apatite fission track evidence for the cretaceous cenozoic cooling history of the qilian shan nw china and for stepwise northeastward growth of the northeastern tibetan plateau since early eocene abstract apatite fission track aft data from hinterland of the qilian shan at the northeastern margin of the tibetan plateau suggest this range has experienced northeastward propagation of surface uplift since early eocene and that crustal shortening occurred in the qilian shan before the late miocene thermochronometry data indicate that the qilian shan experienced a three stage cooling history including 1 rapid initial cooling during cretaceous 2 a stage of slow cooling during late cretaceous early eocene and 3 rapid stepwise cooling in a southwestern northeastern orientation since early eocene cretaceous rapid cooling may be a record of the lhasa block and eurasian collision early cretaceous denudation was followed by tectonic and quasi isothermal quiescence that continued until early eocene early eocene rapid cooling in the south qilian shan may be the first far field response in the qilian shan to the collision and convergence of the indian and eurasian continents from late eocene to middle miocene crustal shortening propagated into the central qilian shan and north qilian shan and produced surface uplift of the entire qilian shan region before the late miocene this study provides a better understanding of the tectonic evolution of the qilian shan and when the far field stress from the india eurasia collision into the northeastern tibetan plateau began

constant elevation of southern tibet over the past 15 million years the uplift of the tibetan plateau an area that is 2 000 km wide to an altitude of about 5 000 m has been shown to modify global climate and to influence monsoon intensity mechanical and thermal models for homogeneous thickening of the lithosphere make specific predictions about uplift rates of the tibetan plateau but the precise history of the uplift of the plateau has yet to be confirmed by observations here we present well preserved fossil leaf assemblages from the namling basin southern tibet dated to approximately 15 myr ago which allow us to reconstruct the temperatures within the basin at that time using a numerical general circulation model to estimate moist static energy at the location of the fossil leaves we reconstruct the elevation of the namling basin 15 myr ago to be 4 689 895 m or 4 638 847 m depending on the reference data used this is comparable to the present day altitude of 4 600 m we conclude that the elevation of the southern tibetan plateau probably has remained unchanged for the past 15 myr

paleoelevation reconstruction of the paleocene eocene gonjo basin se central tibet abstract the topography evolution of the southeastern tibetan plateau provides a constraint for evaluating various geodynamic models of plateau formation we reconstruct the paleocene to eocene paleoelevation of the cenozoic gonjo basin in the qiangtang terrane using oxygen and carbon stable isotopic results from pedogenic carbonates of the lower ranmugou formation lithofacies associations indicate that the lower ranmugou formation was deposited in alluvial fan and fluvial floodplain environments u pb dating of volcanics within the middle ranmugou formation constrains the deposition of the lower ranmugou formation as prior to 43 2 ma paleoelevations are calculated using both a thermodynamic model and an empirical relationship the empirical relationship of elevation 18 o is determined from a series of modern water samples calculated paleoelevations indicate that the gonjo basin attained a minimum average elevation of 2100 2500 m in the early eocene together with recent paleoaltimetry studies in the region it can be concluded that the crust of southeastern tibetan plateau was already thickened by that time the calculation is based on the section in northern gonjo basin where 18 o values of paleosol nodules appear to be unaltered but we cannot rule out the possibility that 18 o values of the pedogenic carbonates had been partially reset our preliminary results favor tectonic models compatible with pre miocene uplift of the se central tibetan plateau

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

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

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

probing the basement of southern tibet evidence from crustal xenoliths entrained in a miocene ultrapotassic dyke abstract a variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12 7 ma ultrapotassic dyke intruding xigaze flysch immediately to the north of the yarlung tsangpo suture zone in southern tibet garnet clinopyroxene plagioclase quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130 1330 c and pressures between 22 and 26 kbar indicating equilibration in the high pressure and ultrahigh temperature granulite field and defining a geotherm of c 16 c km 1 ultramafic xenoliths consist mainly of hornblende and biotite probably of restitic crustal rather than mantle origin and attained peak metamorphic conditions of 920 1130 c and 17 24 kbar whereas felsic granulites equilibrated at 870 900 c at an inferred pressure of 17 kbar in situ u th pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include proterozoic basement rocks late cretaceous calc alkaline tonalites of the gangdese batholith root and or remnants of a neo tethyan oceanic arc certain zircons from a felsic granulite and an ultramafic xenolith have mean 206 pb 238 u ages of 16 8 0 9 ma and 15 6 0 6 ma respectively and monazites from a micaceous xenolith yielded a mean 208 pb 232 th age of 14 4 0 4 ma these results show that the southern tibet basement reached a thickness of c 80 km by 17 14 ma at the latest and has remained unchanged until the present day supplementary material mineral analyses used for pressure temperature estimations and results of 40 ar 30 ar laser single grain fusion experiments are available at http www geolsoc org uk sup18325

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

palynological evidence for the latest oligocene early miocene paleoelevation estimate in the lunpola basin central tibet uplift of the tibetan plateau is ultimately driven by the cenozoic collision between the indian and eurasian plates and their continued convergence one approach for studying the tibetan plateau uplift is to verify the paleoelevation changes from collision to present day this is important for understanding both the tectonics and the climatic effects the new high resolution palynological record of the uppermost oligocene to the lowest miocene strata from the lunpola basin indicates that the vegetation types during the latest oligocene earliest miocene were dominated by mixed coniferous broadleaved forests being different from the modern steppe vegetation by using the coexistence approach to the fossil pollen records after calibration the effects of temperature difference and the lapse rate a maximum paleoelevation of 3190 100 m asl was estimated in the lunpola basin in the latest oligocene earliest miocene being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region

advent of strong south asian monsoon by 20 million years ago abstractthe monsoonal paleoclimate of india has been critical for understanding the tectonic history of himalayan and tibetan uplift over the past 60 my monsoonal circulation in deep time has been inferred from variation in stable isotopes of tooth enamel diatom blooms and dust influx in the indian ocean and the advent of c4 grasses but these proxies are compromised by temperature biotic and source effects our study uses a proxy of carbonate distribution within paleosol profiles to infer appearance of monsoonal circulation of modern strength in the himachal pradesh segment of the himalayan foreland by at least 20 my ago cued to high himalayan deformation and ongoing tibetan plateau uplift and retreat of the paratethys sea paleosol records also demonstrate declining chemical weathering with himalayan and tibetan uplift which was a force for global warming rather than cooling over the past 20 my

miocene volcanism in the lhasa block tibet spatial trends and geodynamic implications miocene ultrapotassic up shoshonitic p and calc alkaline ca volcanism is recognized widely over the tibetan plateau this volcanism occurred after the end of india s oceanic lithosphere subduction beneath the plateau ambiguities about the distribution and significance of this volcanism arise in part from a paucity of geochronologic and geochemical data we have sampled two volcanic fields in the lhasa block 1 the eastern edge of the zabuye salt lake central part of the block 2 the southwestern edge of the yangbajin graben major and trace elements display high k2o 6 06 6 54 over a wide range of sio2 75 03 55 30 na2o 1 32 3 30 and lree hree enrichment with a significant rare earth element fractionation 266 la yb n 6 42 as well as negative nb ta and ti anomalies these features indicate that our samples are chemically identical to the post collision miocene up to p volcanic rocks already identified all over the tibetan plateau and the southern plateau specifically but distinct from the ca rocks found in the lhasa block the miocene volcanics found in the lhasa block present greater chemical variation than the rest of the tibetan plateau 40 ar 39 ar ages on both sanidine and biotite gave ages ranging from 16 16 g 0 12 ma to 16 01 g 0 12 ma and 10 60 g 0 14 ma to 10 88 g 0 17 ma 2 c excluding systematic errors relative to fish canyon sanidine at 28 02 ma for zabuye salt lake and yangying geothermal field volcanics respectively these results are consistent with the range of previously published ages from this part of the tibetan plateau the presence of n s trending dikes and the location of the volcanic fields suggest that local e w extension in the lhasa block was coeval we propose that the synchronous up p and ca volcanism in the lhasa block between 23 and 8 ma is the result of progressively deepening northward subduction of indian continental lithosphere producing asthenospheric upwelling convective thinning delamination of lithospheric mantle fueled by the hot asthenosphere induced partial melting of an enriched sub continental mantle lithosphere as well as eclogitic lower crust this mechanism could also explain the local e w extension observed in the same period 18 10 ma we also propose that lateral migration of the deepening indian continental lithosphere mantle slab could explain the observed younger volcanism in the eastern part of the lhasa terrane

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

evidence for tibetan plateau uplift before 14 myr ago from a new minimum age for east west extension important changes in south asian climate occurred in the late miocene epoch 8 myr ago 1 2 and these have been attributed by some researchers to uplift of the tibetan plateau at about the same time3 5 unfortunately this link has been difficult to test because the timing of plateau uplift remains poorly constrained by independent evidence one way to determine the minimum age of uplift is to establish the initiation age of the north striking normal fault systems in southern tibet that are widely regarded6 10 as being related to gravitational collapse of the tibetan plateau here we report an40ar 39ar age of 14 myr for hydrothermal mica from an extensional fracture belonging to such a fault system in north central nepal this age implies that east west extension began before 14 myr ago in at least some parts of the tibetan plateau suggesting that the plateau attained its high mean elevation well before late miocene time

palaeoaltimetry from energy conservation principles a knowledge of past changes in the mean elevations of large continental areas is important for understanding both dynamic processes in the earth s mantle 1 and the evolution of the global climate 2 but virtually all methods for determining palaeoelevations are problematic in part because changes in either elevation or climate can give rise to the same observed geological phenomena 4 ideally palaeoelevations would be inferred directly from estimates of palaeopressure and it has recently been shown 5 that vesicles in basaltic lava flows preserve a record of atmospheric pressure at the altitude of emplacement however the elevations thus obtained have large errors 1 4 km and the method can at present be applied only to lavas that have had a simple emplacement history 5 palaeobotanical methods for estimating palaeoelevation have received much attention 6 12 but they rely on empirical temperature elevation relationships the uncertainties in which are difficult to evaluate for past climates here we describe an alternative palaeobotanical approach based on energy conservation in the atmosphere in which fossil leaf assemblages are used to infer enthalpy rather than temperature this approach is relatively insensitive to palaeoclimate with an expected error in palaeoelevation of 700 m

paleoaltimetry potentiality of branched gdgts from southern tibet paleoaltimetric reconstructions of the southern tibetan plateau tp are crucial to understand the processes and mechanisms concomitant with the tectonic collision of the indian and eurasian continental plates we measured the branched glycerol dialkyl glycerol tetraether brgdgt indices from 88 surface soils from the southern tp and found that alkaline soils exhibited lower mbt and mbt cbt derived mat mean annual temperature while mbt cbt derived mat exhibited a strong correlation with altitude r 2 0 84 n 63 for all of the localities with neutral and acidic soils differently we found that mbt5me derived mat exhibited a strong relation with altitude even though a mixture of alkaline samples r 2 0 72 n 83 as a result two regional calibrations were developed including a neutral and acidic soil calibration based on mbt cbt mat and a calibration suitable for both acidic and alkaline soils based on mbt5me mat for the southern tp based on this new soil calibration data set and a recent global soil calibration data set founded on mbt5me we calculated paleo mat of approximate to 9 491 15 to 10 381 47 degrees c at approximate to 15 ma respectively for the namling basin applying these soil calibrations the paleoaltitudes of the namling basin can be calculated to have been between 4 360 41 km above sea level asl and 4 430 36 km asl at approximate to 15 ma respectively similar to the paleoaltitudes of approximate to 4 7 5 4 km asl at approximate to 15 ma inferred from the floral physiognomy of namling basin fossils and stable isotopes these findings would suggest the applicability of mbt cbt and or mbt5me indices as paleotopographic and paleotemperature proxies on the southern tp

pleistocene palynology of nepal abstract as part of the himalayas nepal has undergone numerous changes in the past 50 ma folding was responsible for the creation of the kathmandu basin it is here that the most complete sequence of pleistocene sediments in nepal is to be found in this paper the palynology and palynofacies of the gokarna thimi and patan formations is discussed it is shown that a scanning electron microscope is essential in order to identify the sporomorphs accurately without this detailed information it would prove impossible to pinpoint the climatic signal it is also necessary to take the sedimentological regime into consideration before a climatic interpretation can be made the pollen assemblages show that all three formations were deposited during cool conditions with a mean annual temperature 6 7 c lower that at present based on the radiocarbon dates the patan formation would appear to be of late glacial age while the gokarna and thimi formations were deposited during the wurm their exact age is still uncertain as some of the radiocarbon dates are at or beyond the limit of this method it is hoped that optically stimulated luminescence will be able to resolve this problem

an 11 ma old red clay sequence on the eastern chinese loess plateau abstract older red clay deposits on the chinese loess plateau contain information of early paleomonsoon evolution and tectonic history of the ordos platform and the tibetan plateau a well conserved eolian red clay sequence was recently discovered at shilou on the eastern chinese loess plateau paleomagnetic measurements demonstrate that polarity zones recorded in the shilou red clay profile correspond well with polarity zones between c2an 1n and c5n 2n of the gpts and the basal age of the study profile is approximately 11 0 ma field observation grain size frequency distribution and quartz grain morphology suggest a wind blown origin for this sequence this indicates that the eastern loess plateau began to accumulate dust deposits at 11 ma ago implying earlier establishment of the east asian paleomonsoon probably owing to uplifting of the tibetan plateau and ongoing global cooling it also demonstrates that the eastern loess plateau belonging to the ordos platform was slowly uplifted and suffered from erosion in the early neogene and has no conserved eolian deposits older than 11 ma as in the western chinese loess plateau

late neogene environmental changes in the central himalaya related to tectonic uplift and orbital forcing the linkage between tectonic forces and climate evolution remains a matter of much debate and speculation here we present high resolution oxygen and carbon isotope data from an ancient lake basin in the central himalaya these data together with sedimentologic evidence reveal major changes in drainage systems and depositional settings at 7 2 5 5 and 3 2 ma these environmental changes appear to be driven by regional scale tectonics the oxygen isotope record also reveals alternating wet and dry climates with periodicities of 24 and 100 kyr that were likely controlled by orbital forcing paleo temperatures estimated using a fossil based oxygen isotope paleo thermometer are 21 6 ca t 7 ma which is 19 6 c higher than the present day mean annual temperature in the same area the much warmer environment inferred here is consistent with fossil mammalian and pollen assemblages and sediment clay mineralogy as well as carbon isotope data from fossil tooth enamels and paleosol carbonates the estimated temperature difference would require the study area to have been raised by 2 2 5 km since 7 ma to its current elevation of 4100 4500 m above sea level this result can be interpreted as either indicating the presence of a low altitude intermountain basin in the hanging wall of the already formed main central thrust or a protracted development of a north trending rift basin that has experienced changes in drainage system and depositional environment through time

on the causes of mid pliocene warmth and polar amplification the mid pliocene 3 to 3 3 ma ago is a period of sustained global warmth in comparison to the late quaternary 0 to 1 ma ago and has potential to inform predictions of long term future climate change however given that several processes potentially contributed relatively little is understood about the reasons for the observed warmth or the associated polar amplification here using a modelling approach and a novel factorisation method we assess the relative contributions to mid pliocene warmth from elevated co2 lowered orography and vegetation and ice sheet changes the results show that on a global scale the largest contributor to mid pliocene warmth is elevated co2 however in terms of polar amplification changes to ice sheets contribute significantly in the southern hemisphere and orographic changes contribute significantly in the northern hemisphere we also carry out an energy balance analysis which indicates that that on a global scale surface albedo and atmospheric emmissivity changes dominate over cloud changes we investigate the sensitivity of our results to uncertainties in the prescribed co2 and orographic changes to derive uncertainty ranges for the various contributing processes

mass dependent and mass independent sulfur isotope fractionation δ34s and δ33s from brazilian archean and proterozoic sulfide deposits by laser ablation multi collector icp ms abstract mass independent sulfur isotope fractionation mif has been observed in rocks of the geological record older than about 2 45 ga a characteristic which is thought to be related to processes in the neoarchean atmosphere samples recording a mif effect therefore have to contain sulfur of the exogenic sulfur cycle while endogenic sulfur should not show this effect the sulfides analysed from six brazilian deposits represent either exogenic or endogenic sulfur sources with supposed ages ranging from about 1 9 to 2 7 ga sulfur isotopes were analysed by in situ laser ablation mc icp ms a range of experiments were conducted using international and in house isotope standards which were run under various conditions and set ups these include the reference materials iaea s1 iaea s3 nbs123 sphalerite nbs127 barite and in house standards bsb py pyrite and bsb cpy chalcopyrite during six days of analysis an internal precision of sulfide analyses of 0 10 0 15 1 s for 34 s and 0 40 0 60 1 s for 33 s and an accuracy of 0 30 for 34 s and 33 s was achieved the standard measurements define a 33 s 34 s relationship of 33 s 0 513 34 s 0 149 with r 0 9997 which is close to the theoretical relationship for mass dependent fractionation the by far best analytical errors were obtained for natural pyrite reaching a within run precision of about 0 05 0 15 for 34 s 1 s and 0 10 0 15 1 s for 33 s determinations including all precision and accuracy data we arrive at the following 1 s error limits to which sulfur isotope analyses for mif studies obtained with this method are reliable 0 32 0 34 and 0 46 for pyrite 34 s 33 s and 33 s determinations respectively 0 34 0 42 and 0 54 for pyrrhotite and 0 34 0 50 and 0 58 for chalcopyrite pyrites and pyrrhotites from 2200 ma old sediments and volcanics associated with the pilar greenstone belt goias have 34 s from 15 0 to 2 0 and 33 s from 8 0 to 1 0 with 33 s being slightly but not significantly positive pyrites from supposed ca 2060 ma old clastic sediments of the aguas claras formation carajas para have 34 s 9 5 12 5 and 33 s 5 0 6 5 with 33 s close to zero chalcopyrites from the salobo and sequerinha sulfide deposits also carajas are genetically related to 2570 ma old a type alkaline granites with endogenic sources they have 34 s 1 6 2 9 and 33 s 1 0 1 5 and 34 s 0 2 0 9 and 33 s 0 65 respectively with 33 s ranging from 0 15 to 0 56 the only 33 s values of this study which clearly suggest sulfur isotope mif come from the mineralized banded iron formations of the quadrilatero ferrifero minas gerais pyrites from the mina de cuiaba deposit 2700 ma have 34 s 3 8 5 1 and 33 s 2 9 4 8 with 33 s 0 9 2 2 while pyrites and chalcopyrites from sao bento 2720 ma have 34 s 1 6 3 2 and 33 s 1 5 2 8 with 33 s 0 2 1 5 the sulfides represent an epigenetic mineralization derived from supracrustal rocks making part of an exogenic sulfur cycle the study shows that in situ laser ablation icp ms is sufficiently sensitive for detecting mif effects in neoarchean rocks whether or not such samples show mif related 33 s values depends on the age and provenance of the sulfur

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

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

reduced himalayan sediment production 8 myr ago despite an intensified monsoon uplift of the tibetan plateau about 7 8 myr ago1 2 may have been responsible3 5 for the apparent intensification of the asian monsoon 6 10 around that time increases in the oceanic 87sr 86sr ratio during the neogene period have been attributed11 12 to increased erosion from the himalayan orogen it has been suggested that the monsoonal intensification may have enhanced overall erosion rates in the region5 13 if this were the case sediment accumulation rates would have increased in the surrounding basins at this time here we present a reanalysis of stratigraphic data from the indo gangetic foreland and the bengal fan which demonstrates that both of these basins experienced a decline in sediment accumulation rates 8 myr ago thus it seems that monsoonal intensification was accompanied by a decrease in mechanical weathering this decrease could be due to reduced tectonic activity decreased himalayan glaciation or slope stabilization from dense plant cover

age and composition of dikes in southern tibet new constraints on the timing of east west extension and its relationship to postcollisional volcanism controversy exists over whether east west extension in southern tibet is related to plateau uplift or to the accommodation of plate boundary forces relationships between the onset of extension plateau uplift and the thermal state of the lithosphere are critical to this debate we present new data on postcollisional north south trending dikes in southern tibet their ages range from 18 3 2 7 ma to 13 3 0 8 ma and define the onset of regional east west extension in southern tibet dikes are compositionally indistinguishable from postcollisional lavas in southern tibet being either ultrapotassic having a source in the subcontinental lithospheric mantle or calc alkaline with a dominantly crustal origin the ultrapotassic dikes demonstrate that east west extension and subcontinental lithospheric mantle derived magmatism were temporally and spatially linked supporting models that relate the latest phase of plateau uplift to subcontinental lithospheric mantle thinning thus the onset of extension by 18 3 2 7 ma represents the time at which the potential energy of the plateau exceeded convergent boundary forces this places a new age limitation on the attainment of high elevation in southern tibet with implications for models that relate cenozoic monsoon intensification to plateau uplift

recognition of tuffs in the middle upper dingqinghu fm lunpola basin central tibetan plateau constraints on stratigraphic age and implications for paleoclimate abstract the lunpola basin plays a key role in determining the elevation history of the central tibetan plateau which is closely related to uplift dynamics and paleoclimatic evolution however accurate age constraints on the basin stratigraphy reflecting tectonic paleo elevation and climate information have long been vigorously debated mostly due to a lack of absolute age controls here we found two altered tuff layers in the middle upper dingqinghu formation fm in the basin stratigraphic sequence detailed lithological mineralogical and geochemical analyses of the tuffs indicate that they came from trachyandesite and identify analcime as the typical alteration mineral suggesting primary deposition la icp ms zircon u pb dating of the tuffs yields concordant ages of 20 6 0 1 ma and 20 7 0 1 ma indicating that the end of the dingqinghu fm i e the lunpola stratigraphic sequence and the uplift of the plateau to its current high elevations occurred much later than previously estimated the contemporaneous thick black oil shales in the lunpola deep lake and biocoenosis together suggest that the climate was humid and warm during this period

locomotive implication of a pliocene three toed horse skeleton from tibet and its paleo altimetry significance the tibetan plateau is the youngest and highest plateau on earth and its elevation reaches one third of the height of the troposphere with profound dynamic and thermal effects on atmospheric circulation and climate the uplift of the tibetan plateau was an important factor of global climate change during the late cenozoic and strongly influenced the development of the asian monsoon system however there have been heated debates about the history and process of tibetan plateau uplift especially the paleo altimetry in different geological ages here we report a well preserved skeleton of a 4 6 million y old three toed horse hipparion zandaense from the zanda basin southwestern tibet morphological features indicate that h zandaense was a cursorial horse that lived in alpine steppe habitats because this open landscape would be situated above the timberline on the steep southern margin of the tibetan plateau the elevation of the zanda basin at 4 6 ma was estimated to be 4 000 m above sea level using an adjustment to the paleo temperature in the middle pliocene as well as comparison with modern vegetation vertical zones thus we conclude that the southwestern tibetan plateau achieved the present day elevation in the mid pliocene

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

mio pliocene monsoonal record from himalayan foreland basin indian siwalik and its relation to vegetational change carbon and oxygen isotope ratios of soil carbonate nodules and carbon isotope ratio of associated organic matter were measured from three indian siwalik stratigraphic successions in order to reconstruct vegetational history and change in contemporaneous precipitation 13c values of soil carbonates show that from 10 5 to 6 ma the vegetation was c3 type and around 6 ma c4 grasses appeared the 18o variations of soil carbonates suggest that the monsoon system intensified with one probable peak at around 10 5 ma and a clear onset at 6 ma with peak at 5 5 ma after 5 5 ma monsoon strength decreased and attained the modern day condition with minor fluctuations which is supported by marine proxy of upwelling in the arabian sea and sedimentary morphology in siwalik the covariation between 18o and 13c data suggests that a change in precipitation pattern was partly responsible for expansion of c4 grasses in a mixed c3 c4 environment estimation of abundance of c3 and c4 plants using soil carbonate in one case and residual soil organic matter in another may differ this can be explained by assuming that the plant respired co2 is the main contributor of carbon in soil carbonate and may have different isotopic composition from that of the residual organic matter in the soil in addition the abundance estimate of c3 c4 plants also shows variation with time probably caused by change in growing season conditions through time

a methodology for targeting palaeo proxy data acquisition a case study for the terrestrial late miocene when planning the acquisition of new palaeo proxy data for reconstructing past climates many factors influence the decision of where the proxies are to be collected one such influence is the likelihood of recording a significant climate change relative to the modern another consideration which is less often considered is the desire to target regions in which there is significant uncertainty in numerical model predictions of past climate change new proxy data in these regions enables a more rigorous test of model simulations and results in better constraints on the various boundary conditions used to force the models in this paper we present a methodology for targeting new palaeo proxy data based on model simulations we use the terrestrial late miocene 11 6 to 5 3 ma as a case study the late miocene climate provides insights into future climate behavior as it is believed to have been considerably warmer than the modern we carry out a suite of late miocene atmosphere only general circulation model simulations which we initially evaluate relative to an example dataset of terrestrial temperature and precipitation in terms of targeting future data acquisition we locate those regions in the model which exhibit the largest change in temperature and or precipitation relative to the pre industrial we also locate those regions which display the largest variability between the model simulations because new data in these regions are most likely to provide a strict test of the reliability of the model results among other regions the amazon basin the chad basin central canada and northern india are identified as potentially useful areas to collect data

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

erosion history of the tibetan plateau since the last interglacial constraints from the first studies of cosmogenic 10be from tibetan bedrock abstract the cosmogenic 10be exposure histories of in situ bedrock surfaces from the tibetan plateau indicate low erosion rates of

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

stable isotopes reveal southward growth of the himalayan tibetan plateau since the paleocene abstract original stable isotope compositions of carbonates representing conditions in the latest oligocene early miocene kailas and qiabulin areas both in southern tibet record oligocene miocene paleoelevations of the gangdese arc and the himalayan orogen and provide constraints on the formation of the himalayan tibetan plateau oxygen isotope compositions of bivalve shell paleosol and lacustrine carbonates indicate the preservation of unaltered isotopic signals of paleometeoric waters in the kailas and qiabulin areas whereas the oxygen isotopic compositions of liuqu eocene paleosols were likely altered by paleometeoric waters paleoelevation estimates using oxygen isotopes indicate the kailas area was at 4 9 km during 20 19 ma and the qiabulin basin was at 2 0 km during 24 21 ma but rose rapidly to 4 1 km between 21 and 19 ma these results suggest a steep south facing flank on the proto tibetan highland prior to the onset of the india asia collision the himalayan orogen began to be built against the pre existed high 4 5 km gangdese mountains in the early eocene and obtained elevations close to those of the present by the early miocene we propose that the southernmost tibetan plateau and himalayan orogen are the expression of an early eocene to early miocene southward migration of the locus of deformation early stage uplift is linked to the crustal thickening in the early eocene but the dramatic elevation gain in the early miocene may have been caused by indian slab rollback break off and coeval renewed underthrusting behind which late miocene to present east west crustal extension took place

crustal thickening and uplift of the tibetan plateau inferred from receiver function analysis the india eurasia collision crustal thickening and northward convergence leading to uplift of the tibetan plateau have been topics of multidisciplinary studies here we employ the h k stacking technique and depth domain receiver function to constrain the crustal thickness and p and s wave velocity ratio as well as the upper mantle discontinuity our results identify the signature of slab break off and lower crustal delamination in southern tibet which might have induced the mantle upwelling and crustal melting the convergence of the indian plate inducing northward crustal flow might be a major factor that contributes to the uplift and crustal thickening of tibet we also evaluate the e w trending cumulative compression as another dominant factor that contributes to the increase in crustal thickness in the northern tibet 2015 elsevier ltd all rights reserved

geology of the post collisional porphyry copper molybdenum deposit at qulong tibet porphyry deposits are usually thought to form from subduction related calc alkaline magmas in magmatic arc settings although some porphyry deposits also occur in post collisional extensional settings the post collisional deposits remain poorly understood here we describe the igneous geology alteration mineralogy and mineralization history of qulong a newly discovered porphyry cu mo deposit in southern tibet that belongs to the post collisional class the deposit is associated with miocene monzogranite granodiorite intrusions and is hosted partly by jurassic andesitic dacitic volcanic rocks the deposit contains 7 1 mt cu and 0 5 mt mo metal the 19 5 ma granodioritic monzogranitic rongmucuola pluton with diorite enclaves is the earliest miocene intrusive unit it was intruded by a regularly shaped stock p porphyry and then thin dikes x porphyry of monzogranite at about 17 7 ma the main cu mo mineralization is associated with the p porphyry a barren diorite porphyry intruded the p and x porphyries around 15 7 ma petrologic trends of the intrusions suggest that the miocene intrusions have similar origins and probably formed by fractionation of a deeper magma chamber emplacement of miocene porphyries controlled by the qulong anticline is in direct response to the rapid uplift erosion of the gangdese arc batholiths in southern tibet miarolitic cavities and unidirectional solidification textures key evidence for volatile separation have been recognized in the p and x porphyries respectively early potassic alteration characterized by quartz k feldspar anhydrite pervades the p porphyry and rongmucuola pluton laterally this alteration grades into quartz biotite anhydrite k feldspar which affects all miocene intrusions except the latest dioritic porphyry wall rocks of rongmucuola pluton and jurassic andesitic dacitic volcanics within 1 1 5 km of the porphyries are dominated by pervasive potassic alteration an outer halo of propylitic alteration epidote chlorite calcite extends up to 2 km away from the deposit feldspar destructive alteration sericite chlorite clay minerals has overprinted most of the potassic and part of the propylitic alteration the alteration is strongly pervasive in the interior of the porphyry bodies and occurs as vein halos away from the porphyry bodies the earliest quartz k feldspar alteration and veins are barren whereas approximately 60 of the cu reserves is associated with slightly later quartz biotite anhydrite alteration barren assemblages are related to irregular quartz k feldspar anhydrite veins which are truncated by the x porphyry cu sulfide bearing assemblages are associated with discontinuous chalcopyrite biotite and continuous quartz anhydrite chalcopyrite molybdenite veins deposition of cu mo with abundant anhydrite occurred during or between emplacement of closely related porphyries from high temperature magmatically derived fluids and was probably caused by the disproportionation of so

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

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

oligocene miocene 28 13 ma climato tectonic evolution of the northeastern qinghai tibetan plateau evidenced by mineralogical and geochemical records of the xunhua basin abstract changes in sediment composition in the xunhua basin provide insights into the climatic and tectonic evolution of the northeastern qinghai tibetan plateau during the oligocene and miocene here we analyzed the clay mineralogy i e the proportions of smectite illite and chlorite and clay indicators bulk mineral composition i e the amounts of calcite quartz gypsum k feldspar plagioclase dolomite and halite and trace element indicators i e rb sr and ba sr ratios of sediments deposited from 28 to 13 ma in the xunhua basin to reveal the climate and or provenance changes the results suggest that significant changes in sediment provenance occurred at 25 1 ma and 21 6 ma caused respectively by initial uplift and accelerated uplift of the laji shan the xunhua basin experienced warm and humid conditions at 28 0 25 1 ma cool and dry conditions at 25 1 21 6 ma and somewhat warmer and wetter conditions at 21 6 19 2 ma followed by aridification in two steps at 19 2 ma and 13 9 ma the climate cooling event at 25 1 ma corresponds temporally to a major phase of uplift of central tibet relatively warmer and wetter conditions during the early miocene 21 6 19 2 ma are considered to record the influence of the asian summer monsoon and accelerated uplift of the laji shan the shift toward more arid conditions on the northeastern qinghai tibetan plateau at 19 2 13 9 ma was probably driven by uplift of the tibetan plateau and further aridification since 13 9 ma may reflect a weakening of the east asian summer monsoon and global climatic cooling

apatite fission track evidence for miocene denudation history in the gangdese conglomerate belt and yarlung tsangpo river implications for the evolution of southern tibet abstract low temperature thermochronology is used widely in the tibet plateau uplift some researches however have defined the time of rapid denudation as simply rock uplift and have neglected the fact that the rock denudation recorded by fission track ft data was controlled by both surface incision and rock uplift the incision of the yarlung zangbo river had a significant influence on uplift history inversion in southern tibet this paper simulated the bedrock denudation and river incision histories using apatite fission track aft data sampled from the gangdese conglomerate belt which is located in the middle of southern tibet and analyzed the geological meaning of the aft age of each sample the results showed the following 1 in the early miocene 22 16 ma both the value of the denudation rate and the incision rate were high 0 56 mm yr and 0 24 mm yr 2 in the middle late miocene the incision rate 0 12 mm yr was similar to the denudation rate 0 09 0 11 mm yr 3 the historical model between river incision and bedrock denudation revealed a significant difference in the denudation rate during the period ca 8 6 ma combining these data with previously published thermochronological ages and synthesizing these ages with regional geological we arrived at the following conclusions 1 in the early miocene the denudation event probably was caused by a combined result of indian plate rollback and the incision of the yarlung zangbo river 2 in the middle late miocene the denudation rate was consistent with the incision rate which suggested that the denudation episode was caused by climate change associated with asian monsoon intensification 3 after 8 ma the stable and slow incision rate indicated that regional drastic uplift had ceased the paleo elevation of the research area had approached and even exceeded the present day elevation in the late miocene

geochemistry and isotopic study of southern bay of bengal sediments implications for provenance and paleoenvironment during the middle miocene abstract the bay of bengal bob the largest bay in the world is known to receive large amounts of fresh water and suspended particulate matter from different sources the sediments deposited in the bay serve as a repository for paleoenviromental reconstruction studies the miocene epoch is an important interval in geologic time as it is marked by major climatic events that controlled ocean productivity redox conditions and provenance of sediments however limited work has been carried out to establish paleoenviromental changes and provenance of sediments during the miocene here we present detailed geochemical and radiogenic sr nd isotopic results from predominantly middle miocene sediments of ocean drilling program odp site 758a located in the southern bob lat 5 23 n long 90 21 e water depth 2925 m to understand paleoredox conditions paleoproductivity and provenance the results suggest that these sediments are strongly linked to climatically modulated surface processes that affected the region the distribution of redox sensitive element proxies u v cr at interval 17 8 ma points to an oxic depositional environment the major trace and rare earth elements distribution supports prevalence of the indian summer monsoon ism at 12 10 ma productivity proxies babio porg show a decreasing trend during colder events east antarctic ice sheet expansion eais and advent of late miocene cooling lmc events the trace and rare earth element concentrations are generally low except at intervals where glass shards were found the 87sr 86sr and end 0 values indicate that the sediments belong to the high himalayan sedimentary series hhss throughout the middle miocene however prior to initiation of the ism these sediments underwent meteoric alteration in the lowlands before deposition in the bob our records suggest that sediments at odp site 758a may have been introduced into the bob through the irrawaddy yarlung tsangpo drainage system during the entire period of this study the irrawaddy yarlung tsangpo system drained the indus tsangpo suture zone southern tibet the eastern himalayas and the arakan coast before debouching in the bob

synchronous deformation on orogenic plateau margins insights from the arabia eurasia collision abstract the temporal and spatial distribution of deformation during the early phases of plateau formation is poorly known the iranian plateau is developing in response to arabia eurasia convergence and is a potential analog to the early phases of tibetan plateau deformation previous studies document the onset of the iranian plateau growth based on the kinematic history of the zagros to the south and the alborz mountains to the north here we present new detrital apatite fission track aft data from 13 modern rivers of the talesh mountains northwestern iranian plateau these mountains lie immediately south west of the rigid south caspian block a total of 1233 single grain cooling ages were measured and range between 185 and 4 ma deconvolution of grain age data documents three main phases of exhumation including the oligocene 30 23 ma early to middle miocene 18 12 ma and early pliocene 5 ma comparison between cooling ages from the talesh mountains and elsewhere across the iranian plateau indicates widespread plateau formation in the oligocene earlier than previously suggested for the northwestern plateau margin these results highlight deformation on both the northern and southern margins of the plateau over almost the entire history of iranian plateau formation a similar pattern of synchronous deformation on the north northeastern and southern margins of the tibetan plateau has recently been documented and highlights the significance of rigid basement blocks focusing far field deformation for both plateaus

influence of paleorelief on the mid miocene climate variation in southeastern washington northeastern oregon and western idaho usa abstract terrestrial climate proxy records repeatedly show spatial heterogeneity because regional climate condition is largely influenced by the relationship between large scale atmospheric circulation patterns and regional topographic features the paleosols developed on the top of columbia river basalt flows emplaced between 15 3 and 15 8 ma in the northwestern united states show significant spatial variations in the mid miocene soil forming processes the paleosol in the northwestern part of the study area has the least degree of chemical weathering fine scale and very shallow penetrating depth of root traces with the estimated paleoprecipitation and paleotemperature of about 550 mm and 16 c respectively the paleosols in the southeastern part of the study area indicate more intense chemical weathering with the estimated paleoprecipitation and paleotemperature of approximately 1400 to 1500 mm and 17 c respectively the spatial variations in paleo pedogenesis were predominantly affected by spatial heterogeneity in the mid miocene regional climate and regional paleotopographic features taking the other ancient soil forming factors including time parent rock materials and biological activities into account we suggest that intrusions of hot columbia river basalt magma into the crust were responsible for the regional surface uplift and the paleoclimate heterogeneity because the major vent systems of the columbia river basalt eruptions were located in the area where development of the mid miocene high topography existed within the blue mountains paleotopography of the earth s surface can be reconstructed by the paleoprecipitation and paleotemperature estimations from several spatially distributed chrono stratigraphic paleosols although it is difficult to estimate the magnitude of the paleorelief precisely

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

palaeoclimatic estimates for a latest miocene pliocene flora from the siwalik group of bhutan evidence for the development of the south asian monsoon in the eastern himalaya fossil leaf floras from the latest miocene pliocene siwalik group exposed in bhutan sub himalaya are subjected to a clamp climate leaf analysis multivariate program analysis using a high resolution gridded climate calibration the clamp analysis of 27 different morphotypes of fossil leaves indicates a mean annual temperature mat of 24 1 c 2 8 c a cold month mean temperature cmmt of 18 9 c 4 c and a warm month mean temperature wmmt of 27 8 c 3 3 c the analysis also suggests a weak monsoonal climate the monsoon index msi 46 7 present msi 52 with growing season precipitation gsp of 1819 916 mm present gsp 2490 mm here we also compare palaeoclimate estimates of the latest miocene pliocene siwalik group flora from bhutan c 6 to 3 8 ma with those of previously investigated siwalik group floras from the miocene pleistocene of arunachal india and miocene siwalik floras of darjeeling india which characterise the monsoon signature at the time of deposition since all the siwalik floras of the eastern himalaya darjeeling and arunachal pradesh spanning the mid miocene to pleistocene yield almost the same values we suggest that overall the eastern himalayan siwalik climate appears to have been remarkably uniform over the past 15 million years the mat result of the bhutan siwalik flora differs by just 0 6 c from arunachal and 1 2 c from darjeeling siwalik floras for all siwalik fossil assemblages wmmts cmmts and lgss length of the growing season are similar and consistent wmmts around 28 c cmmts around 18 c and lgss around 12 months similarly the mean annual relative humidity rh and specific humidity sh appear to have been uniformly around 80 and 14 g kg respectively throughout the neogene of the eastern himalayan siwaliks changes in the monsoon index suggest that in both bhutan and arunachal sub himalaya there has been little change in the intensity of the monsoon since mid miocene time while further west in the darjeeling area precipitation seasonality has increased since the mid miocene

miocene woods from the qaidam basin on northern qinghai tibet plateau with implications for paleoenvironmental change abstract the qaidam basin with the most complete cenozoic sedimentary preservation in northern qinghai tibet plateau is a key area for studying uplift and environmental change of the plateau three types of woods ulmus ulmaceae leguminosae angiosperm and cupressaceae gymnosperm were recognized from the large scale preservation of fossil woods in late miocene shang youshashan formation in northern qaidam basin on the qinghai tibet plateau both investigations of their nearest living relatives nlrs and previous grassland mammal evidences suggest that there have been temperate deciduous broad leaved forest and needle leaved forest with grass in northern qaidam basin during the late miocene in contrast to the desert vegetation found there nowadays the presence of the ancient forest steppe further implies that the southern part of the plateau used to be adequately low so that the indian and east asian monsoons could approach the northern area and to accommodate the vegetation in late miocene

the late cretaceous continental interior of siberia a challenge for climate models geological evidence from the late cretaceous continental interior of the vilui basin siberia suggests a far wetter warmer and more equable annual climate than general circulation models gcms can reproduce the disparity cannot be bridged by the uncertainties inherent in either the models or the geological climate proxies this implies the mismatch is genuine and that either 1 we have systematic errors in the interpretation calibration of the climate proxies and or 2 lack of full knowledge of the boundary conditions needed for gcm models simulations of this period and or 3 an insufficient understanding of the nature of the coupled atmosphere ocean biosphere system and its representation within climate models during warm climate epochs if it is the third explanation this would have important implications for the prediction of future climates and would suggest that we may currently be underestimating future climate change in such regions

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

middle miocene pedological record of monsoonal climate from nw himalaya jammu kashmir state india abstract the lower siwalik subgroup represented by the dodenal kamlial formation and ramnagar members chinji formation is well exposed at ramnagar district udhampur jammu kashmir state the ramnagar member consists of an alternating sequence of silt and mudstone formed under crevasse splay and flood plain environments of deposition argillisol and gleysol soils are developed on the ramnagar member deposits argillisols formed under well drained conditions at high levels whereas gleysols formed under poorly drained conditions at low levels of the palaeo landscape geochemical and micromorphological studies of the ramnagar member palaeosols suggest formation under wet and humid climatic conditions early uplift of the tibetan plateau himalaya resulted in a contemporaneous change in precipitation and monsoonal climate conditions within the indian region beginning in middle miocene

kinematics of the crust around the ama drime massif southern tibet constraints from paleomagnetic results abstract secondary magnetic remanences are used to study late orogenic rotation and tilting on a e w transect in southern tibet at 28 5 n sampling was performed on both sides of the ama drime massif adm remanent magnetization resides in pyrrhotite formed during metamorphism and is related to the last cooling event through 325 c curie temperature of pyrrhotite the existence of antipodal ptrms demonstrates that the chrm is of thermoremanent origin and was acquired during cooling of the tethyan metasediments penetrative deformation was still going on in ronghbuk area until ca 250 c whereas it was already completed in dinggye area significant departures from the expected field direction during the age of remanence acquisition cannot be interpreted by consistent vertical axis rotation of blocks antagonist deviations on both sides of the adm are explained as tiltings around an horizontal axis striking n20 these tiltings are estimated to be younger than 13 12 ma and they are related to the adm exhumation initiated since 33 ma

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

low elevation of the northern lhasa terrane in the eocene implications for relief development in south tibet the uplift history of tibet is crucial for understanding the geodynamic and palaeoclimatologic evolution of asia however the pattern of plateau uplift through space and time remains unresolved we use stable isotope data from palaeosol carbonates to reconstruct the eocene 46 ma elevation of the tangra yum co region northern lhasa terrane the difference between the oxygen isotopic compositions of the studied palaeosols and eocene surface water near the source of the indian monsoon indicates a palaeoelevation of 2590 730 910 m for tangra yum co present altitude 4600 m a similar palaeoaltitude is obtained by comparing our data with modern soils and taking past environmental changes into account combining our results with published palaeoelevation estimates for tibet suggests significant relief 2 km during the eocene when a low lying basin in the northern lhasa terrane was bounded by the qiangtang and gangdese mountain belts to the north and south respectively

well constrained seismic estimation of pore pressure with uncertainty the safe drilling of wells for hydrocarbon exploration or production requires that the wellbore pressure be maintained between the formation pore pressure and the maximum pressure the formation can withstand without fracturing this task is made more difficult when drilling in overpressured areas which require a quantitative predrill prediction of pore pressure with uncertainty to be made a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated by offset well data however the uncertainty in velocity is often not quantified this example from the gulf of mexico uses seismic velocities with uncertainty derived by combining seismic velocities with well data den boer et al 2006 parameters in the velocity to pore pressure transform are estimated using seismic velocities density logs pressure information and well velocities derived by inverting time depth pairs from check shots in the area pore pressure and associated uncer

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

geochemical evaluation of fenghuoshan group lacustrine carbonates north central tibet implications for the paleoaltimetry of the eocene tibetan plateau abstract a sedimentologic petrologic and geochemical evaluation of lacustrine carbonates from the eocene oligocene fenghuoshan group of north central tibet provides insight into the paleoenvironmental and paleolimnological setting of the hoh xil basin during the mid tertiary fenghuoshan lacustrine rocks consist primarily of carbonate mudstones and wackestones these carbonates are generally less than 3 m in thickness and are intercalated with siliciclastic lacustrine and fluvial alluvial plain deposits individual limestone beds coarsen and contain increasing amounts of siliciclastic material upward fenghuoshan carbonates also contain abundant ostracode bivalve and charaphyte fossils sedimentologic evidence suggests that carbonate deposition occurred in shallow relatively short lived lacustrine systems that were subsequently filled by alluvial deposits of coeval fluvial systems stable c and o isotopic analysis of fenghuoshan carbonates show 18o values ranging from 11 7 to 10 3 vienna pee de

activation of the nyainqentanghla shear zone implications for uplift of the southern tibetan plateau neogene extension of the tibetan plateau is manifested as a series of north south trending graben the most prominent of which is the yadong gulu rift the nyainqen tanghla shan a ne sw trending mountain range 100 km nw of lhasa bounds the western margin of the yangbajian graben the central segment of the yadong gulu rift the eastern edge of the nyainqentanghla massif is marked by a low angle 25 o detachment fault shear zone of amphibolite grade mylonites the noar 3 ar thermal history results from samples collected along two deeply incised valleys within the massif reveal that a rapid cooling event propagated from 8 ma in the core of the range to 4 ma within the high strain zone at the eastern boundary assuming that faulting initiated at high angle 60o thermal histories were fit to a numerical simulation of slip on a normal fault to yield estimates of both the age of fault initiation and the slip rate history the form of the isotopically derived thermal histories are similar to general form predicted by the thermal model and suggests that significant movement began at 8 1 ma in the southern valley goring la and proceeded at an average slip rate of 3 mm yr between 8 and 3 ma a more complex history is required to fit the data from the northern valley balum chun but the timing of initiation and average slip rate are similar to the goring la result numerical simulations in which the fault angle is varied indicate that the isotopically derived temperature histories are inconsistent with slip occurring at low angle 40o because the extension direction of the yangbajian graben is representative of most rifts on the southern tibetan plateau our data suggest that crustal thickness and elevation reached close to their present values by 8 1 ma a carbon isotopic shift in pedogenic carbonates from the siwalik formation at about 7 5 ma appears to reflect intensification of the asian monsoon and by inference that the plateau had attained an important threshold elevation by that time formation of a diffuse plate boundary in the indian oceanic lithosphere beginning at 7 5 8 0 ma is also consistent with this history we suggest that the plateau had attained a threshold area and elevation by 8 1 ma sufficient to trigger these three independent manifestations

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

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

impact of the middle miocene climate transition on elongate cylindrical foraminifera in the subtropical pacific fifty eight species of elongate cylindrical benthic foraminifera here referred to as the extinction group belonging to genera that became extinct during the mid pleistocene climate transition mpt were documented similar to 50 kyr resolution through the early middle miocene 15 13 ma in two sites on opposite sides of the subtropical pacific ocean odp sites 1146 south china sea odp site 1237 southeast pacific the study was undertaken to investigate the response of the extinction group ext gp to the major cooling during the middle miocene climate transition mct to look for clues that might explain the causes of the extinction during the glacials of the mid pleistocene climate transition ext gp faunal differences between the two sites attributed to regional and bathymetric differences in food supply to the seafloor are greater than those that occurred through the 2 myr time span at either site the middle miocene climate transition was not an interval of enhanced species turnover or a decline in ext gp abundance in contrast to the major extinctions that occurred during the mid pleistocene climate transition distinct changes in the composition of the ext gp faunas did occur through this time more pronounced in site 1237 at both sites the pre middle miocene climate transition faunas were transformed into their post middle miocene climate transition composition during the period of major cooling 14 0 13 7 ma during this transition interval the faunal composition swung back and forth between the two end member faunas these faunal changes are attributed to changes in productivity decrease in south china sea increase in southeast pacific brought about by major changes in global climate and continental aridity c 2010 elsevier b v all rights reserved

sensitivity of climate to late cenozoic uplift in southern asia and the american west numerical experiments experiments with general circulation models with no mountains half mountains and full modern mountains show the sensitivity of atmospheric circulation patterns to progressive amounts of uplift the experiments were motivated by geologic evidence for large kilometer scale uplift in the late cenozoic in southern asia and the american west particularly within the last 10 m y in january the amplitude of the mid latitude upper tropospheric planetary waves increased with uplift and the low level winds were progressively blocked or diverted around the topographic features in july the progressive uplift caused monsoonlike circulations to develop in the vicinity of the colorado and tibetan plateaus atmospheric heating rates midtroposphere vertical motion and upper tropospheric planetary wave amplitudes varied approximately linearly with progressive uplift these results suggest that geologically recent kilometer scale uplift may have had climatic consequences comparable in magnitude and pattern to those of earlier stages of uplift comparison of the simulated climatic effects of uplift with the geologic evidence for late cenozoic climatic change especially for the last 10 m y is given in accompanying papers

palaeomonsoon variability in the southern fringe of the badain jaran desert china since 130 ka bp taking the chagelebulu stratigraphic profile as a typical example a comprehensive study has been conducted to elucidate the palaeoclimatic and geomorphic evolution patterns in the southern fringe of lie badain jaran desert which were found to be complex and polycyclic in the past 130 ka however the fluctuating magnitude is not as remarkable as that in the eastern china sandy region the shift in climate from interglacial to glacial and the uplift process of the qinghai xizang plateau are the two leading forces driving the evolution of the climate and desert landforms in this area seventeen cycles of cold dry and warm humid climatic stages were recognized in the upper pleistocene series of the profile the sharp uplift of the qinghai xizang plateau superimposed a cool and arid climatic trend in this area as a result of the climatic changes the desert in this area has undergone multiple stages of expansion and contraction since 130 ka bp the middle holocene epoch and the early stage of the late pleistocene period were the main periods when the sand dunes became stabilized and the early and late phases of the holocene epoch and late phase of the pleistocene epoch were the main periods when the previously stabilized sand dunes became mobile the late phase of the pleistocene epoch was the most mobile stage when the aeolian sand activities formed the essential geomorphic pattern if the badain jaran desert copyright c 2005 john wiley sons ltd

the elevation history of the tibetan plateau and its implications for the asian monsoon abstract the determination of the evolving palaeoaltitude of the tibetan plateau since the india eurasia collision underpins our understanding of how orography in central asia affects the intensity of the monsoon and hence global climate change palaeoaltitudes however cannot be measured directly and need to be inferred from proxy observations that are usually model dependent differing tectonic models for the behaviour of the lithosphere during continental collision have contrasting implications for the elevation of the plateau however two techniques recently employed for determining palaeo elevation are independent of tectonic models the first involving the variation with altitude of oxygen isotopes in precipitation and the second involving the change of leaf morphology with moist static energy of the atmosphere elevation studies have focused on southern tibet largely due to the relative ease of access to the region there is a remarkable unanimity amongst the diverse techniques applied that the altitude of the southern plateau has not significantly changed since at least the mid miocene ca 15 ma arguing for an onset of the monsoon system during or before the early miocene a range of tectonic studies suggest that the northern and eastern parts of the plateau are younger geomorphological features but there are few quantitative constraints of the timing of elevation from these regions of tibet since both the elevation and the surface area of the plateau impact on atmospheric circulation palaeoaltitude studies need to be extended to chart the increasing areas of elevated land surface through time

vast early miocene lakes of the central tibetan plateau lacustrine strata of the wudaoliang group demonstrate that two vast lake complexes covered the central tibetan plateau during early miocene time the wudaoliang group which is characterized by dolostone limestone and marl as thick as 310 350 m lies horizontally or with a slight dip above oligocene reddish brown sandstone and is covered by upper miocene and pliocene mudstone and sandstone the extensive distribution of this group outlines interconnected lake basins of 5000 15 000 km 2 or larger in the north central tibetan plateau such as the wudaoliang beiluhe tuotuohe tongtianhe and east wenquan basins and lake basins 2000 km 2 or larger in the south central plateau such as the ando naqu bangoin lunpola and shuanghu basins these lake basins separated by mountain ranges and islands were linked by water passages in early miocene time when they apparently formed a huge lake complex that covered as much as 100 000 km 2 in the north central tibetan plateau and another one 50 000 km 2 in the south central part of the plateau such immense lakes existed for several million years between ca 23 5 and ca 13 5 ma after the tibetan plateau rose and their interconnected basins define the topography during early miocene time the fossils contained in these basins indicate a change from the warm dry climate of the oligocene to moderately cool and wet conditions at the beginning of the early miocene followed by progressive cooling and drying which suggests continuous uplift during deposition of the wudaoliang group

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

productivity and continental denudation history from the south china sea since the late miocene late miocene recent micropaleontological and geochemical records from ocean drilling program odp site 1143 in the southern south china sea scs indicate that increase and decrease in abundance of siliceous plankton may be controlled mainly by the input of nutrients derived from land and provided by upwelling a high export production event a biogenic bloom event occurred in the southern scs between 12 and 6 ma during this period high ratios of smectite illite chlorite smectite quartz and al k indicate a high weathering intensity of the asian continent possibly due to the intensification of the east asian summer monsoon easm which may have increased the net flux of nutrients to the ocean both directly through terrestrial input and indirectly through upwelling activity a drop in ba ti al ti and ca ti values around 6 ma may indicate a lowering of productivity possibly due to the large consumption of sea surface nutrients by the biogenic bloom alternatively it may indicate a shift in terrigenous input source area at about 5 4 ma a decrease in weathering intensity as indicated by a sudden decrease in the values of smectite illite chlorite smectite quartz and al k might have led to a sudden decrease of terrestrial nutrient input to the scs we suggest that the biogenic bloom ended when nutrients in surface waters were exhausted because of a decrease in supply as well as a decrease in upwelling intensity due to weakening of the easm as a result radiolarians were absent in the studied area between similar to 6 and 3 2 ma at similar to 3 2 ma radiolarians began to recover possibly because the start of northern hemispheric glaciation and the rapid uplift of the tibet plateau led to intensification of the east asian monsoon after the mid pleistocene climate transition at 0 9 ma the abundance and mass accumulation rates of radiolarians increased probably as a result of increased upwelling activity driven by the increasing intensity of the summer monsoon crown copyright c 2009 published by elsevier b v all rights reserved

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

sedimentology sedimentary petrology and paleoecology of the monsoon driven fluvio lacustrine zhada basin sw tibet abstract in this paper we present sedimentologic petrographic and paleoecologic data from a 810 m thick section of late neogene ca 9 7 to 1 ma fluvio lacustrine deposits in the high elevation zhada basin of sw tibet the tectonic evolution of the zhada basin region located between the himalayan mountains in the s and the transhimalayan mountains in the n is poorly understood but sediment accumulation was probably initiated in response to the middle late miocene uplift of the gurla mandhata and leo pargil domes in the e and w respectively the sedimentary record can be subdivided into five stratigraphic units with distinctly different lithofacies associations la these are from bottom to top a bedload dominated fluvial la unit 1 0 90 m a nearshore lacustrine deltaic la unit 2 90 220 m an offshore lacustrine la unit 3 220 500 m a nearshore lacustrine fan delta la unit 4 500 600 m and a fan delta alluvial fan la unit 5 600 810 m clast and heavy mineral compositions revealed sediment supply from two different provenance areas one from the south and one from the north east based on catchment geology of the himalaya and transhimalaya ostracode faunal assemblages are largely comparable to those of modern tibetan lakes and allow the reconstruction of paleo lake environments including lake level changes and salinity the sedimentary pattern shows strong cyclicity at various scales m 10 s m and 100 m small scale cycles are interpreted as intrinsically controlled depositional processes of deltas lobe switching whereas medium and large scale cycles are most likely forced by climate fluctuations the overall evolution of the sedimentologic record includes a strong and rapid increase in fluvial discharge in the uppermost portion of unit 1 a transition from fluvial to lacustrine deposition during deposition of unit 2 rhythmic variations in the style of lacustrine sedimentation during deposition of unit 3 an increase in the supply of coarse clastics starting with deposition of unit 4 and a transition from lacustrine to alluvial sedimentation during deposition of unit 5 we speculate that the increase in discharge and presumably precipitation leading to the establishment of lacustrine conditions in the lower part of the section unit 2 is largely due to regional summer monsoon intensification during the late miocene and that the transition from lacustrine to alluvial sedimentation in the uppper part of the section reflects the onset of northern hemisphere glaciation and winter monsoon strengthening at 2 6 ma

increasing nd isotopic ratio of asian dust indicates progressive uplift of the north tibetan plateau since the middle miocene the time and rate of tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change models predict that the uplift of the north tibetan plateau ntp occurred later than uplift of the south and central tibetan plateau uplift of the ntp is believed to have initiated the aridity in the interior of asia and to have critically affected the evolution of asian monsoon and ultimately global climate the history of ntp uplift has remained uncertain however scenarios range from early miocene to the past million years this work provides new evidence by relating the nd isotopic evolution of asian dust to ntp uplift the sources of the asian dust are located in the arid lands between the ntp and the central asia orogen mass balance calculations indicate that the decreasing e nd values from 8 2 to 10 4 for pacific dust since 15 ma reflects increasing relative contribution of ntp materials 40 to 70 to the dust source as paleoelevation in the central asia orogen has largely remained constant the increasing relative ntp detritus contribution is interpreted to reflect the progressive surface uplift of the ntp at a rate of at least 0 12 mm yr 1 since 15 ma

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

climate impact of high northern vegetation late miocene and present the late miocene belongs to the late phase of the cenozoic climate at that time was still warmer and more humid as compared to today especially in the high latitudes corresponding to the climate situation palaeobotanical evidences support that vegetation in the high northern latitudes changed significantly from the late miocene until today to quantify the climate impact of this vegetation change we analyse how vegetation in the high northern latitudes contribute to climate evolution for that we perform climate modelling sensitivity experiments for the present and for the late miocene tortonian 11 7 ma for our present day sensitivity experiment we introduce the tortonian vegetation in the high northern latitudes for our tortonian sensitivity experiment we introduce the modern vegetation on the same grid cells in the tortonian and in the present the modern vegetation leads to a strong cooling of the northern extratropics up to 4 c nevertheless the meridional heat transports remain nearly unchanged in both cases in general the vegetation impact on climate is similar in the tortonian and in the present however some exceptions occur due to the tethys ocean in the tortonian temperatures decline only weakly in eastern europe and western asia in the tortonian climate temperatures on the sahara realm rise up to 1 5 c while the temperatures do not change remarkably in the present day climate this different behaviour is caused by a stronger and more sensitive hydrological cycle on the sahara region during the tortonian

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing