china samples were collected as transects across the main structures related to palaeozoic crustal accretion events ft results and modeling identify three stages in sample cooling history spanning the mesozoic and tertiary stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 10 c stage two records a period of relative stability with little if any cooling taking place between 75 and 25 20 ma suggesting the altai region had been reduced to an area of low relief support for this can be found in the adjacent junngar basin that received little if any sediment during this interval final stage cooling took place in the miocene at an accelerated rate bringing the sampled rocks to the earth s surface this last stage linked to the far field effects of the himalayan collision most likely generated the surface uplift and relief that define the present day altai mountains

sedimentology and magnetostratigraphy of the tierekesazi cenozoic section in the foreland region of south west tian shan in western china abstract the geology of tian shan provides an excellent example for understanding the intracontinental orogeny in the context of indian eurasian convergence previous studies leave much space in basinfill deposition process to be assessed in the regions west to the talas fergana fault tff we improve the understanding by conducting new investigations on sedimentology and magnetostratigraphy in the tierekesazi section of the foreland region of south west tian shan four lithofacies have been identified i marine lithofacies from the aertashi to bashibulake formations ii lacustrine to fluvial plain lithofacies from the keziluoyi to the middle pakabulake formations iii alluvial sand gravel sheet lithofacies in the upper pakabulake formation and iv conglomerate lithofacies from the atushi to xiyu formations magnetostratigraphic analysis accompanied with biostratigraphic correlation indicates that four lithofacies cover age intervals of ca 65 ma to 34 ma ca 22 1 ma to 12 ma 12 ma to 5 2 ma and 5 2 ma to approximately present with the sediment accumulation rates increasing from ca 2 4 3 3 3 5 compacted decompacted cm ka in the lithofacies i to 12 3 16 17 cm ka in the lithofacies ii to 16 3 19 5 20 6 cm ka in the lithofacies iii and finally to 22 8 22 8 cm ka in the lithofacies iv these results suggest three episodes of sedimentary events combined with previous results these episodes of sedimentary events are attributed to tectonic activities that are widespread along south tian shan we speculate that the oligo miocene boundary event more directly and likely marks the initial underthrusting of the tarim block beneath the south tian shan the mid miocene and mio pliocene boundary events although approximately synchronous between the regions east and west to the tff have different structural expressions in the two regions such difference is proposed to cause the dextral slipping of the tff and more fundamentally likely be driven by the northward indentation of the pamir at this time

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

seismic image of the tarim basin and its collision with tibet a broadband seismic deployment in 1998 1999 in southwestern tarim provided data for imaging the crust and upper mantle across the contact between the tarim block and the tibetan plateau a profile composed of migrated teleseismic receiver functions clearly shows lateral structural changes the crust under the tarim basin is relatively simple the moho discontinuity is mapped at a depth of 42 km near the northern end of the array and dips gently toward the south to 50 km under the kunlun foreland the tarim basin appears to be rigid with little shortening farther to the south the imaging reveals a complex of reflectors in the lower crust and the upper mantle there are both north and south dipping upper mantle structures under the kunlun foreland and kunlun shan region we found the observations to be more consistent with a model of lithospheric collision in which the crust and the upper mantle on both sides interpenetrate and deform

lithostratigraphy petrography and facies analysis of the late cenozoic sediments in the foreland basin of the west kunlun abstract the yecheng profile lying in the southwest tarim basin at the northern foot of the west kunlun mountains comprises 4 5 km of conformable miocene to pliocene strata the lower part of the section the wuqia group is composed of interbedded red mudstone and pale coloured fine sandstone with a thickness of 1700 m the artux formation is 800 m thick and composed of mudstone sandstone with thin gravel and conglomerate beds the upper part of the section known as the xiyu formation consists of 2000 m of cobble and boulder conglomerate intercalated with massive siltstone lenses compositional study of the sandstones in the wuqia group and artux formation indicates that they were sourced from low relief areas of the kunlun region and probably further south from tibet the provenance of the conglomerate in the xiyu formation is the west kunlun mountains compositional trends within the conglomerate indicate that upper palaeozoic marine and mesozoic to tertiary terrestrial silicic rocks were eroded first along with the proterozoic to lower palaeozoic proto tethys metasedimentary rocks erosion into deeper levels of the kunlun mountains provided igneous and high grade metamorphic sediment which first appears 640 m above the base of the xiyu formation lithofacies change from fine grained mudstone and sandstone to coarse clasts coincides with the onset of aeolian sedimentation indicating major shift of regional palaeoclimatic regime although climatic changes may have played an important role in controlling the sedimentary regime worldwide our study of the lithostratigraphy and petrography of the yecheng section suggests that the lithofacies change recorded the progressive unroofing history of the source rocks in the west kunlun mountains

dike filled extensional structures in cenozoic deposits of the kleszczow graben central poland abstract the origin and development of the cenozoic kleszczow graben were strongly influenced by a pre existing fault pattern within the permian mesozoic bedrock dike filled fractures penetrating neogene quaternary deposits analysed in the opencast belchatow browncoal mine follow extensional structural patterns parallel to the axes of the local anticlinal forms established or rejuvenated in the quaternary these structures are particularly well developed along the fold crests the spacing and structural features of the fractures and normal faults are explained in terms of the tensile stress operating in beds subjected to folding the main localities of the quaternary folds precisely align with segments of two deep seated reverse faults the kleszczow kodr b fault and the gomunice piaski fault both are nw se orientated dislocations along a hinge zone of the laramide ekinsko anticline subcropping the cenozoic graben infill in the open mine the origin of the quaternary folds as fault overlying folds is attributed to a young block uplift on the ekinsko anticline area which is well recorded by a strong reduction in thickness of the cenozoic sediments the quaternary succession is reduced in thickness twice as much as the neogene the successive stages of quaternary reactivation of the ekinsko anticline during the cromerian through the late saalian with diminishing intensity are believed to be correlatable with the sequence of glacial rebound events coupled with mobility of the deep rooted fault zone

palaeoenvironmental interpretation of an ice contact glacial lake succession an example from the late devensian of southwest wales uk abstract during the late devensian late weichselian glaciation a number of large proglacial lakes developed in dammed river valleys along the southwest coast of wales u k this paper presents sedimentological data together with a digital terrain model to establish the sedimentation history dynamics and evolution of the largest lake glacial llyn lake teifi buried valley fill sequences within the margins of the former lake basin reveal a thick succession of glaciolacustrine muds which coarsen upward into or are locally abruptly overlain by proximal deltaic subglacial and glaciofluvial deposits sediment delivery pathways represented in the lacustrine succession include gravity flows suspension settling deltaic aggradation and iceberg rafting the latter indicating ice contact conditions the lacustrine muds are variably deformed with a range of syn and post depositional structures some of which indicate subglacial deformation associated with overriding of the lacustrine succession syn depositional structures indicate high sedimentation rates which may explain an absence of bioturbation structures the overall coarsening upward succession and cap of subglacial and or glaciofluvial deposits support recent theories suggesting that glacial llyn teifi formed during glacial advance there is no evidence to support glaciomarine conditions of sedimentation in this area of the irish sea basin

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

late cenozoic geological evolution of the foreland basin bordering the west kunlun range in pulu area constraints on timing of uplift of northern margin of the tibetan plateau 1 with an average elevation of 5000 m the west kunlun range marks northwestern margin of the tibetan plateau and formed as an orogen in response to the collision of india and asia 50 ma ago its history of uplift and erosion in the late cenozoic is recorded in a unique sedimentary sequence exposed through the highest terrace along the southern margin of the tarim basin in pulu area the terrace is composed of coarse grain conglomerate at the bottom alkaline enriched volcanic rocks in the middle and eolian sediments on the top the underlying basement rocks are formed by neogene rocks and paleozoic granite named the xiyu conglomerate the coarse grained conglomerate is assigned a depositional age in the late pliocene and the early pleistocene 3 4 1 6 ma and generally considered to be the products of rapid uplift of the tibetan plateau to reveal the relations between uplift erosion and sedimentation we have collected samples of granite overlain by the xiyu conglomerate for dating the fission track age of apatite the fission track ages date the absolute time of cooling through the track retention temperature of the granite within the west kunlun range to be miocene to early pliocene 20 4 8 ma the cooling event was coeval with the north verging thrusting along the northern boundary fault and the associated foreland basin deposition suggesting that the west kunlun range once underwent significant tectonic uplift in the neogene in contrast to the underlying tertiary foreland basin strata the xiyu conglomerate thins toward the west kunlun range and contains granite pebbles of cooling ages of 93 18 and 12 ma our study suggests that the primary cause for accumulation of the xiyu conglomerate and the correspondent sediments is the increase of erosion and sedimentation rates after the main pulse of tectonic uplift due to quaternary climate change

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

gravity anomalies and the structure of western tibet and the southern tarim basin gravity anomalies across the western part of the tarim basin and the kunlun mountain belt show that this area is not in local isostatic equilibrium these data can be explained if a strong plate underlying the tarim basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest tibet this corroborates norin s inference that late tertiary crustal shortening has occurred in this area by southward underthrusting of the tarim basin beneath the kunlun this study places a lower bound on the amount of underthrusting