what controlled mid late miocene long term aridification in central asia global cooling or tibetan plateau uplift a review abstract debate continues over whether global cooling or uplift of the tibetan plateau provided the first order driver for the aridification moisture levels of central asia throughout the mid late miocene between about 17 and 5 ma this review attempts to throw new light on the relations between the aridification and these two key factors this paper examines the evolution of miocene climate both moisture and temperature within five separate regions of eurasia to help understand the large scale controls of long term moisture in central asia the five regions include 1 europe 2 high latitude asia 3 the east asian monsoon region 4 the south asian monsoon region and 5 central asia itself because moisture reaching central asia has to firstly cross at least one of the other four regions temperature proxy data compiled from these five regions correlate with ocean temperatures from the global deep sea oxygen isotope records furthermore compiled moisture proxy data from the four regions surrounding central asia co vary and correlate with each other this can be explained by positive feedbacks between drying and cooling and supports the assumption that global cooling provides a dominant driving factor for the drying of eurasia global cooling reduces the amount of water vapor held in the atmosphere and thereby can cause terrestrial drying however in central asia the moisture evolution shows less similarity with its surroundings the uplift of the tibetan plateau including the tianshan mountains could provide a possible explanation for this difference the changing topography resulting from uplift events over time and space strongly influenced the moisture patterns in central asia during miocene times future research on the spatial timing and amplitude of tibetan plateau uplift should be useful to understand the moisture processes in central asia during the miocene

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

paleomagnetism of upper cretaceous red beds from the eastern qiangtang block clockwise rotations and latitudinal translation during the india asia collision abstract high temperature magnetization component was isolated between 600 c and 680 c from upper cretaceous red beds in the mangkang area in the eastern end of the qiangtang block tibetan plateau the tilt corrected site mean direction is d s i s 51 3 56 1 with k 31 0 and 95 6 5 corresponding to a paleolatitude of 36 7 6 7 n positive fold and reversal tests indicate a primary magnetization inclination shallowing tests show that inclination bias is not present in the upper cretaceous red beds of the qiangtang block that might induce through depositional and or compaction process however previous paleomagnetic data obtained from cretaceous and paleocene eocene volcanic rocks show that the paleolatitudes of the lhasa block were 17 1 3 3 n and 22 3 4 4 n respectively and 28 7 3 7 n for the central qiangtang block yielded from eocene volcanic rocks these results show that there was a 10 latitudinal discrepancy between the lhasa block and qiangtang relative to eurasia however the mangkang area of the southeastern qiangtang block experienced 3 2 7 8 to 7 3 5 2 southward extrusion and 40 clockwise rotational movement relative to eurasia since the cretaceous which coincided with the early cenozoic rotational extrusion of the indochina and shan thai blocks the crustal deformation in the eastern qiangtang block should have been caused by the indian plate penetrating into eurasia in the eastern end of tibetan plateau and the formation of the eastern himalaya syntaxis since the oligocene miocene

eocene north south trending dikes in central tibet new constraints on the timing of east west extension with implications for early plateau uplift east west extension has been a prominent feature of cenozoic tectonics in central southern tibet and the onset of this extension has been interpreted as indicating the surface uplift of the tibetan plateau to a critical level previous studies suggested that extension started in the neogene between 18 13 ma and 8 ma based on dating results from north south trending normal faults grabens or rifts and dikes we report here the discovery of widespread north south trending diabase and andesitic porphyry dikes in and around the shuang hu graben central tibet where crustal extension has previously been argued to start from 13 5 ma based on mineral ages from graben bounding faults our results show that dikes in this area were mainly formed in the eocene 47 38 ma geochemical and nd sr isotopic data suggest that the diabase dikes originated from partial melting of an enriched lithospheric mantle source metasomatized by melts from subducted continental crust and the andesitic porphyry dikes were probably derived from interactions between the subducted continental crust derived melts and the mantle given that north south trending eocene dikes are found widely dispersed in central tibet we argue that the onset of east west extension and likely regional uplift of the tibetan plateau began much earlier than previously thought our study implies that a large part of the tibetan plateau had already attained near maximum elevation in the eocene and is consistent with recent investigations regarding the middle late eocene 47 34 ma initiation of aridification in asia evidence from contemporary global oceanic o sr isotope curves and temperatures and the carbon cycle 2010 elsevier b v

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

reactive transport modeling of the interaction between water and a cementitious grout in a fractured rock application to onkalo finland grouting of water conducting fractures with low alkali cement is foreseen for the potential future repository for spent nuclear fuel in finland onkalo a possible consequence of the interaction between groundwater and grout is the formation of high ph solutions which will be able to react with the host rock gneisses and alter its mineralogy and porosity a reactive transport modeling study of this possible alteration has been conducted first the hydration of the low alkali cementitious grout has been modeled using results from the literature as a guide the hydrated cement is characterized by the absence of portlandite and the presence of a c s h gel with a ca si ratio about 0 8 after tens of years ca si is about 1 7 in ordinary portland cement second calculations have simulated the interaction between flowing water and grout and the formation of an alkalinity plume which flows beyond the grouted section of the fracture the calculations include the hydration and simultaneous leaching of the grout through diffusive exchange between the porewater in the grout and the flowing water in the fracture the formation of an alkaline plume is extremely limited when the low ph grout is used even when using a grout with a lower silica fume content the extent and magnitude of the alkaline plume is quite minor these results are in qualitative agreement with monitoring at onkalo

rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste the interaction of groundwater with cement in a geological disposal facility gdf for intermediate level radioactive waste will produce a high ph leachate plume such a plume may alter the physical and chemical properties of the gdf host rock however the geochemical and mineralogical processes which may occur in such systems over timescales relevant for geological disposal remain unclear this study has extended the timescale for laboratory experiments and shown that after 15 years two distinct phases of reaction may occur during alteration of a dolomite rich rock at high ph in these experiments the dissolution of primary silicate minerals and the formation of secondary calcium silicate hydrate c s h phases containing varying amounts of aluminium and potassium c a k s h during the early stages of reaction up to 15 months have been superseded as the systems have evolved after 15 years significant dedolomitisation mgca co3 2 2oh mg oh 2 caco3 co32 aq has led to the formation of magnesium silicates such as saponite and talc containing variable amounts of aluminium and potassium mg al k silicates and calcite at the expense of the early formed c a k s h phases this occured in high ph solutions representative of two different periods of cement leachate evolution with little difference in the alteration processes in either a koh and naoh or a ca oh 2 dominated solution but a greater extent of alteration in the higher ph koh naoh leachate the high ph alteration of the rock over 15 years also increased the rock s sorption capacity for u vi the results of this study provide a detailed insight into the longer term reactions occurring during the interaction of cement leachate and dolomite rich rock in the geosphere these processes have the potential to impact on radionuclide transport from a geodisposal facility and are therefore important in underpinning any safety case for geological disposal

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

crustal structure across longmenshan fault belt from passive source seismic profiling 1 we analyse receiver functions from 29 broad band seismographs along a 380 km profile across the longmenshan lms fault belt to determine crustal structure beneath the east tibetan margin and sichuan basin the moho deepens from about 50 km under songpan ganzi in east tibet to about 60 km beneath the lms and then shallows to about 35 km under the western sichuan basin the average crustal vp vs ratios vary in the range 1 75 1 88 under songpan ganzi in east tibet 1 8 2 0 under the lms and decrease systematically across the nw part of the sichuan basin to less than 1 70 a negative phase arrival above the moho under songpan ganzi and sichuan basin is interpreted as a ps conversion from the top of a low velocity layer in the lower crust the very high crustal vp vs ratio and negative polarity ps conversion at the top of lower crust in east tibet are inferred to be seismic signatures of a low viscosity channel in the eastern margin of the tibetan plateau the lateral variation of moho topography crustal vp vs ratio and negative polarity ps conversion at the top of the lower crust along the profile seem consistent with a model of lower crust flow or tectonic escape

contribution of induced magnetization to magnetization of seamounts a fundamental assumption in modelling seamount magnetic anomalies is that the contribution of induced magnetization is negligible the general consistency of seamount and non seamount palaeopoles scarcity of poles skewed toward the present field direction and the high ratio of remanent to induced magnetization koenigsberger ratio of many oceanic basalts have been cited as evidence supporting this assumption1 2 recent discussions concerning the dominance of normally magnetized seamounts have focused attention on the possible role of viscous and induced magnetization in seamount anomalies3 6 here we determine natural remanent magnetization initial volume susceptibility and the koenigsberger ratio for more than 2 000 samples from a subaerially exposed seamount section on la palma canary islands table 1 by contrast to results from the oceanic crust and ophiolites these data indicate that a variety of rock types are potential magnetic sources the significant induced component of intrusives underscores the importance of the lithological distribution in determining the character of seamount magnetic anomalies the la palma data together with a plausible lithological distribution indicate that induced magnetization may account for one sixth of seamount magnetization

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

geodetic measurement of crustal motion in southwest china global positioning system measurements performed over a 2 4 yr period confirm the xianshuihe xiaojiang fault system as one of the primary active structures in southwest china stations southwest of these faults show southerly motions of 5 15 mm yr relative to the western sichuan basin and stations in a 200 km geodetic network located northwest of the basin move at only 0 5 mm yr these results are consistent with clockwise rotation of southwestern sichuan and western yunnan about the eastern tibetan syntaxis accommodated by left lateral slip of 12 4 mm yr on the xianshuihe xiaojiang fault system the results imply that if eastward extrusion of crustal material from the plateau occurs at present it is not accommodated by east west shortening along the margin of the plateau and must involve wholesale eastward motion of low lying regions to the east

paleomagnetic study of cretaceous rocks from pu er western yunnan china evidence of internal deformation of the indochina block abstract cretaceous red sandstones and siltstones were collected at 31 sties for paleomagnetic investigation from the jingxing and nanxin formation around pu er 23 0 n 101 0 e western part of yunnan province china in order to examine quantitative amount of tectonic deformation of the simao terrane due to collision of india with asia after stepwise thermal demagnetization the high temperature component magnetization with unblocking temperature of around 680 c is isolated positive field tests show that the high temperature component magnetization from 25 sites is primary for the cretaceous formations a tilt corrected mean direction is d 59 9 i 45 2 with 95 5 1 corresponding to a paleopole at 35 8 n 173 1 e with a 95 5 6 comparison with cretaceous paleomagnetic pole of the whole china block indicates that amount of clockwise rotation in the pu er area is evaluated to be 46 9 with respect to the whole china block which is consistent with large amount of rotation in the mengla and jinggu areas 47 and 66 in the central part of the simao terrane clockwise rotation of the central part is larger by more than 20 compared to the yunlong and yongping areas of northern part of the simao terrane suggesting that the simao terrane experienced internal deformation the southward displacement of the pu er area expected from inclination data is 7 5 6 6 with respect to the chuan dian fragment which is a similar estimate to other areas in the simao terrane and the indochina block while the simao terrane displaced southward by 800 km together with clockwise rotation of 30 as a whole further clockwise rotation occurred in the central part

quantitative climate reconstructions of the late miocene xiaolongtan megaflora from yunnan southwest china the late miocene xiaolongtan megaflora from kaiyuan in southeast yunnan 23 degrees 48 45 n 103 degrees 11 52 e 1050 m a s l was chosen for palaeoclimatic reconstruction using three quantitative techniques i e the coexistence approach ca leaf margin analysis lma and the climate leaf analysis multivariate program clamp the reconstructed climatic parameters are also compared with those of the two adjacent miocene floras currently available in yunnan i e the early to middle miocene carpological mangdan flora 24 degrees 24 n 97 degrees 49 e 1620 m a s l and the late miocene luhe palynoflora 25 degrees 10 n 101 degrees 22 e 1930 m a s l quantitative analyses of the xiaolongtan flora supports the previous qualitative results of a southern humid subtropical climate being more humid and having a slightly higher mean annual temperature mat than today the mats calculated by ca lma and clamp overlap 16 7 19 2 degrees c 22 3 2 05 degrees c 18 1 1 2 degrees c respectively and are close to the present day value 19 7 degrees c the overlapping of temperatures derived using the three techniques is unusual and probably related to the low latitude of the xiaolongtan area and the southern subtropical nature of its vegetation both the mean temperatures of the warmest month wmt and of the coldest month cmt reconstructed by ca wmt 25 4 26 0 degrees c cmt 7 7 8 7 degrees c and clamp wmt 25 9 1 6 degrees c cmt 10 8 1 9 degrees c are similar to those of today wmt 24 3 degrees c cmt 12 8 degrees c but great changes appear in the mean annual precipitation map the clamp results suggest a higher precipitation 1964 335 9 mm than ca 1215 1639 mm but they are much higher than the present map 820 5 mm this is consistent with results from the luhe palynoflora which also developed under a warmer subtropical climate with higher precipitation 803 6 1254 7 mm than that of today 815 9 mm in contrast the mangdan flora situated in a more complicated topographic region to the west of xiaolongtan and near the sino myanmar border implies a slightly lower precipitation 1170 1300 mm than that of today 1300 1400 mm overall the wetter climate during the late miocene around the xiaolongtan area suggests that the himalayas had not yet uplifted to its present altitudes at that time c 2009 elsevier b v all rights reserved

carbonate oxygen isotope paleoaltimetry evaluating the effect of diagenesis on paleoelevation estimates for the tibetan plateau carbonate oxygen isotope paleoaltimetry is based on analysis of the d 18 o value of carbonate precipitated from surface water deciphering the diagenetic history is important for establishing whether particular carbonates are accurate recorders of paleosurface waters which reflect paleoelevation this study provides examples from southern east central and northeastern tibet of approaches aimed at evaluating the diagenetic history of lacustrine micrites and pedogenic carbonates the most desirable technique for avoiding erroneous interpretations related to diagenetic overprinting is to analyze carbonates that are known to be primary such as aragonitic shell material in rocks that do not contain shell material we have compared lacustrine micrites and pedogenic carbonates to diagenetic carbonate phases to determine the effects of diagenesis on the isotopic composition of primary carbonates where the potential effects of diagenesis are subtle or ambiguous we have evaluated the fidelity of the carbonate record from systematic trends in c and o isotopes that agree with other interpretations of paleoenvironment such as high frequency covariance in c and o that corresponds with changes in the mg concentration of carbonates using these strategies we have determined that diagenesis has not affected the isotopic composition of carbonates in the late miocene pliocene thakkhola graben in southern tibet and the oligocene to pliocene linxia basin in northeastern tibet in the case of paleogene basins in east central tibet however ambiguity in data precludes the determination of diagenetic effects d 2004 elsevier b v all rights reserved

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

the andean type gangdese mountains paleoelevation record from the paleocene eocene linzhou basin abstract paleoelevation reconstruction using oxygen isotopes is making a significant contribution to understanding the cenozoic uplift of the himalayas and the tibetan plateau this paper presents new oxygen and carbon isotopic compositions from well dated tertiary paleosols lacustrine calcareous carbonates and marls from the nianbo 60 54 ma and upper pana formations 51 48 ma of the linzizong group in the linzhou penbo basin the sediments of the nianbo formation which are 180 m thick were deposited in alluvial fans braided rivers fan deltas and on nearshore to offshore lacustrine settings whereas those of the upper pana formation are 100 m thick and are comprised predominantly of proximal alluvial fan and braided river deposits correlations between the lithofacies and stable isotopic compositions suggest that the basin was mainly a hydrologically open environment it is confirmed that the 18 o c and 13 c c values from nianbo and pana formations have not yet been reset by late stage diagenesis based on petrographic examination oxygen isotope of the fossil ostracodes and tectonic deformation of strata the paleoelevations are reconstructed using the corrected most negative paleosurface water 18 o psw values these imply that the linzhou area had attained an elevation of 4500 400 m during the period of the indo asian collision i e achieved a near present elevation and may form an andean type mountain range stretching the gangdese arc before collision the gangdese mountains probably maintained high elevations since at least the paleocene and could play a crucial role in the climate change in the interior of the tibetan plateau during the early cenozoic the paleogeomorphic scenario of the eocene tibet is proposed to exist at two high mountains in excess of 4500 m that sandwiched a low elevation basin

reactive transport modeling of the interaction between a high ph plume and a fractured marl the case of wellenberg abstract in the context of the proposed low and intermediate level radioactive waste repository at wellenberg switzerland calculations simulating the interaction between hyperalkaline solutions and a fractured marl at 25 c have been performed the aim of these calculations is to evaluate the possible effects of mineral dissolution and precipitation on porosity and permeability changes in such a fractured marl and their impact on repository performance solute transport and chemical reaction are considered in both a high permeability zone fracture where advection is important and the wall rock where diffusion is the dominant transport mechanism the mineral reactions are promoted by the interaction between hyperalkaline solutions derived from the degradation of cement a major component of the engineered barrier system in the repository and the host rock both diffusive dispersive and advective solute transport are taken into account in the calculations mineral reactions are described by kinetic rate laws the fluid flow system under consideration is a two dimensional porous medium marl 1 porosity with a high permeability zone simulating a fracture 10 porosity crossing the domain the dimensions of the domain are 6 m per 1 m and the fracture width is 10 cm the fluid flow field is updated during the course of the simulations permeabilities are updated according to kozeny s equation the composition of the solutions entering the domain is derived from modeling studies of the degradation of cement under the conditions at the proposed underground repository at wellenberg two different cases have been considered in the calculations these 2 cases are representative of 2 different stages in the process of degradation of cement ph 13 5 and ph 12 5 in both cases the flow velocity in the fracture diminishes with time due to a decrease in porosity this decrease in porosity is caused by the precipitation of calcite replacement of dolomite by calcite and other secondary minerals brucite sepiolite analcime natrolite tobermorite however the decrease in porosity and flow velocity is much more pronounced in the lower ph case the extent of the zone of mineral alteration along the fracture is also much more limited in the lower ph case the reduction of porosity in the fractures would be highly beneficial for repository performance since it would mean that the solutions coming from the repository and potentially carrying radionuclides in solution would have to flow through low conductive rock before they would be able to get to higher conductive features the biggest uncertainty in the reaction rates used in the calculations arises from the surface areas of the primary minerals additional calculations making use of smaller surface areas have also been performed the results show that the smaller surface areas and therefore smaller reaction rates result in a smaller reactivity of the system and smaller porosity changes

structural setting of the 2008 mw 7 9 wenchuan china earthquake the 2008 m w 7 9 wenchuan earthquake ruptured an imbricate thrust system in the longmen shan range which forms the eastern boundary of the tibetan plateau we use seismic reflection data and surface geology to construct geologic cross sections and a three dimensional 3d fault model in the range front the rupture was complex with slip on both the steeply dipping beichuan fault and the more shallowly dipping pengguan fault which appear to merge at depth in contrast only the beichuan fault ruptured in the north with the transition near a lateral fault offset thus the earthquake involved multiple thrust splays and breached a significant segment boundary to investigate the tectonic setting of the earthquake we extend our previous measurements of crustal shortening hubbard and shaw 2009 into the interior of the range and show that shortening correlates with topography this suggests that upper crustal shortening can produce the high topography of the longmen shan without calling on other uplift mechanisms based on this understanding we model the thrust belt as a critical taper wedge to assess what rock and fault strengths are required to explain the topographic slopes within the range front and basin the low taper within the basin is consistent with a weak detachment f 0 1 while a slightly stronger f 0 3 0 4 detachment is necessary to explain the higher taper of the range front this difference may relate to the localization of the detachment within a triassic evaporite sequence within the basin while the faults beneath the range front are rooted in precambrian metasedimentary or igneous rocks critical taper theory implies that shortening in the range front where the 2008 wenchuan earthquake occurred is many times greater than in the basin consistent with our shortening measurements we examine the implications of these findings for seismic hazard assessment in the region and in other active mountain belts around the world

c3 c4 vegetation evolution over the last 7 0 myr in the chinese loess plateau evidence from pedogenic carbonate δ13c the stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at lingtai the chinese loess plateau this sequence is composed of 130 m of tertiary red clay deposits with a basal age of 7 05 ma overlain by 175 m of pleistocene loess in the field we identified ca 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess these carbonate nodule horizons are formed by leaching and re precipitation of carbonate from the eolian material the d13c record of soil carbonate indicates a major expansion of c 4 plants at ca 4 0 myr in the loess plateau this event is comparable in timing with the expansion of c 4 plants in northern north america cerling et al 1997 nature 389 153 158 but is ca 3 million years later than the c 4 biomass expansion in pakistan quade et al 1989 nature 342 163 166 the pedogenic characteristics of the soils and the d18o record in the red clay suggest that the c 4 plant expansion in the loess plateau was not driven by local climatic changes which may support cerling et al s 1997 assertion that the decline of atmospheric co 2 levels in the neogene is responsible for this global vegetation change our record also implies that the tibetan plateau could have been uplifted to a critical height in the late miocene thus resulting in the formation of the atmospheric great east asia trough 2000 elsevier science b v all rights reserved

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

multi site surface complexation modelling of se iv sorption on biotite abstract a surface complexation model of se iv sorption on biotite with one type of strong sorption sites and two types of weak sorption sites were developed based on experimental data obtained from titration sorption edge and sorption isotherm experiments titration data was collected using a batch wise manner together with backtitration to calibrate the effect of mineral dissolution in 0 01 m kclo4 background electrolytes from ph 3 to 11 in an inert atmosphere glovebox further calibrations of the titration curve include proton exchange and cation exchange in which the calculations of cation occupancies on biotite surfaces were taken into account the sorption edge measurements were determined by measuring the sorption of 10 9 m total se with a radioactive se 75 tracer on converted biotite in 0 01 m kclo4 solution from ph 3 to 11 se sorption was observed to be strongly dependent on ph surface complexation modelling was performed by deriving a set of optimized parameters that can fit titration sorption edge and sorption isotherm at ph 7 7 experimental data a castep code implemented into materials studio was used to calculate the site densities and site types on the biotite surfaces weak sorption sites with site densities of 3 2 sites nm2 and 1 4 sites nm2 were derived from the codes and used in the sorption model a computer code that coupled phreeqc with python was developed for the fitting and optimizing processes the model was validated by sorption data at ph 9 5 the results show that the model can provide quantitative predicts of se iv sorption in groundwater conditions of a deep geological repository and help improve the performance assessments by giving more convincing estimates of the release of radionuclides towards aquifers and biosphere

pollen evidence for an eocene to miocene elevation of central southern tibet predating the rise of the high himalaya quantifying the elevation history of the 2000 km wide tibetan plateau to an average elevation of 5 km is important for understanding key aspects of cenozoic global climate change collision tectonics and the evolution of the asian monsoon yet quantitative measures of cenozoic surface height change across tibet remain few and are sometimes contradictory here we report the first exploratory application of a modified co existence approach coa using previously published fossil pollen records to reconstruct quantitatively the cenozoic minimum palaeoaltitudes of gangdise nyainqentanglha area of the tibetan plateau gcm simulations were used to adjust eocene and miocene raw coa values for secular climate change and changes in palaeolatitude this modelled correction increased the coa derived altitudes by 895 96 m to give a minimum overall eocene altitude of 3295 3495 m the miocene correction factor of 481 25 m gave an overall minimum altitude estimate of 3000 3150 m for the holocene coa returns four equally likely elevations of 4800 4950 m 3800 3900 m 3000 3100 m and 2900 3000 m the first of these is indistinguishable from the present day regional average while the others suggest significant upslope pollen transport both the eocene and miocene palynologically derived height estimates are consistent with suggestions of significant core plateau elevation by the eocene but are likely to underestimate the true palaeoelevation due to pre himalayan upslope pollen transport

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

constructing the longmen shan eastern tibetan plateau margin insights from low temperature thermochronology 1 contrasting models of upper crustal shortening versus lower crustal flow have been proposed to explain the formation of thickened crust in the longmen shan lms eastern tibetan plateau tp margin these models require different structural kinematics along the lms whose structural geometry is defined by three parallel nw dipping fault zones from foreland southeast to hinterland northwest they are the guanxian anxian fault yingxiu beichuan fault ybf and wenchuan maowen fault wmf newly derived and previously published low temperature thermochronology data from the lms were synthesized to constrain the spatial exhumation and test previous models the results show that 1 exhumation increases abruptly across the range bounding ybf suggesting the fault being the main thrust boundary between the lms and the sichuan basin to the east 2 younger late cenozoic cooling ages are found on the hinterland wmf where a dichotomy of ages on the hanging wall versus footwall suggests late cenozoic thrust activity and 3 toward the hinterland to the west exhumation rates decrease twofold over a distance of 30 40 km this exhumation pattern indicates a westward decrease of tectonic uplift providing the regional topography approached a steady state whereby exhumation is in balance with tectonic uplift the observed exhumation estimates support an upper crustal configuration where thrusts in the lms merge gradually into a gentle detachment seated at a depth of 20 30 km results of this study support a revised upper crustal thrusting model

mineralogical alteration and associated permeability changes induced by a high ph plume modeling of a granite core infiltration experiment abstract within the framework of the hpf project hyperalkaline plume in fractured rock at the grimsel test site switzerland a small scale core infiltration experiment was performed at the university of bern a high ph solution was continuously injected under a constant pressure gradient into a cylindrical core of granite containing a fracture this high ph solution was a synthetic version of solutions characteristic of early stages in the degradation of cement the interaction between the rock and the solutions was reflected by significant changes in the composition of the injected solution and a decrease in the permeability of the rock changes in the mineralogy and porosity of the fault gouge filling the fracture were only minor one dimensional reactive transport modeling using a modified version of the gimrt code was used to interpret the results of the experiment dispersive and advective solute transport mineral reaction kinetics and a coupling between porosity and permeability changes were taken into account in order to obtain a reasonable agreement between models and experimental results reactive surface areas of the order of 10 5 m 2 m 3 rock had to be used these values are much smaller than the values measured for the fault gouge filling the fracture which are in the order of 10 6 10 7 m 2 m 3 rock however the results could be improved by adding a small fraction of fine grained mineral which could explain the high initial peaks in al and si concentration with the inclusion of this fine grained fraction the initial surface areas in the model were within the range of the measured specific surface areas of the fault gouge the fact that the decrease in permeability was significant despite the minor changes in mineralogy suggests that permeability may be controlled by changes in the structure of the rock pore geometries rather than by only the bulk volumetric porosity changes

quantifying landscape differences across the tibetan plateau implications for topographic relief evolution 1 we quantify the bulk topographic characteristics of the tibet qinghai plateau with specific focus on three representative regions northern central and southeastern tibet quantitative landscape information is extracted from shuttle radar topography mission digital elevation models we find that the morphology of the tibetan plateau is nonuniform with systematic regional differences the northern and central parts of the plateau are characterized by what we suggest to call positive topography i e a topography in which elevation is positively correlated with relief and mean slope a major change from the internally drained central part of tibet to the externally drained part of eastern tibet is accompanied by a transition from low to high relief and from positive to negative topography i e a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope relief in eastern tibet is largest along rivers as they cross an ancient eroded plateau margin at high angle to the major strike slip faults the yalong yulong thrust belt implying strong structural control of regional topography we propose that the evolution of river systems and drainage efficiency the ability of rivers to transport sediments out of the orogen coupled with tectonic uplift is the simplest mechanism to explain systematic regional differences in tibetan landscapes basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief this mode of smoothing started concurrently with tectonic construction of the relief as most clearly illustrated today in the qilian shan qaidam region of the northeastern plateau in the interior of tibet further passive filling due to internal drainage only continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening thus diachronous beveling at high elevation produced the low relief surface of the high plateau in southeast tibet headward retreat of external drainages brought back in the global ocean base level first disrupting then interrupting the relief reduction process it produced a transitional topography by dissecting the old remnant plateau surface which introduced younger and steeper incision of this hitherto preserved high base level this provides a unifying mechanism for the formation of the low relief plateau interior and for the origin of the high elevation low relief relict surface in southeastern tibet our analysis brings forth the importance of surface processes in particular drainage efficiency in shaping plateau morphology and landscape relief such key processes appear to have been mostly ignored in numerical models of plateau deformation our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift low relief surface first formed at low elevation extending all the way to the south china sea shore before being warped upward in the late miocene pliocene by lower crustal channel flow

tibetan uplift prior to the eocene oligocene climate transition evidence from pollen analysis of the xining basin uplift of the tibetan plateau and the himalayas since the onset of the indo asia collision is held responsible for asian aridifi cation and monsoon intensifi cation but may also have gradually cooled global climate leading to the 34 ma eocene oligocene transition to unravel the interplay between tibetan uplift and global climate proxy records of asian paleoenvironments constrained by accurate age models are needed for the paleogene period here we report the 38 ma appearance of high altitude vegetation recovered from palynological assemblages in precisely dated lacustrine sediments from the xining basin of the northeastern tibetan plateau region this result confi rms previous evidence for important regional uplift in the central and northern tibetan plateau regions during the early stage of the indo asia collision this is consistent with the idea that the associated increase in rock weathering and erosion contributed to lowering of atmospheric co 2 leading to the eocene oligocene transition

the clumped isotope geothermometer in soil and paleosol carbonate we studied both modern soils and buried paleosols in order to understand the relationship of temperature t c 47 estimated from clumped isotope compositions 47 of soil carbonates to actual surface and burial temperatures carbonates from modern soils with differing rainfall seasonality were sampled from arizona nevada tibet pakistan and india t c 47 obtained from these soils shows that soil carbonate forms in the warmest months of the year in the late morning to afternoon and probably in response to intense soil dewatering t c 47 obtained from modern soil carbonate ranges from 10 8 to 39 5 c on average t c 47 exceeds mean annual temperature by 10 15 c due to summertime bias in soil carbonate formation and to summertime ground heating by incident solar radiation secondary controls on t c 47 are soil depth and shading site mean annual air temperature maat across a broad range 0 30 c of site temperatures is highly correlated with t c 47 from soils following the equation maat c 1 20 t c 47 0 21 72 r 2 0 92 where t c 47 0 is the effective air temperature at the site estimated from t c 47 the effective air temperature represents the air temperature required to account for the t c 47 at each site after consideration of variations in t c 47 with soil depth and ground heating the highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from t c 47 in paleosol carbonate assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites t c 47 0 decreases systematically with elevation gain in the himalaya following the equation elevation m 229 t c 47 0 9300 r 2 0 95 assuming that temperature varied similarly with elevation in the past this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates we also measured t c 47 from long sequences of deeply buried 5 km paleosol carbonate in the himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition we found that paleosol carbonate faithfully records plausible soil t c 47 down to 2 5 4 km burial depth or 90 125 c deeper than this and above this temperature t c 47 in paleosol carbonate is reset to temperatures 40 c we observe 40 c as the upper limit for t c 47 in modern soils from soil depths 25 cm and therefore that t c 47 40 c obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present or non primary temperatures produced by resetting during diagenesis if representative this limits the use of t c 47 to reconstruct ancient surface temperature to modestly buried 3 4 km paleosol carbonates despite diagenetic resetting of 47 values 18 o and 13 c values of the same deeply buried paleosol carbonate appear unaltered we conclude that solid state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open system exchange of paleosol carbonate with significant quantities of water or other phases

multiproxy paleoaltimetry of the late oligocene pliocene oiyug basin southern tibet the stable isotope compositions of carbonate and organic samples from the oiyug basin in southern tibet allows for model calculations of the oligocene to pliocene paleoelevation of the south central tibetan plateau we measured the oxygen isotope composition of pedogenic and lacustrine calcite dolomite and siderite and the hydrogen isotope composition of n alkanes from plant waxes to reconstruct the 18o and d values of oiyug basin paleometeoric water calculated water isotope values from oiyug basin carbonate and organic samples respectively are in close agreement suggesting the preservation of an unaltered paleometeoric water isotopic signal in these archives late oligocene middle miocene paleoelevation estimates from groundwater pedogenic calcite and lacustrine dolomite indicate basin elevations of 4 1 km 1 2 1 6 km plant wax n alkanes d and lacustrine siderite 18o compositions of middle miocene 15 ma samples indicate paleoelevations of 5 1 km 1 3 1 9 km this estimated elevation is similar to the 5 4 km paleoelevation estimate based on fossil floral physiognomy from the same stratigraphic interval calculated late miocene pliocene paleoelevation estimates derived from the 18o composition of lacustrine marls and carbonate siderite concretions as well as the d from plant wax n alkanes indicate a mean elevation of 5 5 km 1 4 2 0 km at 5 ma although calculated mean paleoelevations for the oiyug basin all fall within the errors associated with the model calculations the close agreement of the different paleoelevation proxies provides an additional degree of confidence in the fidelity of the calculated paleoelevations calculated paleoelevations indicate a possible increase in oiyug basin elevations of 1 4 km between the early and late miocene given the modern oiyug basin elevation of 4 3 km study results allow for a possible 1 km decrease in elevation since the early pliocene these findings in conjunction with other tibetan paleoaltimetry studies are consistent with tectonic models supporting high elevations of the tibetan plateau since the initiation of india asia collision during the eocene and subsequent late cenozoic extensional collapse

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

predicting paleoelevation of tibet and the himalaya from δ18o vs altitude gradients in meteoric water across the nepal himalaya the 18o value of meteoric water varies with elevation providing a means to reconstruct paleoelevation if the 18o values of paleowater are known in this study we determined the 18o values of water 18omw from small tributaries along the seti river and kali gandaki in the nepal himalaya we found that 18omw values decrease with increasing altitude for both transects 18omw vs altitude along the kali gandaki in west central nepal fit a second order polynomial curve consistent with increasing depletion of 18o with increasing elevation as predicted by a rayleigh type fractionation process this modern 18omw vs altitude relationship can be used to constrain paleoelevation from the 18o values of miocene pliocene carbonate 18oc deposited in the thakkhola graben in the southern tibetan plateau paleoelevations of 3800 480 m to 5900 350 are predicted for the older tetang formation and 4500 430 m to 6300 330 m for the younger thakkhola formation these paleoelevation estimates suggest that by 11 ma the southern tibetan plateau was at a similar elevation to modern

the formation and expansion of the eastern proto tibetan plateau insights from low temperature thermochronology abstract we report new apatite fission track aft ages and thermal modeling results from the central songpan ganzi central and easternmost lhasa and eastern qiangtang blocks to provide robust constraints on the extent and expansion of the proto tibetan plateau our results reveal two main stages of rapid cooling events in different geological units the central songpan ganzi central lhasa and eastern qiangtang blocks underwent a phase of rapid cooling event during the paleocene early eocene 62 40 ma followed by extremely slow cooling since then such a sharp transition from relatively rapid to very slow cooling in approximately 40 ma in a large area suggest the eastern part of the proto tibetan plateau had formed since 40 ma the easternmost lhasa block experienced a stage of rapid cooling during the late eocene oligocene 40 24 ma this stage of rapid cooling event was coeval with the first stage of rapid cooling event in the longmen shan thrust belt suggestive of the eastward expansion of the eastern part of the proto tibetan plateau our paleogene aft ages and their corresponding rapid exhumation synthesized with other thermochronological and paleoaltimetry data are not consistent with those of the predictions from the channel flow model instead these observations favor the outward extrusion model the eastward expansion of the proto tibetan plateau improved the previous northward and southward growth model

rupture of deep faults in the 2008 wenchuan earthquake and uplift of the longmen shan the longmen shan mountains rise up 6 000 m over a distance of just 100 km but the mechanisms driving formation of this striking topography are debated analyses of crustal movements during the 2008 wenchuan earthquake suggest that fault induced uplift plays a role in building the high topography

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

longmen shan fold thrust belt and its relation to the western sichuan basin in central china new insights from hydrocarbon exploration the longmen shan fold thrust belt is one of the key regions of demonstrable mesozoic cenozoic tectonic evolution in china and the sichuan basin was the first natural gas producing area in china in this article the structural features of the longmen shan belt are presented using both seismic profiles and field data the complex structures of the northeast trending longmen shan fold thrust belt and its foreland in the western sichuan basin are formed by southeast directed thrusting several eastward verging rootless thrust sheets and imbricates of cambrian triassic rocks have been recognized in the northern longmen shan belt evidence suggests that the northern longmen shan belt experienced at least two major periods of deformation in the late triassic and cenozoic however the southern longmen shan belt is represented by the basement involved thrust structures and klippen and its major periods of deformation were in the latest cretaceous early cenozoic sedimentary features in the western sichuan basin reflect a two phase flexural loading history and illustrate that the late triassic foreland basin extends along the foredeep of the entire length of the longmen shan belt but the uppermost cretaceous paleogene rejuvenated foreland basin is restricted in the southern part of the western sichuan basin structural geometries suggest that prospective traps are mainly developed in the frontal zone of the longmen shan fold thrust belt and in the southern part of the western sichuan basin one of the major contributions of this article is finding preexisting paleozoic rift basins under the cenozoic thin skinned thrust belts which represent a new potential hydrocarbon play

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

focused modern denudation of the longmen shan margin eastern tibetan plateau we use river sediment load data to map the pattern of modern denudation across the longmen shan margin of the tibetan plateau suspended sediment load with corrections of bed load and solute load contributions is used to calculate watershed averaged denudation rates decadal erosion is spatially heterogeneous and seasonally modulated by monsoon flows which account for 80 90 of the sediment load enhanced denudation occurs in a 50 km wide band on the hanging wall of the longmen shan and huya fault zones reaching 0 5 0 8 mm yr these rates are similar to kyr scale rates deduced from cosmogenic 10be and to myr scale rates from low temperature thermochronology the sediment flux derived erosion rates decrease with increasing distance plateauward to less than 0 05 mm yr at a distance 200 km northwest of the foot of the longmen shan the gradient in precipitation across this margin alone cannot explain the one order of magnitude spatial difference in erosion rather the river sediment load data delineates a zone of relatively rapid denudation around active faults that carry the longmen shan in their hanging wall from the similarity of denudation rates measured over myr kyr and decadal time scales we propose that erosion of the longmen shan margin has approached a flux steady state the erosional efflux is balanced by advection of rock toward the longmen margin above the 20 nw dipping ramp of the margin bounding fault our results suggest that high amounts of landslide material mobilized by earthquakes such as the mw 7 9 2008 wenchuan event are gradually removed by rivers smoothing sediment flux over time our results also suggest that caution should be exercised when interpreting young cooling ages as evidence of the initiation of plateau uplift advection of an already high plateau into the belt of higher erosion rate at the longmen shan could also give rise to an abrupt cooling history

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

structural and thermal characters of the longmen shan sichuan china article i nfo the longmen shan sichuan china is characterised by an unusual morphology which results from a triassic prism tectonics and a more recent neogene thick skin thrusting among its specific features isthe high elevation of the internal zones incontinuity with the songpan garze fold and thrust belt sg which is associated with an abrupt 20 km moho offset between the sichuan basin and the tibetan plateau as revealed by the analysis of teleseismic data acquired by a dense seismic network the jump in crustal thickness is located at the apex of the wenchuan shear zone wsz and marks the western boundary of the metamorphosed units of sg characterized by temperatures varying from 590 c down to 300 c as commonly observed in mature accretionary wedges both the structural style marked by intense shortening in tight kink folds and geophysical data suggest the presence of an horizontal discontinuity at 15 km depth over a thick crust 63 km the longmen shan east of the wsz is characterized by thick skin detachment which thrusts the internal sedimentary unitsandtheproterozoicbasementoverthe seriesof thesichuanbasindepositedona thinnercrust of 44 km thick the majorfront isthebeichuanfault zone bfz which broughtthe internalzones onto triassic and jurassic series with lower temperatures less than 400 c locally temperatures of 425 c are found just below the klippes these results are in agreement with an original contact of the sg zone represented by an accretionary wedge of sediments thrusted over the margin of the continental crust of the yangtze craton in the early stage indosinian of the evolution the present day slow e w component of the convergence added to the difference in crustal thickness caused the yangtze crust to indent the songpan tibetan crust which was softened by a high thermal regime asaresponsetheedgeofthetibetcrustwasinflatedtothebottom upto70 km whereastothetop the crystalline massif were exhumed and pushed the deformation eastward as emerging and blind thrusts this configuration reflects a moderate shortening of the crust which behaves as a soft thick material abutting the

the interaction of the eastward extrusion of the songpan ganzi terrane and the crustal rotational movement of the sichuan basin since the late paleogene evidence from cretaceous and paleogene paleomagnetic data sets of the sichuan basin

miocene high elevation landscape of the eastern tibetan plateau the high topography of central asia is the most distinctive expression of the india asia collision yet a broad understanding of the timing and processes involved in the development of the tibetan plateau remains elusive here we investigate the neogene songpan basin located on the eastern margin of the plateau using oxygen isotope paleoaltimetry to determine when the steep longmen shan margin obtained its present elevations hydrologically open lacustrine and fluvial alluvial authigenic carbonates from the basin record the paleoelevations of the eastern tibetan plateau and suggest that the area has attained near present elevations of 3000 m by the late miocene this reconstruction is consistent with the results from the comparison of pollen fossils to their nearest living relatives in this area 2750 3050 m we propose that the eastern tibetan plateau may have attained significant elevations prior to the late miocene through an uplift scenario involving eastward growth of the plateau between the eocene and the miocene two tectonic processes either crustal shortening in the oligocene miocene or eastward propagation of weakened lower crust starting in the eocene most likely thickened the crust and raised the surface of the eastern tibetan plateau to its present elevation by the late miocene

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

quantitative reconstruction of the late miocene monsoon climates of southwest china a case study of the lincang flora from yunnan province the miocene lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern yunnan sw china and the evolution of monsoon intensity three quantitative methods were chosen for this reconstruction i e leaf margin analysis lma climate leaf analysis multivariate program clamp and the coexistence approach ca these methods however yield inconsistent results particularly for the precipitation as also shown in european and other east asian cenozoic floras the wide range of the reconstructed climatic parameters includes the mean annual temperature mat of 18 5 24 7 degrees c and the mean annual precipitation map of 1213 3711 mm compared with the modem lincang climate mat 17 3 degrees c map 1178 7 mm the miocene climate is slightly warmer wetter and has a higher temperature seasonality a detailed comparison on the palaeoclimatic variables with the coeval late miocene xiaolongtan flora from the eastern part of yunnan allows us to investigate the development and interactions of both south asian and east asian monsoons during the late miocene in southwest china now under strong influence of these monsoon systems our results suggest that the monsoon climate has already been established in southwest yunnan during the late miocene furthermore our results support that both southeast asian and east asian monsoons co occurred in yunnan during the late miocene c 2010 elsevier b v all rights reserved

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

thermochronologic evidence for plateau formation in central tibet by 45 ma the timing of tibetan plateau development remains elusive despite its importance for evaluating models of continental lithosphere deformation and associated changes in surface elevation and climate we present new thermochronologic data biotite and k feldspar 40 ar 39 ar apatite fi ssion track and apatite u th he from the central tibetan plateau lhasa and qiangtang terranes the data indicate that over large regions rocks underwent rapid to moderate cooling and exhumation during cretaceous to eocene time this was coeval with 50 upper crustal shortening suggesting substantial crustal thickening and surface elevation gain thermal modeling of combined thermochronometers requires exhumation of most samples to depths of 3 km between 85 and 45 ma followed by a decrease in erosional exhumation rate to low values of 0 05 mm yr the thermochronological results when interpreted in the context of the deformation and paleoaltimetric history are best explained by a scenario of plateau growth that began locally in central tibet during the late cretaceous and expanded to encompass most of central tibet by 45 ma

asian eocene monsoons as revealed by leaf architectural signatures abstract the onset and development of the asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations coupled with a diversity of definitions and metrics characterizing monsoon phenomena have generated much debate failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the inter tropical convergence zone itcz from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils leaf form adapts to the prevailing climate particularly under the extreme seasonal stresses imposed by monsoons so it is likely that fossil leaves carry a unique signature of past monsoon regimes leaf form trait spectra obtained from fossils from eocene basins in southern china were compared with those seen in modern leaves growing under known climate regimes the fossil leaf trait spectra including those derived from previously published fossil floras from northwestern india were most similar to those found in vegetation exposed to the modern indonesia australia monsoon i am which is largely a product of seasonal migrations of the itcz the presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in eocene time across southern asia the characteristics of the modern topographically enhanced south asia monsoon had yet to develop by the eocene leaves in south asia had become well adapted to an i am type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the eocene no fossil trait spectra typical of exposure to the modern east asia monsoon were seen suggesting the effects of this system in southern china were a much later development

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

e w extension at 19 ma in the kung co area s tibet evidence for contemporaneous e w and n s extension in the himalayan orogen abstract active faulting in southern tibet consists of n s trending extensional faults and linked strike slip faults which are an expression of regional e w extension a second type of extensional deformation associated with n s movement is also recognized this extension is expressed as a series of shear zones and normal faults in the high himalayas the southern tibetan detachment system and mid crustal rocks exposed in metamorphic domes reported constraints on the timing of movements associated with these two phases of extension indicate that n s extension predates the onset of e w extension however only a few studies have provided clear constraints on the timing of e w extension and the extent to which the two kinematically distinct domains of extension were contemporaneous is unclear the kung co fault in southern tibet is a major n s trending normal fault the associated e w extension is locally expressed as high strain ductile deformation both field and microstructural observations show that this deformation occurred synchronously with granite intrusion previously reported u pb zircon dating shows granite crystallization took place at around 19 ma implying that ductile e w extension in the kung co area was also active at around 19 ma this is the oldest documented example of e w extension in tibet and shows that e w extension was at least locally contemporaneous with n s extension to the south at shallower crustal levels simultaneous mid crustal n s extension and upper crustal e w extension may be explained by southward flow of tibetan crust with a divergent radial component

paleogene high elevations in the qiangtang terrane central tibetan plateau abstract the timing of uplift of the tibetan plateau remains controversial with estimates varying from eocene to more recent than pliocene in particular the paleoaltimetry of the qiangtang terrane on the central tibetan plateau is completely unknown here we present new stable isotope results of fluvial lacustrine carbonate cement pedogenic carbonate and marl from the kangtuo and suonahu formations deposited between 51 and 28 ma in the heihuling bamaoqiongzong area of the northern qiangtang terrane the lithofacies associations indicate that the kangtuo formation was deposited in alluvial fan and fluvial floodplain environments and the suonahu formation was deposited in near shore lacustrine playa lake and channelized fluvial environments carbon and oxygen isotope values coupled with the sedimentary facies interpretations point to evaporation and low respiration rates in the eocene oligocene paleosols suggesting an arid climate in the high qiangtang area at the time the 18opsw values of paleo surface water reconstructed from the lowest i e the least evaporated 18oc pdb values of the unaltered authigenic carbonates are used to make the minimum estimates of the average paleoelevation of the drainage basin the paleoelevation of the northern qiangtang terrane is reconstructed as above 5000 m by at least the middle oligocene 28 ma similar to the present elevation in this area the aridity and the positive shift in oxygen isotope values of surface waters in our study area may suggest that the high lhasa terrane established by the middle oligocene blocked the northward transport of tropical moisture maintenance of high elevation 5000 m from at least the oligocene to the present suggests that the qiangtang crust was already thickened by that time and that underthrusting of india beneath asia since then has continued to provide additional material while at the same time driving asian lower crust eastward by crustal flow

two dimensional reactive transport modeling of the alteration of a fractured limestone by hyperalkaline solutions at maqarin jordan abstract two dimensional reactive transport modeling of the maqarin eastern springs site a natural analogue for the alteration of a fractured limestone by high ph portland cement waters has been performed using the crunchflow code these 2d calculations included transport by advection dispersion diffusion along a single fracture and diffusion in the wall rock solute transport was coupled to mineral dissolution and precipitation a limited sensitivity analysis evaluated the effect of different values of primary mineral surface areas flow velocity and sulfate concentration of the inflowing high ph solution major secondary minerals include ettringite thaumasite c s h c a s h and calcite c s h c a s h precipitation is controlled by the dissolution of primary silicates ettringite precipitation is controlled by diffusion of sulfate and aluminum from the wall rock to the fracture with aluminum provided by the dissolution of albite calcite precipitation is controlled by diffusion of carbonate from the wall rock extents of porosity sealing along the fracture and in the fracture wall rock interface depend on assumptions regarding flow velocity and composition of the high ph solution the multiple episodes of fracture sealing and reactivation evidenced in the fracture infills were not included in the simulations results can qualitatively reproduce the reported decrease in porosity in the fractures and in the wall rock next to the fractures instances of porosity increase next to fractures caused by carbonate dissolution were not reproduced by the calculations

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

palaeo altimetry of the late eocene to miocene lunpola basin central tibet the elevation history of the tibetan plateau provides direct insight into the tectonic processes associated with continent continent collisions here we present oxygen isotope based estimates of the palaeo altimetry of late eocene and younger deposits of the lunpola basin in the centre of the plateau which indicate that the surface of tibet has been at an elevation of more than 4 kilometres for at least the past 35 million years we conclude that crustal but not mantle thickening models combined with plate kinematic solutions of india asia convergence are compatible with palaeo elevation estimates across the tibetan plateau

the late miocene through present paleoelevation history of southwestern tibet recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre and post mid miocene uplift of the southern tibetan plateau we examined this issue by analysis of well preserved fossil mollusks and plant remains from the zhada basin in southwestern tibet which ranges in age from 9 2 to paleoenvironmental modeling and physical evidence shows that the climate in zhada basin was cold and arid indistinguishable from modern the 13cpm values of well preserved vascular plant material increase from 23 4 to 26 8 permil at the base of the zhada formation to as high as 8 4 permil above 250 to 300 m this shift denotes the expansion of c4 biomass in this high arid watershed at 7 ma and thus corresponds to the c3 c4 transition observed in neogene deposits of the northern indian sub continent

paleoclimatic estimation reveals a weak winter monsoon in southwestern china during the late miocene evidence from plant macrofossils the late miocene xianfeng flora of yunnan province southwestern china was chosen to reconstruct the paleoclimate and the intensity of the asian monsoon three available quantitative climate reconstruction methods from fossil plants i e leaf margin analysis lma the climate leaf analysis multivariate program clamp and the coexistence approach ca were used in this study mats mean annual temperatures resulting from these three approaches i e lma 17 2 2 38 degrees c clamp 15 43 1 25 degrees c ca 17 2 21 7 degrees c appear to have been higher than the present 14 9 degrees c suggesting a much warmer climate in the late miocene both the growing season precipitation gsp from clamp 1908 7 217 7 mm and mean annual precipitation map from ca 1206 0 1613 0 mm estimates are higher than modern values 1003 2 mm gsp and 1038 mm map respectively indicating a more humid climate during the late miocene by comparing these with climates reconstructed from neighboring late miocene floras we conclude that the general late miocene climate appears warmer and more humid than present conditions in southwestern china furthermore the evident differences in estimated monthly temperatures between the summer and winter and precipitations between the humid and dry seasons indicate the existence of seasonality though not as strong as that of today difference in precipitation of dry season indicates a marked strengthening in the winter monsoon since the late miocene a new monsoon intensity index has also been defined based on precipitation seasonality to investigate the intensity of the asian monsoon c 2012 elsevier b v all rights reserved

east central asian climate evolved with the northward migration of the high proto tibetan plateau the evolution of cenozoic climate patterns in asia has been linked to uplift of the tibetan plateau tp retreat of the paratethys sea and global cooling however less attention has been placed on the latitudinal change of the tp here we report new climate modeling to explore how modern climate changes as a function of topographic growth and spatial migration of the tp our results show that the northward displacement of the uplifted proto tp within the subtropics can significantly affect the wind and precipitation pattern over east central asia by compiling proxy based climatic records paleolatitudinal and paleoelevational evolution models of the proto tp and in comparison with previous modeling under a global paleogeography we suggest that the northward migration of the proto tp in the paleogene could have intensified the aridity in central asia but its influence on east asian precipitation and monsoonal circulation could be dependent on the paleogeography and other boundary conditions plain language summary the evolution of the asian monsoons and aridification of asia s interior are thought to be driven by tibetan himalayan uplift recent geological observations suggest that the uplifted proto tibetan plateau proto tp migrated northward in the subtropics since the early eocene and reached its present position by the latest oligocene we therefore simulated the effects of this process on east central asian climate our climate modeling shows the northward migration of the high proto tp from 21 29 degrees n to 29 37 degrees n can significantly change the present day wind and precipitation patterns over east central asia especially central asia become drier because of the displacement of the anomalous dry belt caused by large scale atmospheric subsidence we further suggest that forcing by the paleolatitudinal migration of the high proto tp within the subtropics from the eocene to the earliest miocene could have drove the central asian paleoclimate to dryer conditions but migration might not be the sole parameter that governed the east asian monsoon during the paleogene

late cenozoic evolution of the central longmen shan eastern tibet insight from u th he thermochronometry 1 this article presents u th he thermochronological data from the longmen shan belt eastern tibet located between the songpan garze terrane and the yangtze craton this mountain range is one of the steepest margins of the tibetan plateau and an important area for the comprehension of the mechanisms that control the dynamics of such plateau borders in terms of spatial distribution of deformation or timing of topographic building we describe several age elevation transects and perform forward modeling of our data to derive quantitative information on the exhumation of the range a major phase of exhumation started at 8 11 ma with an average rate of 0 65 mm a a1 comparison of zircon and apatite ages indicates that the eastern part of the range may have experienced a significant decrease in exhumation since 2 3 ma we use the distribution of finite exhumation across the major faults of the area to quantify their dip slip throw rate over the last 10 ma the beichuan fault which was activated during the 2008 sichuan earthquake is the major active structure of the longmen shan since the late miocene with an average thrusting slip rate between 0 4 and 1 mm a a1 conversely over the same time period only minor dip slip activity occurred on the wenchuan fault zone this distribution in space and time of exhumation and deformation is discussed and compared to the different proposed models for the geodynamical evolution of the eastern tibetan margin it also provides an important long term perspective to put in context the destructive 2008 sichuan earthquake that struck the central longmen shan

stable isotopes of surface water across the longmenshan margin of the eastern tibetan plateau characterization of the stable isotope compositions 18o and d of modern day surface waters traversing mountain ranges and bordering continental plateaus is important for refining climate models and establishing modern isotope elevation gradients along mountain ranges the longmenshan margin of the tibetan plateau is a steep 4 km topographic front situated near the boundaries between westerlies and asian monsoon moisture sources and is previously unexplored with respect to the variation in water isotopic composition with elevation this study reports stable isotope data from 101 water samples collected from streams springs and ponds along the min river minjiang watershed which traverses the longmenshan margin local meteoric water lines d excess values and surrounding precipitation and river water data sets suggest that precipitation across the longmenshan margin is dominated by the east asian summer monsoon the increase in d excess values with increasing catchment elevation breaks down as local moisture recycling becomes important at elevations 3 km a s l along the min river however the 18ow and dw values decrease with increasing catchment elevation which fit second order polynomial curves and are well approximated by a simple rayleigh fractionation processes the temperature corrected oxygen values in authigenic carbonates from the pleistocene zoige basin north of the min river watershed yield elevations equivalent to present by the oxygen isotope elevation relationship of the longmenshan margin

thermochronological constraints on the late cenozoic morphotectonic evolution of the min shan the eastern margin of the tibetan plateau

high ph plume from low alkali cement fracture grouting reactive transport modeling and comparison with ph monitoring at onkalo finland grouting of water conducting fractures with low alkali cement is foreseen for the potential future repository for spent nuclear fuel in finland onkalo site a possible consequence is the formation of high ph solutions which will be able to react with the host rock calculations have been performed including the hydration and simultaneous leaching of the grout the effect of different possible groundwater compositions has been studied the results show that after grouting the duration of the initial high ph peak is short 0 5 a which compares well with observations at a test borehole magnesium in the groundwater induces the precipitation of brucite at the grout fracture interface which consumes oh in the longer term the results show a gradually decaying ph tail ph 9 controlled by the precipitation of calcite at the grout fracture interface the duration of this tail correlates inversely with the carbonate content of the inflowing groundwater a major finding of this study is that mineral precipitation controls the formation of a potential high ph plume by consuming alkalinity and limiting diffusive solute exchange between the grout and the circulating groundwater as a consequence assumption of long term interaction between rocks or engineering barrier materials with flowing high ph 12 solutions may not be very realistic

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

differential exhumation in response to episodic thrusting along the eastern margin of the tibetan plateau abstract thermochronological data from the songpan ganze fold belt and longmen mountains thrust nappe belt on the eastern margin of the tibetan plateau in central china reveal several phases of differential cooling across major listric thrust faults since early cretaceous times differential cooling indicated by distinct breaks in age data across discrete compressional structures was superimposed upon a regional cooling pattern following the late triassic indosinian orogeny 40ar 39ar data from muscovite from the central and southern longmen mountains thrust nappe belt suggest a phase of differential cooling across the wenchuan maouwen shear zone during the early cretaceous the zircon fission track data also indicate differential cooling across a zone of brittle re activation on the eastern margin of the wenchuan maouwen shear zone during the mid tertiary between 38 and 10 ma apatite fission track data from the central and southern longmen mountains thrust nappe belt reveal differential cooling across the yingxiu beichuan and erwangmiao faults during the miocene forward modelling of apatite fission track data from the northern longmen mountains thrust nappe belt suggests relatively slow regional cooling through the mesozoic and early tertiary followed by accelerated cooling during the miocene beginning at ca 20 ma to present day regional cooling is attributed to erosion during exhumation of the evolving longmen mountains thrust nappe belt lmtnb following the indosinian orogeny differential cooling across the wenchuan maouwen shear zone and the yingxiu beichuan and erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults thermochronological data from the longmen mountains thrust nappe belt reveal a greater amount of differential exhumation across thrust faults from north to south this observation is in accord with the prevalence of proterozoic and sinian basement in the hanging walls of thrust faults in the central and southern longmen mountains the two most recent phases of reactivation occurred following the initial collision of india with eurasia suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the lmtnb

understanding the geologic evolution of northern tibetan plateau with multiple thermochronometers abstract the early onset of deformation following the india asia collision neogene expanse of uplift and complex systems that comprise strike slip faults thrust faults and intermontane basins characterize the cenozoic tectonism of northern tibetan plateau and raise two prominent questions in orogenic geodynamics 1 what mechanism s control s the transfer of stress related to the india asia collision across the distance of 2000 km and 2 why the development of high topography was delayed in the northern tibetan plateau and what does it reveal about how the internal forces and external boundary conditions evolved to address these two questions we reconstruct a holistic spatial temporal deformation history of the northern tibetan plateau by using a range of thermochronometers with closure temperature spanning from 350 c to 60 70 c this multi thermochronometer study reveals three stages of faulting related cooling in the early cretaceous in paleocene eocene and in middle late miocene we observe that paleocene eocene deformation was spatially restricted and mostly occurred on reactivated cretaceous structures indicating a control of pre existing weakness on early cenozoic deformation extensive neogene deformation contrasts with restricted paleocene eocene deformation and relatively quiescent shortening during the oligocene early miocene which implies a change in the regional tectonics regime global plate reconstructions show that this tectonic reorganization is coeval with an increase in pacific asia plate convergence rates we argue that this change in regional tectonics is a result of increasing constrictive environment of the eastern plate boundary which changed the behavior of the altyn tagh fault the boundary fault of northern tibetan plateau causing it to change from feeding slip into structures out of the plateau to feeding slip into structures at plateau margins