cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

integrated silurian conodont and carbonate carbon isotope stratigraphy of the east central appalachian basin abstract the eastern and southeastern margins of the appalachian basin contain extensive exposures of telychian through pridoli upper silurian strata litho and biostratigraphic analyses of these strata over the last century provided a general means for their chronostratigraphic correlation to global series and stage boundaries however a rarity of zonally diagnostic fauna limited precise correlation both within and beyond the appalachian basin recent conodont biostratigraphic studies substantially revised the chronostratigraphic position of these strata by more than a series in some cases much of the interval however remained biostratigraphically unzoned and the precise position of series and stage boundaries remained tentative to improve the chronostratigraphic correlation of these strata to global series and stage boundaries we provide new integrated conodont and high resolution 13ccarb chemostratigraphic analyses from two outcrops located in west virginia and virginia spanning the upper rose hill through tonoloway formations upper telychian through pridoli these new data show that the silurian carbon isotope record for this portion of the appalachian basin is shifted to more negative 13ccarb values than typical global data however the overall isotopic records appear correlative at least within the appalachian basin thereby providing a means for future correlation within the basin for intervals in which biostratigraphy is traditionally lacking these coupled data demonstrate that the ireviken and mulde excursions are contained within our sections the high amplitude lau excursion was however not observed and the present biostratigraphic data suggest that a majority of the ludlow series was either not recorded or was later removed by erosion these coupled analyses therefore indicate that the ludlow pridoli boundary resides within the wills creek formation and we propose that the overlying isotopic record presented here records the late ludlow carbon isotope excursion llcie and silale low previously identified only within the baltic basin

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

fast late pleistocene slip rate on the leng long ling segment of the haiyuan fault qinghai china 1 fieldwork along the western haiyuan fault where it cuts young glacial landforms in the leng long ling range qinghai northeastern tibet yields new constraints on its long term left slip rate our mapping near 101 85 e based on aerial photographs 1 50 000 topographic maps and spot images shows glacial valley edges and lateral moraines offset 200 m by the fault quartz rich cobbles were sampled on top of one moraine for in situ 10be and 26al cosmogenic nuclide dating among 12 dated samples the 6 oldest show ages clustering at 10 300 339 years this age probably reflects the time of last reshaping of the moraine before the valley glacier withdrew south of the fault around the end of the younger dryas 11 000 years b p assuming that the 200 40 m moraine offset started to be recorded after glacial retreat across the fault constrains the late pleistocene slip rate on the leng long ling segment of the haiyuan fault to be 19 5 mm yr

late pleistocene holocene slip rate of the zhangye thrust qilian shan china and implications for the active growth of the northeastern tibetan plateau 1 we derive a slip rate for a thrust at the central qilian shan mountain front by combining structural investigations satellite imagery topographic profiling luminescence dating and 10be exposure dating the seismically active zhangye thrust transects late pleistocene alluvial fan deposits and forms a prominent north facing scarp the fault consists of two segments that differ in orientation scarp height and age a series of loess covered terraces records the uplift history of the western thrust segment loess accumulation on all terraces started at 8 5 1 5 kyr and postdates terrace formation gravels from the highest terrace yielded a 10be exposure age of 90 11 kyr which dates the onset of faulting with a displacement of 55 60 m derived from fault scarp profiles this yields a vertical slip rate of 0 64 0 08 mm yr 1 along the eastern thrust segment three 10be ages from the uplifted alluvial fan constrain that faulting started at 31 5 kyr together with a displacement of 25 30 m this leads to a vertical faulting rate of 0 88 0 16 mm yr 1 a dip estimate of 40 to 60 for the fault plane combined with lower and upper limits of 0 6 and 0 9 mm yr 1 for the vertical slip rate gives minimum and maximum horizontal shortening rates of 0 4 and 1 1 mm yr 1 across the zhangye thrust our results are consistent with geologic and gps constraints which suggest that nne directed shortening across the northeastern tibetan plateau is distributed on several active faults with a total shortening rate of 4 to 10 mm yr 1

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

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

the influence of seawater carbonate chemistry mineralogy and diagenesis on calcium isotope variations in lower middle triassic carbonate rocks abstract the geological calcium cycle is linked to the geological carbon cycle through the weathering and burial of carbonate rocks as a result calcium ca isotope ratios 44ca 40ca expressed as 44 40ca can help to constrain ancient carbon cycle dynamics if ca cycle behavior can be reconstructed however the 44 40ca of carbonate rocks is influenced not only by the 44 40ca of seawater but also by diagenetic processes and fractionation associated with carbonate precipitation in this study we investigate the dominant controls on carbonate 44 40ca in upper permian to middle triassic limestones ca 253 to 244 ma from south china and turkey this time interval is ideal for assessing controls on ca isotope ratios in carbonate rocks because fluctuations in seawater 44 40ca may be expected based on several large carbon isotope 13c excursions ranging from 2 to 8 parallel negative 13c and 44 40ca excursions were previously identified across the end permian extinction horizon here we find a second negative excursion in 44 40ca of 0 2 within lower triassic strata in both south china and turkey however this excursion is not synchronous between regions and thus cannot be interpreted to reflect secular change in the 44 40ca of global seawater additionally 44 40ca values from turkey are consistently 0 3 lower than contemporaneous samples from south china providing further support for local or regional influences by measuring 44 40ca and sr concentrations sr in two stratigraphic sections located at opposite margins of the paleo tethys ocean we can determine whether the data represent global conditions e g secular variations in the 44 40ca of seawater versus local controls e g original mineralogy or diagenetic alteration the sr and 44 40ca data from this study are best described statistically by a log linear correlation that also exists in many previously published datasets of various geological ages using a model of early marine diagenetic water rock interaction we illustrate that this general correlation can be explained by the chemical evolution of bulk carbonate sediment samples with different initial mineralogical compositions that subsequently underwent recrystallization although early diagenetic resetting and carbonate mineralogy strongly influence the carbonate 44 40ca values the relationship between sr and 44 40ca holds potential for reconstructing first order secular changes in seawater 44 40ca composition

corrigendum to calcium isotope constraints on the marine carbon cycle and caco 3 deposition during the late silurian ludfordian positive δ 13 c excursion earth planet sci lett 451 2016 31 40

tectonic development of the samail ophiolite high precision u pb zircon geochronology and sm nd isotopic constraints on crustal growth and emplacement 1 new high precision single grain u pb zircon geochronology and whole rock nd isotopic data provide insight into the magmatic and tectonic development of the samail ophiolite the analyzed rocks can be broadly divided into two groups based on their structural position dates and isotopic composition an older group related to on axis magmatism and a younger group of post ridge dikes sills and stocks on axis gabbros tonalites and trondhjemites yielded th corrected 206pb 238u dates from 96 441 0 062 to 95 478 0 056 ma these dates combined with dates from rioux et al 2012 suggest that most of the ophiolite crust formed at an oceanic spreading center in 1 ma the post ridge intrusions come from all depths in the crust the upper mantle and the metamorphic sole post ridge gabbros tonalites and trondhjemites from the crust and mantle yielded th corrected 206pb 238u dates of 95 405 0 062 to 95 077 0 062 ma a small trondhjemitic pod from the metamorphic sole yielded younger th corrected 206pb 238u dates of 94 90 0 38 to 94 69 0 12 ma isotopic data suggest two distinct sources for the post ridge magmas five of the gabbros and tonalites from the crust have end 96 ma 6 90 0 12 to 7 88 0 16 and two trondhjemites from the upper mantle and metamorphic sole have end 96 ma 7 77 0 08 and 7 01 0 16 the negative end t and u pb dates from the mantle dike require that subduction or thrusting was established below the ophiolite 0 25 0 5 ma after formation of the crust the bimodal isotopic composition of post ridge magmas may reflect coeval decompression and or fluid fluxed melting of the mantle and melting dehydration or assimilation of sediment in the down going plate at this time the new data place temporal constraints on mid ocean ridge and supra subduction zone models for ophiolite formation

low slip rates and long term preservation of geomorphic features in central asia in order to understand the dynamics of the india asia collision zone it is important to know the strain distribution in central asia whose determination relies on the slip rates for active faults1 2 3 4 5 many previous slip rate estimates of faults in central asia were based on the assumption that offset landforms are younger than the last glacial maximum 20 kyr ago 6 7 8 9 10 11 in contrast here we present surface exposure ages of 40 to 170 kyr obtained using cosmogenic nuclide dating for a series of terraces near a thrust at the northern margin of the tibetan plateau combined with the tectonic offset the ages imply a long term slip rate of only about 0 35 mm yr 1 for the active thrust an order of magnitude lower than rates obtained from the assumption that the terraces formed after the last glacial maximum our data demonstrate that the preservation potential of geomorphic features in central asia is higher than commonly assumed

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

earthquake slip vectors and estimates of present day plate motions although horizontal slip directions determined for earthquakes along transform faults and shallow subduction thrust faults are commonly assumed to parallel the direction of motion between two plates systematic biases of earthquake slip vectors relative to the local long term average plate direction can be introduced by a variety of causes including deformation of forearcs above subduction zones unmodeled lateral velocity heterogeneities near earthquake sources and unrecognized changes in plate velocities within the averaging interval of the kinematic model given that earthquake slip vectors comprise nearly two thirds of the data used to derive the nuvel 1 model for present day global plate velocities it is important to determine the extent to which potential systematic biases of earthquake slip vectors could degrade estimates of plate velocities given by nuvel 1 here two alternative models for global plate velocities are derived and compared to nuvel 1 the first model nuvel sz is derived from a data set that omits the 240 subduction zone sup vectors in the nuvel 1 data set but includes all remaining 882 kinematic data the velocities predicted by nuvel sz and nuvel 1 differ little with maximum differences of only 1 mm yr 1 and 2 along all plate boundaries except those surrounding the caribbean plate the second model nuvel g is derived from a data set that omits all 724 earthquake sup vectors but includes the remaining 277 spreading rates and 121 transform fault azimuths velocities predicted by nuvel g and nuvel 1 also differ little with maximum differences of 2 mm yr 1 and 4 except for the caribbean plate boundaries these results indicate that even in the unlikely event that all earthquake slip vectors in the nuvel 1 data set are unreliable recorders of long term plate directions the slip vectors do not significantly degrade the model it thus appears that the decision to use or not to use earthquake slip vectors to derive a global plate motion model has little practical effect on the ability to derive an accurate description of present day plate velocities little emphasis is placed on the changes in estimates of caribbean plate velocities that occur upon exclusion of earthquake slip vectors nearly all of the data from caribbean plate boundaries are suspect and it is unlikely that the nuvel sz or nuvel g models represent a significantly improved description of caribbean plate velocities comparison of 677 slip vectors from transform faults to directions predicted by nuvel g shows statistically insignificant differences along 12 of 15 spreading centers the good agreement between the nearly instantaneous estimates of slip directions provided by slip vectors and the longer term average directions given by nuvel g suggest that in general transform fault slip vectors parallel the longer term average directions along transform faults interestingly a statistically significant difference between slip vectors from right slipping and left slipping transform faults is noted for nearly all spreading centers with slip vectors along right slipping and left slipping faults rotated clockwise and counterclockwise respectively from the predicted direction the cause of this bias is unknown but may be related to biases introduced by unmodeled lateral heterogeneities in the mantle near transform faults

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

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

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

bounds on the holocene slip rate of the haiyuan fault north central china abstract we measured the offsets of six stream valleys of 30 to 90 m along the northwest southeast trending left lateral haiyuan strike slip fault in north central china minimum ages of these offsets were determined to estimate lower bounds for the holocene slip rate the most reliable bounds are 7 6 1 0 and 6 7 1 0 mm yr with three others that are smaller 3 4 0 7 3 5 0 9 and 4 1 0 4 mm yr and one large value 16 4 5 9 mm yr that we doubt thus the average holocene slip rate of the haiyuan fault is larger than 6 mm yr and probably exceeds 7 mm yr if the average slip rate of 5 to 10 mm yr for the quaternary period is applicable to the holocene epoch the average rate is 8 2 mm yr

21ne versus 10be and 26al exposure ages of fluvial terraces the influence of crustal ne in quartz abstract the accuracy of 21 ne surface exposure ages depends critically on the correction for a trapped ne component commonly the amount of cosmogenic ne used to calculate 21 ne exposure ages is considered to be the ne excess relative to a trapped component of atmospheric composition 21 ne 20 ne 0 00296 here we document a trapped ne component in quartz samples from a series of river terraces at the northern margin of tibet hetzel et al nature 417 2002 428 432 which has a non atmospheric 21 ne 20 ne ratio varying from 0 00299 to 0 00398 vacuum crushing of amalgamated samples each derived from 30 80 quartz clasts revealed that the non atmospheric trapped component is present in fluid inclusions it has probably been incorporated into the quartz crystals during their growth in veins at low grade metamorphic conditions only if the amount of cosmogenic 21 ne is determined relative to this trapped component are the calculated 21 ne exposure ages consistent with the relative ages of the tectonically induced terraces and in agreement with independent 10 be and 26 al exposure ages of the fluvial terraces a significant in situ production of nucleogenic 21 ne by the reaction 18 o n 21 ne in the paleozoic quartz minerals is ruled out by extremely low u contents of the order of 1 5 ppb all ages have been corrected for an inherited cosmogenic component that results from cosmic ray exposure during erosion of the host rock and transport of the clasts to the terraces the origin of the trapped component from crustal fluids is supported by high 40 ar 36 ar ratios of 2000 6000 and slightly elevated 136 xe 132 xe ratios relative to air which can be explained by radioactive decay of 40 k and spontaneous fission of u in the crust

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

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

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