detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

why are geomagnetic excursions not always recorded in sediments constraints from post depositional remanent magnetization lock in modelling abstract many geomagnetic excursions have been documented during the brunhes chron however high resolution paleomagnetic studies of sediments often provide evidence of few if any excursions we have investigated the reasons for this observation by modelling the post depositional remanent magnetization pdrm lock in process a cubic lock in function produces more rapid lock in compared to linear and exponential functions proposed in the literature we therefore used a cubic function to model best case scenarios for the quality of the paleomagnetic record when a high frequency geomagnetic input signal is convolved with the sediment lock in function for a wide range of sedimentation rates even for a lock in depth of 10 cm where 95 of the pdrm is locked in 5 cm below the surface mixed layer an input signal containing abundant excursions with 1 kyr duration is smoothed so drastically at low sedimentation rates 1 3 cm kyr that no excursions are recorded excursions are further attenuated by increasing the lock in depth as well as by sampling at discrete stratigraphic intervals the pdrm process acts as a low pass filter for high frequency secular variation signals even at moderate sedimentation rates 10 cm kyr we have also modelled the effects of modulation of sedimentation rate by a climatic forcing function e g insolation even though the average sedimentation rate might be substantial pdrm recording becomes much less reliable in intervals where sedimentation rates are lowest in these cases some excursions are reliably recorded in detail while others may not be recorded at all our modelling suggests that in order to consistently detect the presence of geomagnetic excursions it is ideal to work with sediments that maintain minimum sedimentation rates above 10 cm kyr if the normal spectrum of geomagnetic field behaviour contains abundant excursions failure to document excursions in many apparently high resolution analyses probably results from pdrm lock in within relatively slowly deposited sediments or to unrecognized intervals of slow sedimentation in environments with higher average sedimentation rates

late cenozoic tectonic evolution of the northwestern tien shan new age estimates for the initiation of mountain building the tien shan are the quintessential intracontinental range situated more than 1000 km north of the suture between india and asia their initiation and growth in the cenozoic however remain poorly understood in this study we present stratigraphic detrital fission track and magnetostratigraphic results that provide a basis for reconstructing the cenozoic tectonic evolution of the kyrgyz range and adjacent chu basin in the northwestern tien shan detrital fission track thermochronology indicates that the northwestern tien shan was tectonically quiescent for much of the cenozoic prior to uplift and exhumation in the late miocene the kyrgyz range was buried by sediments shed from highlands to the south and or east paired bedrock fission track and u th he ages from a sampling transect of 2 4 km relief demonstrate that rapid exhumation commenced at ca 11 ma initial thrusting in the hinterland was followed by evaporite accumulation 0 4 km m y which coincided with erosion of the pre 11 ma strata that mantled the kyrgyz range between 10 and 3 ma bedrockexhumation rates decreased to 0 3 km m y while sedimentation rates decelerated initially to 0 25 km m y before accelerating to 0 4 km m y at 4 5 ma detrital fission track results indicate that by 4 5 ma

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

anisotropy of magnetic susceptibility of the jingou river section implications for late cenozoic uplift of the tian shan better constraints on the uplift history of tian shan will increase our understanding of both mountain building processes and deformation patterns related to the india asian collision anisotropy of magnetic susceptibility ams holds great potential to track variations in tectonic strain which is ultimately responsible for mountain uplift here we present an ams record spanning the interval of 28 4 ma from the fluviolucastrine jingou river section in the tian shan foreland rock magnetic measurements show that the ams are dominated by antiferromagnetic hematite and some paramagnetic minerals both of which have a crystallographic preferred orientation and therefore the ams sequence may be applied to reconstruct tectonic strain although the principal minimum k min direction is nearly perpendicular to the bedding plane indicative of a predominantly sedimentary fabric for the section the tightly grouped principal maximum k max parallel to the fold axis suggests that the section was subject to an embryonic deformation at least since the late oligocene the k max direction is most likely associated with the n s strain caused by the india asian collision during the intervals of 23 3 20 0 ma and 16 5 14 0 ma the strain markedly increased as evidenced by more tightly grouped k max directions and k min largely distributed within a clear n s girdle these two intervals are accompanied by changes in sedimentary facies higher energy conditions and doubled sedimentation rates and are interpreted as the periods when the tian shan experienced significant uplift a conceptual model is tentatively proposed to reconcile various timings for the tian shan uplift

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

magnetostratigraphy of the miocene pleistocene surai khola siwaliks in west nepal summary phic age dating has been carried out on sandstones of a wellexposed continuous 5500 m thick miocene pleistocene section in the surai khola area west nepal the section is situated in the siwalik range which consists of molasse sediments from the himalaya progressive demagnetization and isothermal remanence experiments prove that haematite is the carrier of the characteristic remanent magnetization chrm throughout the entire section the final polarity sequence is based on 436 samples of which 233 have normal and 203 reverse polarity antiparallel mean directions of the normally and reversely polarized samples indicate that the chrm is of primary origin comparison of the polarity sequence with a standard polarity time scale yields a time period for the section between chron lr or chron 2r matuyama and probably chron 5ab between 1 2 myr and about 13 myr

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

spatial patterns of late quaternary river incision along the northern tian shan foreland abstract river incision rate is widely used to track changes in tectonics or climate over time and space however the feasibility of utilizing the spatial variations of river incision to reconstruct past tectonic and climatic processes remains unclear here we focus on the spatial patterns of river incision along the northern chinese tian shan foreland three alluvial fans fp feh and flh are determined as the alluvial fan context of river incision and terrace classification providing the geomorphological framework across the foreland region four rivers i e the kuitun jingou manas and urumqi rivers from the western central and eastern part of the foreland are used to reconstruct the paleogeomorphology from the reference which is the best preserved terrace of each river system with ages clustering in different parts of the latest pleistocene early holocene the depth of incision constrained by the reference terrace of each river is obtained by comparing the present day topography and the reconstructed one the resulting profile of channel incision depth and rate of each analyzed river displays an overall decreasing downstream trend from the maximum where the river exits from the mountain range to zero such a trend has been attributed to the progressive lowering of the river gradient that was caused by the adjusted ratio of sediment input versus water discharge induced by climate change superimposing on the decreasing downstream trend an obvious step can also easily be observed onto the profile of channel incision of each river downstream of which channel incision is significantly less the step occurs near the thrust fault controlling growth of the outermost anticline through which each river cuts thereby implying the key role of local rock uplift in forming the river incision step the former observation implies that at the same timescale more river incision at the exit from the mountain range does not necessarily mean stronger climatic forcing of incision there we thus propose that in a foreland setting it should be the temporal pattern of river incision rather than its spatial variation that is helpful for unraveling the change in the forcing factor of downcutting

comment on magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china baochun huang john d a piper shoutao peng tao liu zhong li qingchen wang rixiang zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 abstract the recent publication of magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china by b c huang j d a piper s t peng t liu z li q c wang r x zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 discusses the cenozoic uplift history of the tianshan mountains by studying the magnetostratigraphy of paleogene to neogene continental sediments from two sections located in the kuche basin at the northern edge of the tarim basin to support their conclusion they reinterpreted a magnetostratigraphic study of the yaha section which lies 10 km south of their sections we previously published j charreau s gilder y chen s dominguez j p avouac s sen m jolivet y li and w wang magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tianshan mountains geology 34 3 2006 181 184 here 1 we argue that the interpretations of the sedimentation rate changes they proposed for the kuche sections are partially invalid 2 we disagree with their reinterpretation of the age of the yaha section and 3 we think that the way they interpret their ams data is incorrect

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

mesozoic paleomagnetic results of the tarim craton tertiary relative motion between china and siberia paleomagnetic poles from two late jurassic to late cretaceous stratigraphic sections on the northern boundary of the tarim craton in western china are concordant with poles of similar age from eastern china when combined with previously published data these new results suggest that the major tectonic blocks which comprise china the tarim yangtze and sino korean cratons have been arranged in approximately their present relative configuration since cretaceous times the averaged cretaceous paleomagnetic pole for china is significantly different from the averaged cretaceous pole for siberia the difference may reflect significant relative post cretaceous motion between the composite china terrane and the siberian craton alternatively the cretaceous pole for siberia may not be reliable

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

gravel deposits on the margins of the qinghai xizang plateau and their environmental significance abstract the thick deposits of quaternary gravels found along the margins of the qinghai xizang tibet plateau have been studied for decades here we concentrate on two sediment series widely developed along the kunlun tian shan and qilian mountains the xiyu formation a molassic series of lower pleistocene age and the middle and upper pleistocene gobi gravels these two series with their contained fossil assemblages throw light on the question of the mean altitudes and uplift rates of the tibetan plateau during the quaternary and on the related problem of the vigour and penetration of advected summer monsoonal moisture into central asia the sedimentary series on the northern piedmonts of the tibetan plateau considered here challege the view that plateau uplift accelerated in the upper pleistocene they indicate that the plateau had reached mean altitudes in the range 4000 5000 m perhaps by the end of the lower pleistocene and certainly by the middle pleistocene this diminished the incursion of southerly monsoonal moisture and so imposed arid and semi arid conditions across much of a vast region north of the plateau which among other effects precluded widespread mountain glaciation in the lower pleistocene and general ice sheet glaciation of the tibetan plateau as a whole

discordant paleomagnetic direction in miocene rocks from the central tarim basin evidence for local deformation and inclination shallowing from exposures at the southeastern end of the maza tagh range in the central tarim basin latitude 38 5 n longitude 80 5 e 55 paleomagnetic sites were collected from red mudstones and sandstones of the miocene wuqia formation thermal demagnetization revealed a high unblocking temperature characteristic remanent magnetization chrm five sites collected across a kink fold yield a positive fold test at 99 confidence level the mean directions computed from normal and reversed polarity sites are antipodal suggesting a primary origin for the chrm in stratigraphic coordinates the final set of 30 site mean chrm directions yields a section mean direction inclination i 29 4 declination d 24 7 k95 6 2 when compared to the miocene expected direction at 20 ma the observed direction indicates 30 8 5 5 flattening of inclination and 15 3 6 7 clockwise vertical axis rotation anisotropy of magnetic susceptibility measurements on 155 samples show a strong foliation of 1 092 with a subvertical minimum susceptibility axis these observations indicate a rock magnetic depositional or compaction shallowed origin for the inclination flattening the clockwise deflection of the observed declination can be interpreted as either 1 15 3 6 7 clockwise rotation of the entire tarim basin since the miocene or 2 a local km scale structural deformation it is not a simple matter to discard the interpretation of 15 3 6 7 clockwise rotation of the tarim basin because the fastest rates of rotation determined from global positioning system and slip rate studies of quaternary faults could produce such a rotation if extrapolated to 20 ma nevertheless we argue that local deformation is the preferred interpretation because the map pattern of local structures shows v20 clockwise deflection toward the southeastern end of the maza tagh range where the paleomagnetic samples were collected 2002 elsevier science b v all rights reserved

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

new space geodetic constraints on the distribution of deformation in central asia abstract results from repeated measurements across a 90 sites global positioning system network in central asia provide direct evidence of current high rates of tectonic deformation far north of the india eurasia suture zone the data help to quantify both the partitioning of deformation within the seismically active tien shan and northern pamirs as well as the ongoing rotation of virtually undeformed blocks such as the tarim with respect to stable eurasia the nnw to sse shortening rates derived from the computations reach values of 23 3 mm yr 1 over the ranges studied suggesting that regional deformation rates have increased considerably within the study area since the onset of cenozoic shortening 20 25 myr ago

quaternary climate change and the formation of river terraces across growing anticlines on the north flank of the tien shan china nested stream terraces warped upward over actively growing anticlines along the north flank of the tien shan in western china appear to record alternating phases of valley widening and incision differences of relative heights between remnants of four separate strath terraces along one river and between two such terraces along another reach 100 to 120 m over the crests of the anticlines we infer that this spacing is due to alternating stages of valley widening and rapid incision associated with climate changes with a periodicity of 100 kyr the crests of the anticlines appear to emerge from the aggrading flanks of the anticlines at an average rate of about 1 mm a the maximum heights of 25 and 35 10 m for the lowest terraces above their projected initial profiles imply ages of roughly 25 kyr and 35 kyr 10 kyr hence they suggest that flood plains which were abandoned to form the terraces developed adjacent to active stream beds during the last glacial period when climates were relatively

mass transfer between eastern tien shan and adjacent basins central asia constraints on regional tectonics and topography summary using depths and ages derived from isopachs drill holes or cross sections it is possible to reconstruct the space time depositional history of a sedimentary basin drill holes and cross sections give the local sedimentation history while isopachs allow the definition of the spatial distribution of the sediments assuming several simple hypotheses such as similarity of the strata and regional applicability of results derived from local analyses one can reconstruct balanced maps of the solid or grain volumes and hence the mass of sediments deposited during several time intervals since the palaeogene applying this method to the tarim and dzungar basins nw china we estimate the total cenozoic solid phase volume and mass of sediments stored to be 1358 f 520 x lo3 km3 36 7 f 14 x 1017 kg and 172 f 56 x lo3 km3 4 6 f 1 5 x 1017 kg respectively the reconstruction also enables us to detect two main pulses in the sedimentation the first around 17 ma affected only the northern part of the tarim basin also known as the kucha or kuche depression at the foot of the tien shan mountains and supports the idea that the presently active shortening regime in that range started at that time the second 5 to 6 ma affected most of the depositional areas of the region and may have an even greater geographical extent assuming local isostasy we estimate the volume of shortening induced by the rotation of the tarim block relative to siberia and stored in the range and adjacent basins to be between 1 15 x lo6 and 4 23 x lo6 km3 this correspbnds to a clockwise rotation of between 2 5 and 8 7 we use these results in two simple models of self similar growth of pyramidal topographies that approximately fit the eastern tien shan

paleomagnetic study of cenozoic sediments from the zaisan basin se kazakhstan and the chuya depression siberian altai tectonic implications for central asia abstract this paper presents new paleomagnetic results on cenozoic rocks from northern central asia eighteen sites were sampled in pliocene to miocene clays and sandy clays of the zaisan basin southeastern kazakhstan and 12 sites in the upper oligocene to pleistocene clays and sandstones of the chuya depression siberian altai thermal demagnetization of isothermal remanent magnetization irm showed that hematite and magnetite are the main ferromagnetic minerals in the deposits of the zaisan basin stepwise thermal demagnetization up to 640 660 c isolated a characteristic chrm component of either normal or reverse polarity at nine sites at two other sites the great circles convergence method yielded a definite direction measurements of the anisotropy of magnetic susceptibility showed that the hematite bearing sediments preserved their depositional fabric these results suggest a primary origin of the chrm and were substantiated by positive fold and reversal tests the mean paleomagnetic direction for the zaisan basin d 9 i 59 k 19 95 11 is close to the expected direction derived from the apw path of eurasia j geophys res 96 1991 4029 and shows that the basin did not rotated relative to stable asia during the tertiary in the upper pliocene pleistocene sandstones of the chuya depression a very stable chrm carried by hematite was found its mean direction d 9 i 46 k 25 95 7 is characterized by declination close to the one excepted for early quaternary whereas inclination is lower in the middle miocene to lower pliocene clays and sandstones a stable chrm of both normal and reverse polarities carried by magnetite was isolated its mean direction d 332 i 63 k 31 95 4 is deviated with respect to the reference direction and implies a neogene 39 8 counterclockwise rotation of the chuya depression relative to stable asia these results and those from the literature suggest that the different amount of rotation found in the two basins is related to a sharp variation in their tectonic style predominantly compressive in the zaisan basin and transpressive in the siberian altai at a larger scale the pattern of vertical axis rotations deduced from paleomagnetic data in northern central asia is consistent with the hypothesis of a large left lateral shear zone running from the pamirs to the baikal heterogeneous rotations however indicate changes in style of faulting along the shear zone and local effect for the domains with the largest rotations

mass accumulation rates in asia during the cenozoic summary this work establishes estimates of mass accumulation rates in 18 mostly offshore sedimentary basins in asia since the beginning of the cenozoic 66 ma the estimates were derived from isopach maps cross sections and drill holes or stratigraphic columns assuming regional similarity of the strata average solid phase volumes and accumulation rates were calculated for nine epochs approximately corresponding to geological periods palaeocene 66 58 ma eocene 58 37 ma oligocene 37 30 and 30 24 ma miocene 24 17 17 11 and 11 5 ma pliocene 5 2 ma and quaternary 2 0 ma these rates shed new light on the geological history of asia since the onset of the collision of india with asia 50 ma the overall average accumulation rates curve for asian sedimentary basins since the beginning of the tertiary shows an exponential form with slow accumulation rates less than 0 5 106 km3 myr 1 until the beginning of the oligocene more than 15 myr after the onset of the collision from the oligocene onwards rates increase quickly in an exponential manner reaching their maximum values in the quaternary more than 1 5 106 km3 myr 1 from these observations we suggest that extrusion and crustal shortening are complementary processes that have been successively dominant throughout the india eurasia collision history at smaller scales one may distinguish between independent histories at the subcontinental and basin scales this permits a comparison of the relative importance of tectonic and climatic erosion processes affecting the different mountain belts of asia during the cenozoic

new cretaceous paleomagnetic poles from the tarim basin northwestern china most paleomagnetic studies of the tarim have been focused on the paleozoic with little data published for mesozoic rocks however the ancient configuration of this part of asia has been affected by the indian eurasian collision during the second french chinese karakorum expedition from kashkar to kunjerab in the autumn of 1990 we sampled about 500 cores from 53 sites of upper and lower cretaceous red sandstones from three areas near uytak yingjisha and wuqia 38 5 39 5 n 75 76 5 8 isothermal remanent magnetization acquisition indicates the presence of minerals with high magnetic coercivity stepwise thermal demagnetization confirms that hematite is the dominant carrier and allowed the separation of low temperature components ltc 600 c in most samples the mean direction of ltcs is aligned with that of the present earth field normal and reversed polarities have been found for the htcs of each age group htcs show positive fold tests for at least one sub study where the attitudes of bedding were sufficiently different to allow the test to be performed more important the four sub studies from yingjisha and wuqia give fully compatible results results from the uytak area show a wide dispersion in declinations as could be expected from the rather severe deformation and proximity to major thrust and strike slip faults data obtained in the kuche area from northern tarim by li and co workers and in southern junggar by chen and co workers are statistically identical to the new data from yingjisha and wuqia data from paicheng in northern tarim appear to have been subject to local rotation excluding those sites which appear from paleomagnetic study to have been significantly rotated we calculated a mean cretaceous pole for the tarim basin at 69 1 n 223 88 ass 3 5 n 5 this result indicates that the total post cretaceous rotation of tarim relative to junggar and to eurasia has been negligible 2 6 6 1 and 0 4 4 6 respectively continental shortening and rotation between tarim and junggar within the tien shan are not resolved by paleomagnetism although the values obtained 400 t 600 km 3 6 are compatible with tectonic models of the range a major discrepancy warranting further geological investigation is that between the tarim and north china block poles which would imply some 1400 1060 km of north south relative displacement

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

holocene hydrological changes inferred from alluvial stream entrenchment in north tian shan northwestern china abstract we analyze the possible contribution of climate change or tectonics on fluvial incision from the study of a case example along the northern flank of tian shan the rivers that exit the high range fed large alluvial fans by the end of the last glacial period they have since deeply entrenched the piedmont by as much as 300 m we have surveyed several terraces that were cut and abandoned during river entrenchment providing information on intermediate positions of the riverbed during downcutting they suggest a gradual decline in river slope during a major phase of incision throughout the holocene tectonic uplift affects only a zone about 5 km wide corresponding to a growing anticline and is shown to account for about 10 of total incision incision was therefore most probably driven by climate change from observed fluvial incision we estimate the water discharge in excess of that needed to carry the sediments supplied by hillslope erosion in the headwaters we used a model based on a transpor

late cenozoic transtensional fault belt discovered on the boundary of the awati sag in the northwestern tarim basin late cenozoic transtensional fault belt was discovered on shajingzi fault belt nw boundary of the awati sag in the northwestern tarim basin and numerous quaternary normal faults were discovered on aqia and tumuxiuke fault belts sw boundary of awati this discovery reveals quaternary normal fault activity in the tarim basin for the first time it is also a new discovery in the southern flank of tianshan mountains shajingzi transtensional fault belt is made up of numerous small normal faults horizontally the normal faults are arranged in right step en echelon patterns along the preexisting shajingzi basement fault forming a sinistral transtensional normal fault belt in profile they cut through the paleozoic to the mid quaternary and combine to form negative flower structures the late cenozoic normal faults on the sw boundary of awati sag were distributed mainly in the uplift side of the preexisting aqia and tumuxiuke basement involved faults and combined to form small horst and graben structures in profile based on the intensive seismic interpretation careful fault mapping and growth index analysis we conclude that the normal fault activity of shajingzi transtensional fault belt began from late pliocene and ceased in late pleistocene mid quaternary and the normal faulting on the sw boundary of awati sag began from the very beginning of quaternary and ceased in pleistocene the normal faulting on awati s sw boundary began a little later than those on the nw boundary the origin of shajingzi transtensional normal fault belt was due to the left lateral strike slip occurred in the southern flank of tianshan and then due to the eastward escape of the awati block a tensional stress developed the normal faults on its sw boundary

addendum to late cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the tian shan mountains by jimin sun qinghai xu and baochun huang 1 sun et al 2007 constructed a magnetostratigraphic record of the kuitun river section xinjiang province china and reinterpreted a magnetostratigraphic record from the same section previously published by charreau et al 2005 in this paper we show that sun et al miscorrelated their column with respect to that of charreau et al a compatible correlation recognized by both sides is presented

magnetic fabric development in the tertiary accretionary complex in the boso and miura peninsulas of central japan it has been demonstrated that the anisotropy of magnetic susceptibility ams is a sensitive indicator for distinguishing various processes that had acted during and after the deposition of sediments recently much attention has been focused on proving its usefulness in distinguishing early deformation signatures in sediments which show no visible grain scale deformation here we present the ams results of the neogene miura group of central japan which was formed by arc arc collision tectonics with subdivisions of two contrasting tectonic provinces the southern province a highly deformed accretionary prism and slope basin and the northern province a gently deformed forearc basin samples were collected from 21 sites in both tectonic settings we obtained from axes orientations three typical fabric domains considered to represent sedimentary tectonically deformed and their intermediate types the shape parameters of ams also revealed distinctions clearly sedimentary fabrics are more foliated and anisotropic deformed fabrics show a more prolate shape and are closer to being isotropic the sedimentary fabrics predominate in the northern forearc basin sequence whereas the intermediate and deformed fabrics occur predominantly in the southern province the general trend of the shape of the magnetic fabric in studied sediments reveals a clear evolution in the pattern of the isotropic tectonic fabric constructed from foliated sedimentary fabric

building the northern tien shan integrated thermal structural and topographic constraints abstract paired apatite fission track and u th he dates provide the first late cenozoic cooling ages for the northern tien shan these data clearly argue for pulsed deformation since the late miocene with early 10 11 ma and late 0 3 ma intervals of rapid exhumation separated by an extended interval of much slower rates by integrating these bedrock cooling rates with shortening estimates derived from a balanced section detrital cooling ages and geomorphological estimates of conditions before deformation we reconstruct a four stage history of range growth and exhumation following 100 m yr of tectonic quiescence abruptly accelerated rock uplift exhumation and cooling in the kyrgyz range commenced at 11 ma with rates exceeding 1 km m yr during the subsequent 7 m yr deformation and cooling rates decreased three to sixfold before accelerating by comparable amounts during the past 3 m yr since mid miocene times the surface elevation of the kyrgyz range has increased 2 km consistent with

role of the tian shan mountains and pamir plateau in increasing spatiotemporal differentiation of precipitation over interior asia abstractnumerical simulations were conducted to determine the impact of the tian shan mountains and pamir plateau on arid conditions over interior asia these topographies are crucial for the diffe

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

a successful rock magnetic technique for correctng paleomagnetic inclination shallowing case study of the nacimiento formation new mexico the accuracy of an inclination shallowing correction technique was tested on the remanence of the paleocene nacimiento formation the correction assumes that changes in paleomagnetic inclination during deformation will be directly related to changes in remanence anisotropy the remanence anisotropy is also a function of the magnetic anisotropy of the individual magnetic grains the nacimiento formation was selected for this test because its inclination is shallow by 7 to 8 and previous paleomagnetic studies indicate that it has a primary remanence with a well constrained age and that magnetic overprints are minimal tectonics are an unlikely explanation for its shallow inclination these conditions allow the inclination corrected remanence to be compared to a well defined paleomagnetic pole to determine the accuracy of the technique the characteristic remanence from 20 nacimiento sites was isolated by alternating field and thermal demagnetization and was corrected using the anisotropy of anhysteretic remanence measured for three to five samples per site individual particle anisotropy was determined by drying a magnetic separate epoxy mixture in a 35 50 mt magnetic field laboratory compaction of disaggregated nacimiento material was also used to yield an effective individual magnetic particle anisotropy the two techniques resulted in similar values for individual particle anisotropy and similar inclination shallowing corrections both corrections were successful and the inclination corrected formation mean direction was indistinguishable from the direction predicted by north america s paleocene paleopole the inclination shallowing correction technique reported here should be applied routinely in paleomagnetic studies provided that the remanence is a primary depositional remanence that has been affected only by syndepositional or early postdepositional processes e g compaction

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

changes in the strength of the iceland scotland overflow water in the last 200 000 years evidence from magnetic anisotropy analysis of core su90 33 abstract results from a high resolution study of magnetic anisotropy combined with mineral magnetic analysis clay analysis and oxygen isotopes stratigraphy are reported for core su90 33 located 60 34 4n 22 05 1w at 2400 m water depth along the iceland scotland overflow water isow a branch of the north atlantic deep water nadw this core covers the last 6 climatic stages the main magnetic mineral is low ti content magnetite with very slight changes in the grain size the susceptibility record corrected for the carbonate content indicates down core variations in the amount of magnetite which largely co vary with the changes in the proportion of smectite in the clay fraction both parameters are climatically controlled with lower values during glacial than during interglacial periods the measurements of the anisotropy of magnetic susceptibility document down core changes in the degree of anisotropy with significantly higher values during interglacial periods than during glacial times these changes appear to be related to differences in the degree of alignment of the magnetic particles and not to changes in grain shape providing evidence that they arise from changes in strength of the bottom water circulation therefore the strength of the contour current associated to the transport of the isow appears to have been significantly larger during climatic stages 5 3 and 1 than during stages 6 4 and 2

paleomagnetism and tectonics of the southern tarim basin northwestern china we report late carboniferous permian and early tertiary paleomagnetic data from the southern tarim basin prefolding magnetizations were isolated in each case the late carboniferous permian and early tertiary poles lie at 64 6 n 166 5 e a95 6 3 and 58 1 n 202 0 e a95 12 7 respectively the late jurassic to early tertiary j3 e1 paleolatitudes of tarim and several basins throughout central asia are similar yet significantly 10 to 20 shallower than those predicted by the eurasian apparent polar wander path resolving this discrepancy remains a major problem in asian paleomagnetism discordance of the late paleozoic poles from tarim and siberia suggest that tarim has rotated about 30 counterclockwise with respect to siberia since the permian where paleomagnetic samples of both late carboniferous to early triassic c3 t1 and j3 e1 ages were collected from the same area of tarim a great circle passes through the means of the poles and the sampling locality this suggests that 1 only a difference in inclination and not declination distinguishes the two data sets and 2 vertical axis block rotations of the c3 e1 strata occurred after e1 although based on data of lesser quality the mean early to middle jurassic j1 2 pole from tarim differs significantly from the eurasian reference pole requiring radical tectonic solutions to resolve them the tarim j1 2 pole is indistinguishable from both the mean j3 e1 and c3 t1 poles the similarity of all the poles and the analogous tectonic setting of present day central asia to that of the late paleozoic in eastern north america raises the question whether all the data from tarim are overprinted

early evolution of salt structures in the north louisiana salt basin abstract several salt diapirs and pillows in southern and central north louisiana have been studied utilizing approximately 355 miles 570 km of seismic reflection data and information from 57 deep well holes the use of seismic profiles coupled with deep well hole data is the most advantageous method to document regional salt tectonism through time three stages pillow diapir and post diapir stages are required to explain salt stock growth through time in the north louisiana salt basin the pillow stage and its associated primary peripheral sinks exhibit 11 34 thinning over pillow crests and 12 50 overthickening in the primary peripheral sinks in the basin thinning values as great as 87 and overthickening values as high as 400 are inferred for pre diapiric juvenile salt pillows the diapir stage and its associated secondary peripheral sinks exhibit 50 250 overthickening this stage is characterized by piercement diapirisin and the withdrawal of large volumes of salt from the flanks of the pillow the post diapir stage and its associated peripheral sinks exhibit less than 45 overthickening moreover in some instances dome growth is in a steady state with sedimentation growth stages are generally confined to the following stratigraphic units smackover to knowles pillow stage calvin diapir stage and winn and younger sediments post diapir stage the above considerations lead to the following conclusions on diapirism in the north louisiana salt basin 1 onset of the diapiric event was early late jurassic in the southern and central portion of the basin and later early cretaceous in the northern portion 2 the initial diapiric event is much more rapid and intense in the southern and central diapirs when compared with the later diapiric event in the northern diapirs 3 regional depocenter shifting relative sea level local erosion with salt extrusion and rapid depositional loading of sediments are the major controls on diapirism in the basin

new constraints on the india asia collision the lower miocene gangrinboche conglomerates yarlung tsangpo suture zone se tibet abstract lower miocene conglomerates crop out along the length of the yarlung tsangpo suture zone on the southern margin of the lhasa terrane these conglomerates known by various local names are correlated herein as the gangrinboche conglomerates all units exhibit broadly similar stratigraphic histories and a basal depositional contact upon an eroded surface of rocks of the lhasa terrane is ubiquitous at most localities the tops of sections are either removed by erosion or truncated by north directed thrusts these conglomeratic molasse units developed in response to the india asia collision and record aspects of its development in all units initial clast derivation was from the lhasa terrane on the northern margin of the yarlung tsangpo suture zone up section the first appearance of clasts derived from terranes within the suture zone and the northern margin of india all of which lie to the south of any outcrops of gangrinboche conglomerates is observed although these units were previously thought to be eocene analysis of fossil and structural constraints indicates early miocene deposition as development of the gangrinboche conglomerates records a significant phase in the evolution of the india asia collision understanding of their age and stratigraphic evolution has wider implications for regional tectonic models

late cenozoic increase in accumulation rates of terrestrial sediment how might climate change have affected erosion rates abstract accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents although not everywhere apparently erosion has increased in elevated terrain regardless of when last tectonically active or what the present day climate in many regions sediment coarsened abruptly in late pliocene time sparser data suggest increased sedimentation rates at 15 ma approximately when oxygen isotopes in benthic foraminifera imply high latitude cooling if climate change effected accelerated erosion understanding how it did so remains the challenge some obvious candidates such as lowered sea level leading to erosion of continental shelves or increased glaciation account for increased sedimentation in some but not all areas perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 3 4 ma when large oscillations in climate with periods of 20 000 40 000 years developed and de

middle pleistocene climate and habitat change at zhoukoudian china from the carbon and oxygen isotopic record from herbivore tooth enamel the pleistocene deposits at zhoukoudian often referred to as the bpeking manq site contain dental remains from a diverse group of herbivores including equus sanmeniensis cervus elaphus cervus nippon megaloceros pachyosteus sus lydekkeri and dicerorhinus choukoutienensis the carbon and oxygen isotopic compositions of structural carbonate within the enamel of these teeth are used to reconstruct the paleodiet and paleoenvironment of the mammals the d 13 c values of enamel from zhoukoudian range from 2 3x to 13 0x indicating that these mammals consumed between 25 and 100 c3 plants the presence of significant amounts of c4 plants in the diets of some herbivore species indicates that at the onset of the middle pleistocene local habitats included mixed c3 c4 vegetation by approximately 470 000 yr ago c3 plants dominated the diets of herbivores studied suggesting that the abundance of c4 flora had decreased in the area for all deer analyzed in this study the values of d 13 c and d 18 o decrease substantially from about 720 000 to 470 000 yr ago this trend may be due to a strengthening of the winter monsoon during the middle pleistocene

magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china abstract magnetostratigraphic and rock magnetic results from 1006 horizons in paleogene and neogene sediments between the upper kumugeliemu formation and the base of the kuche formation within the kuche depression of the tarim basin nw china are used to evaluate postcollisional uplift and deformation in the tian shan range characteristic remanences with both normal and reversed polarity were isolated by thermal demagnetization generally between 300 and 690 c and a composite magnetostratigraphy is constructed from data at 969 accepted levels correlating with polarity chrons c12n to c3r dated between 31 0 and 5 5 ma on the ck95 geomagnetic polarity time scale observed height dependent changes of rock magnetic parameters km and ams ellipsoid parameters indicate that these sediments were influenced by weak deformation with the succession accumulated before 15 ma recording the effects of compressive deformation this finding together with two substantial increases in accumulation rate at 16 17 and 7 ma define a framework for cenozoic uplift and deformation of the tian shan range we argue that thrusting in the south of the range was probably initiated at 20 ma and followed by rapid uplift at 16 17 ma on the assumption that sediment accumulation in western china was still predominately tectonically controlled at 7 ma another later pulse of rapid uplift with a much larger regional influence is also recognized in the tian shan the kuche depression was subjected to two postcollisional phases of rotational deformation with clockwise rotation prior to 12 ma 1 36 ma succeeded by counterclockwise rotation at 1 64 ma after 12 ma and possibly continuing to the present day this rotational deformation is not temporally related to the history of basin formation resolved from the magnetostratigraphy and may be linked to block interactions with adjoining terranes

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

magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tian shan mountains we report a magnetostratigraphic and rock magnetic study of the yaha section located on the southern flank of the central tian shan mountains asia our results show a two fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca 11 ma after 11 ma sedimentation rate remained remarkably constant until at least 5 2 ma these findings are consistent with sedimentary records from other sections surrounding the tian shan we conclude that uplift and erosion of the tian shan accelerated ca 11 ma long after the onset of the collision between india and asia and that the range rapidly evolved toward a steady state geometry via a balance between tectonic and erosion processes

magnetostratigraphy of syntectonic growth strata and implications for the late cenozoic deformation in the baicheng depression southern tian shan abstract the collision between india and eurasia in the cenozoic has caused a series of intracontinental deformation in the foreland basins of tian shan but there are debates about the timing of tectonic deformation and the relationship between tectonic uplift and sediment accumulation in the foreland basins based on the magnetostratigraphy of growth strata in the baicheng depression southern tian shan we suggest that an episode of crustal shortening in the late cenozoic evidenced by syntectonic growth strata in the kelasu yiqikelike structural belt kysb initiated at 5 3 ma since then the sedimentation rate accelerated abruptly and coarse molasse deposits accumulated combined with the results of growth strata on both flanks of tian shan and the fact that the xiyu formation on the southern limb of the kasangtuokai anticline was involved into the growth strata we conclude that the period from 7 5 ma to the early pleistocene was one of the important episodes of intracontinental deformation in the foreland basins of tian shan as a response to the cenozoic collision between india and eurasia

influence of the tibetan plateau and its northern margins on the mid latitude westerly jet over central asia in summer abstract the upper troposphere westerly jet is currently maintained in the mid latitudes of central asia during summer the strength and movement of which are closely related to the variations in precipitation in arid central asia however little is known about how this westerly jet has changed during the cenozoic although it is known that the tibetan plateau has a crucial role in the modern asian climate we conducted a set of numerical experiments to examine the effects of the tibetan plateau and the topography of its northern margins the pamir plateau the tian shan mountains and the mongolian plateau on the westerly jet in summer the mid latitude westerly jet is significantly intensified with the uplift of the tibetan plateau the center of the jet stream moves about 1 to the north this strengthening and shift in the westerly jet are primarily due to the strong atmospheric heat source induced by the uplift of the tibetan plateau with the inclusion of the pamir plateau and tian shan mountains the westerly winds in the northern axis of the jet are strengthened while the southern part is weakened resulting in a continuous northward shift in the westerly jet stream similar to the effects of the tibetan plateau anomalous diabatic heating appears with the inclusion of the pamir plateau and tian shan mountains and the intensity of the westerly jet is slightly weakened the westerly jet is also weakened but stops moving northward when the mongolian plateau is uplifted this is a result of continuous northward warming the mid latitude westerly jet therefore experienced distinct changes during the cenozoic in association with the development of the atmospheric heat source in summer as a result of the stepwise uplift of the tibetan plateau tian shan mountains and mongolian plateau this may have influenced the aridity of the asian interior and the transport of eolian dust

organic carbon sulphur and iron in recent semi euxinic sediments of kau bay indonesia kau bay island of halmahera eastern indonesia is a 470 m deep basin separated from the pacific ocean by a sill that is at present only 40 m below sea level during weichselian time the sea level dropped below the depth of the sill and freshwater sediments were deposited these sediments are rich in organic matter corg 2 6 wt with terrigenous isotope characteristics 13corg 28 to 30 and are also rich in sulphur s 4 wt this sulphur enrichment is interpreted to be a late diagenetic feature related to diffusion of dissolved sulphate and sulphide from the marine sediments into the freshwater sediments the sulphur in these sediments has a 34s value of 15 the overlying holocene sediments consist of marine muds deposited in alternating low oxygen and h2s bearing bottom waters the marine sediments are also rich in organic matter corg 2 6 wt but of mixed terrigenous and marine origin 13c 25 to 19 moreover the sulphur content of these holocene sediments is lower s 1 2 wt and isotopically lighter 34s 20 in addition to pyrite large amounts of acid volatile sulphur avs compounds accumulate in kau bay the reactive iron content of the sediment limits the amount of iron that is sulphidized while the supply of oxidants controls the limited conversion of avs to pyrite total and reactive iron contents are strongly correlated with the amount of terrigenous organic matter as a consequence of their common provenance and depositional histories the marine sediments in kau bay show no simple relation between organic carbon and sulphur

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

paleomagnetic study of mesozoic continental sediments along the northern tien shan china and heterogeneous strain in central asia a paleomagnetic study of rocks from the northern foot of the tien shan and the southern border of the dzungar basin east of urumqi 44 2 n 86 0 e spanning ages from middle jurassic to early tertiary was carried out to constrain the tectonic evolution in central asia since mesozoic time five middle jurassic sites reveal a remagnetized direction close to the present earth field in geographic coordinates d 6 6 i 72 6 95 7 4 thirteen out of 17 upper jurassic and lower cretaceous sites yield a characteristic direction stratigraphic coordinates of d 12 7 i 48 6 95 5 5 nine of 16 upper cretaceous and lower tertiary sites provide a characteristic direction of d 12 5 i 51 3 95 6 9 the latter two directions pass fold and reversal tests the pole positions are close to each other and to the besse and courtillot 1989 1990 eurasian apparent polar wander path for ages ranging from 130 to 70 ma however the difference in paleolatitudes amounts to about 5 9 3 7 which could indicate significant continental shortening in the altai mountains and perhaps further north subsequent to india asia collision the pole positions from the dzungar basin are close to those found for the tarim li et al 1988a leading to an insignificant paleolatitude difference 3 0 6 9 but showing a larger difference in declination 8 6 8 7 these paleomagnetic results are compatible with a model of heterogeneous deformation in the western part of the collision zone between india and siberia a significant shortening in the altai a slight counterclockwise rotation of the dzungar block the westward increasing shortening in the tien shan with attendant clockwise rotation of the tarim block are all consistent with this model in which tibet the tien shan and the altai undergo differential strain along strike in a relay fashion with the total india siberia convergence remaining approximately constant

magnetostratigraphy and rock magnetism of the neogene kuitun he section northwest china implications for late cenozoic uplift of the tianshan mountains in order to better constrain the tectonic evolution of central asia under the influence of the india asia collision we carried out a magnetostratigraphic study at the kuitun he section on the northern flank of the tianshan range northwest china a total of 801 samples were collected from a 1559 m thick section which is composed mainly of fluvio lacustrine sandstone and conglomerate stepwise thermal and alternating field demagnetization isolated a linear magnetization component that decays univectorally toward the origin and likely represents a primary magnetization principally carried by magnetite from this component 29 magnetic polarity intervals were identified they correlate between 3 1 and 10 5 ma with the reference magnetic polarity time scale indicating a relatively constant sedimentation rate with an average of 0 21 0 01 mm year we also performed a suite of rock magnetic experiments designed to track time transgressive changes in the sedimentary record from the rock magnetic parameters together with the constant sedimentation rate we conclude that the tianshan mountains were actively uplifting by 10 5 ma

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

spatiotemporal patterns of the late quaternary deformation across the northern chinese tian shan foreland abstract the investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt here we focus on the spatiotemporal patterns of the late quaternary deformation along the north piedmont of the chinese tian shan a mountain range formed by the ongoing india asia collision by using a terrace as the reference and applying the area conservation method the holocene shortening rate of the halaande anticline a fold of the distal structure belt iii in the foreland is estimated to 2 14 0 24 mm yr for the first time similarly we re calculate the holocene shortening rates of the other anticlines of belt ii iii using the magnitude of shortening documented by river terraces and the terrace formation ages published previously the summed holocene 103 year timescale shortening rates of individual anticlines along n s transects are 2 4 mm yr consistent with the late pleistocene 104 year timescale shortening rate but about 2 6 times higher than the long term 106 year timescale average shortening rate of 1 mm yr during the past several million years together with the shortening rates of individual anticlines at the 103 year 104 year and 106 year scales these observations imply that the deformation across the northern chinese tian shan foreland has accelerated since at least late pleistocene by summing the late quaternary rates of shortening in the southern chinese tian shan foreland 4 5 mm yr and the intermontane basins in the hinterland of the tian shan 2 mm yr the late quaternary rate of shortening across the tian shan range between longitude 83 e and 87 e amounts to 9 0 1 0 mm yr approximately matching the modern shortening rate of 8 mm yr derived from the gps measurements these results imply i that the deformation across the tian shan range and its foreland basins between longitude 83 e and 87 e could have not been changed significantly since at least late pleistocene ii that in the northern chinese tian shan foreland the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the holocene or even geodetic rate of deformation

magnetochronology of the upper cenozoic strata in the southwestern chinese tian shan rates of pleistocene folding and thrusting abstract the southwestern chinese tian shan of central asia is an actively deforming part of the indian asian collision system paleomagnetic investigations of two plio pleistocene terrestrial successions provide the first detailed magnetostratigraphy for the upper cenozoic strata in this region paleomagnetic samples were collected from 358 sites within the atushi formation and xiyu formation across the atushi talanghe anticline near atushi thermal demagnetization behavior reversal and fold tests of paleomagnetic stability indicate that the characteristic remanence directions were acquired before tilting and folding of the strata a composite magnetostratigraphic section for this sequence correlates with the mammoth subchron to the jaramillo subchron between 3 3 and 1 07 myr of the geomagnetic polarity timescale of cande and kent j geophys res 100 1995 6093 6095 the mean declination 349 3 in the boguzihe section indicates a counterclockwise vertical axis rotation 11 2 during the past 1 4 myr the conglomeratic xiyu formation is time transgressive along its progradational contact with the underlying atushi formation across a map distance of 6 km the basal contact ranges from less than 1 0 myr in the ganhangou section to 1 9 myr in the boguzihe section to the southwest and to 2 8 myr on the northwest limb of the anticline northeastward lateral propagation and growth of the atushi talanghe anticline initiated at 1 4 myr in the boguzihe and 1 2 myr in the ganhangou the cross section in the boguzihe provides a conservative maximum estimate of shortening rate of 3 3 4 4 mm yr and uplift rate of 3 mm yr this rate represents about half of the geodetically determined shortening rate between the northern tarim basin and the kyrgyz tian shan wang et al acta seismol sin 22 2000 263 270 reiger et al earth planet sci lett 191 2001 157 165 during fold growth over the past 1 4 myr the crest of the atushi talanghe anticline eroded at an average rate of 2 6 2 7 mm yr

neogene uplift of the tian shan mountains observed in the magnetic record of the jingou river section northwest china the tian shan mountains constitute central asia s longest and highest mountain range understanding their cenozoic uplift history thus bears on mountain building processes in general and on how deformation has occurred under the influence of the india asia collision in particular in order to help decipher the uplift history of the tian shan we collected 970 samples for magnetostratigraphic analysis along a 4571 m thick section at the jingou river xinjiang province china stepwise alternating field and thermal demagnetization isolate a linear magnetization component that is interpreted as primary from this component a magnetostratigraphic column composed of 67 polarity chrons are correlated with the reference geomagnetic polarity timescale between 1 ma and 23 6 ma with some uncertainty below 21 ma this correlation places precise temporal control on the neogene stratigraphy of the southern junggar basin and provides evidence for two significant stepwise increases in sediment accumulation rate at 16 15 ma and 11 10 ma rock magnetic parameters also undergo important changes at 16 15 ma and 11 10 ma that correlate with changes in sedimentary depositional environments together with previous work we conclude that growth history of the modern tian shan mountains includes two pulses of uplift and erosion at 16 15 ma and 11 10 ma middle to upper tertiary rocks around the tian shan record very young 5 ma counterclockwise paleomagnetic rotations on the order of 15 to 20 which are interpreted as because of strain partitioning with a component of sinistral shear that localized rotations in the piedmont

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

strong interannual variation of the indian summer monsoon in the late miocene the modern asian monsoon system exhibits strong interannual variation which has profound environmental and economical impacts it has been well documented that the mean asian monsoon state underwent significant changes in the late miocene 11 5 ma ago but how the interannual variability of the monsoon climate evolved during this period is still largely unknown in this study a long term simulation of the late miocene with a fully coupled atmosphere ocean general circulation model echam5 mpi om at t31l19 resolution is used to explore the interannual variation of the indian summer monsoon ism in the late miocene the regional climate model cosmo clm with a higher spatial resolution 1 1 is further employed to better characterize the spatial patterns of these variations our results show that although the mean ism circulation is weaker in the late miocene runs its interannual variation is as strong as or even stronger than at present and the dominant periods 2 6 2 7 years are shorter than at present 3 4 8 4 years it is noticed that while the extratropical influence on the ism variability is weaker than present a persistent el nino southern oscillation with stronger than present interannual variability is observed in our late miocene run this may have maintained a strong interannual variation of the ism with a shorter period in the late miocene our findings do not only improve our understanding of the asian monsoon evolution in the late miocene but also shed light on the future changes in the interannual variability of the ism

late cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the tian shan mountains 1 the folded neogene deposits in the northern foreland basin of the tian shan mountains provide important information about tectonic history and environmental changes of northwestern china on the basis of lithostratigraphic and magnetostratigraphic evidence we develop a new chronology for the previous studied kuitun he section our palynological study on the late miocene pliocene sediment of the dushanzi section yields new information about vegetation and climate change during the period of 8 7 2 58 ma the results indicate that steppe taxa artemisia and chenopodiaceae were generally dominant in the studied areas between 8 7 and 2 58 ma implying that a dry climate has occurred in the inland basins of northwestern china at least since 8 7 ma ago although the general climate pattern indicated by our palynological results displays to some extent of drought a warm and humid phase occurred at 5 8 3 9 ma ago this climatic optimum is comparable with the other records from the chinese loess plateau central japan the sub himalayan zone and the marine eustatic sea level rise implying this seems to be at least a regional climatic optimum

a new paleogeographic configuration of the eurasian landmass resolves a paleomagnetic paradox of the tarim basin china 1 new paleomagnetic data from permian red beds and middle jurassic limestones from the tarim basin pose a paradox their declinations are similar to upper carboniferous to neogene rocks collected from the same sections and their inclinations parallel present values when assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects then the paleolatitudes of all upper carboniferous to present rocks from tarim are indistinguishable local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin our middle jurassic data positions tarim 23 6 8 4 farther south than that predicted from the coeval reference pole for eurasia however no geologic argument exists to support the closure of a large ocean basin between tarim and siberia since the middle jurassic thus the paradox are the rocks from tarim totally overprinted or is the middle mesozoic part of the reference eurasian apparent polar wander path erroneous several lines of evidence suggest the tarim rocks are not remagnetized we conclude that tarim has experienced little or no apparent polar wander since the carboniferous moreover our middle mesozoic reconstruction of eurasia using the new middle jurassic pole from tarim results in a more geologically compatible solution for the eastern asian blocks over previous reconstructions

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

quaternary folding of the eastern tian shan northwest china abstract the tian shan east west trending more than 2000 km is one of most active intracontinental mountain building belts that resulted from india eurasia collision during cenozoic in this study quaternary folding related to intracontinental mountain building of the tian shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images landsat thematic mapper tm enhanced thematic mapper etm and india remote sensing irs pan combined with field geologic and geomorphic observations and seismic reflection profiles analyses of spatial temporal features of quaternary folded structure indicate that the early quaternary folds are widely distributed in both piedmont and intermontane basins whereas the late quaternary active folds are mainly concentrated on the northern range fronts field observations indicate that quaternary folds are mainly characterized by fault related folding the formation and migration of quaternary folding are likely related to decollement surfaces beneath the fold and fault zone as revealed by seismic reflection profiles moreover analysis of growth strata indicates that the quaternary folding began in late stage of early pleistocene 2 1 1 2 ma finally tectonic evolution model of the quaternary deformation in the tian shan is presented this model shows that the quaternary folding and faulting gradually migrate toward the range fronts due to the continuous compression related to india eurasia collision during quaternary time as a result the high topographic relief of the tian shan was formed