silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

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

lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

continental crust composition constrained by measurements of crustal poisson s ratio deciphering the geological evolution of the earth s continental crust requires knowledge of its bulk composition and global variability the main uncertainties are associated with the composition of the lower crust seismic measurements probe the elastic properties of the crust at depth from which composition can be inferred of particular note is poisson s ratio this elastic parameter can be determined uniquely from the ratio of p to s wave seismic velocity and provides a better diagnostic of crustal composition than either p or s wave velocity alone1 previous attempts to measure have been limited by difficulties in obtaining coincident p and s wave data sampling the entire crust2 here we report 76 new estimates of crustal spanning all of the continents except antarctica we find that on average increases with the age of the crust our results strongly support the presence of a mafic lower crust beneath cratons and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions followed by magmatic underplating or a model in which crust formation processes have changed since the precambrian era

transdimensional inversion of scattered body waves for 1d s wave velocity structure application to the tengchong volcanic area southwestern china abstract inversion of receiver functions is commonly used to recover the s wave velocity structure beneath seismic stations traditional approaches are based on deconvolved waveforms where the horizontal component of p wave seismograms is deconvolved by the vertical component deconvolution of noisy seismograms is a numerically unstable process that needs to be stabilized by regularization parameters this biases noise statistics making it difficult to estimate uncertainties in observed receiver functions for bayesian inference this study proposes a method to directly invert observed radial waveforms and to better account for data noise in a bayesian formulation we illustrate its feasibility with two synthetic tests having different types of noises added to seismograms then a real site application is performed to obtain the 1 d s wave velocity structure beneath a seismic station located in the tengchong volcanic area southwestern china surface wave dispersion measurements spanning periods from 8 to 65 s are jointly inverted with p waveforms the results show a complex s wave velocity structure as two low velocity zones are observed in the crust and uppermost mantle suggesting the existence of magma chambers or zones of partial melt the upper magma chambers may be the heart source that cause the thermal activity on the surface

crustal structure in the tengchong volcanic area and position of the magma chambers abstract in this paper we extract 1500 p receiver functions in the tengchong volcanic area from 211 teleseismic events recorded at nine digital seismic stations a common conversion point stacking technique is used to improve the signal to noise ratio and to get the time delays of the ps ppps psps ppss phases within grids of 10 km 10 km finally the crustal thickness and poisson s ratio are calculated the results show that the crustal thickness ranges from 28 to 40 km and the poisson s ratio ranges from 0 28 to 0 36 there exist two mantle uplifting sites each with a horizontal scale of about 30 km 30 km one in mazhan tengchong maanshan and the other in wuhe longjiang tuantian the high poisson s ratio is consistently located within these two sites recorded shocks with ms 2 0 reveal that most of the shocks are distributed around the two sites and few are located at the centers the shocks the geothermal distribution and the crustal structure suggest that the magma is still active and the two mantle uplifting sites detected may be the positions of two magma chambers in the crust

evidence for northeastern tibetan plateau uplift between 25 and 20 ma in the sedimentary archive of the xining basin northwestern china the growth history of the tibetan plateau provides a valuable natural laboratory to understand tectonic processes of the india asia collision and their impact on and interactions with asian and global climate change however both tibetan plateau growth and asian paleoenvironments are generally poorly documented in pre pliocene times and reflect limited temporal coverage for different parts of the plateau here we present magnetostratigraphic results from the xining basin at the ne margin of the tibetan plateau precisely dating the record between the earliest oligocene 33 ma to the middle miocene 16 ma the pattern of observed paleomagnetic polarity zones is unequivocally correlated to the geomagnetic polarity time scale gpts indicating relatively constant and low sediment accumulation rates 32 m myr except for a peculiar period of unstable accumulation between 25 3 and 19 7ma at the beginning of this interval a marked permanent increase in magnetite content of the sediments is observed and likely relates to a change in provenance we directly relate this unstable period of sediment accumulation and provenance change to the coeval exhumation recently reported by low temperature thermochronology from the laji shan range which subsequently formed the southernmargin of the xining basin evidence for ne tibet tectonismat 25 20 ma can be associated with widespread deformation over the entire himalayan tibetan orogen at this time which may be linked to the coeval appearance of monsoon climate in eastern asia and the onset of central asian desertification

the quaternary eruptive sequence of the tengchong volcanic group southwestern china abstract the tengchong volcanic group in sw china is situated along the ns oriented tectonic belt in the southeastern margin of the tibetan plateau the volcanic field has experienced intense tectonic stress due to the continuous subduction of the indian plate under the eurasian plate and throughout quaternary has experienced pervasive volcanism the present volcanic rocks cover the successive domains of basic intermediate group ii and acid group i rocks belonging to the high k calc alkaline series correspondingly the eruption types of the tengchong volcanoes roughly fall into two categories explosive eruptions with large amounts of volcaniclastics and lava and moderately quiet central eruptions with small amounts of scoria and lava overflow according to systematic geochronological dating methods such as k ar ar ar 14c ams and osl dating as well as field work we separate the eruptive sequence of the tengchong volcanic group during the quaternary into four subsequences the early pleistocene middle pleistocene late pleistocene and the holocene epoch the early to middle quaternary eruption sequence consists of a series of explosive eruptions with almost all the eruptive dacitic volcaniclasts and lava constituting the bottom layer of the tengchong basin the tengchong volcanism reached its climax in the late pleistocene when it formed numerous cinder cones a series of moderately quiet central eruptions occurred in the late quaternary and basic and intermediate acid volcanic rocks formed the upper layer of the basin from this study three volcanoes are determined to be of holocene age and we conclude that the volcanic activity moved from the south and periphery to the north and center and ended in the heikongshan eruption 3600 years ago

calcium isotope δ44 40ca variations of neogene planktonic foraminifera measurements of the calcium isotopic composition 44 40ca of planktonic foraminifera from the western equatorial pacific and the indian sector of the southern ocean show variations of about 0 6 over the past 24 myr the stacked 44 40ca record of globigerinoides trilobus and globigerina bulloides indicates a minimum in 44 40casw seawater calcium at 15 to 16 ma and a subsequent general increase toward the present interrupted by a second minimum at 3 to 5 ma applying a coupled calcium carbon cycle model we find two scenarios that can explain a large portion of the observed 44 40casw variations in both cases variations in the ca input flux to the ocean without proportional changes in the carbonate flux are invoked the first scenario increases the riverine calcium input to the ocean without a proportional increase of the carbonate flux the second scenario generates an additional calcium flux from the exchange of ca by mg during dolomitization in both cases the calcium flux variations lead to drastic changes in the seawater ca concentrations on million year timescales our 44 40casw record therefore indicates that the global calcium cycle may be much more dynamic than previously assumed

sr and nd isotope compositions of alluvial sediments from the ganga basin and their use as potential proxies for source identification and apportionment abstract the sr 87sr 86sr and nd end values isotopic composition of sediments transported by the ganga fluvial system and deposited within the ganga basin have been used by other studies to identify and characterize sediment provenance isotopic data have also been used for the purpose of quantitative source apportionment furthermore isotopic signatures of sediments imply the higher himalaya hhs source to be the major contributor of sediments to the ganga basin and bay of bengal contrary to the few studies from the adjacent indus basin to the west that inferred higher erosion and sediment contribution from the lesser himalaya lhs source in recent times in the present study we test the reliability of using 87sr 86sr and or end of river sediments as proxies for source s characterization and their apportionment first we compiled all available sr and nd isotope ratios of the ganga basin sediments as well as their probable sources reported in earlier studies after subjecting the data set to statistical scrutiny and removing outliers we carefully evaluated spatial variability in the isotopic composition vis a vis the composition of lithologies drained by a complex network of both the himalayan and the peninsular sourced tributaries in the ganga fluvial system our analysis shows a large isotope compositional overlap among probable sources which suggests that application of isotopic composition of the ganga basin sediments as a proxy for provenance is not straight forward and is fraught with complications following the general notion that the ganga basin sediments are primarily derived from the hhs and lhs sources we performed monte carlo simulations aimed to model the isotopic composition of sediment mixture these results show greater uncertainty associated with quantitative source apportionment estimates given the available set of isotopic constraints compared to the 87sr 86sr ratios that can be modified during fluvial transport the end values serve as more reliable provenance indicator although the use of this parameter for source apportionment may still have a large amount of uncertainty nevertheless a kernel density estimate kde plot of end of river sediments suggests the influence of various source lithologies on the end pattern of the ganga main channel sediments and indicates presence of dominantly hhs and lhs sourced sediments the average end of sediments along the ganga main channel shows distinct change at places in the plains due to local influence of contributing tributaries most likely peninsular sourced tributaries at present virtually no isotopic data is available on the sediments of peninsular sourced tributaries which makes it difficult to assess the contribution of cratonic sources to the isotopic budget of the ganga basin sediments particularly in the ganga yamuna interfluve regions

significance of weathering himalayan metasedimentary rocks and leucogranites for the sr isotope evolution of seawater during the early miocene changes in 87 sr 86 sr ratios of seawater may reflect varying rates of chemical weathering or variations in the isotopic compositions of continental rocks undergoing weathering the unusually high dissolved sr concentrations and 87 sr 86 sr ratios that characterize the ganges and brahmaputra tsangpo river systems are a consequence of weathering early proterozoic age metasedimentary rocks and anatectic miocene granites exposed on the southern slopes of the himalayas on average the metasedimentary rocks are characterized by abundances of 87 sr about twice those of the derived granites the rapid rise in 87 sr 86 sr ratios of seawater during the early miocene was virtually coincident with metamorphism and anatexis of himalayan metasedimentary rocks model calculations indicate that 50 75 of the overall change in 87 sr 86 sr ratios for seawater between 20 and 15 ma could have resulted from exposure of himalayan metasedimentary rocks to chemical weathering rapid tectonically controlled exhumation of the metasedimentary rocks is required to expose these lithologies by 20 18 ma to generate the increase in the 87 sr flux of the trans himalayan rivers during the early miocene

sr isotopic signature of the ganga alluvial plain and its implication to sr flux of the ganga river system the influx of sr responsible for increase in marine sr has been attributed to rise of himalaya and weathering of the himalayan rocks the rivers draining himalaya to the ocean by the northern part of the indian sub continent comprising the ganga alluvial plain gap along with central parts of the himalaya and the northern part of the indian craton are held responsible for the transformation of sr isotopic signature the gap is basically formed by the himalayan derived sediments and serves as transient zone between the source himalaya and the sink bay of bengal the gomati river an important alluvial tributary of the ganga river draining nearly 30 500 km2 area of gap is the only river which is originating from the gap the river recycles the himalayan derived sediments and transport its weathering products into the ganga river and finally to bay of bengal 11 water samples were collected from the gomati river and its intrabasinal lakes for measurement of sr isotopic composition sr concentration of gomati river water is about 335 g l which is about five times higher than the world s average of river water 70 g l and nearly three times higher than the ganga river water in the himalaya 130 g l the sr isotopic ratios reported are also higher than global average runoff 0 7119 and to modern seawater 0 7092 values strong geochemical sediment water interaction appearing on surface is responsible for the dissolved sr isotopic ratios in the river water higher sr isotopic rations found during post monsoon than in pre monsoon season indicate the importance of fluxes due to monsoonal erosion of the gap into the gomati river monsoon precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved sr load into the alluvial plain rivers this study establishes that elevated 87sr 86sr ratios of the gomati river are due to input of chemical weathering of alluvial material present in the ganga alluvial plain

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

strontium isotope composition of runoff from a glaciated carbonate terrain abstract the relationship between subglacial chemical weathering processes and the sr isotope composition of runoff from robertson glacier alberta canada is investigated this glacier rests on predominantly carbonate bedrock of upper devonian age but silicate minerals are also present the provenance of solute in meltwaters is found to vary systematically with solute concentration and by inference subglacial water residence time in dilute waters the principal process of solute acquisition is calcite dissolution fueled by protons derived from the dissolution of co 2 and subsequent dissociation of carbonic acid at higher solute concentrations dolomite dissolution coupled to sulfide oxidation is more important sr concentration is found to increase with total solute concentration in two separate meltwater streams draining from the glacier but 87 sr 86 sr only increases in the eastern melt stream carbonate and k feldspar sources are shown to dominate the sr content of the western stream irrespective of concentration they also dominate the sr content of the eastern stream at low and intermediate concentrations but at higher concentrations muscovite with high 87 sr 86 sr is also an important sr source this reflects the outcrop of muscovite bearing lithologies in the catchment of the eastern stream and an increase in the rate of weathering of k silicates relative to that of carbonates as more concentrated solutions approach saturation with respect to carbonates nonstoichiometric release of 87 sr 86 sr and preferential release of sr over k from freshly ground k silicate surfaces may also occur this may help to explain the radiogenic nature of runoff from distributed subglacial drainage systems which are characterized by long water rock contact times and water flow through environments in which crushing and grinding of bedrock are active processes although the exchangeable sr in tills has higher 87 sr 86 sr than local carbonate bedrock only the more concentrated meltwaters from the eastern stream display similarly high values the most dilute waters which probably transport the bulk of the dissolved sr flux from the glacier have 87 sr 86 sr characteristic of local carbonate bedrock thus the results suggest that although enhanced weathering of silicate minerals containing radiogenic sr such as muscovite does occur in glaciated carbonate terrains it is unlikely to contribute to any enhanced flux of radiogenic sr from glaciated continental surfaces to the oceans

chemical weathering rates in the alaknanda bhagirathi river basins in himalayas india abstract the alaknanda and bhagirathi rivers flow through the higher and lesser himalayas and confluence at devprayag which represents the origin of the ganga or ganges river in the present study a vast number of temporal and spatial samples of the river waters were collected and analyzed for major cations and anions in addition more recent and time series water flow data have been obtained and based on these inputs a more refined dissolved flux rates have been estimated the alaknanda and bhagirathi rivers show significant variations in chemical compositions during different seasons carbonate rock weathering is responsible for more than 70 of the chemical compositions in the river waters the chemical weathering rates show seasonal variations and are much higher during non monsoon season the dissolved flux of alaknanda river is much higher 1 80 106 tons yr 1 as compared to the bhagirathi river 0 34 106 tons yr 1 the chemical weathering rates in the basin vary between 85 and 155 tons km 2 yr 1 which is significantly higher compared to the global average of 24 tons km 2 yr 1

neogene syn tectonic sedimentation in the eastern margin of arakan bengal basins and its implications on for the indian asian collision in western myanmar abstract the arakan basin is one of the major sedimentary basins formed in the frontal part of the himalayan orogenic belt since the late cenozoic defining one of the four major sedimentary basins of myanmar it is geomorphologically and tectonically differentiated from the others the study area along the westernmost edge of myanmar is separated from the arakan yoma indo burman ranges by a narrow coastal strip and is bordered by the bay of bengal to the west regional stratigraphic correlation and the geological age of the siliciclastic sequences were established based on planktonic foraminiferal zonation deep marine slope and shelf environments during early to middle miocene ca 21 5 11 ma and a southward prograded shelf delta environment during late miocene to pliocene time were determined the early miocene underthrusting along the himalayan front is well documented by the forced regressive sedimentation patterns in the slope and shelf systems sediments of which derived from the paleo ganges brahmaputra river systems in the bengal arakan basins sequential evolution of the miocene successions manifests in forced regressive wedged systems tracts these evolved through slope by passing and slumping and following deep marine channel in filling began to accumulate an increasing sediment load due to the rapid fall of sea level by the uplift in the hinterlands during the early to early middle miocene the formation of a shelf delta systems marks a dramatic shift in the evolution of the southward prograding delta systems following a eustatic sea level low in the foreland areas erosional off loading with foreland uplifting caused a wide active fluvial systems and formed transverse rivers distally in the late middle to late miocene

tectonic controls on the late miocene holocene volcanic eruptions of the tengchong volcanic field along the southeastern margin of the tibetan plateau abstract the tengchong volcanic field located along the southeastern margin of the tibetan plateau experienced multiple eruption stages since the late miocene including time intervals of 5 5 4 0 ma 3 9 0 9 ma 0 8 0 01 ma and younger than 0 01 ma these eruption stages produced different volcanic rocks principally basaltic and basaltic andesite series at the same time or prior to volcanic eruptions in the tengchong volcanic field ne nne trending rift basins and ns striking normal faults formed during the late miocene pliocene in addition rapid exhumation of the neighboring mountains occurred at 6 5 ma constrained by apatite fission track dating and its thermochronological modeling at present the state of stress in the tengchong volcanic field and its surroundings is nne ne compression and wnw nw extension based on seismic foci mechanisms petrologic and geochemical data indicate that the source of the tengchong volcanic rocks belongs to an intracontinental tectonic setting but not a subduction or collision zone between indian and eurasian plates since the late miocene the dextral strike slip motion of the sagaing fault induced e w extension the sagaing dextral strike slip motion might disturb the lower crust upper mantle of the tengchong block resulting in the partial melting of the upper mantle which in turn induced volcanic eruptions characterized by mature island arc features

an sh hybrid method and shear velocity structures in the lowermost mantle beneath the central pacific and south atlantic oceans 1 an sh hybrid method is developed for calculating synthetic seismograms involving two dimensional localized heterogeneous structures the hybrid method is a combination of analytic and numerical methods with the numerical method finite difference applied in the heterogeneous region only and analytical methods applied outside the region generalized ray theory solutions from a seismic source are used to initiate the finite difference calculation and seismic responses at the earth s surface are obtained from the finite difference output by applying the kirchhoff theory we apply the hybrid method and study sh wave propagation near the bottom of the mantle the shear velocity structures and the interaction of sh waves with these velocity structures at the base of the mantle beneath the central pacific and south atlantic oceans are of particular importance the observed sh waves sampling these two regions of the core mantle boundary show very different characteristics across the epicentral distance range of 83 108 the sh waves sampling the core mantle boundary beneath the central pacific show a linearly increasing delay of 4 s from 98 to 108 and discernible scs phases up to an epicentral distance of 102 the sh waves propagating through the base of the mantle beneath the south atlantic ocean on the other hand exhibit a linearly increasing delay of 10 s from 98 to 108 discernible multiple scs phases with a same slowness as the direct sh waves up to 108 and rapid variations of waveforms across small epicentral distances synthetic tests indicate that while the observations sampling the central pacific can be explained by a negative shear velocity gradient of 3 relative to the preliminary reference earth model at the bottom 300 km of the mantle those sampling the south atlantic ocean require a 300 km thick bottom boundary layer with a larger negative velocity gradient up to 10 and steeply dipping edges the negative velocity gradient at the base of mantle beneath the south atlantic ocean can be best explained by partial melt driven by a compositional change produced in the early earth s history and a vertical thermal gradient within the layer while that beneath the central pacific may reasonably be attributed to pure thermal effects within a thermal boundary layer

a review on the analysis of the crustal and upper mantle structure using receiver functions abstract the discontinuities in the earth such as moho lithosphere asthenosphere boundary lab 410 and 660 km discontinuities are characterized with an abrupt jump in velocities of p and s waves the depths of these discontinuities are an important parameter to investigate tectonic evolution in the lithosphere receiver functions technique with teleseismic events is very suitable for studying the crust and upper mantle structure beneath stations thus becoming one of the standard tools for such study the principle of receiver functions is to separate the converted ps or sp phases generated at the discontinuities beneath stations in the case that the direct p or s is a delta function in this paper the methods of receiver function analysis are collected from literatures we introduce the coordinate transform technique for the separation of ps or sp waves the deconvolution algorithm to extract p and s receiver functions the waveform fitting method to invert for s wave velocity structure the stacking technique to improve signals and the migration from time series to depth domain with some illustrative examples the care that should be taken in study of the crustal and upper mantle structure using receiver functions are summarized

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

structure and significance of s wave velocity and poisson s ratio in the crust beneath the eastern side of the qinghai tibet plateau the receiver functions of body waves of distant earthquakes obtained for the regions beneath 41 digital stations lhasa and ganz in tibet mandalay and rangoon in myanmar shio in india chto in thailand and station network in sichuan and yunnan were used to invert for s wave structure in the crust and upper mantle in sichuan yunnan and their surrounding areas meanwhile the distribution characteristics of the poisson s ration and the crustal thickness in sichuan and yunnan areas were also obtained results indicate that the depth of moho beneath the eastern side of qinghai tibetan plateau varies strikingly it is obvious that the greatest changes in crustal thickness occur in a north south direction the crustal thickness decreases from north to south being as thick as 70 km in eastern tibet the northern portion of our area of interest and less than 30 km in chaing mai and rangoon the southern portion of our area there are however exceptions regarding the trend the thickness exhibits an east west variation trend in the area from ma erkong kongding in sichuan to lijiang in yunnan in general the jinpingshan longmenshan fault and anninghe fault can be taken as the boundaries of this exception area the thickness in kongding in the west is 68 km while it is only 39 km in yongchuan in the east moreover the poisson s ratio values in the blocks of central sichuan and sichuan yunnan diamond are high and a low velocity layer in the crust of this area can be obviously detected the distribution characteristics of the high poisson s ratio and the low velocity of the crust in this block correspond to the tectonic structure being in contrast with the surrounding areas combining with the distribution features of the modern tectonic stress field it is deduced that the sichuan yunnan area is probably the channel through which the materials of the lithosphere flow eastward

chemical erosion rates of river basins of the ganga system in the himalaya reanalysis based on inversion of dissolved major ions sr and 87sr 86sr 1 available data on chemical and sr isotopic composition of the headwaters of the ganga and its tributaries in the himalaya are analyzed using inverse and the forward models to quantify the silicate and carbonate erosion rates in their basins and to parameterize the controlling factors of contemporary chemical erosion the estimates of silicate derived cations based on the inverse model are lower on average by 20 than that derived from the forward model a result attributable to differences in the release ratios of major ions between the two models the inverse model yields the best fit values for the release ratio of various major ions based on measured river chemistry and therefore is more likely to be representative of the basins unlike the forward model in which the release ratios are assumed among the various tributaries the kosi and the bhagirathi have relatively larger contributions from silicate weathering to the cation budget with high 87sr 86sr consistent with the lithologies of their basins which are dominated by silicates the ganga river system in the himalaya is known to be supersaturated with respect to calcite during lean flow periods the inverse model calculates the extent of ca loss to be between 10 40 with the highest for the gandak the silicate and carbonate erosion rates for these himalayan rivers are relatively higher in the ranges of 9 9 17 6 and 12 4 92 3 tons km2 yr respectively compared to other global rivers the higher chemical erosion rates in these river basins could be due to intense physical erosion caused by their higher relief and runoff

dynamics of the tengchong volcanic region in the southeastern tibetan plateau a numerical study abstract the constraints of surface heat flow and lithospheric structure were used to investigate the dynamics of the tengchong volcanic region based on thermal mechanical modeling three different boundary conditions representing three types of tectonic movements were modeled to discuss the thermal state and lithospheric deformation the compressive model shows that the subduction of the indian plate causes the upwelling of asthenosphere beneath the tengchong block in this process upwelling of the asthenosphere causes thinning of the lithosphere beneath the tengchong block however the surface heat flow of this model is not consistent with the observations the regional extension model shows that under the extension the asthenosphere upwells along the preexisting weak suture zone in the southeastern tibetan plateau the thickness of lithosphere is the thinnest along the suture zone and the surface heat flow is the highest however the extension time was found to generally need 10 15 myr to conform to the surface heat flow however this is not consistent with accepted geochronological data when a boundary condition from compression to extension is imposed both the surface heat flow and the lithospheric structure fit well with the observations the results show that the subduction of the indian plate leads to the upwelling of the asthenosphere which causes a thinned lithosphere beneath the tengchong block since the late miocene 8 5 ma the extension or extrusion has been predominant the thermal erosion of the lithosphere caused by upwelling of the asthenosphere renders the lithosphere even thinner along the bangong nujiang suture zone the upwelling of the asthenosphere provides an upward driving force and high temperature environment for the tengchong volcanic region these findings suggest that the origin of the tengchong volcanic region is caused by both the subduction of the indian plate and regional extension across the bangong nujiang suture zone

reply to comments by n sultan on sedimentation controls on methane hydrate dynamics across glacial interglacial stages an example from international ocean discovery program site u1517 hikurangi margin

analysis of the crustal thickness and poisson s ratio in eastern tibet from teleseismic receiver functions summary crustal thickness and poisson s ratio are two key parameters for investigating tectonic setting and evolution the h k technique has become popular to determinate their values in recent years however ifacomplexstructureexistsinthecrust thereverberatedphasesfromdifferent depths may interfere with each other resulting in reduction or even absence of the ppps phase from the moho such that the h k algorithm may not reveal unambiguous estimates of these two parameters in this paper the h k technique is applied to process a synthetic receiver function for a test case the result of which is compared with that from direct picking of the time delays of the converted and reverberated phases then we process the observational data recorded at two stations in eastern tibet determine the crustal thickness and the velocity ratio using the two methods compare the result with that obtained by xu et al a t the same location and analyse the potential causes for discrepancy as well as the reliability of the two methods finally the crustal thickness and the poisson s ratio in eastern tibet and sichuan basin are determined from the receiver functions recorded at 51 broad band stations using the two different methods the results indicate that the crustal thickness from the time delays is thicker than that from the h k algorithm near the eastern himalayan syntaxis and the crustal poisson s ratio in the rigid sichuan basin from the time delays ranges from 0 26 to 0 28 which are more reasonable than that from the h k 0 28 to 0 34 additionally the poisson s ratio under the faults from the time delays is found to be higher than those on the two sides which is consistent with the tectonic background and previous study

constraining melt geometries beneath the afar depression ethiopia from teleseismic receiver functions the anisotropic h κ stacking technique understanding the nature of the crust has long been a goal for seismologists when imaging the earth this is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption receiver functions and the h stacking h technique are often used to constrain crustal thickness h and the ratio of p to s wave velocities in this paper i show that it is essential to consider anisotropy when performing h i show that in a medium with horizontally transverse isotropy a strong variation in with back azimuth is present which characterizes the anisotropic medium in a vertically transverse isotropic medium no variation in with back azimuth is observed but is increased across all back azimuths thus estimates of are more difficult to relate to composition than previously thought i extend these models to melt induced anisotropy and show that similar patterns are observed but with more significant variations and increases in based on these observations i develop a new anisotropic h stacking technique which inverts h data for melt fraction aspect ratio and orientation of melt inclusions i apply this to data for the afar depression and show that melt is stored in interconnected stacked sills in the lower crust which likely supply the recent volcanic eruptions and dike intrusions this new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

magmatic fluid input explaining the geochemical anomaly of very high arsenic in some southern tibetan geothermal waters abstract tibet is characterized by extremely high terrestrial heat flow and widely distributed hydrothermal systems among which many are discharging geothermal waters with extremely high arsenic concentrations from over 10 mg l to up to 126 mg l the distribution of these high arsenic waters is basically in accordance with the location of the indian continental subduction zone a detailed analysis indicates that host rock leaching alone cannot explain the observed arsenic anomaly instead substantial contribution of arsenic from the underlying magma chambers is postulated which are likely mantle derived intrusions that have been severely contaminated by the very thick crustal material below southern tibet possibly including deep seated arsenic rich sedimentary rocks alternatively the partial melts at crustal depths reflected by the detected low velocity and or high conductivity anomalies in southern tibet serving as the magmatic heat source of the high arsenic hydrothermal systems may also form indirectly under the high temperature conditions generated by mantle upwelling or due to crustal thickening low sulfide concentrations further promote high dissolved arsenic concentrations with little formation of thioarsenates and no precipitation of limiting arsenic sulfide phases in contrast mantle magmas less affected by crustal contamination serving as the heat source of many hydrothermal systems in rift zones and hot spots worldwide where the crust is thinner are releasing magmatic fluids lower in arsenic and higher in mantle sulfur species overall the existence of a magmatic heat source alone does not ensure the formation of geothermal waters with very high arsenic concentrations and geothermal waters from sedimentary rock hosted systems are neither necessarily arsenic rich the most critical factor controlling the arsenic concentration of geothermal water discharging from a magmatic hydrothermal system is the geological genesis of the magma fluid and its chemical composition

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

crustal structure in tengchong volcano geothermal area western yunnan china abstract based upon the deep seismic sounding profiles carried out in the tengchong volcano geothermal area tvga western yunnan province of china a 2 d crustal p velocity structure is obtained by use of finite difference inversion and forward travel time fitting method the crustal model shows that a low velocity anomaly zone exists in the upper crust which is related to geothermal activity two faults the longling ruili fault and tengchong fault on the profile extend from surface to the lower crust and the tengchong fault likely penetrates the moho moreover based on teleseismic receiver functions on a temporary seismic network s wave velocity structures beneath the geothermal field show low s wave velocity in the upper crust from results of geophysical survey the crust of tvga is characterized by low p wave and s wave velocities low resistivity high heat flow value and low q the upper mantle p wave velocity is also low this suggests presence of magma in the crust derived from the upper mantle the low velocity anomaly in upper crust may be related to the magma differentiation the tengchong volcanic area is located on the northeast edge of the indian eurasian plate collision zone away from the eastern boundary of the indian plate by about 450 km based on the results of this paper and related studies the tengchong volcanoes can be classified as plate boundary volcanoes

metamorphic decarbonation silicate weathering and the long term carbon cycle the seawater 87sr 86sr curve implies a 50 100 myr episodicity in weathering rate which requires a corresponding variation in co2 degassing from the solid earth to the atmosphere it is proposed that this is caused by orogenesis which both produces co2 as a result of metamorphic decarbonation reactions and consumes extra co2 as a consequence of erosion enhanced weathering global climate on the geological time scale is therefore conttolled by the difference between the relatively large and variable orogenic moderated degassing and weathering co2 fluxes

lithospheric structure and its relationship to seismic and volcanic activity in southwest china 1 the sichuan yunnan region in southwest china is located in the boundary area between the active tibetan plateau to the west and the stable south china platform to the east this region is characterized by complex cenozoic structures and active seismotectonics in this study we have used over 30 000 arrival times from 1315 local earthquakes recorded by 172 seismic stations to determine a detailed three dimensional 3 d p wave velocity structure of the lithosphere down to 85 km depth in this region we have taken into account the complex morphology of the moho discontinuity to conduct the tomographic inversions which leads to a better result than that with a flat moho as in the previous studies our results show that large velocity variations of up to 7 exist in the crust and upper mantle in the sichuan yunnan region the velocity image of the upper crust correlates with the surface geological features the sichuan basin is imaged as a prominent low velocity zone while the panzhihua mining district is imaged as a high velocity feature velocity changes are visible across some of the large fault zones and the faults and some large crustal earthquakes seem to occur at the boundary areas between slow and fast velocity anomalies some of the faults such as the red river fault may have cut through the crust and reached up to the upper mantle under the tengchong volcanic area strong low velocity zones are visible down to 85 km depth with a lateral extent of about 100 km suggesting the existence of magma chambers under the volcano it is unclear how the tengchong intraplate volcanism was generated it may be related to the collision processes between the indian plate burma microplate and the eurasian plate and the possible subduction of the burma microplate under the eurasian plate another possibility is that it was caused by the extensional fractures of the lithosphere and the upward intrusion of the hot asthenospheric materials it is also possible that the tengchong volcanism represents a hot spot with a lower mantle origin

magma mixing recorded by sr isotopes of plagioclase from dacites of the quaternary tengchong volcanic field se tibetan plateau abstract the tengchong volcanic field east of the burma arc in sw china comprises numerous quaternary volcanoes the volcanic rocks can be grouped into four units numbered 1 4 from oldest to youngest units 1 3 and 4 are composed of trachybasalt basaltic trachyandesite and trachyandesite respectively whereas unit 2 consists of hornblende dacite primary minerals in the dacite include plagioclase clinopyroxene amphibole and magnetite all set in a glassy groundmass some of the dacites are moderately to highly weathered and show effects of low temperature alteration with loss on ignition loi up to 9 6 wt and positive correlations of loi with al2o3 but negative correlations with sio2 cao and na2o fresh dacites loi plagioclase in the fresh dacite has relatively high sr contents and 87sr 86sr ratios ranging from 0 7050 to 07125 except for one value of 0 7516 whereas plagioclase in the altered dacite has low sr contents and highly variable sr isotopic compositions 0 7039 0 7138 indistinguishable from those of the fresh rocks both an values and sr isotopic compositions of the plagioclase indicate mixing of mantle and crustally derived magmas we therefore propose that mantle derived basaltic magma caused partial melting of the lower middle crust and that mixing of the mafic and felsic magmas produced the dacite in staging magma chambers the dacites contain minerals crystallized from both the mafic and felsic magmas as well as a few xenocrysts plucked from the country rocks

three dimensional velocity structure of crust and upper mantle in southwestern china and its tectonic implications using p and s arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations this paper presents a three dimensional crustal and upper mantle velocity structure of southwestern china 21 34 n 97 105 e southwestern china lies in the transition zone between the uplifted tibetan plateau to the west and the yangtze continental platform to the east in the upper crust a positive velocity anomaly exists in the sichuan basin whereas a large scale negative velocity anomaly exists in the western sichuan plateau consistent with the upper crustal structure under the southern tibetan plateau the boundary between these two anomaly zones is the longmen shan fault the negative velocity anomalies at 50 km depth in the tengchong volcanic area and the panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle the red river fault is the boundary between the positive and negative velocity anomalies at 50 km depth the overall features of the crustal and the upper mantle structures in southwestern china are a low average velocity large crustal thickness variations the existence of a high conductivity layer in the crust or and upper mantle and a high heat flow value all these features are closely related to the collision between the indian and the asian plates

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

the lithosphere asthenosphere boundary beneath the western united states summary s receiver functions from 67 broad band seismic stations in the western united states clearly reveal the existence of a mantle discontinuity with velocity reduction downward which we interpret as the lithosphere asthenosphere boundary lab the average depth of the lab is 70 km the boundary is relatively sharp with an overall sharpness of less than 20 km the boundary is more prominent south of the mendocino triple junction where the farallon plate has completely subducted this may indicate partial melts at the base of the lithosphere caused by the upwelling of the asthenospheric flow through the slab window a double low velocity zone is observed at base of the lithosphere beneath southern sierra nevada implying a second melting zone at a depth of 100 km well correlated with previous studies of lithospheric delamination in the area

u series ages of young volcanoes from the southeastern tibetan plateau holocene eruptions and magma evolution timescales abstract the tengchong volcanic field in southwestern china represents rare quaternary volcanic eruptions and associated active geothermal activities on the southeastern margin of the tibetan plateau the reported eruption ages for the 3 youngest tengchong volcanoes heikongshan dayingshan maanshan are highly variable 3 0 482 ka because of the challenge to accurately and precisely date young volcanic rocks by radiometric methods here we use high resolution 238u 230th 226ra disequilibria to constrain the eruption ages and magma evolution timescales all 3 young volcanoes exhibit whole rock 226ra 230th disequilibrium ranging from 1 27 to 1 71 indicating eruption ages of 230th ages of zircons from heikongshan dayingshan and maanshan zircon age populations are 54 6 13 ka and 94 9 4 1 ka for heikongshan 59 6 5 8 and 90 1 8 4 for dayingshan and 53 8 8 7 ka and 76 5 11 ka for maanshan magma residence times for all 3 volcanoes are 50 kyr for a shallow stage and 85 kyr for a deep stage in a two stage magma chamber system below tengchong the similar zircon age distributions for the 3 volcanoes from tengchong indicate simultaneous magmatism at 90 ka and 55 ka and imply interconnected nature of these volcanoes

shallow methane hydrate system controls ongoing downslope sediment transport in a low velocity active submarine landslide complex hikurangi margin new zealand morphological and seismic data from a submarine landslide complex east of new zealand indicate flow like deformation within gas hydrate bearing sediment this creeping deformation occurs immediately downslope of where the base of gas hydrate stability reaches the seafloor suggesting involvement of gas hydrates we present evidence that contrary to conventional views gas hydrates can directly destabilize the seafloor three mechanisms could explain how the shallow gas hydrate system could control these landslides 1 gas hydrate dissociation could result in excess pore pressure within the upper reaches of the landslide 2 overpressure below low permeability gas hydrate bearing sediments could cause hydrofracturing in the gas hydrate zone valving excess pore pressure into the landslide body 3 gas hydrate bearing sediment could exhibit time dependent plastic deformation enabling glacial style deformation we favor the final hypothesis that the landslides are actually creeping seafloor glaciers the viability of rheologically controlled deformation of a hydrate sediment mix is supported by recent laboratory observations of time dependent deformation behavior of gas hydrate bearing sands the controlling hydrate is likely to be strongly dependent on formation controls and intersediment hydrate morphology our results constitute a paradigm shift for evaluating the effect of gas hydrates on seafloor strength which given the widespread occurrence of gas hydrates in the submarine environment may require a reevaluation of slope stability following future climate forced variation in bottom water temperature

geochemistry dissolved elemental flux rates and dissolution kinetics of lithologies of alaknanda and bhagirathi rivers in himalayas india alaknanda and bhagirathi ab river basins in the himalayan region in india expose lithologies comprising mainly of granites low high grade metamorphics shales and carbonates which in conjunction with the monsoon rains and glacial melt control water chemistry and dissolved elemental flux rates in the present study we monitored two locations a srinagar on the alaknanda river and b maneri on the bhagirathi river for daily variations in total suspended sediments major ions and dissolved silica over one complete year july 2004 june 2005 based on long term discharge data discharge weighted composition and dissolved elemental flux rates with respect to ca mg hco3 si of the river were estimated the information thus obtained has substantially added up to the existing chemical data of these rivers and has refined the flux rates our high frequency samples provide informations such as a water chemical compositions that show a large temporal and spatial variation and b carbonate lithology that controls water chemistry predominantly the dissolution kinetics of various lithologies namely leucogranite gneiss quartzite phyllite and shale of the ab river basins were studied through batch experiments at controlled temperature 25 and 5 c and ph 8 4 condition in laboratory these lithologies undergo slow rates of dissolution 10 13 to 10 15 mol m2 s while field weathering rates based on dissolved elemental flux rates in the ab rivers are much higher 10 8 to 10 9 mol m2 s extremely high physical weathering rates in ab rivers which enhance chemical weathering significantly mainly attribute this wide discrepancy in laboratory derived rates of representative basin rocks and dissolved elemental fluxes in the field however laboratory simulated experiments facilitate to quantify elemental release rates understand the kinetics of the dissolution reactions and compare their roles at individual level

the groundwater geochemistry of the bengal basin weathering chemsorption and trace metal flux to the oceans sixty eight groundwater samples from the ganges brahmaputra floodplain in the bengal basin were analyzed to assess the groundwater geochemistry the subsurface hydrology the buffering effects of sediments on trace metal concentrations and their isotopic compositions and the magnitude of the subsurface trace element flux to the bay of bengal and to the global ocean samples obtained from depths of 10 to 350 m were measured for major and trace elements dissolved gas and tritium on the basis of the 3he 3h ages the groundwater at depth 30 150 m appears to be continually replenished indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the bay of bengal using the 3he 3h groundwater age depth relationship to calculate a recharge rate of 60 20 cm yr we estimate a subsurface discharge into the bay of bengal of 1 5 0 5 1011 m3 yr or 15 of the surface ganges brahmaputra river gbr flux several trace elements especially sr and ba display elevated concentrations averaging 7 to 9 times the surface gbr water values the submarine groundwater fluxes of sr and ba to the oceans are 8 2 2 108 and 1 5 0 3 108 mol yr or 3 3 and 1 2 respectively of the world total or equal to the surface gbr sr and ba estimated fluxes our groundwater flux for ba agrees with the estimate of moore 1997 3 108 3 109 mol yr on the basis of measured ba and ra excesses in the bay of bengal other trace metals such as u and mo are at low but measurable levels and are not major contributors to the global flux in this river system a comparison of the sr and ba concentrations plus 87sr 86sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core suggests that weathering of carbonates and minor silicates coupled with cation exchange plus adsorption and desorption reactions controls the trace element concentrations and 87sr 86sr isotopic compositions in both the groundwater and river water our data also imply that other coastal floodplains e g the mekong and the irrawaddy rivers that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the sr isotopic evolution in seawater

fine crustal and uppermost mantle s wave velocity structure beneath the tengchong volcanic area inferred from receiver function and surface wave dispersion constraints on magma chamber distribution the tengchong volcanic area is located in the southeastern margin of the collision zone between the indian and eurasian plates it is one of the youngest intraplate volcano groups in mainland china imaging the s wave velocity structure of the crustal and uppermost mantle beneath the tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity in this study we analyze teleseismic data from nine broadband seismic stations in the tengchong earthquake monitoring network we then image the crustal and uppermost mantle s wave velocity structure by joint analysis of receiver functions and surface wave dispersion the results reveal widely distributed low velocity zones we find four possible magma chambers in the upper to middle crust and one in the uppermost mantle the chamber in the uppermost mantle locates in the depth range from 55 to 70 km the four magma chambers in the crust occur at different depths ranging from the depth of 7 to 25 km in general they may be the heat sources for the high geothermal activity at the surface based on the fine crustal and uppermost mantle s wave velocity structure we propose a model for the distribution of the magma chambers

erosion of the seafloor at the top of the gas hydrate stability zone on the hikurangi margin new zealand 1 the dissociation of gas hydrates in sediment pores is thought to decrease seafloor strength potentially facilitating submarine slides because of the generation of overpressured gas and the melting of load bearing or cementing solid hydrate here we present findings that suggest gas hydrates may lead to a previously unknown mechanism of seafloor erosion gas hydrate bearing sub sea ridges on the hikurangi margin are eroded close to the top of the hydrate stability field in the ocean we hypothesize that gas hydrate instability may lead to ridge erosion by a combination of two processes hydrate destabilization caused by depressurization during ridge uplift and repeated pore volume expansion and contraction from hydrate dissociation and formation triggered by fluctuating water temperatures

lateritic bauxite in central germany and implications for miocene palaeoclimate intense chemical weathering during middle miocene times led to the formation of deep ferralitic weathering profiles on the vogelsberg basaltic massif saprolite more than 50 m thick was formed and in its higher parts bauxite concretions developed by absolute accumulation of aluminium the tops of the profiles consist mostly of allochthonous lateritic bauxite which has been mined intensively in the past similar high latitude bauxites occur on the paleogene basalts of ireland these formed during a phase of recognized greenhouse conditions with a climatic optimum near the paleocene eocene boundary while during the miocene the climate was already changing toward quaternary icehouse conditions however the occurrence of deep weathering profiles with lateritic bauxite at the high palaeolatitude of 45 n may be interpreted as pointing to extreme climatic conditions also during the middle miocene the associated laterites and bauxites on middle miocene basalts 17 15 ma provide evidence for a global climatic optimum around 17 14 5 ma reduced uplift rates of the himalayan tibetan plateau and associated reduced co2 consumption coupled with additional volcanogenic co2 production could have induced high atmospheric co2 and an intensification of the global greenhouse effect this may be reflected in accelerated chemical weathering and bauxite formation basalt volcanism has thus provided both a source eruption and a sink via weathering of co2

climate change during the last 150 million years reconstruction from a carbon cycle model variations of the atmospheric co2 level and the global mean surface temperature during the last 150 ma are reconstructed by using a carbon cycle model with high resolution input data in this model the organic carbon budget and the co2 degassing from the mantle both of which would characterize the carbon cycle during the cretaceous are considered and the silicate weathering process is formulated consistently with an abrupt increase in the marine strontium isotope record for the last 40 ma the second order variations of the atmospheric co2 level and the global mean surface temperature in addition to the first order cooling trend are obtained by using high resolution data of carbon isotopic composition of marine limestone seafloor spreading rate and production rate of oceanic plateau basalt the results obtained from this model are in good agreement with the previous estimates of palaeo co2 level and palaeoclimate inferred from geological biogeochemical and palaeontological models and records the system analyses of the carbon cycle model to understand the cause of the climate change show that the dominant controlling factors for the first order cooling trend of climate change during the last 150 ma are tectonic forcing such as decrease in volcanic activity and the formation and uplift of the himalayas and the tibetan plateau and to a lesser extent biological forcing such as the increase in the soil biological activity the mid cretaceous was very warm because of the high co2 level 4 5 pal maintained by the enhanced co2 degassing rate due to the increased mantle plume activities and seafloor spreading rates at that time although the enhanced organic carbon burial would have a tendency to decrease the co2 level effectively at that period the variation of organic carbon burial rate may have been responsible for the second order climate change during the last 150 ma

comprehensive crustal structure and seismological evidence for lower crustal flow in the southeastern margin of tibet revealed by receiver functions abstract the lower crustal flow model has become an interesting proposal to describe the growth and expansion of eastern tibet to date however the geophysical results are not definitive due to the non uniqueness of the solutions found through data inversion and the resolution limitations in this study the polarity of p to s converted phases at intra crustal interfaces are analyzed in order to reveal evidence for low seismic velocity and lower crustal flow in southeastern tibet we are interested in a joint study that is both a mapping of the crustal structure moho topography and poisson s ratio and an attempt to constrain an iclvz we have determined the crustal thickness and poisson s ratio from p prfs and s srfs receiver functions acquired in 108 permanent seismic stations deployed in the sichuan and yunnan areas also we have obtained 98 measurements of pms phase splitting parameters at the array stations the crustal thickness provided by prfs is consistent with that given by srfs it varies from 60 km in the songpan ganzi sg fold system and the northern part of the sichuan yunnan diamond shaped block sydsb near the eastern himalayan syntaxis to 33 km in southern yunnan the poisson s ratio varies mostly from 0 24 to 0 32 the highest values 0 28 0 32 are found along the axis formed by the longmenshan fault the lijiang jinhe fault and in the tengchong volcano area the value of 0 28 observed in sydsb and the sg fold system is attributed to the presence of a low velocity zone in the lower crust and partly to the great sediment thickness in sichuan basin the crust is clearly anisotropic in the southeastern margin of tibet the fast wave polarization direction exhibits a nw se regional bias while the time delay varies between 0 07 s and 1 27 s being the average 0 54 s 0 12 s implying the existence a strong shear zone in the lower crust based on the negative polarity observed after the direct p wave in teleseismic receiver functions we have detected an intra crustal low velocity zone iclvz in a wide region including east and southeast of tibet and southern yunnan so both the shear zone and iclvz suggest the existence of lower crustal flow the reverberation ppps and psps ppss phases at the moho are clearly weaker in sydsb and the sg fold system than in the indochina block and eastern yunnan implying that sydsb has a structure and tectonic history different from indochina on its west side and eastern yunnan on its east side the above results provide seismological evidence for a lower crustal flow spreading from the eastern tibet and that in its advance southward has invaded sydsb widely crossed the lijiang jinhe fault and reached southern yunnan

comment on sedimentation controls on methane hydrate dynamics across glacial interglacial stages an example from international ocean discovery program site u1517 hikurangi margin by e j screaton et al

geochemical consequences of increased late cenozoic weathering rates and the global co2 balance since 100 ma large imbalances in the relative net co2 flux over the last 100 m y are obtained from independently derived estimates of co2 uptake by weathering and organic carbon burial and of co2 outgassing assumed proportional to the mean mid ocean ridge mor spreading and mantle plume production mpp rates increasing the river flux of ca mg p and c by 50 since 30 ma to parallel the proposed increase in the sr river flux needed to explain the sr isotopic evolution of seawater richter et al 1992 has a large impact on the global carbon cycle by reducing the excess net co2 imbalance in the late cenozoic co2 uptake is calculated by assuming that 19 of the ca river flux and 60 of the mg river flux are derived from weathering silicates and that mg is removed in the oceans by 1 1 molar exchange reactions with calcsilicates an increase in the mg river flux combined with an overall decrease in the mor spreading rate predicts as much as a factor of 2 increase in the seawater mg concentration since 100 ma the net organic carbon burial flux burial minus weathering largely reflects changes in the bulk carbonate 13c record and to a lesser extent variations in the net carbonate burial flux and mean 13c value of the carbonate weathering flux organic carbon burial efficiency is markedly less than that of p from the middle middle miocene to the present because of early diagenetic transfer of organic p to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations the large co2 imbalance of the late cretaceous requires significantly less carbonate subduction or greater weathering rates a co2 balance can be achieved in the miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted variations in shallow water carbonate burial and hence the global carbonate record are currently too poorly known to differentiate between the above possibilities the decrease in the excess co2 flux generally parallels the trend to cooler climate inferred from the 18o record but periods of large co2 imbalance generally precede 18o shifts by several million years

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes

oyster shells as recorders of short term oscillations of salinity and temperature during deposition of coral bioherms and reefs in the miocene lorca basin se spain abstract we use 18 o and 13 c of oyster shells inferred seawater 18 o w and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo salinities of marginal marine waters of the miocene lorca basin spain salinities ranged from 22 to 32 psu during growth of coral bioherms and carpets of the soriana and parrilla formations and from 35 to 39 psu during deposition of the hondo formation reef complex the periods with lower modeled salinities correspond with deltaic and alluvial fan sedimentation in the area the modeling is supported by 87 sr 86 sr data and provides new insights into the evolution of the local depositional settings departures of sr isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities and the non oceanic 87 sr 86 sr preserved in individual oyster shells was probably sourced from uplifted aquitanian burdigalian limestones 87 sr 86 sr values that plot along the global ocean sr isotope curve for the late miocene indicate a tortonian age for the upper part of the soriana formation and the parrilla formation and a messinian age for the hondo formation more generally we demonstrate how the chemical analyses of oyster shells provide additional information regarding short term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods

magma system beneath tengchong volcanic zone inferred from local earthquake seismic tomography abstract the tengchong volcanic zone tcvz located in the southeastern part of the india eurasia collision zone is characterized by large scale volcano groups significant thermal activities and active seismicity to reveal the magma system we present new 3 d models of vp vs and vp vs ratio to 10 km depth beneath the tcvz based on the tomographic inversion of p and s wave arrival times from local earthquakes recorded by 10 broadband seismic stations we use arrival times to construct a reference velocity model checkerboard and jackknife tests are carried out to assess the reliability of the inversion results at shallow depths we suggest that the complex distribution of high vp vs ratio is the result of a combination of water and magmatic activity at depth of 10 km only three areas show obvious high vp vs ratio corresponding to areas of high relative geothermal value observed through hot springs at the surface we suggest that the three high vp vs ratio areas are magma chambers the upwelling volatiles heat the water in the shallow layer inducing the corresponding high relative geothermal value at the surface meanwhile the magma chamber beneath rehai spring which corresponds to high he3 he4 ratio may be fed by mantle magma we suggest that the heikongshan volcano and dayingshan volcano are fed by the magma chambers and that maanshan volcano is separated from the magma we also infer that the significant geothermal activity and active seismicity beneath rehai spring are the result of interaction between the magma and hot water reservoir

seismic structure beneath the tengchong volcanic area southwest china from receiver function analysis abstract tengchong is a young volcanic area on the collision boundary between the indian and euro asian plates of the southeastern tibetan margin holocene volcanoes are concentrated in the tengchong basin where they align an n s trending string like cluster to study the magma activity and its relation with the volcanoes we deployed a passive seismic observation across the volcanic area in northern tengchong using tele seismic data and receiver function technique we determined the s wave velocity structure beneath nine temporary stations results show that the tengchong basin is underlain by prominent low velocity zones that are associated with the magma chambers of the volcanoes in the north a small and less pronounced magma chamber lies beneath two crater lakes with a depth range of 9 16 km and a lateral width of

moho depth seismicity and seismogenic structure in china mainland abstract the study of the crust upper mantle structure based on wide angle seismic profiles performed in china mainland since 1958 has provided tighter constraints on the architecture and deformation of the lithosphere but the link between the seismic velocity structure and the seismogenic layer of the crust is still an open problem in which we are particularly interested starting from the crustal p wave velocity models obtained along numerous seismic profiles we have mapped the moho depth beneath east asia the results demonstrate that the average moho depth is about 35 km in southeast china 38 km in north and northeast china 51 km in northwest china and 65 km in tibet the moho depth varies between 20 and 28 km in the continental margin and sea area most of the earthquakes in china mainland have magnitude lower than 4 0 and generally occur in the uppermost 20 km of the crust and therefore above the moho discontinuity the average focal depth is found at 10 km in southeast china 12 km in north and northeast china 15 km in northwest china and 13 km in the tibetan plateau the ratio of the average focal depth to the moho depth is approximately 0 3 taking the lower bound of the natural seismicity as the depth above which is located 90 of the foci of earthquakes we have found this limit at depths of 21 41 30 and 36 km in each of the mentioned blocks respectively in north and northeast china some earthquakes occur below the moho at 41 km depth on average versus 38 km although the average focal depth observed here is of only 12 km once defined the seismogenic layer as the layer that concentrates 80 of the released seismic energy we have found that the difference in seismic velocity with respect to the other two crustal layers which extend above and below varies from 0 1 to 0 9 km s in east asia this finding enables to discriminate the place with greater or lesser capacity to generate seismic energy a difference in seismic velocity bigger than 0 9 km s would mean that the layer has an earthquake generating capacity lesser than the seismogenic layer as greatly happens in south china and northwest china while a smaller velocity difference would imply that the layer has a comparable seismogenic capacity as happens in tibet

the significance of himalayan rivers for silicate weathering rates evidence from the bhote kosi tributary the significance of weathering by himalayan runoff for both the sr isotope marine record and the removal of atmospheric co2 through silicate dissolution has been examined by systematic sampling of dissolved loads and bedloads from the bhote kosi a tributary of the ganges that rises in tibet from tethyan sediment bedrock and traverses the major himalayan lithologies of eastern nepal before debouching onto the gangetic plains throughout the section the cation geochemistry of water samples is dominated by ca and mg ions suggesting that carbonates are the predominant lithology undergoing dissolution particularly within the lesser himalayas as the river transects the metasedimentary and granitic lithologies of the high himalayas the sr isotope ratio of the bedload rises rapidly closely reflecting the isotope geochemistry of the bedrock in contrast the 87sr 86sr ratio of the dissolved load remains roughly constant 0 719 0 723 downstream of the main central thrust where the river transects the carbonate bearing lithologies of the lesser himalayas the 87sr 86sr ratio of the dissolved load rises sharply 0 768 the relative contributions of silicate and carbonate weathering from each of the main himalayan units has been estimated from major cation sr concentration and sr isotope mass balance equations these calculations suggest that the high sr and high 87sr 86sr characteristics of riverine analyses arise initially from a component dissolved from the tibetan sedimentary series which is substantially enhanced by input weathering fluxes particularly as the river traverses the lesser himalayas whilst mechanical erosion is maximised within the high himalayan crystalline series as confirmed by 143nd 144nd ratios from the bedload at least 63 of the dissolved load is acquired by chemical weathering of bedrock lithologies and or of transported particulates within the lesser himalayas enhanced by higher ambient temperatures and slower discharge rates this may involve continued dissolution of the high himalayan crystalline series particulates in addition to lesser himalayan lithologies although himalayan rivers collectively have a major influence on the sr isotope marine record the high 87sr 86sr ratios of their dissolved load results from the mixing of a small component 90 of carbonate derived material some of which is characterised by a high 87sr 86sr ratio up to 0 8 elevated 87sr 86sr ratios in rivers are therefore not necessarily indicative of anomalously high dissolution rates of silicates

systematic variations in c o and sr isotopes and elemental concentrations in neoproterozoic carbonates in namibia implications for a glacial to interglacial transition abstract we analyzed c o and sr isotopic compositions of neoproterozoic cap carbonates overlying a glacial deposit in namibia to trace environmental changes following the glaciation the three isotopic records showed coherent and phased changes that corresponded to the stratigraphic variation a lower rhythmite unit had three intervals which were distinguished by isotopic variations and mineral type in the basal interval 13 c increased exponentially from a negative value 4 3 pee dee belemnite pdb 13 c values were relatively constant in the middle interval and increased again to positive values in the top interval indicating a phased removal of 13 c depleted carbon from the surface ocean the gradual increase to larger values 6 in the upper stromatolite unit was interpreted to reflect a change in seawater composition resulting from biological activity after environmental recovery from the glacial episode 18 o values and sr isotopic ratios decreased in the basal interval and approached stable values in the middle interval they increased in the upper interval and fluctuated in the stromatolite unit on the basis of geochemical screening criteria for detecting diagenetic alteration of sr isotopes the middle interval of the rhythmite unit with a minimum 87 sr 86 sr ratio of 0 70685 was interpreted to have retained the primary value or to have the least altered sr isotopic composition the basal interval which had ratios 0 718 at its base as high as those of old sialic rocks was interpreted as having altered sr isotopic ratios the high sr isotopic ratios at the base of this interval gradually decreased to near the minimum value at the top of the interval and other isotopic compositions and trace element concentrations showed systematic variations such systematic variations except for the variation in na concentration can be explained by a progressive diagenetic fluid rock interaction alternatively they might reflect a compositional transition from a local transport limited water following the glaciation to global well mixed seawater

major and trace element geochemistry in upper ganga river in the himalayas india chemical weathering and resulting water compositions in the upper ganga river in the himalayas were studied for the first time temporal and spatial sampling for a 1 year period monthly intervals was carried out and analyzed for dissolved major elements trace elements rare earth elements ree and strontium isotopic compositions amounts of physical and chemical loads show large seasonal variations and the overall physical load dominates over chemical load by a factor of more than three the dominant physical weathering is also reflected in high quartz and illite mica contents in suspended sediments large seasonal variations also occur in major elemental concentrations the water type is categorized as hco3 so42 ca2 dominant which constitute 60 of the total water composition on an average only about 5 12 of hco3 is derived from silicate lithology indicating the predominance of carbonate lithology in water chemistry in the head waters of the ganga river more than 80 na and k are derived from silicate lithology the silicate lithology is responsible for the release of low sr with extremely radiogenic sr 87sr 86 sr 0 75 in bhagirathi at devprayag however there is evidence for other end member lithologies for sr other than carbonate and silicate lithology trace elements concentrations do not indicate any pollution although presence of arsenic could be a cause for concern high uranium mobilization from silicate rocks is also observed the ree is much less compared to other major world rivers such as the amazon perhaps because in the present study only samples filtered through 0 2 m were analysed negative eu anomalies in suspended sediments is due to the excess carbonate rock weathering in the source area

seasonal variation of the solute and suspended sediment load in gangotri glacier meltwater central himalaya india abstract a systematic study on the seasonal variation of major cations and anions was carried out to understand the source of dissolved ions as well as the geochemical weathering processes controlling the meltwater chemistry of gangotri glacier calcium and magnesium are the major cations while sulphate is the dominant anion followed by bicarbonate the high ratios of ca mg na k ca na mg na hco3 na and low ratio of na k tz for pre monsoon monsoon and post monsoon seasons indicate the dominance of carbonate weathering which is a major source of the dissolved ions in the meltwater of gangotri glacier followed by silicate weathering high equivalent ratios of na cl and k cl as compared to sea water indicate relatively lesser contribution from atmospheric input to the chemical composition of meltwater correlation matrix and factor analysis were used to identify various factors controlling the major ion chemistry marked seasonal and diurnal variations were observed in the dissolved ions and suspended sediment concentration daily mean suspended sediment concentration for pre monsoon monsoon and post monsoon was observed as 1719 3281 and 445 mgl 1 respectively highest suspended sediment load was observed in monsoon season followed by pre monsoon and post monsoon seasons the cation denudation rates of gangotri glacier meltwater were calculated to be 42 2 46 5 and 15 9 t km 2 y 1 for pre monsoon june only monsoon and post monsoon respectively these values are higher than that of other himalayan glaciers whereas physical weathering rate of the gangotri glacier catchment was observed to be 7056 15 344 and 588 t km 2 y 1 for pre monsoon june only monsoon and post monsoon respectively much higher than the indian and world averages of river

insight into the origin of the tengchong intraplate volcano and seismotectonics in southwest china from local and teleseismic data received 18 june 2008 revised 22 february 2009 accepted 10 march 2009 published 13 may 2009 1 a high resolution tomographic image of the crust and upper mantle under yunnan province in southwest china was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense yunnan seismic network the grid spacing of the tomographic model is 70 km 78 km in the horizontal directions and 4 70 km in depth our resulting model shows a clear low velocity low v 0 3 with respect to the average one dimensional velocity model column extending from the surface down to about 400 km depth under the active tengchong volcano and some high velocity high v anomalies existing in the mantle transition zone furthermore the low vanomaly extends horizontally toward the northeast at 250 to 400 km depth combining our tomographic results with geochemical and geological investigations we infer that the tengchong volcano is a rift related volcano caused by the subduction and dehydration of the indian plate as well as corner flow in the mantle wedge though the subducted slab is a continental plate our results show that the upwelling flow under tengchong originates at 400 km depth a prominent low v anomaly along the red river fault zone extends down to the upper mantle 100 km depth reflecting that the red river fault zone may have cut through the crust to the upper mantle the two dayao earthquakes m 6 1 and m 6 2 in 2003 occurred on the margin of high v anomalies and are underlain by a prominent low v anomaly in the lower crust and upper mantle suggesting that the dayao earthquakes may be associated with fluids released from the dehydration of the subducted indian slab these results are significantly improved compared with previous studies and provide new seismic constraints on the dynamic processes of the india asia collision

estimation of atmospheric co2 uptake by silicate weathering in the himalayas and the tibetan plateau a review of existing fluvial geochemical data

comment on excess pore pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach by wenyue xu and leonid n germanovich while it is well accepted that gas hydrate dissociation at the base of the gas hydrate stability zone ghsz can generate high excess pore pressure and leads to sediment deformation the consequence in terms of pore pressure of the dissolution of the gas hydrate at the top of the gas hydrate occurrence zone ghoz remains neglected the purpose of this comment on xu and germanovich 2006 article is to demonstrate that gas hydrate dissolution in the ghsz may generate excess pore pressure and to point out the risk related to hydrate dissolution at the top of the ghoz

sedimentation controls on methane hydrate dynamics across glacial interglacial stages an example from international ocean discovery program site u1517 hikurangi margin

nd and sr isotope characteristics of quaternary indo gangetic plain sediments source distinctiveness in different geographic regions and its geological significance quaternary sediments of the himalayan foreland basin known also as the indo gangetic plains have been studied for their sr and nd isotope geochemistry to constrain their sources and to infer their geological significance the data show a large variation in the sr 87 sr 86 values and relatively a minor variation in the epsilon nd 0 values for compositionally homogeneous sediments sediments of the ganga yamuna and satluj systems have high sr 87 sr 86 0 75 and low epsilon nd 0 16 all relative to the previous group suggesting their derivation from the sub himalayan sediments including tertiary subathu formation the subathu was likely derived from the indus tsangpo suture zone basaltic volcanics and tibetan sedimentary series the thar desert ghaggar river sediments are isotopically similar to those of the indus plain indicating a shared provenance either immediate or ultimate the exposed sediments of the incised yamuna river at kalpi in the ganga yamuna plains were derived from peninsular india these southern ganga yamuna plain sediments are isotopically similar to the thar desert ghaggar river sediments although the juvenile components of their provenance differ the vindhyans deccan traps and indus tsangpo suture zone volcanics respectively in the southern ganga plain the peninsular wedge of sediments could be present at depths below about 12 m interbedded or mixed with himalayan sediments the isotope geochemistry of sediments also shows that the earliest influx of the himalayan sediments to the ganga yamuna interfluve occurred around 68 70 ka this indicates that the yamuna river has been flowing in the region at least since the late pleistocene the dynamic relationship between the yamuna and chambal rivers in the region negates the idea of yamuna being a tributary of ghaggar saraswati river system during the harappan time 3500 to 1900 bc