dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

deuterium hydrogen exchange in olivine implications for point defects and electrical conductivity 1 knowledge about hydrogen self diffusion dh is critical for determining mantle hydrogen distribution and understanding point defects also chemical diffusion of hydrogen in olivine such as redox exchange with polarons dredox depends on dh in this study deuterium 2h was exchanged into hydrogen 1h saturated single crystals of san carlos olivine between 750 and 900 c at 2 gpa we measured and fit the resulting 2h profiles to obtain dh 100 10 4 9 1 4 e 140 30kj mol rt m2 s which is 1 log unit lower than dredox 100 with similar activation enthalpy ha by comparing these two diffusion coefficients we estimate the small polaron diffusion coefficient additionally we estimate dh in the 010 and 001 orientations demonstrating that dh is highly anisotropic in olivine these dhvalues were used with the nernst einstein relation to estimate the electrical conductivity by hydrogen in olivine h 101 1 e 130kj mol rt s m for 10 2 wt h2o that is lower in magnitude than previous measurements our results suggest that hydrogen alone cannot account for high electrical conductivity anomalies observed at asthenospheric depths 10 2 to 10 1 s m the maximum anisotropic variation of dh and hin olivine is 2 log units between 750 and 900 c and increases when extrapolated to higher temperature 3 3 at 1400 c anisotropy observed in the mantle may indicate substantial amounts of hydrogen in olivine with lattice preferred orientation

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

local erosion rates versus active tectonics cosmic ray exposure modelling in provence south east france over the past decade in situ produced cosmogenic nuclides have revolutionised the study of landscape evolution in particular numerous studies have demonstrated that in active tectonic settings cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long term deformation rates in western european countries erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates in this study we present the results of a depth profiling technique applied to alluvial terraces located along the rhone and the moyenne durance rivers the expected decrease with depth of the measured 10be concentrations has been modelled using a 2 inversion method in order to constrain the exposure history of the alluvial sediments the results suggest that 1 over the quaternary the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m myr in southeastern france and 2 providing a fairly good bracketing of the exposure age the modelled abandonment age of alluvial terraces affected by the moyenne durance fault allows estimating incision rates comparing the alluvial terrace elevations with topographic river profiles and a minimum vertical slip rate value of roughly 0 02 mm yr for the southern segment of the moyenne durance fault

slip rate at the north eastern front of the qilian shan china terra nova 22 180 187 2010 abstract we constrain the slip rate for the frontal thrust of the qilian shan north eastern tibet by combining structural investigations satellite imagery topographic profiling and 10be exposure dating we surveyed two terrace levels and from each we took 6 7 samples in profiles dug to depths of 2 m these constrain inheritance and determine the precise ages of abandonment of the terraces 29 9 7 8 ka for the upper terrace and 16 3 4 4 ka for the lower one topographic profiles with a determination of burial of the footwall by sediment yield offsets of the surfaces of 96 4 4 4 and 40 1 2 8 m the average vertical rate is 2 8 1 3 mm a 1 with a horizontal slip rate of 2 5 mm a 1 this rate is higher than those determined farther north on similar structures but is consistent with the gps velocity field and accounts for roughly half of the geodetic shortening across the qilian shan

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

how flat is tibet high resolution digital topography three arc second grid for most of tibet provides new information to characterize the relief of the highest and largest plateau on earth the arid to semiarid central and northern part of the plateau interior has low relief average slopes of over 250 m windows and a mean elevation of 5023 m above sea level at moderate wavelengths of m relief is or less for most of tibet as opposed to the much higher relief of up to 6 km on the plateau edges where glacial and fluvial dissection is greater because of higher levels of precipitation the only faults manifesting significant topographic relief are the relatively small scale generally north trending graben systems primarily in southern tibet and several large scale fault systems near the edges of tibet the flatness of tibet implies that 1 there has been little deformation especially shortening of the uppermost crust north of the graben systems during the late cenozoic and 2 shallow crustal isostatic compensation has been acting to level the surface of the plateau

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

active faulting mountain growth and erosion at the margins of the tibetan plateau constrained by in situ produced cosmogenic nuclides abstract the india asia collision zone is a key area for understanding continental plateau formation and mountain building two fundamental questions in this context are how the northeastward motion of india is partitioned between strike slip and thrust faults and how mountain building is counteracted by erosion cosmogenic nuclides allow us to address these questions because they provide age constraints on tectonically offset landforms and constraints on erosion rates after considerable debate on whether or not major strike slip faults move at high rates of up to 20 30 mm yr and absorb most of the continental deformation it now appears that the three largest faults altyn tagh haiyuan kunlun have millennial slip rates of no more than 8 13 mm yr consistent with rates of elastic strain accumulation determined by geodetic methods furthermore a significant portion of the lateral slip on these faults is transferred to thrust faults within the collision zone both observations indicate that the eastward tectonic escape of material along these faults is less important than often assumed with respect to mountain building and erosion cosmogenic nuclide studies show that thrust faults at the northeastern and eastern margins of tibet qilian shan longmen shan have vertical slip rates of 0 3 to 2 mm yr while catchment wide erosion rates vary from 0 02 to 1 0 mm yr with high relief areas eroding significantly faster than the plateau interior and growing mountains in the foreland the deeply incised regions have apparently reached an erosional steady state in which rock uplift is balanced by erosion river terraces at active mountain fronts document repeated changes between sediment deposition and fluvial incision during the quaternary incision and terrace formation occurred predominantly at glacial interglacial transitions but also during interglacial periods hence flights of terraces at the fault bounded mountain fronts record the interplay between sustained rock uplift and a temporally variable climate

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

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

dating of erosion surface and terraces in the eastern qilian shan northwest china the actively deformed foreland of eastern qilian shan mountains contains well preserved geomorphic features such as erosion surfaces river terraces and tectonically uplifted alluvial fans providing suitable archives for research on regional tectonic activities and palaeoclimatic changes these geomorphic surfaces are well dated by using a combination of magnetostratigraphy electron spin resonance thermoluminescence infra red stimulated luminescence radiocarbon dating and correlation with the well established loess palaeosol sequences of china our results show that the erosion surface formed about 1 4 ma ago and the age of river terraces is 1 24 ma 820 860 ka 780 ka 420 440 ka 230 250 ka 140 ka 60 ka and 10 ka respectively valley incision rates of e 0 09 0 25 m ka 1 have been identified the repetitive stratigraphic and geomorphic pattern of these terraces indicates the fluvial sedimentation incision cycles are tightly associated with the 100 ka glacial interglacial climatic cycles copyright c 2006 john wiley sons ltd

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

tibet uplift and erosion abstract the 5 km high tibetan plateau is an outstanding topographic feature on the earth today its horziontal extent elevation and location cause significant effects on modern atmospheric circulation and climate so the history of uplift of the surface of tibet is linked to cenozoic climate changes at local regional and perhaps global scales geological and geophysical studies of the plateau are contributing data on the present and past deformation of the tibetan lithosphere that has formed the plateau primarily during the cenozoic the principal of isostasy then can be used to estimate the elevation history of the surface for a given deformation history different parts of tibet probably had different uplift histories but presently available data are not sufficient for distinguishing many contrasts in one scenario cretaceous and early cenozoic north south distributed shortening of tibetan crust and mantle lithosphere probably caused significant uplift of the surface relative to sea level to perhaps half of the present elevation by the early miocene thinning of the high density mantle portion of the lithosphere during the miocene may then have allowed the thick tibetan crust to rise close to its present elevation perhaps higher before 8 ma since then slow east west extension of tibet probably reduced the crustal thickness slightly and may have caused the elevation of the plateau to decrease during the late cenozoic erosion of tibet unlike narrow mountain belts has been unable to match the uplift of a broad plateau orographic precipitation and efficient river networks concentrate erosion on the edges while the interior is protected from significant erosion despite its lofty elevation the southern edge of the plateau the himalaya has suffered a minimum of 25 km of denudation since the miocene while central tibet shows little or no sign of major erosion since that time the gangdese arc in southern tibet was rapidly eroded during the mid miocene when 4 km of rock apparently were removed from the surface as shown by mineral cooling ages this pulse of erosion was probably caused by a combination of local thrust system movement and changes in base level and precipitation due to relative elevation changes between the gangdese and the himalaya to the south the modern long wavelength flatness of tibet is unlikely to have been caused by erosion and indicates viscous flow at some level of the lithosphere has been acting to level the plateau surface

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

rapid slip along the central altyn tagh fault morphochronologic evidence from cherchen he and sulamu tagh consistent with the d 18 o record from the guliya ice cap in the west kunlun the features of interest were all formed by glacial and fluvial processes subsequent to marine isotope stage 5e with the youngest features having formed during the early holocene optimum this near field morphochronological slip rate is averaged over many earthquake cycles and is hence little affected by interseismic strain it is kinematically consistent with other somewhat lower geomorphic slip rate measurements to the east the average rate and lower bounds obtained from alternate interpretational models 18 4 mm yr cannot be reconciled with the most rece geodetic measurements 7 mm yr suggesting that interseismic strain and interactions with adjacent faults may lead to disparate geologic and geodetic rate estimates this late pleistocene holocene morphochronologic rate would imply that at this longitude the altyn tagh fault on the north edge of tibet might absorb almost as much of india s convergence relative to siberia as the himalayan main frontal thrust does on the southern edge of the plateau index terms 1035 geochemistry geochronology 1208 geodesy and gravity crustal movements intraplate 8110 8102 tectonophysics continental contractional orogenic belts 8107 tectonophysics continental neotectonics keywords slip rates cosmogenic dating indo asian collision

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

quantifying kinetic fractionation in bunker cave speleothems using δ47 abstract isotopic signals in speleothems are used for investigating paleoclimate variability on land and are useful to constrain the dating of prominent climate events a quantitative use however is limited by an incomplete understanding of parameters contributing to the carbon and oxygen isotope signals these include external and environmental parameters such as 18 o of cave drip waters as well as internal parameters associated with speleothem formation such as the presence of non equilibrium effects and especially the magnitude of their isotopic shifts we explore the use of clumped isotopes as a new tool for investigating the kinetic isotope effect in speleothems holocene and modern speleothems from bunker cave germany as well as modern material from the adjacent dechen cave are all offset from the equilibrium relationship due to kinetic fractionation this kinetic offset in clumped isotopes is observed in a stalagmite despite mostly negative hendy tests providing a sensitive indicator for kinetic fractionation in cave carbonates the temperature dependence of the clumped isotope values 0 005 per c is low compared to the observed magnitude of kinetic offsets between 0 021 and 0 075 so that the mean offsets in apparent temperatures due to kinetic isotope effects are on the order of 10 c as a result clumped isotopes are useful in identifying temporal variations in the kinetic fractionation in a stalagmite when the temperatures during the speleothem growth period are either relatively constant variations the variations in the kinetic isotope fractionation in bunker cave are associated with changing drip water super saturation with periods of stronger prior calcite precipitation associated with lower kinetic offsets in the speleothem calcite in contrast stalagmite growth rates show no direct correlation with the degree of kinetic fractionation in the investigated range 13 1500 m a

lithospheric flexure in the sichuan basin and longmen shan at the eastern edge of tibet 1 the mountain range at the steep eastern edge of the tibetan plateau the longmen shan was deformed by a mw7 9 earthquake with oblique thrust and strike slip motion in 2008 the tectonic processes and structure of the lithosphere beneath this range have been controversial gravity measurements reflect the distribution of mass within the earth including the large load of rock above the geoid in mountain ranges we investigate the response of the lithosphere to the load of the longmen shan and estimate the flexural rigidity or effective elastic thicknessteusing new gravity data acquired by recent satellites and the combined goco2s and eigen 6c datasets the free air gravity anomalies over the longmen shan show that its mass is supported by flexure of the adjacent sichuan basin lithosphere similar to the flexural support of the himalayas analysis of a stacked profile of the free air anomalies shows that the effective elastic thickness of the basin lithosphere is greater than 10 km but has a broad minimum misfit function with no upper limit on the thickness two dimensional admittance analysis shows thete of easternmost tibet is very low approximately 7 km

three dimensional surface displacement of the 2008 may 12 sichuan earthquake china derived from synthetic aperture radar evidence for rupture on a blind thrust summary the sichuan earthquake mw 7 9 struck the longmen shan lms range front china on 2008 may 12 affecting an area of moderate historical seismicity where little active shortening has been previously reported recent studies based on space geodesy have succeeded in retrieving the far field surface displacements caused by the earthquake but the near field 25 km from the faults coseismic surface displacement is still poorly constrained thus shallow fault geometry and shallow coseismic slip are still poorly resolved here for the first time for this earthquake we combine c and l band synthetic aperture radar offsets data from ascending and descending tracks to invert for the 3 d surface displacement in the near coseismic field of the sichuan earthquake our data coupled with a simple elastic dislocation model provide new results strongly suggesting the presence of a blind thrust striking along the range front and being active at depth during the earthquake the presence of a rupture on a blind thrust brings new evidence for an out of sequence thrusting event and new elements for interpreting the tectonic strain partitioning in the lms which has important implications both for seismic hazard assessment and long term evolution of the mountain belt

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

mechanical analysis of controls on strain partitioning in the himalayas of central nepal we present a mechanical analysis of the problem of slip partitioning between the major thrust systems in a collisional range we focus on two structures in the himalayas of central nepal the main himalayan thrust mht and the main central thrust mct we use finite element modeling to test the influence of various parameters such as friction coefficients and surface processes and we investigate how they affect the distribution of deformation between these two faults we observe that reproduction of the late quaternary kinematic pattern across the range with our model requires strict conditions on the friction coefficients such that the mht is very weak whereas the mct is significantly stronger the most important parameter that controls slip partitioning appears to be the dip angle of the mct with a gentler or steeper mct promoting or inhibiting slip respectively we also show that transient loading and unloading through focused glacial erosion in the higher part of the range can unclamp the mct and allow a significant increase in slip rates the results of this mechanical sensitivity investigation have important implications for the dynamics of the himalayan wedge and point toward along strike structural variations as a first order control on slip partitioning

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

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

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

a deforming block model for the present day tectonics of tibet 1 we use gps data from 45 sites across the tibetan plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the india eurasia collision zone the plateau is cut by a few major rapidly slipping strike slip fault zones with broadly distributed strain between those zones the gps velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau the boundaries of the four blocks in this model correspond to the major rapidly slipping faults a rigid block model with a smaller number of blocks fits the data poorly and can be rejected we estimate that 5 9 0 7 mm yr of extension in the n69 w direction occurs on the yadong gulu rift south of the plateau localized extension may extend as far north as the nyainqentanglha range we find 7 4 0 7 mm yr of right lateral slip on the karakorum jiali fault zone significantly slower than that previously estimated from offset geologic features our deforming block model and a two dimensional single fault screw dislocation model give lower and upper bounds of 4 4 1 1 and 10 3 0 4 mm yr on the slip rate on the kunlun fault respectively comparable in its highest to the long term slip rate observed geologically the distributed deformation is surprisingly uniform over the tibetan plateau qaidam basin and qilian shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction n32 e this strain field is a combination of shortening and extension that produces little net dilatation 1 area loss per million years at present the broadly distributed strain most likely represents slip on many faults each with a relatively low slip rate distributed conjugate strike slip faulting is the most plausible mechanism to produce the observed strains as supported by the record of medium to large earthquakes within the plateau the distributed deformation is just as important in the accommodation of the total india eurasia convergence as is slip on the major faults the eastward motion of central tibet is as large as 50 of the convergence rate between india and eurasia however this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike slip faults as suggested by past extrusion models instead much of this eastward extrusion is driven by the internal extension of the plateau our inference is in agreement with the model of f shen et al 2001 that suggested east west extension north south contraction and eastward plateau growth dominate the present tectonics of the tibetan plateau

deciphering the rate of mountain growth during topographic presteady state an example from the ne margin of the tibetan plateau 1 we use field investigations topographic profiles and 10be exposure dating to constrain the growth rate of the yumu shan a thrust bounded mountain range at the northeastern margin of tibet wind gaps fault scarps at the mountain front and hanging paleocatchments indicate that the yumu shan is growing both laterally and vertically scarp profiles and 10be ages yield rock uplift rates of 500 and 800 mm ka 1 for the eastern and central parts of the range respectively the fact that the rock uplift rate in the high center of the yumu shan exceeds catchment wide 10be denudation rates which range from 180 to 280 mm ka 1 indicates that the mountain range continues to rise and has not yet reached a topographic steady state combining the total structural relief of the range with the rates of rock uplift and denudation suggests that the growth of the yumu shan started 3 7 0 9 ma ago

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

growth of faults by accumulation of seismic slip the accommodation of large strains in the upper crust is largely achieved by the accumulation of displacement on faults observation shows that as a fault accumulates displacement it grows in size i e its surface area and its length increase here we address the question for an increase in the amount of displacement on a fault by how much would the length of the fault change it is argued by cowie and scholz 1992a that the displacement on a fault is linearly related to the length of the fault this simple result is expanded upon in this paper by assuming that a fault accumulates displacement by repeated earthquakes two different approaches are presented the first approach considers the balance that must be achieved between the energy available for deformation and the work involved in creating new fault surface area as the fault grows the available energy is provided by changes in strain energy when the fault slips the second approach is to construct a geometrical model for fault growth using the scaling relationship between the slip during a single earthquake and the length of the rupture the total displacement on a fault is the sum of the slips contributed by many earthquakes the usefulness of these two approaches is that the growth of a fault over geologic time can be described by parameters that can be obtained from earthquake and fault data the models presented here predict that 1 the maximum amount a fault can grow in a single earthquake that ruptures the entire fault is of the order of 1 of its previous length and 2 the work of faulting may account for 10 of the total energy available during an earthquake the energy lost from the system is accounted for by work done against friction and seismic radiation consequences of fault growth for the segmentation and thus seismogenic potential of a fault over geologic time are discussed using predictions of the theory

geomorphic constraints on active mountain growth by the lateral propagation of fault related folding a case study on yumu shan ne tibet the mountain range of the yumu shan in ne tibet is the topographic expression of actively growing fault related folds developed in the hanging walls of a system of mostly northeast vergent blind thrusts here we present a tibetan example on the geomorphic response to lateral fold propagation using both qualitative analysis of the geomorphic characteristics of this region e g wind and water gaps drainage density and along strike topography of the range crest and quantitative analysis based on cosmogenic be 10 surface exposure dating and optically stimulated luminescence dating on the rates of uplift and lateral propagation of the anticline the elevations of the past positions of successively deflected paleo rivers show a systematic decrease toward the eastern tip of the anticline in tandem with an eastward decrease in drainage density combining the age data obtained by cosmogenic be 10 and osl dating methods with the heights of abandoned terraces we calculated average uplift and lateral propagation rates of similar to 378 mm ka over the past similar to 185 ka and similar to 40 mm yr over the past similar to 150 ka respectively our single site evaluation of the relation between tear faulting and channel deflection suggests that the tear faulting occurs along weakened bedrock already dissected by the former stream this finding is inconsistent with the conventional hypothesis that the route of the deflecting stream is controlled by the orientation of the tear faulting zone topographic vertical and lateral fold growth of the yumu shan were probably driven by the eastward propagation of a blind thrust since the late neogene following the initial deposition of sediments in the hexi corridor which were transported from the qilian shan c 2011 elsevier ltd all rights reserved the mountain range of the yumu shan in ne tibet is the topographic expression of actively growing fault related folds developed in the hanging walls of a system of mostly northeast vergent blind thrusts here we present a tibetan example on the geomorphic response to lateral fold propagation using both qualitative analysis of the geomorphic characteristics of this region e g wind and water gaps drainage density and along strike topography of the range crest and quantitative analysis based on cosmogenic be 10 surface exposure dating and optically stimulated luminescence dating on the rates of uplift and lateral propagation of the anticline the elevations of the past positions of successively deflected paleo rivers show a systematic decrease toward the eastern tip of the anticline in tandem with an eastward decrease in drainage density combining the age data obtained by cosmogenic be 10 and osl dating methods with the heights of abandoned terraces we calculated average uplift and lateral propagation rates of similar to 378 mm ka over the past similar to 185 ka and similar to 40 mm yr over the past similar to 150 ka respectively our single site evaluation of the relation between tear faulting and channel deflection suggests that the tear faulting occurs along weakened bedrock already dissected by the former stream this finding is inconsistent with the conventional hypothesis that the route of the deflecting stream is controlled by the orientation of the tear faulting zone topographic vertical and lateral fold growth of the yumu shan were probably driven by the eastward propagation of a blind thrust since the late neogene following the initial deposition of sediments in the hexi corridor which were transported from the qilian shan c 2011 elsevier ltd all rights reserved