effect of aridification on carbon isotopic variation and ecologic evolution at 5 3 ma in the asian interior article history the cenozoic era is marked by dramatic climatic and ecological changes the timing of the emergence and the subsequent expansions of c4 grasses are prominent biological events on earth in china thick cenozoic deposits in the tarim and junggar basins which are located in the asian interior provide important geological archives for studying paleoenvironmental changes here we use carbon isotope compositions of organic matter to reconstruct the history of ecologic evolution during the late cenozoic in the tarim and junggar basins the results show that there is a shift to slightly higher 13 cv alues at 5 3 ma indicating a change in terrestrial ecosystems in the asian interior driven by an increased regional aridity rather than decreasing atmospheric pco2 levels the weakened water vapor transportation related to the retreat of paratethys ocean and the enhanced rain shadow effect of mountain uplift during the

late oligocene early miocene birth of the taklimakan desert as the world s second largest sand sea and one of the most important dust sources to the global aerosol system the formation of the taklimakan desert marks a major environmental event in central asia during the cenozoic determining when and how the desert formed holds the key to better understanding the tectonic climatic linkage in this critical region however the age of the taklimakan remains controversial with the dominant view being from 3 4 ma to 7 ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert in this study we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy we constrained the initial desertification to be late oligocene to early miocene between 26 7 ma and 22 6 ma we suggest that the taklimakan desert was formed as a response to a combination of widespread regional aridification and increased erosion in the surrounding mountain fronts both of which are closely linked to the tectonic uplift of the tibetan pamir plateau and tian shan which had reached a climatically sensitive threshold at this time

late miocene stepwise aridification in the asian interior and the interplay between tectonics and climate abstract the mid latitudinal central asian continent is characterized by large sand deserts and gobi stony desert in this context it is of interest to study the timing and forcing mechanisms of aridification in the region here we present multiple geochemical climatic proxies from late cenozoic strata in the tarim basin of northwestern china a region sensitive to climatic change the results yield long term climatic records covering a time interval of 13 3 to 2 5 ma we find that a general trend towards a dry climate was superimposed by two stepwise aridification events the first lesser aridity phase occurred at 7 5 3 ma and the second extreme aridity episode was initiated at 5 3 ma based on the correlation between climatic change and regional tectonic events we propose a mechanism to explain the climatic variations the general long term drying trend since the mid miocene was a response to global climatic cooling while the stepwise aridification since the latest miocene was controlled mainly by regional tectonic uplift

effects of lateral viscosity variations on postglacial rebound implications for recent sea level trends global sea level changes have been occurring since the last pleistocene deglaciation recently the contribution of current postglacial rebound to local sea level variations has been removed by means of a radially stratified earth model in order to assess the amount of sea level rise due to recent climatic changes the authors have studied the effects of lateral variations in the viscosity structure on the postglacial uplift rates along the continental margins finite element calculations in cylindrical geometry show that the spread in the cumulative vertical displacement may be affected by 20 in the presence of lateral rheological contrasts but the vertical rates of deformation can attain differences of up to 50 for the different models horizontal deformation rates along continental margins are much more affected by the lateral variations in viscosity and can be used in the future as constraints on mantle rheology

unusual radar echoes from the greenland ice sheet airborne radar images of part of the greenland ice sheet reveal icy terrain whose radar properties are unique among radar studied terrestrial surfaces but resemble those of jupiter s icy galilean satellites the 5 6 and 24 centimeter wavelength echoes from the greenland percolation zone like the 3 5 and 13 centimeter wavelength echoes from the icy satellites are extremely intense and have anomalous circular and linear polarization ratios however the detailed subsurface configurations of the galilean satellite regoliths where heterogeneities are the product of prolonged meteoroid bombardment are unlikely to resemble that within the greenland percolation zone where heterogeneities are the product of seasonal melting and refreezing

miocene volcaniclastic sequence within the xiyu formation from source to sink implications for drainage development and tectonic evolution in eastern pamir nw tibetan plateau

the sir c x sar synthetic aperture radar system the spaceborne imaging radar c x band synthetic aperture radar sir c x sar was a joint united states german italian space agency imaging radar system successfully flown aboard the shuttle endeavor in april 1994 and again in september october 1994 the multifaceted sir c x sar represents a major technological step forward in radar remote sensing and is the first spaceborne multifrequency polarimetric sar the united states developed sir c operated at l and c band each with quad polarization the sir c antenna was an active phased array with the capability for electronic beam steering and multiple swath width illumination the german italian x sar operated at x band with a single polarization using a slotted waveguide antenna mechanically steerable in elevation sir c and x sar were designed to operate synchronously collecting data over common sites synchronously a total of 143 hours 93 terabits of sar data were recorded on tape

retrieving snowpack properties and accumulation estimates from a combination of sar and scatterometer measurements this study combines two satellite radar techniques low resolution c ku band scatterometer and high resolution c band synthetic aperture radar sar for glaciological studies in particular mass balance estimations three parameters expressing the mean backscattering and its dependency on azimuth and incidence angle are used to describe and classify the antarctic ice sheets backscattering behavior simple linear regression analyses are carried out between ground truth accumulation data and the sar backscattering coefficient along continuous profile lines from this we parameterize the accumulation rate separately for certain snow pack regimes we find that sar data can be used to map mass balance changes however only within limited areas applying this method therefore generally requires accurate ground truth for regional calibration together with additional information regarding mean air temperature or elevation this investigation focuses on the area of dronning maud land antarctica we present the first high resolution accumulation map based on sar data for the surrounding area of the epica deep ice core drilling site kohnen which is compared to reliable ground truth records as well as to a surface mass balance map interpolated from these at low resolution

new insights into the magnetic variations of aeolian sands in the tarim basin and its paleoclimatic implications abstract the tarim basin where aeolian activity is widespread has been regarded as a major source for global dust production therefore knowledge about variation of magnetic parameters in aeolian sands from the tarim basin has a global significance systematic rock magnetic studies of aeolian sands from this region are still scarce because of the vast area and poor accessibility of the basin in this paper multi parameter rock magnetic investigations of a larger number of aeolian sand samples from a wide area in the tarim basin have been conducted we find that magnetic properties of aeolian sands are controlled by changes in the concentration of larger pseudo single domain and multidomain magnetite grains which are produced by weathering and erosional processes in the surrounding mountain regions in addition aeolian sands collected from different geographic regions of the tarim basin exhibit different magnetic properties suggesting that selective wind and river transport and low temperature oxidation might play a critical role for the magnetic properties of aeolian sands in the tarim basin our study also provides a better understanding of the complex relationships between magnetic properties and source materials for pliocene deposits in the basin

mountain building and earth rotation summary whereas the present day true polar wander and the secular non tidal acceleration of the earth have usually been attributed to postglacial rebound it has recently been suggested that non glacially induced vertical tectonic movements taking place under non isostatic conditions can also be effective in changing the earth s rotation we present a case study in which we analyse the effects of some simple uplift histories of the himalayas and the tibetan plateau on the rotational axis and on the second degree zonal harmonic of the geoid for time scales of up to a few million years we first assume a permanent amount of overcompensation which is consistent with observed geoid anomalies over the himalayas and then we model by means of the normal mode techniques the viscous relaxation in the mantle with the elastic lithosphere supporting elastically 2 per cent of isostatic disequilibrium in our normal mode analysis the earth is divided into five layers an effectively elastic lithosphere a viscoelastic shallow upper mantle transition zone and lower mantle characterized by the maxwell rheology and an inviscid core the readjustment of the equatorial bulge due to viscous flow in the mantle is taken into account in our studies by solving the linearized liouville equations for the conservation of angular momentum via the love numbers formalism polar wander is sensitive to the rate of relaxation of the modes m1 and m2 due to the discontinuities between the three mantle layers positioned at 420 and 670 kilometres depth the rate of readjustment is sensitive to the viscosity of the transition zone whenever the lower mantle shallow upper mantle viscosity ratio is small the highest present day velocity of polar wander due to himalayan and tibetan plateau uplift is estimated to be 1 myr 1 for an isoviscous mantle that has the same magnitude of the observed value reduced to 0 1 myr 1 for a factor 50 viscosity increase in the lower mantle these numbers are about the same as those found from postglacial rebound that occurs on the short time scale of a thousand years instead of the million years of our analysis but represent upper bounds for mountain building obtained only in the case in which a permanent deviation from isostasy of at least 2 per cent is assumed in general the proposed mechanism is less efficient in driving long term rotation instabilities than deep seated processes characterized by the same time scale of a million years such as subduction polar wander velocity is extremely sensitive to the depth of the uncompensated anomalous root of the topography for the models in which full mantle relaxation is allowed

cenozoic crustal shortening between the pamir and tien shan and a reconstruction of the pamir tien shan transition zone for the cretaceous and palaeogene the magnitude of the late cenozoic crustal shortening during convergence of the pamir and tien shan was determined using a contemporary pattern consisting of facies zones palaeomagnetic data regarding the rotation of tectonic units and data on the structure of the tadjik depression by late cenozoic cretaceous and palaeogene facies zones were cut by the vakhsh trans alay overthrust and darvaz strike slip faults and a significant part of the cretaceous palaeogene tadjik basin was overthrust by the pamir massif the sediments of easternmost part of the basin are preserved in the tarim depression the facies zones of the southern slope of the afghan tadjik basin were deformed and moved northward a pattern of facies zones indicates a convergence between the pamir and tien shan over a distance of 300 400 km a number of cross sections through the tadjik depression were used to establish the structure before folding a rotation of tectonic units indicated by structural data conforms to the angles of rotation as determined in palaeomagnetic studies the data suggest 300 km of convergence between the pamir and tien shan stratigraphic lithological structural and palaeomagnetic data formed the basis for the construction of the palinspastically restored palaeogeographic and sedimentologic environments for the tadjik shallow sea basin which was situated between the pamir and tien shan before their convergence in the late cenozoic the maps were constructed for the eight stratigraphic levels of the cretaceous and palaeogene the tadjik sea was a bay in the enormous turan sea in the early aptian this bay was located in what is now the afghan tadjik basin in late cretaceous the eastern shore of the bay lay 600 700 km further eastward and in the eocene marine environments extended even further eastward but after the rupelian continental environments occupied all of this region 2000 elsevier science b v all rights reserved

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

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

late neogene loess deposition in southern tarim basin tectonic and palaeoenvironmental implications abstract uplift of the tibetan plateau during the late cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the kunlun and altyn mountains in the southern tarim basin early neogene sediments are characterised by sandstone siltstone and red mudstone representing floodplain to distal alluvial fan environments the early pliocene artux formation consists of medium grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone the late pliocene to early pleistocene xiyu formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits sedimentological investigation together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the xiyu and artux formations point to an aeolian origin suggesting desertic conditions in the tarim basin by the early pliocene the onset of aeolian sedimentation in the southern tarim basin coincided with uplift of the northern tibetan plateau inferred from the lithofacies change from fine grained mudstone and sandstone to coarse clasts tibetan plateau uplift resulted in the shift of sedimentary environments northwards into the southern tarim basin and could well have triggered the onset of full aridity in the taklimakan region as a whole

estimation of glacier ice extinction using long wavelength airborne pol insar in the recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research this paper describes the estimation of ice extinctions through the modeling of polarimetric interferometric sar pol insar coherences as a combination of a surface contribution from the snow firn interface and wind induced sastrugi features and a volume response ground to volume scattering ratios derived from a novel polarimetric decomposition are used in conjunction with pol insar coherence magnitudes to invert the extinction of the ice layer the inversion is performed for experimental airborne pol insar data at l band and p band acquired by the german aerospace center s dlr e sar system over the austfonna ice cap in svalbard norway as part of the 2007 icesar campaign extinction dependences on frequency and glacier facie are investigated and validation is performed comparing ground penetrating radar data to sar backscatter and extinction values best extinction results are obtained at shallow incidence angles with small wavenumbers and for low ground to volume scattering ratios for swath areas in mid range to far range accuracies of 25 in extinction are anticipated when averaging over 100 effective looks for a four baseline inversion constraining solutions to vertical wavenumbers of 0 01 kz 0 1 to allow inversion using single baseline pol insar the proposed model is of limited complexity suggested extensions for a more realistic scattering scenario include incorporating multiple englacial ice scattering layers and improving the way multiple baselines are combined

indentation of the pamirs with respect to the northern margin of tibet constraints from the tarim basin sedimentary record the pamirs represent the indented westward continuation of the northern margin of the tibetan plateau dividing the tarim and tajik basins their evolution may be a key factor influencing aridification of the asian interior yet the tectonics of the pamir salient are poorly understood we present a provenance study of the aertashi section a paleogene to late neogene clastic succession deposited in the tarim basin to the north of the nw margin of tibet the west kunlun and to the east of the pamirs our detrital zircon u pb ages coupled with zircon fission track bulk rock sm nd and petrography data document changes in contributing source terranes during the oligocene to miocene which can be correlated to regional tectonics we propose a model for the evolution of the pamir and west kunlun wkl in which the wkl formed topography since at least 200 ma by 25 ma movement along the pamir bounding faults such as the kashgar yecheng transfer system had commenced marking the onset of pamir indentation into the tarim tajik basin this is coincident with basinward expansion of the northern wkl margin which changed the palaeodrainage pattern within the kunlun progressively cutting off the more southerly wkl sources from the tarim basin an abrupt change in the provenance and facies of sediments at aertashi has a maximum age of 14 ma this change records when the pamir indenter had propagated sufficiently far north that the north pamir was now located proximal to the aertashi region

paleocene initial indentation and early growth of the pamir as recorded in the western tarim basin abstract it is presently unclear as to when and how the pamir were uplifted to their current elevation because a cenozoic sedimentary record is lacking on the pamir plateau and the pamir domes only record metamorphism associated with crustal shortening since 37 ma studies of the tectonic and geomorphological evolution of the pamir in the early stages of the india asia continental collision are also lacking the western tarim basin at the northeastern margin of the pamir provides an ideal opportunity to investigate their formation and evolution four cretaceous paleogene stratigraphic sections were examined in this study from these we infer that the west kunlun mountains were topographic highs during the mesozoic that divided the adjacent central pamir tianshuihai terrane from the tarim basin this paleo topographic configuration lasted until a marine transgression occurred in the aksai chin and central pamir areas in the latest cretaceous provenance analysis indicates that sediments in the western tarim basin were derived solely from the west kunlun mountains until the paleocene the appearance of pamir derived detrital zircons in paleocene and eocene strata of the tarim basin suggests that the pamir was experiencing uplift and reached an elevation similar to or even higher than the west kunlun mountains at that time the sandstone composition documents a provenance change from a stable continental block to an active thrust belt of the proto west kunlun mountains indicating that the western tarim basin evolved from an intraplate to a foreland basin setting during the paleocene alluvial fan conglomerates were deposited along the northeastern margin of the pamir and a thick gypsum unit began to be deposited in the tarim basin all these lines of evidence indicate that the north verging thrusting foreland basin subsidence uplift and northward indentation of the pamir began in the paleocene 62 58 ma

early middle miocene tectonic uplift of the northwestern part of the qinghai tibetan plateau evidenced by geochemical and mineralogical records in the western tarim basin the tarim basin in western china has been receiving continuous marine to lacustrine deposits during the cenozoic as a foreland basin of the qinghai tibetan plateau qtp clay mineralogy and geochemical proxy data from these sedimentary archives can shed light on climate and tectonic trends here we report on an abrupt mineralogical and weathering shift at 17 ma 1 myr in the miocene qimugan section in the northwestern part of the qinghai tibetan plateau the rapid shift involves decreasing trends of chemical weathering indices rb sr and ba sr ratios and of minor and immobile elements with respect to upper crust composition as well as increasing trends of na al and na ti ratios smectite chlorite and calcite contents we ascribe these trends to changing source rocks due to uplift of the northern part of the qtp leading to exposures of younger intrusive bodies and older gneisses schists and carbonate rich rocks these uplifts potentially caused regional aridification reducing chemical weathering the dating is indirect via magnetostratigraphically dated ostracod biostratigraphy and detrital zircon chronology and currently not good enough to compare the shift accurately in time with the onset of the global middle miocene climate optimum mmco at 16 5 ma nevertheless regional tectonics seem to have dominated over global climate as the warmer mmco is expected to have increased weathering indices and decreased na al and na ti rather than the observed reverse trends

lithospheric structure of tibet and western north america mechanisms of uplift and a comparative study we seek to determine the mantle lid thickness of the lithosphere and to constrain the mechanisms that are responsible for the cenozoic uplift of the tibetan plateau located behind the himalaya collision zone and the western united states located behind the san andreas transform convergent plate boundary selected first p arrivals of international seismological centre isc data at distances less than 22 are analyzed by the two station method to constrain the upper mantle structure of the basin and range br colorado plateau cp great plains gp and tibetan plateau tp the data are presented as plots of apparent velocity versus distance to the second station we show that these observations of apparent velocities versus distance as well as those that concern the attenuation of sn provide estimates of the mantle lid thicknesses we obtain the following mantle lid thicknesses br 20 40 km cp 35 50 km gp 150 195 km and tp 135 180 km sn is not observed for paths beneath the br and cp while sn efficiently propagates beneath the gp sn is also observed beneath most of tibet except in the north central part of the tp a possible interpretation of our observations is that indian continental lithosphere underthrusts only about the southern 2 3 of tibet

overview of results of spaceborne imaging radar c x band synthetic aperture radar sir c x sar the spaceborne imaging radar c x band synthetic aperture radar sir c x sar was launched on the space shuttle endeavour for two ten day missions in the spring and fall of 1994 radar data from these missions are being used to better understand the dynamic global environment during each mission radar images of over 300 sites around the earth were obtained returning over a terabit of data sir c x sar science investigations were focused on quantifying radar s ability to estimate surface properties of importance to understanding global change and focused studies in geology ecology hydrology and oceanography as well as radar calibration and electromagnetic theory studies in addition the second flight featured an interferometry experiment where digital elevation maps were obtained by interfering data from the first and second shuttle flight and from successive days on the second flight sir c x sar data have been used to validate algorithms which produce maps of vegetation type and biomass snow soil and vegetation moisture and the distribution of wetlands developed with earlier aircraft data

problems in the extrapolation of laboratory rheological data abstract the many types of variables and deformation regimes that need to be taken into account in extrapolating rheological behaviour from the laboratory to the earth are reviewed the problems of extrapolation are then illustrated with two particular cases in the case of divine rich rocks recent experimental work indicates that within present uncertainties of extrapolation the flow in the upper mantle could be either grain size dependent and near newtonian or grain size independent and distinctly non newtonian both types of behaviour would be influenced by the present of trace amounts of water in the case of quartz rich rocks the uncertainties are even greater and it is still premature to attempt any extrapolation to geological conditions except as an upper bound the fugacity and the scale of dispersion of the water are probably two important variables but the quantitative laws governing their influence are not yet clear

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

snow mapping in alpine regions with synthetic aperture radar active microwave sensors can discriminate snow from other surfaces in all weather conditions and their spatial resolution is compatible with the topographic variation in alpine regions using data acquired with the nasa airsar in the otztal alps in 1989 and 1991 the authors examine the usage of synthetic aperture radar sar to map snow and glacier covered areas by comparing polarimetric sar data to images from the landsat thematic mapper obtained under clear conditions one week after the sar flight the authors found that sar data at 5 3 ghz c band can discriminate between areas covered by snow from those that are ice free however they are less suited to discrimination of glacier ice from snow and rock the overall pixel by pixel accuracies 74 from vv polarization alone with topographic information 76 from polarimetric sar without any topographic information and 79 from polarimetric sar with topographic information are high enough to justify the use of sar as the data source in areas that are too cloud covered to obtain data from the thematic mapper this is especially true for snow discrimination where accuracies exceed 80 because mapping of a transient snow cover during a cloudy melt season is often difficult with an optical sensor the airsar survey was carried out in summer during a heavy rainstorm when the snow surfaces were unusually rough even better results for snow discrimination can be expected for mapping in the spring when snow is usually smoother

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

depth variations of azimuthal anisotropy beneath the tian shan mt range nw china from ambient noise tomography abstract seismic anisotropy beneath the tian shan mt range has been well studied with shear wave splitting the origin of asthenospheric anisotropy is mainly attributed to the north south shortening however the crustal anisotropy and its depth variation are poorly constrained in this study we focus on inversion of rayleigh wave phase velocity azimuthal anisotropy in the 5 35 s period bands beneath the tian shan mt range through analysis of continuous seismic ambient noise we use approximately 7 months of available continuous seismic data recorded by 31 broadband seismic stations deployed in the tian shan mt range the tomographic results reveal substantial variations in the azimuthal anisotropy with an increase in the depth in the upper crustal depths the orogen parallel or orogen subparallel azimuthal anisotropy observed in the tian shan mt range likely originates from the lattice preferred orientation of crustal minerals in response to compression whereas the orogen perpendicular or orogen sub perpendicular azimuthal anisotropy in the southern and northern piedmont of the tian shan mt range is related to the stress alignment of cracks fractures due to ongoing north south shortening the pattern of azimuthal anisotropy in the middle to lower crustal and upper most mantle is different from that at the upper crustal depths an orogen perpendicular or orogen sub perpendicular fast direction associated with prominent lower velocities has been observed north and south of lake issyk kul the spatial correlation between the azimuthal anisotropy and the lower velocity anomalies at the middle to lower crustal and upper most mantle depths may suggest a warm melt rich upper mantle below the tian shan mt range which could be attributed to the upwelling asthenospheric mantle flow in that region

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

removal of terrain effects from sar satellite imagery of arctic tundra synthetic aperture radar sar images of the earth s terrestrial surface contain geometric and radiometric image effects which are caused by varying terrain elevation and slope the radiometric effects tend to mask signal variations caused by other physical variables such as soil moisture and surface vegetation type which are known to influence sar backscatter signals as a result raw sar images are of limited use in classifying surface vegetation type or quantifying the spatial distribution of soil moisture in regions of terrain relief the authors present a technique for removing radiometric terrain effects from sar images image correction was carried out in two steps first an existing modeling package was used in combination with digital elevation data in order to map the raw image pixels onto a geodetic coordinate system thereby removing the geometric portion of the image distortion radiometric effects were then removed with the aid of a backscatter model which treats the reflected radiation as a combination of diffuse lambertian and specular components parameters in the backscatter model were determined by comparing two c band sar images of a test area in a region of arctic tundra which were taken from ascending and descending orbit tracks of the ers 1 satellite the ascending and descending images displayed reductions in pixel value variance of 30 and 13 respectively after processing direct comparison of the two test area images reveals a dramatic improvement in image similarity after processing

mapping seasonal snow with sir c x sar in mountainous areas abstract the objective of this study is to examine the capability of sir c x sar to map seasonal snow covers in alpine regions we develop two classification trees the first classifier can map snow and discriminate dry from wet snow but it requires a digital elevation model dem for radiometric terrain correction and reduction of the effect of local incidence angle the second classifer can map wet snow without using a dem we demonstrate some processing techniques that are necessary to discriminate wet snow from smooth bare surfaces and to discriminate dry snow from short vegetation for validation we compare our results with snow maps of both binary and snow fraction classifications obtained from the landsat thematic mapper tm at about the same time the sar is about 77 as accurate as the tm binary classification but it underestimates snow cover when compared with snow fraction classification with the major differences occurring for mixed pixels of snow and trees

monitoring glacier zones and snow firn line changes in the qinghai tibetan plateau using c band sar imagery abstract small glaciers and ice caps in mountainous areas are often sensitive indicators of local and global climate change in this paper typical continental glaciers the dongkemadi and its neighbouring glaciers in the central area of the qinghai tibetan plateau are monitored using multi sensor c band synthetic aperture radar sar imagery the study includes analysis of the alternating processes of ablation and freezing the glacier zones detected on sar images and the changing snow firn line across different days seasons and years experiments show that in late summer the wet snow firn ice boundary which is termed the late summer wet snow firn line wsfl is easily detected on sar images and it is relatively stable over multiple days also the detected late summer wsfl and the recorded yearly equilibrium line which reflects glacier mass balance are close in a positive mass balance year but the detected late summer wsfl is lower than the equilibrium line in a negative mass balance year by combining pit and sar observations it was found that the firn can be divided into two parts on the glaciers the thick firn that lies in the neve basin is distinct on sar images in winter but the firn surrounding the basin with thickness ranging from 0 to 20 cm is difficult to recognize the thick firn line the lower boundary of neve basin is stable in observations eight years apart based on the c band vv polarization sar image experiments field work and existing records the spatiotemporal backscatter signature specific to the typical continental glacier is identified the spatiotemporal backscatter signature helps to understand mass balance proxies and surface melt patterns of the glaciers in sar images

cenozoic thermo tectonic evolution of the northeastern pamir revealed by zircon and apatite fission track thermochronology abstract the northeastern pamir is a key location to explore asian intracontinental tectonic processes during the cenozoic new zircon fission track zft data show a 20 to 50 km wide region of partially reset ages on the northeastern margin of the pamir salient interpreted as an exhumed and tilted partial annealing zone paz widespread zft age peaks at 50 ma within the zft paz likely date early motion of the kashgar yecheng transfer system kyts but suggest this fault system was narrower in the early cenozoic than it is today apatite fission track aft ages of 10 6 ma combined with field observations across the kyts hint at an episode of strong thrusting related exhumational cooling which indicates that the modern fault system probably formed at this time to the southwest of the kyts the combination of new fission track and existing thermochronology data allows establishing temperature time trajectories that present diachronous rapid cooling from 450 to 120 c in the sares 13 10 ma muztagata 10 7 ma and kongur shan 3 1 ma domes rapid cooling in the eastern sares and southern muztagata massifs is driven by doming as supported by kinematic analyses of the shen ti fault successive rapid cooling of these massifs confirms eastward propagation of doming processes shortly postdating magma emplacement at 11 ma we propose that the synchronicity of regional tectonism magmatism and metamorphism implies that strong crustal thickening and contraction occurred beneath the northeastern pamir during the middle late miocene possibly associated with initial collision between the pamir and tian shan

the age of the taklimakan desert the taklimakan desert is located in the foreland basin of the tibetan plateau we report here the results of stratigraphic investigations of a 1626 meter thick sequence with interbedded wind blown silt from the southern marginal taklimakan desert because the studied section is located downwind of the desert the eolian silt accumulation is closely linked to desert formation our new evidence indicates that shifting sand dunes prevailed in the tarim basin by at least 5 3 million years ago as they do today we attribute this event to late cenozoic climatic deterioration as well as to changes in atmospheric circulation induced by tibetan plateau uplift

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

cause and effect among thrust and normal faulting anatectic melting and exhumation in the himalaya the transition from compression to extension in a regime of overall convergence in a narrow mountain belt requires a change with time in at least one of the following horizontal normal stress applied to the belt by its surroundings the distribution of shear traction on the base of the belt the constitutive relation between stress and strain rate of material in the belt itself the surface height of the belt the following processes could have caused one or other of these changes in the himalaya in miocene time and thus could have triggered the onset of extension by normal faulting on planes parallel to thrust faults that were active at the same time the shear stress on the thrust fault at the base of the himalaya could have decreased for instance because of melting on the fault plane alternatively the creation of a new deeper thrust fault and hence a new locus of convergence could have initiated extensional faulting if the distribution of shear stress on the new thrust fault were unable to support the himalaya above it the himalaya could have been weakened by an increase in pore fluid pressure for instance owing to metamorphic dehydration reactions within the wedge the himalaya could have been elevated for instance following the detachment of a tongue of mantle lithosphere from beneath it or by the underthrusting of a lens of material beneath its base the apparent simultaneity of thrust and normal faulting on nearly parallel planes of anatexis and of exhumation in the himalaya in miocene time can be explained if normal faulting was responsible for most of the exhumation and through decompression melting for anatexis existing data suggest that the most probable cause for miocene normal faulting was either uplift of the himalaya or the cessation of slip on the main central thrust at the base of the orogenic wedge and the creation of a new deeper thrust fault and a new base to the deforming himalaya 1993 the geological society

analysis of synthetic aperture radar data collected over the southwestern greenland ice sheet analyses of the first aircraft multi frequency polarimetric synthetic aperture radar sar data acquired over the southwestern greenland ice sheet are presented data were collected on 31 august 1989 by the jet propulsion laboratory sar using the nasa dc 8 aircraft along with curvilinear patterns associated with large scale morphologic features such as crevasses lakes and streams frequency and polarization dependencies are observed in the p l and c band image products

mid late miocene deformation of the northern kuqa fold and thrust belt southern chinese tian shan an apatite u th sm he study abstract the kuqa fold and thrust belt developed in response to cenozoic southward shortening between the chinese tian shan and the tarim basin this study aims to constrain the timing of the late cenozoic deformation by determining the onset time of enhanced rock cooling using apatite u th sm he thermochronometry eight sedimentary samples were collected from triassic to cretaceous strata exposed along a 17 km n s transect cross cutting the northern kuqa fold and thrust belt single grain ahe ages from these samples mostly cluster around 8 16 ma and are younger than their depositional ages older ahe ages show a positive relationship with eu a proxy for radiation damage modelling of the observed age eu relationships suggest a phase of enhanced cooling and erosion initiated at mid late miocene time 10 20 ma in the northern kuqa fold and thrust belt this result is consistent with a coeval abrupt increase of sedimentation rate in the foreland kuqa depression south of the study area indicating a mid late miocene phase of shortening in the northern kuqa fold and thrust belt

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

polarimetric sar data compensation for terrain azimuth slope variation this paper addresses the problem of polarimetric sar polsar data correction for changes in radar cross sections which are caused by azimuth slopes most radiometric slope corrections remove slope effects to account for the effective scattering pixel area however few studies address the slope effect on the radar cross section as a function of polarization states the authors propose two approaches to compensate for this azimuth slope effect for polsar data in the first approach the digital elevation model dem obtained from interferometric sar or from other means is used to estimate orientation angles and in the second approach orientation angles are derived directly from the polsar data they have developed three new methods to implement this second approach one is based on the right right and left left circular polarizations and the other two are based on cloude s and huynelt s decompositions the results are compared with the original polarization signature method using the dem generated orientation angles as the reference polsar data is then compensated using the derived orientation angles significant changes were observed in many elements of the coherency matrix the compensated polsar data should improve the accuracy of geophysical parameter estimation techniques nasa jpl airsar data for an area in central california is used for illustration

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

the sensitivity of stationary waves to variations in the basic state zonal flow abstract a linear primitive equation stationary wave model having high vertical and meridional resolution is used to examine the sensitivity of orographically forced primarily by himalayas stationary waves at middle and high latitudes to variations in the basic state zonal wind distribution we find relatively little sensitivity to the winds in high latitude but remarkable sensitivity to small variations in the subtropical jet fluctuations well within the range of observed variability in the jet can lead to large variations in the stationary waves of the high latitude stratosphere and to large changes even in tropospheric stationery waves implications for both sudden warmings and large scale weather are discussed

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

seasonal and short term variability of multifrequency polarimetric radar backscatter of alpine terrain from sir c x sar and airsar data signatures of glaciated and ice free areas were analyzed from polarimetric sar data at c l and p band and single polarization x band data the data base includes an airsar scene from june 25 1991 and sir c x sar images from april and october 1994 srl 1 and srl 2 acquired over the high alpine test site o spl uml tztal in austria the environmental conditions were different at the time of the three experiments ground measurements meteorological observations and backscattering modeling are the basis for interpreting the backscattering signatures seasonal differences are due mainly to the presence or absence of snow and due to changes of its properties short term variations of snow conditions can be monitored at c and x band for unglaciated areas the surface roughness has a dominant influence on backscattering in all seasons the dependence of the mean backscattering and correlation coefficients on the incidence angle was analyzed spectral and depolarization ratios and the magnitude of the hhvv correlation coefficient were selected as components of the multidimensional feature vector for studying the target separability good separability was found between the accumulation and ablation areas on the glaciers whereas on ice free areas the dominance of surface roughness limits the discrimination of different surface types short term variations of backscattering have significant impact for the classification of accumulation and ablation areas on glaciers as verified by comparisons with field data

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

tectonic evolution of the pamir recorded in the western tarim basin china sedimentologic and magnetostratigraphic analyses of the aertashi section the northward indentation of the pamir salient into the tarim basin at the western syntaxis of the india asia collision zone is the focus of controversial models linking lithospheric to surface and atmospheric processes here we report on tectonic events recorded in the most complete and best dated sedimentary sequences from the western tarim basin flanking the eastern pamir the aertashi section based on sedimentologic provenance and magnetostratigraphic analyses increased tectonic subsidence and a shift from marine to continental fluvio deltaic deposition at 41 ma indicate that far field deformation from the south started to affect the tarim region a sediment accumulation hiatus from 24 3 to 21 6 ma followed by deposition of proximal conglomerates is linked to fault propagation into the tarim basin from 21 6 to 15 0 ma increasing accumulation rates of fining upward clastics is interpreted as the expression of a major dextral transtensional system linking the kunlun to the tian shan ahead of the northward pamir indentation at 15 0 ma the appearance of north pamir sourced conglomerates followed at 11 ma by central pamir sourced volcanics coincides with a shift to e w compression clockwise vertical axis rotations and the onset of growth strata associated with the activation of the local east vergent qimugen thrust wedge together this enables us to interpret that pamir indentation into tarim had started by 24 3 ma reached the study location by 15 0 ma and had passed it by 11 ma providing kinematic constraints on proposed tectonic models involving intracontinental subduction and delamination

changes in the earth s rotation by tectonic movements present day true polar wander and the secular non tidal acceleration of the earth are usually attributed to post glacial rebound in the models which relate this rebound to changes in rotation the mantle is assumed to relax passively to the melted ice loads the lithosphere is usually modeled as a highly viscous upper layer in these models having viscosities which exceed mantle viscosities by several orders of magnitude we propose that lithospheric processes unrelated to post glacial rebound and taking place under non isostatic conditions are also able to induce non negligible influences on the earth s rotation examples of such processes are mountain building and erosion foundering flexure of oceanic basins and lithospheric snapbacking resulting from detachment of subducting slabs lithospheric and crustal rheologies and intraplate stresses are the dominant factors in these mechanisms contrary to the mantle rheologies which are assumed to dominate the process of post glacial rebound

cenozoic paleo environmental evolution of the pamir tien shan convergence zone abstract the retreat of the tethys sea and the uplift of the tibetan plateau play the critical roles in driving asian climatic changes during the cenozoic in the pamir tien shan convergence zone over 3000 m of cenozoic successions consisting of marine deposits in the lower continental clay and fine sand in the middle and molasse in the upper part record the evolution of the tethys sea the asian aridification and the deformation of the pamir in this work the existing biostratigraphic subdivisions and new electronic spinning resonance dating results were used to assign ages to formations within the ulugqat section sedimentary facies analysis and multi proxy indices were used to reconstruct the paleo environmental evolution the results show 1 the pamir tien shan convergence zone has undergone progressive environmental changes from shallow marine before 34 ma to arid land at 23 ma and finally to inter mountain basin by 5 3 ma 2 the overall increase in mean size of grains decrease in redness in magnetic susceptibility and in proportion of the ultrafine component of the sediments studied revealed a long term strengthening in potential energy to transporting medium cooling and enhanced continental aridity respectively 3 the easternmost edge of the tethys sea prevailed in the western tarim basin from late cretaceous to early cenozoic and finally retreated from this region around the eocene oligocene transition which in turn strengthened the asian aridification 4 accumulation of molasse with an upper age of 1 ma suggests that the deformation front of the pamir migrated to this area at or before that time

exhumation history of the west kunlun mountains northwestern tibet evidence for a long lived rejuvenated orogen abstract how and when the northwestern tibetan plateau originated and developed upon pre existing crustal and topographic features is not well understood to address this question we present an integrated analysis of detrital zircon u pb and fission track double dating of cenozoic synorogenic sediments from the kekeya and sanju sections in the southwestern tarim basin these data help establishing a new chronostratigraphic framework for the sanju section and confirm a recent revision of the chronostratigraphy at kekeya detrital zircon fission track ages present prominent triassic early jurassic 250 170 ma and early cretaceous 130 100 ma static age peaks and paleocene early miocene 60 21 ma to eocene late miocene 39 7 ma moving age peaks representing source exhumation triassic early jurassic static peak ages document unroofing of the kunlun terrane probably related to the subduction of paleotethys oceanic lithosphere in combination with the occurrence of synorogenic sediments on both flanks of the kunlun terrane these data suggest that an ancient west kunlun range had emerged above sea level by triassic early jurassic times early cretaceous fission track peak ages are interpreted to document exhumation related to thrusting along the tam karaul fault kinematically correlated to the main pamir thrust further west widespread middle late mesozoic crustal shortening and thickening likely enhanced the early mesozoic topography paleocene early eocene fission track peak ages are presumably partially reset limited regional exhumation indicates that the early cenozoic topographic and crustal pattern of the west kunlun may be largely preserved from the middle late mesozoic the main pamir tam karaul thrust belt could be a first order tectonic feature bounding the northwestern margin of the middle late mesozoic to early cenozoic tibetan plateau toward the tarim basin late oligocene early miocene steady exhumation at a rate of 0 9 km myr is likely related to initial thrusting of the tiklik fault and reactivation of the tam karaul thrust thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the west kunlun orogen at this time this episode of exhumation and uplift associated with magmatism across western tibet is compatible with a double sided lithospheric wedge model primarily driven by breakoff of the indian crustal slab accelerated exhumation of the mountain front at a rate of 1 1 km myr since 15 ma supports active compressional deformation at the margins of the northwestern tibetan plateau we thus propose that the west kunlun mountains are a long lived topographic unit dating back to triassic early jurassic times and have experienced middle late mesozoic to early cenozoic rejuvenation and late oligocene miocene expansion

changes in rotation induced by pleistocene ice masses with stratified analytical earth models the rotational response of the earth to pleistocene deglaciation is studied by means of a multilayered viscoelastic earth model based on the preliminary reference earth model prem incompressible viscoelastic deformation is evaluated from a self compressed initial state the novelty of our approach stands on the application of a fully analytical normal mode theory to the response of the earth to surface loads and variations in the centrifugal potential for large numbers of viscoelastic layers as requested by prem assuming that both present day true polar wander tpw and changes in the second degree component of the geopotential are solely due to pleistocene postglacial rebound we obtain for a two layer viscosity model that the upper mantle viscosity must be lowered to about 1 5 1020 pa s with respect to the classical value of 1021 pa s this upper mantle viscosity is accompanied by an increase of the lower mantle viscosity by a factor of 25 in agreement with some recent relative sealevel rsl data analyses and convectively supported long wavelength geoid anomalies when the viscosity contrast is located at 1470 km depth tpw and require a viscosity of 1021 pa s in the upper part of the mantle above 1470 km depth with a moderate viscosity increase in the lowermost portion of the mantle this result indicates that a viscosity of 1021 pa s is appropriate for a wider portion of the mantle than the upper mantle in agreement with haskell s 1935 estimate that was not limited to the seismically inferred 670 km boundary

measurements of snow and glacier covered areas with single polarization sar climatological and hydrological investigations in mountainous regions frequently require delineation of the areas covered by snow and glacial ice active microwave sensors can discriminate snow and glacier from other targets are effective under all weather conditions and have a spatial resolution compatible with the topographic variation in alpine regions using data acquired with the nasa airsar which operates at three frequencies and four combinations of polarization we examine the usage of synthetic aperture radar sar to map snow and glacier covered areas in order to assess the available sars that operate from satellites we analyze single frequency single polarization data and we compare our results with images from the landsat thematic mapper obtained under clear conditions only a few days after the sar flight single polarization c band 5 3 ghz sar data can discriminate between areas covered by wet snow from those that are ice free but do not easily separate glacier ice from snow and rock l band sar 1 25 ghz data cannot discriminate between snow and glacier ice the accuracy 74 of sar is high enough to justify its use as the data source in areas that are too cloud covered to obtain reliable data from the thematic mapper

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

from sea level to high elevation in 15 million years uplift history of the northern tibetan plateau margin in the altun shan approximately 1300 in of oligocene miocene clastic strata are exposed along the miran river in the southeastern tarim basin where the adjacent altun shan form the topographic escarpment of the northern tibetan plateau the sedimentary section is faulted against proterozoic rocks of the altun shan in the footwall of the south dipping oblique reverse northern altyn tagh fault oligocene lower miocene strata consist of fine grained rocks that record low gradient depositional systems mid miocene and younger rocks consist of coarse conglomerate derived from the altun shan and deposited by high gradient depositional systems the change to coarse high gradient depositional systems with detrital source areas coincident with the modern miran river drainage is interpreted to mark the onset of uplift of the altun shan on the northern altyn tagh fault and its erosional exhumation the age of the change from pre orogenic to synorogenic sedimentation is constrained by a foraminifera assemblage at the base of the conglomeratic section that includes early middle miocene planktonic foraminifera this interpretation is also supported by apatite fission track and u th he ages and thermal models that indicate rapid miocene cooling and hence rapid exhumation of the altun shan in addition to defining the age of the synorogenic section the foraminifera assemblage contains planktonic taxa indicating a connection to open marine waters and benthic assemblages typical of brackish to near sea level paleobathymetry thus micropaleontologic evidence demonstrates that the miran river locality now at 1400 in elevation was at sea level approximately 15 million years ago thus in addition to constraining the age of surface uplift and exhumation of the altun shan the principal mountain range of the tibetan plateau in this region as 15 to 16 ma the foraminifera assemblage indicates that the se tarim basin off the northern edge of the plateau had an average surface uplift rate of nearly 100 m m y for the past 15 million years these results suggest that shortening in the altun shan and uplift of the range significantly post dated the initiation of large scale strike slip on the altyn tagh fault and that regional surface uplift mechanisms operated in the tarim basin beyond the margins of the tibetan plateau

lithostratigraphy petrography and facies analysis of the late cenozoic sediments in the foreland basin of the west kunlun abstract the yecheng profile lying in the southwest tarim basin at the northern foot of the west kunlun mountains comprises 4 5 km of conformable miocene to pliocene strata the lower part of the section the wuqia group is composed of interbedded red mudstone and pale coloured fine sandstone with a thickness of 1700 m the artux formation is 800 m thick and composed of mudstone sandstone with thin gravel and conglomerate beds the upper part of the section known as the xiyu formation consists of 2000 m of cobble and boulder conglomerate intercalated with massive siltstone lenses compositional study of the sandstones in the wuqia group and artux formation indicates that they were sourced from low relief areas of the kunlun region and probably further south from tibet the provenance of the conglomerate in the xiyu formation is the west kunlun mountains compositional trends within the conglomerate indicate that upper palaeozoic marine and mesozoic to tertiary terrestrial silicic rocks were eroded first along with the proterozoic to lower palaeozoic proto tethys metasedimentary rocks erosion into deeper levels of the kunlun mountains provided igneous and high grade metamorphic sediment which first appears 640 m above the base of the xiyu formation lithofacies change from fine grained mudstone and sandstone to coarse clasts coincides with the onset of aeolian sedimentation indicating major shift of regional palaeoclimatic regime although climatic changes may have played an important role in controlling the sedimentary regime worldwide our study of the lithostratigraphy and petrography of the yecheng section suggests that the lithofacies change recorded the progressive unroofing history of the source rocks in the west kunlun mountains

detachment of part of the downgoing slab and uplift of the new hebrides vanuatu islands several seisniological observations suggest that there is a gap within the downgoing slab of australian lithosphere plunging beneath the new hebrides and ages of elevated coral tenaces on the new hebrides islands suggest that the islands arc rising rapidly we suggest that the creation of the gap in the slab within the last 1 m y occurred by part of the slab detaching from the rest and sinking rapidly into the underlying asthenosphere this lowered the downward force on the slab at shallower depths and therefore on the overriding plate and the continued decrease of this force as the deeper slab sinks freely has allowed the islands above it to rise although this suggestion cannot account for all aspects of the uplift of the islands it provides a simple mechanism for explaining the fairly young uplift and its distribution along the new hebrides arc

the effect of topography on sar calibration during normal synthetic aperture radar sar processing a flat earth is assumed when performing radiometric corrections such as antenna pattern and scattering area removal the authors examine the effects of topographic variations on these corrections local slopes will cause the actual scattering area to be different from that calculated using the flat earth assumption it is shown that this effect may easily cause calibration errors larger than a decibel ignoring the topography during antenna pattern removal may also introduce errors of several decibels in the case of airborne systems the effect of topography on antenna pattern removal is expected to be negligible for spaceborne sars the authors show how these effects can be taken into account if a digital elevation model is available for the imaged area the errors are quantified for two different types of terrain a moderate relief area near tombstone az and a high relief area near oetztal in the austrian alps the authors show errors for two well known radar systems the c band ers 1 spaceborne radar system and the three frequency nasa jpl airborne sar system airsar

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

the himalayan riddle of the free air satellite gravity and a possible solution abstract the satellite derived free air anomaly over the himalayas in india is positive bordered on the south by a negative the positive free air anomaly is so strong that it deceptively indicates isostatic undercompensation of the himalayas implying a thinner crust below than is normally expected for their elevation range the paper explains that one should not consider isolated anomalies over a structure but the average of all the anomaly values produced by the source while determining the level of isostatic compensation the average anomaly over the himalayas does not put the often cited theory of overcompensation into any dispute

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

polarimetric decomposition over glacier ice using long wavelength airborne polsar in recent years there has been increased interest in using synthetic aperture radar sar to study and monitor glaciers and ice sheets for glaciological and climate change research however due to the medium s complexity sar backscattering from ice remains poorly understood including the relative importance of scattering from surface and volume layers and also dependences on frequency and glacier zone extreme weather conditions can result in quickly changing surface conditions influencing backscatter signatures while leaving the underlying volume of interest unchanged surface and volume components must thus be separated in order to infer information regarding the properties of the ice volume this paper describes a three component scattering model to decompose polarimetric sar polsar images of glacier ice total backscatter is modeled as the incoherent summation of surface volume and sastrugi wind induced feature components the proposed model adapts and extends the freeman and durden decomposition for an ice volume scenario in which the volume is a dielectric medium forms of the model for both random and oriented volumes are considered and a new oriented sastrugi component is introduced which is able to explain backscatter behavior between different winter scenes validation is performed with airborne polsar data at l and p band collected using the e sar system of the german aerospace center over the austfonna ice cap in svalbard norway as part of the icesar campaign

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

comment on cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression by tao zhang xiaomin fang chunhui song erwin appel and yadong wang tectonophysics 2014 doi 10 1016 j tecto 2014 04 044 abstract the recent paper entitled cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression by zhang et al tectonophysics 2014 doi 10 1016 j tecto 2014 04 044 discusses the cenozoic tectonic deformation and uplift of the south tianshan mountains by integrating tectonic investigations seismostratigraphic analysis and paleomagnetic dating of the thrust fold belt in the kuqa depression at the southern border of the tianshan to support their conclusions the authors have reinterpreted a high resolution magnetostratigraphic study of the kezilenuer section in a paper entitled magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china by huang et al earth and planetary science letters volume 251 pages 346 364 2006 we note here i that apparent conflicts in definition of the xiyu formation in the kuche depression as proposed by zhang et al 2014 require amplification and ii argue that their age assignment for the kezilenuer section is incorrect and yields an anomalously low sedimentation rate for the infilling of this foreland basin

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less

synthetic aperture radar calibration using reference reflectors a simple expression for the terrain backscatter coefficient is derived in terms of the integrated power of an adjacent known radar reflector in a synthetic aperture radar sar image it is shown that this technique for sar image calibration is independent of the radar system focus or partial coherence and thereby possesses an important advantage over the usual technique which relies on an estimate of the peak of the reflector impulse response results from airborne sar overflights of corner reflectors and active radar calibrators are used to demonstrate the validity and consistency of the method and to show that the method is robust under defocus caused by an incorrect fm rate or inadequate motion compensation of data collected during turbulence it is also shown that the fading errors associated with the integral method are comparable to or slightly worse than those associated with the peak estimation method however this small disadvantage is outweighed by the fact that the integral method is independent of actual resolution

eocene seawater retreat from the southwest tarim basin and implications for early cenozoic tectonic evolution in the pamir plateau article i nfo the pamir plateau lies in the western end of the india eurasia collision zone being an unusual example for studying crustal shortening and evolution of the neotethys ocean here we present new results from the southwestern margin of the tarim basin for discussing tectonic history in the northern pamir plateau as well as for providing precise dates of the final seawater retreat from the studied region our results indicate that early uplift of the northern edge of the pamir plateau occurred at about 55 ma but this uplift preceded the closure of the link between the neotethys and the tarim basin five marine transgression and regression cycles occurred during the early eocene mostly in response to global eustatic sea level fluctuations and the final seawater retreat from the southwest tarim basin occurred at about 47 ma another uplift episode started 34 ma supported by the accumulation of coarse molasse deposits as well as our palynological evi dence suggesting that the convergence between the pamir plateau and the tian shan ranges accelerated since the beginning of the early oligocene