chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

major and trace element abundances and strontium isotopes in the nyong basin rivers cameroon constraints on chemical weathering processes and elements transport mechanisms in humid tropical environments this paper aims to improve our understanding of chemical weathering processes and element transport mechanisms in the humid tropical environments we studied the nyong river basin 27 800 km2 located on the northwestern part ntem complex of the congo craton central africa the dissolved concentrations i e 0 20 m of major and trace elements dissolved organic carbon doc and the 87sr 86sr ratios have been measured in more than 20 rivers draining watersheds with various surface areas 1 to 28 000 km2 all these rivers exhibit low major cations concentrations i e na mg k ca but high concentrations of some trace elements al fe th zr y ree silica and doc the total dissolved load tds is low 20 mg l 1 and dominated by silica and organic matter the comparison of different watersheds shows us that chemical weathering is more efficient in the small unit watersheds all the sampled rivers exhibit a wide range of 87sr 86sr ratios and high ca na ratio that can be explained by the heterogeneity of the crystalline rock constituting the cratonic basement four selected rivers mengong awout soo and nyong having different drainage areas and hydrological parameters were sampled over a 2 year period collected data show that all these rivers present the same monthly seasonal variations with higher concentrations during rainy season and lower concentrations during dry season this implies that the weathering and transport mechanisms of small watersheds can be extended to the whole nyong basin in the small unit watersheds chemical weathering mainly occurs in swamp zones where mineral dissolution is enhanced by humic substances these swamp zones constitute a pool of organic rich water which can be quickly mobilized during rain seasons in these waters doc and insoluble element concentrations e g al fe and th were strongly correlated which show the key role of organic colloidal matter in the transport of some insoluble elements some other relationships al vs fe ree vs al were also examined in order to get information about chemical weathering or element transport based on these data it has been concluded that the chemical composition of these river waters is controlled by geomorphic and historic factors e g thick cation poor soil in contrast the present day climatic parameters high rainfall and temperature play a minor role in water chemistry regulation even though they are likely to enhance mineral dissolution even if organic matter favors mineral dissolution chemical weathering in this area is low compared to other world regions which suggest on a global scale a relatively small effect of these environments on the co2 consumption

nanometric inclusions of carbonates in kokchetav diamonds from kazakhstan a new constraint for the depth of metamorphic diamond crystallization abstract previous studies have revealed that microdiamonds from the kokchetav ultra high pressure metamorphic terrane of kazakhstan contain nanometric scale inclusions of si fe ti and cr oxides because the structure of sio 2 inclusions was not confirmed to be coesite or stishovite due to their very small size such diamonds formerly served only as an indicator of a minimum pressure ca 4 gpa geothermobarometry applied to kokchetav diamond bearing rocks yielded a wide range of conditions t 700 c 1250 c and p 4 9 gpa our paper presents transmission electron microscopy studies with focused ion beam assistance that indicate that diamonds from marbles contain inclusions of aragonite caco 3 and magnesite mgco 3 and that aragonite and nitrogen bearing nanometric particles are associated with dislocations reflecting diamond growth at relatively high temperature conditions we determined the boundary of dolomite stability using the reaction camg co 3 2 dolomite caco 3 aragonite mgco 3 this allowed us to utilize available experimental data to evaluate the pressure at which diamond was crystallized taking into consideration uncertainties existing between experimental data produced in different laboratories we propose the pressure for kokchetav diamond crystallization to be 6 to 9 gpa this evaluation is based on the assumption that temperature was determined correctly as 980 c minimum and 1250 c maximum for diamond grade dolomitic marbles our data provide strong evidence that the metasedimentary rocks of the kokchetav massif containing diamonds were subducted to the depth of 190 280 km

topographic characteristics of laboratory induced shear fractures the topography of laboratory induced shear fracture surfaces of westerly granite was studied three types of fracture surfaces were examined 1 a fresh fracture from the shear failure of an intact sample under polyaxial loading 2 40 mpa 3 15 mpa 2 a shear fracture subjected to frictional sliding of 100 m under polyaxial loading 3 a shear fracture subjected to frictional sliding of 800 m under conventional triaxial loading 1 2 3 40 mpa both sliding distances are within the range of the grain size of westerly granite the results are represented by a power spectral method

seasonal contributions of catchment weathering and eolian dust to river water chemistry northeastern tibetan plateau chemical and sr isotopic constraints relative to winter it is noticeable that both the lowest and the highest 87 sr 86 sr values of the buha river waters occurred in the monsoon season indicating a sensitive response of carbonate versus silicate weathering sources to hydrological forcing on a seasonal basis a significant decrease in na cation together with lower sr isotope ratios is consistent with a greater proportion of carbonate weathering relative to silicate weathering in the early monsoon season high temperature and increased rainfall during the peak of the monsoon facilitate an increased proportion of ions derived from silicates partly from groundwaters to river water in other seasons elemental and 87 sr 86 sr ratios vary much less indicating a constant ratio of silicate to carbonate weathering consistent with limited variation in discharge our results highlight that in a semiarid region where climatic conditions vary seasonally in addition to silicate and carbonate contributions supply from eolian dust may also play a significant role in controlling seasonal variations in chemistry of river waters

the fluvial geochemistry of the rivers of eastern siberia i tributaries of the lena river draining the sedimentary platform of the siberian craton abstract the response of continental weathering rates to changing climate and atmospheric pco 2 is of considerable importance both to the interpretation of the geological sedimentary record and to predictions of the effects of future anthropogenic influences while comprehensive work on the controlling mechanisms of contemporary chemical and mechanical weathering has been carried out in the tropics and to a lesser extent in the strongly perturbed northern temperate latitudes very little is known about the peri glacial environments in the subarctic and arctic thus the effects of climate essentially temperature and runoff on the rates of atmospheric co 2 consumption by weathering are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large rivers of eastern siberia the lena yana indigirka kolyma anadyr and numerous lesser streams which drain a pristine high latitude region that has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts common to western eurasia and north america the scale of the terrain sampled in terms of area is comparable to that of the continental united states or the amazon orinoco and includes a similarly diverse range of geologic and climatic environments in this paper the chemical fluxes from the western region the very large ancient and geologically stable sedimentary basin precambrian to quaternary of the siberian platform will be presented and compared to published results from analogous terrains in the tropical basins of china while the range in the chemical signatures of the various tributaries included here 60 sampled is large this mainly reflects lithology rather than the weathering environment the areal chemical fluxes are comparable to those of the chinese rivers being dominated by the dissolution of carbonates and evaporites the net consumption of atmospheric co 2 by aluminosilicate weathering is minor as it is in the tropical basins it is much smaller than in active orogenic belts in similar latitudes e g the fraser and yukon but comparable to those of the mackenzie tributaries that drain the eastern slope of the rockies lithology exerts the dominant influence in determining the weathering yield from sedimentary terrains and for a largely carbonate evaporite terrain climate does not have a direct effect

chemical and strontium isotopic characteristics of the rivers around the badain jaran desert northwest china implication of river solute origin and chemical weathering the chemical and strontium isotopic compositions of four major rivers heihe shule beida and shiyang around the badain jaran desert northwestern china were measured to understand the solute sources of surface water and rock weathering in the arid region these rivers have high total cationic charge tz and total dissolved solids tds averaging at 7379 eq and 511 mg l 1 which are significantly higher than the global river average the increase in tds and major ions na cl and so4 2 and tds concentrations from upper to lower reaches is ascribed to the evaporite dissolution and the effect of evaporation in the arid and semiarid areas 87sr 86sr isotopic ratios of these rivers range between 0 71019 and 0 71628 with an average of 0 71328 the chemical and 87sr 86sr isotopic analyses indicate that three reservoirs evaporites carbonates and silicates contribute to the total dissolved loads the contributions of the different reservoirs to the dissolved load are first calculated using a forward method in this area the calculated results show that the dissolved cation load is dominated by carbonates weathering and evaporites dissolution and their contribution account for about 80 of the total dissolved cations for the rivers around the badain jaran desert the proportion of the dissolved cations from silicates weathering is 23 5 10 8 12 1 and 18 2 and the weathering rate of silicates is 0 81 0 76 2 04 and 0 93 ton km 2 a 1 for heihe shule beida and shiyang respectively

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

mineralogical variation of sr nd isotopic and elemental compositions in loess and desert sand from the central loess plateau in china as a provenance tracer of wet and dry deposition in the northwestern pacific we determined sr and nd isotopic compositions and major trace and rare earth element ree compositions of evaporite and detrital minerals in loess and desert sand from the central loess plateau clp where 80 of the loess deposits in china are found the loess exhibited a narrow range of variation in 87sr 86sr 0 715 0 001 a sequential extraction experiment on the loess however showed that water and acetic acid hoac soluble minerals mainly halite and calcite hydrochloric acid hcl soluble minerals chlorite and phosphate and hcl insoluble minerals illite kaolinite smectite vermiculite feldspar and quartz have distinct 87sr 86sr ratios approximately 0 7111 0 0004 0 7141 0 0004 and 0 7195 0 0010 respectively the water and hoac soluble ratios were regionally uniform and were close to the 87sr 86sr value of river water from the huanghe yellow river and the maximum 87sr 86sr value of spring rainwater in japan suggesting selective solution of eolian halite and calcite into the chinese river water and into the japanese rainwater the mineralogical elemental and sr nd isotopic compositions of hcl soluble and insoluble minerals in the clp loess were different from those of the northern desert sand but were indistinguishable from those of its fine grained fraction supporting the view that the loess is composed of the fine grained fraction of desert sand that was transported to the southeast in the atmosphere the 87sr 86sr end and gd yb values of hcl insoluble minerals in the clp loess were almost identical to those of airborne dust soil minerals and deep sea sediments in the northwestern pacific considered to be of eolian origin suggesting dissolution of the loess evaporite minerals during atmospheric transportation these relationships demonstrate the usefulness of sr isotopes of water and hoac soluble minerals and sr and nd isotope ratios and ree compositions of acid insoluble minerals in loess as provenance markers for wet and dry deposition respectively

water geochemistry of the xijiang basin rivers south china chemical weathering and co2 consumption abstract the xijiang river the mainstream of the zhujiang pearl river which is the second largest river in china in terms of discharge flows through a large carbonate rock region in south china the chemical and sr isotopic compositions of the xijiang waters were determined during the high flow season in order to understand the chemical weathering processes associated co2 consumption and anthropogenic influences within the carbonate dominated basin the major ion compositions of the river waters are characterized by the dominance of ca2 mg2 hco 3 and are significantly rich in so 4 2 the so 4 2 is mainly derived from the oxidation of sulfide minerals and acid precipitation caused by coal combustion chemical and sr isotopic compositions of the river waters indicate that four reservoirs carbonates silicates evaporites and anthropogenic inputs contribute to the total dissolved loads the chemical weathering rates of carbonates and silicates for the xijiang basin are estimated to be approximately 78 5 and 7 45 ton km 2 a 1 respectively the total chemical weathering rate of rocks for the xijiang basin is approximately 86 1 ton km 2 a 1 or 42 mm ka 1 which is much higher than global mean values the budgets of co2 consumption by carbonate and silicate weathering are estimated to be 284 109 and 54 3 109 mol a 1 respectively it would appear that h2so4 is involved as a proton donor in weathering reactions in the xijiang basin calculated results show that the contribution of cations from rock weathering induced by h2so4 accounts for approximately 11 2 results from this study show that the flux of co2 released into the atmosphere is approximately 0 1 106 mol c km 2 a 1 or 0 41 1012 g c a 1 produced by h2so4 induced carbonate weathering in the basin when extrapolated to the entire surface area of carbonate in sw china the flux of co2 released to the atmosphere by h2so4 induced carbonate weathering is about 1 41 1012 g c a 1

major element chemistry of the changjiang yangtze river the chemistry of major elements ca mg na k hco3 so4 cl and si in the river water of the changjiang yangtze river was studied based on continuously monitored data at 191 stations in the drainage basin for the period 1958 1990 the results show that the total dissolved solid tds concentration of the changjiang varies over an order of magnitude throughout the basin 49 7 518 1 mg l with a medium tds concentration of 205 9 mg l about three times the global average in contrast the tds at a given main channel station varies only slightly in different seasons with a variation factor less than 2 0 despite a substantial water dilution in the summer flood season the major element chemistry of the changjiang is mainly controlled by rock weathering with the anion hco3 and the cation ca dominating the major ion composition due to the abundance of carbonate rocks in the basin a persistently increasing trend has been observed in the concentrations of so4 and to a lesser extent cl in the changjiang a signature of considerable anthropogenic impacts e g acid deposition flux calculations at datong the most downstream main channel station without tidal influence indicate that the changjiang transports ca 154 106 tons year of tds to the sea second only to the amazon in the world

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

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

the first large scale bioavailable sr isotope map of china and its implication for provenance studies abstract strontium isotope ratio 87sr 86sr has been widely used to trace human migrations across geologically distinct landscapes in archaeological and forensic sciences 87sr 86sr based provenance studies require a detailed strontium reference map to make valid interpretations of mobility patterns for a given region in this study we first review the previous development for 87sr 86sr isoscapes relevant to research on migration and then present the first map of bioavailable 87sr 86sr ratios for china based on 1935 measurements on biosphere samples collated from published research and supplemented by our targeted collection strategy the results show that 87sr 86sr ratios in china span a large range and exhibit regional patterns largely dependent on the divergent geological conditions of each of china s tectonic blocks we further combine river water 87sr 86sr ratios with lithology integrated elemental data and chemical weathering rates to determine which dominant weathering patterns e g silicate carbonate or evaporite have the most significant influence on 87sr 86sr ratios the low ranges of 87sr 86sr ratios 0 7125 appear in the cathaysia block as well as some orogenic belts and the southeastern margin of the tibetan plateau likely due to the influence of the metamorphic rocks and granitoid sources additionally topography differential weathering among lithologies and eolian deposits e g loess are also significant factors that influence 87sr 86sr ratios in china our study reveals that the large variation of 87sr 86sr ratios across china is predominately driven by geological conditions revealing that future sr isotope provenance studies can shed on ancient and historical migrations in china

metamorphism and deformation of blueschist belts and their tectonic implications north qilian mountains china abstract two blueschist belts in the north qilian mountains occur in middle cambrian and lower ordovician strata and strike n30 35 w for about 500 km along the caledonian fold belt on the south west margin of the sino korean plate the styles of metamorphism and deformation are quite different in the two belts the middle cambrian to ordovician rocks in the high grade belt are mainly blueschists and c type eclogites in which six phases of lower and upper crustal deformation have been recognized the rocks contain glaucophane phengite epidote clinozoisite chlorite garnet stilpnomelane piedmontite albite titanite and quartz the estimated p t conditions of eclogites are 340 10 c 8 1 kbar and of blueschist 380 c 6 7 kbar the ordovician rocks in the low grade belt are characterized by ductile to brittle deformation in the middle to upper crust the low grade blueschists contain glaucophane lawsonite pumpellyite aragonite albite and chlorite the estimated p t conditions are 150 250 c and 4 7 kbar k ar and 39ar 40ar geochronology on glaucophane and phengite from the high grade blueschist belt suggest two stages of metamorphism at 460 440 and 400 380 ma which may represent the times of subduction and orogeny the subduction metamorphism of the northern low grade blueschist belt took place approximately at the end of the ordovician

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

geochemical and geomorphological evidence for the provenance of aeolian deposits in the badain jaran desert northwestern china abstract identifying provenance of aeolian deposits in the mid latitude deserts of asia is essential for understanding formation and changes of earth surface processes due to palaeoclimatic fluctuations while some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter dune lacustrine sediments research on provenance of desert sands in the vast asian mid latitude deserts is still rare in this paper we present new geochemical data which provide insight to the provenance of dune sands in the badain jaran desert northwestern china an important part of this desert belt we sampled aeolian and lacustrine sediments in various parts of the badain jaran desert and examined their major trace and rare earth elements ree in bulk samples coarse and fine fractions respectively in addition we took and analyzed samples from a rarely known dune field with red sands northeast of the badain jaran our results show that the sands from the badain jaran desert are generally different from those in the red sand dune field in terms of ree pattern and geochemical characteristics suggesting different sediment origins geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite granitoids and granodiorite comparing the immobile trace elements and ree ratios of the samples from the badain jaran desert red sand dune field with rocks of granite granitoids in their potential source areas we conclude that 1 the aeolian deposits in the badain jaran desert are predominantly derived from the qilian mountains northeastern tibetan plateau initially via fluvial processes 2 the altay mountains and mongolian gobi are the ultimate source areas for the red sand dune field 3 the altai mountains and mongolian gobi in the northwest that could produce massive amounts of materials via intensive deflation and alluvial process are additional sand sources of the badain jaran desert although their contribution is of secondary significance as the badain jaran desert acts as sediment sinks of sediments from the qilian mountains of northeastern tibetan plateau via fluvial processes it is likely that zircon grains of loess on the chinese loess plateau with age distributions similar to those of the northern tibetan plateau could be derived from the badain jaran desert as the wind data suggest

electrical conductivity of brine saturated fractured rock a theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors fluid and rock conductivities initial fracture aperture and contact area fracture surface geometry asperity height distribution and tip curvature elastic moduli of the rock and confining pressure or normal stress acting across the fracture the conductivity in the fracture plane decreases approximately in proportion to log pressure but the conductivity is influenced by the increased contact area and hence flow path tortuosity along the fracture surface at elevated pressures electrical conductivity in fractures is more affected by flow path tortuosity than is permeability the dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground saw cut surfaces in a variety of rocks under confining pressures to 200 mpa the conductivity decreased approximately in proportion to log pressure there was little effect of

geochemistry of the dissolved load of the changjiang basin rivers anthropogenic impacts and chemical weathering abstract this study focuses on the chemical and sr isotopic compositions of the dissolved load of the rivers of the changjiang basin one of the largest riverine systems in the world water samples were collected in august 2006 from the main tributaries and the main changjiang channel the chemical and isotopic analyses indicated that four major reservoirs carbonates silicates evaporites and agriculture urban effluents contribute to the total dissolved solutes the overall chemical weathering carbonate and silicate rate for the changjiang is approximately 40 ton km2 year or 19 mm kyr similar to that of the ganges brahmaputra system and the basin is characterized by carbonate and silicate weathering rates ranging from 17 to 56 ton km2 year and from 0 7 to 7 1 ton km2 year respectively in the lower reach of the changjiang main channel the weathering rates are estimated to be 36 and 2 2 ton km2 year for carbonates and silicates respectively it appears that sulphuric acid may dominate chemical weathering reactions for some sub basins the budgets of co2 consumption are estimated to be 646 109 and 191 109 mol year by carbonate and silicate weathering respectively the contribution of the anthropogenic inputs to the cationic tds of the changjiang is estimated to be 15 20 for the most downstream stations our study suggested that the changjiang is strongly impacted by human activities and is very sensitive to the change of land use

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

euclidean and fractal models for the description of rock surface roughness accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength the flow of fluids in joints and fractures the seismic behavior of faults and the formation of gouge and breccia in fault zones real rock surfaces can be described using self similar and self affine fractal models of surface roughness if a surface is self similar a small portion of the surface when magnified isotropically will appear statistically identical to the entire surface if a surface is self affine a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface at least two parameters are required to describe a fractal model one parameter typically describes how roughness changes with scale while the other specifies the variance or surface slope at a reference scale the divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data power spectra from self similar surfaces have slopes of 3 on log log plots of power spectral density versus spatial frequency while spectra from self affine surfaces have slopes other than 3 power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency the topography of many natural rock surfaces including both fractures and faults is approximately self similar within the 6 5 order of magnitude wide wavelength band of 10 m to 40 m within smaller wavelength bands natural rock surfaces may exhibit self affine behavior

silicate weathering and co2 consumption deduced from the seven chinese rivers originating in the qinghai tibet plateau abstract we present river chemical data for the seven chinese rivers the jinsha jiang yalong jiang min jiang dadu he lancang jiang nu jiang and huang he originating in the qinghai tibet plateau our sampling locations are near sites where the seven rivers flow down the plateau water samples were collected in both high water periods summer and low water periods winter our study shows that most of the ca mg and hco 3 in the seven rivers are derived from the carbonate weathering and only small fractions 10 of the cations are derived from silicate weathering the chemical erosion rates of silicate and carbonate range from 1 1 mm ka 1 to 3 4 mm ka 1 and from 7 5 mm ka 1 to 29 9 mm ka 1 respectively the long term co 2 consumption by silicate weathering in the seven chinese river basins ranges from 0 7 10 5 mol km 2 a 1 to 3 7 10 5 mol km 2 a 1 based on our analysis of chemical data from the seven chinese rivers and the previously published data of the ganges brahmaputra and indus the main ten rivers originating in the himalaya and qinghai tibet plateau consume 328 10 9 mol a 1 of atmospheric co 2 this is only 3 8 of the co 2 consumption derived from global silicate weathering 8700 10 9 mol a 1 indicating that the chemical weathering of the himalaya and qinghai tibet plateau makes a very small contribution to the reduction of the global atmospheric co 2 concentration

chemical and physical weathering in the min jiang a headwater tributary of the yangtze river abstract the min jiang is a major headwater tributary of the yangtze chang jiang its source is in the undeveloped eastern tibetan plateau but it flows through the heavily populated sichuan four rivers basin on its way to join the yangtze main channel the dissolved major element composition was determined in the tibetan headwaters at the rising stage and at four hydrologic stations in a monthly time series the min jiang is alkaline and has high dissolved load compared to other world rivers carbonate weathering dominates especially in the source region of the min jiang main channel and silicate weathering and evaporite dissolution gain some importance in the dadu he tributary the si na k ratios of the dissolved load and the clay mineralogy of the bed material suggest that silicate weathering in the watershed is superficial i e soluble cations are being preferentially leached many major elements show lower concentrations at high summer discharge but there is also additional input such that the concentration discharge relationship is not purely a result of dilution the discharge weighted total dissolved solid tds flux based on data from the three upstream monitoring stations is 10 10 6 tons year 6 of the yangtze at mouth and the chemical denudation rate as measured by tds yield is 115 tons km 2 year for the min jiang higher than the average yangtze basin 85 tons km 2 year the common extrapolation using annual average discharge and spot sampling of dissolved and suspended material during rising or falling stage can reasonably estimate chemical fluxes to 20 but seriously underestimate the physical flux sampling the peak flash flow is critical for the suspended particulate material concentrations of so 4 cl and ca are significantly elevated as the river debouches onto the populated sichuan basin

the contact between opposing fault surfaces at dixie valley nevada and implications for fault mechanics well exposed normal fault surfaces from dixie valley nevada provide a unique opportunity to study the contact properties of fault surfaces because it is possible to examine both the hanging wall and footwall surfaces of a fault zone which was once seismically active the topography of the individual surfaces as well as the aperture or gap between the two surfaces was measured using surface profiling instruments and a resin replication technique these measurements enable frictional parameters of the surfaces most notably the characteristic decay distance dc to be calculated using contact theory although the individual surfaces are approximately self similar and fractal the aperture between the opposing surfaces is a stationary quantity because the surfaces are well correlated at dimensions larger than approximately 2 mm consequently contact theory can be used to calculate an average size for contact spots between the surfaces and by inference a characteristic decay distance dc for frictional slip between the surfaces direct inspection of resin replicas of the aperture allows an independent estimate of average contact spot size both approaches give contact spot diameters of 0 16 mm and dc of 0 01 0 1 mm because the individual surfaces of the fault are fractal and approximately self similar correlation between the surfaces should decrease significantly during slip events particularly if slip rates are high seismic events decreased correlation between the surfaces should lead to larger contact spot sizes and hence larger dc thus critical slip distances for natural faults should evolve concurrently with seismic fault slip

chemical weathering in the upper huang he yellow river draining the eastern qinghai tibet plateau we examined the fluvial geochemistry of the huang he yellow river in its headwaters to determine natural chemical weathering rates on the northeastern qinghai tibet plateau where anthropogenic impact is considered small qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution most samples are supersaturated with respect to calcite dolomite and atmospheric co2 with moderate 0 710 0 715 87 sr 86 sr ratios while six out of 21 total samples have especially high concentrations of na ca mg cl and so4 from weathering of evaporites we used inversion model calculations to apportion the total dissolved cations to rain evaporite carbonate and silicate origin the samples are either carbonate or evaporite dominated but the relative contributions of the four sources vary widely among samples net co2 consumption rates by silicate weathering 6 120 10 3 mol km 2 yr are low and have a relative uncertainty of 40 we extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide the ganges brahmaputra draining the himalayan front has higher co2 consumption rates 110 570 10 3 mol km 2 yr and more radiogenic 87 sr 86 sr 0 715 1 24 than the upper huang he but the rivers at higher latitudes are similar to or lower than the upper huang he in co2 uptake by silicate weathering in these orogenic zones silicate weathering rates are only weakly coupled with temperature and become independent of runoff above 800 mm yr copyright 2005 elsevier ltd

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

chemical weathering in the upper reaches of xijiang river draining the yunnan guizhou plateau southwest china abstract chemical and strontium isotopic compositions of nanpanjiang river and beipanjiang river in the upper reaches of xijiang river draining the yunnan guizhou plateau southwest china were measured with a main purpose to understand the rock weathering and associated co 2 consumption rates in the karstic landform dominated area the chemical ion composition of the river water is characterized by dominance of ca 2 mg 2 and hco 3 and so 4 2 which account for more than 90 of total ion concentration 87 sr 86 sr ratios of nanpanjiang river water range between 0 7080 and 0 7140 while those of most beipanjiang river water vary within a limited range from 0 7075 to 0 7085 weathering of carbonate rocks dominate chemistry of major ions especially in the water of beipanjiang river whereas weathering of silicate minerals in the upper reaches of nanpanjiang river basin is obvious in addition to carbonate weathering mainly according to the sr isotopic composition of the river water analyses of the stoichiometry of the river water show that the water chemistry is controlled by carbonate dissolution not only by carbonic but also by sulfuric acid and indicate that sulfuric acid plays an important role in carbonate weathering the sulfate in river water is mainly from atmospheric input by coal combustion industries and from oxidation of sulfide minerals during weathering of coal containing strata and coal mining in the catchment the chemical weathering rates of silicate and carbonate and associated co 2 consumption rates by both carbonic and sulfuric acid and by only carbonic acid are respectively estimated the results show that chemical weathering rates of carbonate and silicate weathering in beipanjiang river basin are higher than those of nanpanjiang river basin showing linkages of geology and geography in the catchment to crustal weathering the involvement of sulfuric acid in carbonate weathering greatly enhances the carbonate weathering but lowers the co 2 consumption rates indicating that sulfide acid is an important agent to rock weathering and the role of sulfide acid should further be clarified in view of the regional and global budget of co 2

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

chemical weathering and co2 consumption in the xijiang river basin south china monthly samples of riverine water were collected and analyzed for the concentrations of major ions ca2 mg2 k na hco3 so42 cl no3 dissolved silicon and total dissolved solids tds at wuzhou hydrological station located between the middle and lower reaches of the xijiang river xjr from march 2005 to april 2006 more frequent sampling and analysis were carried out during the catastrophic flooding in june 2005 stoichiometric analysis was applied for tracing sources of major ions and estimating co2 consumption from the chemical weathering of rocks the results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the xjr some 81 20 of the riverine cations originated from the chemical weathering processes induced by carbonic acid 11 32 by sulfuric acid and the other 7 48 from the dissolution of gypsum and precipitates of sea salts within the drainage basin the co2 flux consumed by the rock chemical weathering within the xjr basin is 2 37 x 10 11 mol y 1 of which 0 64 x 10 11 mol y 1 results from silicate rock chemical weathering and 1 73 x 10 11 mol y 1 results from carbonate rock chemical weathering the co2 consumption comprises 0 38 x 10 11 mol during the 9 d catastrophic flooding the co2 consumption from rock chemical weathering in humid subtropical zones regulates atmospheric co2 level and constitutes a significant part of the global carbon budget the carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention c 2008 elsevier b v all rights reserved

early palaeozoic north qaidam uhp metamorphic belt on the north eastern tibetan plateau and a paired subduction model an early palaeozoic uhp metamorphic belt was recently discovered in the north qaidam mountains in the north eastern part of the tibet plateau the belt contains abundant eclogite with lesser amounts of garnet peridotite and gneiss the paragneiss contains abundant zircon with coesite inclusions whereas the eclogite has garnet with coesite pseudomorphs and omphacite with exsolved quartz the calculated peak metamorphic conditions for the eclogite are t 730 c and p 2 8 gpa the garnet peridotites are magnesium rich with mg s 100 mg mg fe up to 92 olivine in the peridotites is highly magnesian fo 91 5 and tio2 poor and is typical of low t garnet peridotites calculated peak metamorphic conditions for the peridotites are t 837 c and p 2 5 gpa u pb and sm nd isotope dating indicate that continental subduction started during the early ordovician 495 ma the north qaidam uhp together with the north qilian hp belt about 300 km to the north constitute a pair of genetically related early palaeozoic subduction zones along the northern margin of the tibet plateau

statistics of earthquake stress drops on a heterogeneous fault in an elastic half space we investigate properties of earthquake stress drops in simulations of evolving seismicity and stress field on a heterogeneous fault the model consists of an inherently discrete strike slip fault surrounded by a 3d elastic half space we consider various spatial distributions of frictional properties and analyze results generated by 150 300 model years in all cases the self organized heterogeneous initial stress distributions at the times of earthquake failure lead to stress drops that are systematically lower than those predicted for a homogeneous process in particular the large system sized events have stress drops that are consistently 25 of predictions based on the average fault strength the type and amount of assumed spatial heterogeneity on the fault affect the stress drop statistics of small earthquakes m l 5 more than those of the larger events this produces a decrease in the range of stress drops as the earthquake magnitudes increase the results can resolve the discrepancy between traditional estimates of stress drops and seismological observations the general tendency for low stress drops of large events provides a rationale for reducing the statistical estimates of potential ground motion associated with large earthquakes

simple mathematical model of a rough fracture a simple mathematical model of rough walled fractures in rock is described which requires the specification of only three main parameters the fractal dimension the rms roughness at a reference length scale and a length scale describing the degree of mismatch between the two fracture surfaces fractured samples collected from natural joints and laboratory specimens have been profiled to determine the range of these three parameters in nature it is shown how this surface roughness model can be implemented on a computer allowing future detailed study of the mechanical and transport properties of single fractures and the scale dependence of these properties

a cold early palaeozoic subduction zone in the north qilian mountains nw china petrological and u pb geochronological constraints the north qilian high pressure hp low temperature lt metamorphic belt is composed mainly of blueschists eclogites and greenschist facies rocks it formed within an early palaeozoic accretionary wedge associated with the subduction of the oceanic crust and is considered to be one of the best preserved hp lt metamorphic belts in china here we report new lawsonite bearing eclogites and eclogitic rocks enclosed within epidote blueschists in the north qilian mountains five samples contain unaltered lawsonite coexisting with omphacite and phengite as inclusions in garnet indicating eclogite facies garnet growth and lawsonite pseudomorphs were observed in garnet from an additional 11 eclogites and eclogitic rocks peak pressure conditions estimated from lawsonite omphacite phengite garnet assemblages were 2 1 2 4 gpa at temperatures of 420 510 c in or near the stability field of lawsonite eclogite and implying formation under an apparent geothermal gradient of 6 8 c km 1 consistent with metamorphism in a cold subduction zone shrimp u pb dating of zircon from two lawsonite bearing eclogitic metabasites yields ages of 489 7 ma and 477 16 ma respectively cl images and mineral inclusions in zircon grains indicate that these ages reflect an eclogite facies metamorphism an age of 502 16 ma is recorded in igneous cores of zircon grains from one lawsonite pseudomorph bearing eclogite which is in agreement with the formation age of early ordovician for some ophiolite sequences in the north qilian mountains and may be associated with a period of oceanic crust formation the petrological and chronological data demonstrate the existence of a cold early palaeozoic subduction zone in the north qilian mountains

water geochemistry of the rivers around the taklimakan desert nw china crustal weathering and evaporation processes in arid land abstract major ion and sr2 concentrations and sr isotopic compositions of four major rivers in the tarim basin nw china were measured these rivers in the arid lands have high total cation concentrations tz ranging from 2 3 to 46 4 meq l 1 which are significantly higher than those of the global river average tz 0 725 meq l 1 ca2 mg2 and na in these rivers are the major cations together accounting for 95 of the total cations the total dissolved solids in the keriya and gaz rivers gradually increase from their upper to lower reaches these general features of these rivers show a strong effect of evaporation and the dissolution of the evaporates in the desert areas the chemical and isotopic compositions of these rivers are largely controlled by the geological signatures of their drainage areas the rivers at the northern foot of the kunlun mountains an old terrain show higher 87 sr 86 sr ratios of 0 7111 0 7154 compared to the aksu river 87 sr 86 sr 0 7103 0 7105 draining a relatively young area the end member identification by the intercorrelations between chemical and isotopic ratios shows three main sources which are derived from weathering of silicates carbonates and evaporates the yurongkash river keriya river and the small rivers flowing from the northern foot of the kunlun mountains have high total ion concentrations and are characterized by high na ca mg ca and k ca mole ratios 1 4 30 0 5 3 5 and 0 06 0 7 respectively showing a strong influence of soil salts on the other hand the aksu and gaz rivers draining regions in the western part of the tianshan mountains and kunlun mountains are dilute with respect to the amount of total dissolved solids and show low na ca mole ratio from 0 2 to 2 mg ca from 0 15 to 2 and k ca from 0 03 to 2 suggestive of a strong influence of carbonate weathering