fluvial geochemistry of rivers draining karst terrain in southwest china abstract samples of water from rivers draining karst areas within guizhou province china the wujiang qingshuijiang and wuyanghe rivers were analyzed for dissolved major element concentrations hco 3 no 3 so 4 2 cl ca 2 mg 2 k na sr2 and 87sr 86sr to quantify the rates of chemical weathering of rocks and associated atmospheric co2 consumption in a typical karst area the analyzed water samples in rivers draining karst areas typically show a dominance of ca2 mg2 and hco 3 and are rich in so 4 2 the waters of the wujiang river contain high sr2 concentrations 0 61 7 19 mol l and low 87sr 86sr values 0 7074 0 7115 while the waters of the qingshuijiang river which drains silicate strata yield high sr isotopic ratios 0 7088 0 7155 and low sr2 concentrations 0 18 1 45 mol l the chemical and isotopic compositions of these waters are largely controlled by the lithology of the basin stoichiometric analyses show that the water chemistry is controlled by carbonate dissolution under the influence of carbonic and sulfuric acid the rates of chemical weathering of rocks within the studied basin were estimated based on the chemical budget calculated for each of the three analyzed rivers the weathering rates estimated for silicate rocks were 6 7 10 7 t km2 yr while those for carbonate rocks were 67 116 t km2 yr we also calculated the rates of chemical weathering of carbonate rock and related rate of co2 consumption by carbonic and sulfuric acid combined and by carbonic acid alone the results show that the involvement of sulfuric acid in weathering processes strongly enhances the rate of carbonate weathering but lowers the rate of co2 consumption the catchment of the wujiang river is dominated by a coal bearing formation and a coal mine is operated within the catchment the consumption of co2 shows a marked decrease from 844 103 mol km2 yr in the case of carbonate weathering by carbonic acid alone to 546 103 mol km2 yr in the case of carbonate weathering by both sulfuric and carbonic acid no atmospheric co2 is consumed during weathering of the carbonate rocks by sulfuric acid consequently this form of weathering represents a net source of co2 to the atmosphere in the guizhou karst area

ca sr and 87sr 86sr geochemistry of disseminated calcite in himalayan silicate rocks from nanga parbat influence on river water chemistry trace amounts of disseminated calcite were identified in gneiss schist and granite bedrock sampled from the raikhot watershed and other locations within the nanga parbat massif of northern pakistan the calcite grains occur interstitially within individual silicate minerals at grain boundaries and as fracture fillings that transect the mineralogic fabric of the rock disseminated calcite composes is 0 29 wt of silicate rocks sampled in the raikhot watershed and has ca sr mol nmol and 87sr 86sr ratios that range from 0 878 to 5 33 and from 0 794 039 to 0 930 619 respectively elsewhere in the nanga parbat region disseminated calcite composes 3 6 wt of the silicate rock samples and has ca sr mol nmol and 87sr 86sr ratios that range from 0 535 to 3 33 and from 0 715 757 to 0 771 244 respectively for all samples the 87sr 86sr ratios of disseminated calcite are similar to the 87sr 86sr ratios measured in the silicate host rock within the partially glaciated raikhot watershed the rapid weathering of disseminated calcite with high ca sr and 87sr 86sr ratios has a strong influence on the chemical composition of stream water and exceeds contributions from silicate mineral dissolution comparisons of disseminated calcite compositions with source water chemistry throughout the himalaya suggest that disseminated calcite may be a more important component of himalayan silicate rocks than previously recognized therefore calculations relating the sr isotope geochemistry of himalayan rivers to atmospheric co2 consumption should consider this widespread and compositionally variable carbonate end member

the late neogene 87sr 86sr record of lowland himalayan rivers fossil shells and paleosol carbonate from ancestral himalayan river deposits provide a 87 sr 86 sr record of lowland himalayan river water during the late neogene reconstructed 87 sr 86 sr river values increased sharply in the late miocene probably marking the beginning of exhumation of high 87 sr 86 sr metalimestones more in the central than in the western himalayas these results imply that the marine 87 sr 86 sr record may not be a proxy for silicate weathering or consumption of atmospheric co 2 resulting from that weathering

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

palaeointensity results for historic lavas from mt etna using microwave demagnetization remagnetization in a modified thellier type experiment summary the bane of conventional thellier type palaeointensity experiments is the thermal alteration of the samples during experimentation however high frequency microwaves can be used to stimulate the magnetic minerals directly thus eliminating the need for the bulk sample to be heated walton et al 1993 the microwave technique has been successfully applied to ceramics shaw et al 1996 1999 and here we present results for historic lavas from mt etna sicily 20 samples were randomly selected from 10 diverent historic flows dating from 1843 to 1983 hysteresis parameters were monitored as a check for alteration during experimentation and minimal alteration was found rock magnetic analysis and af plus microwave demagnetizations were carried out on all samples and microwave intensity analysis was carried out on those samples that were stable to microwave demagnetization 16 in total with one exception all samples gave high quality intensity results two or three subsamples from each sample were investigated and a weighted average calculated to give a single estimate of the field when the intensity values were compared with the sv model based on direct observatory measurements bloxham gubbins 1985 it was found that those samples that contained a high multidomain md component gave intensity values around 20 per cent lower than expected this can be explained by the cooling rate evect dodson mcclelland brown 1980 and or the presence of an md component mcclelland et al 1996 those samples with the lowest numbers of md grains gave field values which within error were the same as those for the model or slightly too high this is compatible with the cooling rate evect

palaeomagnetic investigation of tertiary lava from barrington tops nsw australia using thermal and microwave techniques abstract tertiary lava 53 ma from barrington tops new south wales australia has been studied using conventional thermal and microwave techniques twenty seven flows in two sections were sampled and their rock magnetic characteristics determined on heating the majority of samples exhibited a single curie temperature at around 200 c indicating a titanium rich titanomagnetite some samples exhibited two magnetic phases and a few a single low titanium titanomagnetite phase thermal demagnetisation yielded a mean direction of d 189 5 i 63 6 95 4 3 which corroborates the previous findings of wellman et al geophys j r astron soc 18 1969 371 395 a pilot conventional thellier palaeointensity analysis was unsuccessful mainly due to the samples being highly susceptible to thermo chemical alteration far greater success was achieved 58 using the microwave palaeointensity technique where heating of the bulk sample and hence alteration is vastly reduced palaeointensity estimates range from 3 to 28 t mean 11 5 t which assuming that the remanence is a primary thermal remanent magnetisation indicates a low field intensity a fifth of the present day value in the early tertiary this study demonstrates the applicability of the microwave palaeointensity technique to ancient lava

strontium isotopes and major ion chemistry in the chambal river system india implications to silicate erosion rates of the ganga article i nfo much higher than the global mean river water a significant fraction of solute abundance in the chambal river is derived from sodium salts unlike the himalayan rivers which exhibit dominance of ca mg salts it is estimated that the chambal river supplies about one third of sodium via the yamuna to the ganga at rajshahi bangladesh with only 6 5 of water discharge the presence of na salts not associated with chloride in the chambal headwaters constraints the application of na na corrected for cl as an index of silicate derived component this finding brings out the need to revisit the estimates of silicate erosion rate ser and associated co2 consumption in the ganga basin downstream allahabad based on na as an index the sr concentration in the chambal tributaries varied from 1 9 m to 5 9 m and 87 sr

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

role of hydraulic diffusivity in the decrease of weathering rates over time summary springs emerging within massifs of crystalline rocks were monitored for discharge rate q and the q values combined with geomorphic and hydrographic parameters in a hydrologic model to calculate hydraulic conductivity k and effective porosity n e of the spring watersheds the spring waters several borehole waters and rain water were analyzed for major dissolved compounds strontium and isotopes 18 o 2 h 13 c and 87 sr 86 sr with a shift to less negative values 18 o and 2 h were fitted by a line approximately parallel to the gmwl but no significant dependence on altitude was found the 18 o and 2h values correlate better with those of precipitation amount the 87 sr 86 sr ratios in drilled well waters correlate positively with the depth of water circulation reported in the borehole logs the corresponding regression equations were used to extrapolate the depth of hydraulic circuits within the spring watersheds the previous data together with groundwater travel times calculated by a water balance model and with reactions of granite metassediment plagioclase and biotite precipitating halloysite gibbsite and vermiculite were assembled in a mass balance model to calculate solute flux weathering rates of plagioclase w pl the w pl s were described as a function of d k n e where d is the hydraulic diffusivity the discrepancies between the w pl values and solid state rates based on the differences between elemental isotopic and mineral compositions measured in present day regoliths and in the assumed protolith were assigned to a decrease in d over time from values in the protolith to values in the weathered aquifer

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

tracing sr isotopic composition in space and time across the yangtze river basin abstract variation of dissolved 87 sr 86 sr in the yangtze river is poorly documented compared to other tibetan sourced rivers here we trace the sr isotopic composition in space and time across the yangtze river basin using a systematic sampling strategy the 87 sr 86 sr values of samples collected at different depths within the water column at three gauge stations located in the upper middle and lower reaches of the river are very similar indicating a well mixed water body at a given location data from basin wide samples shows low 87 sr 86 sr values in the upper reaches while higher 87 sr 86 sr values in the middle lower reaches which mainly reflect the controls of source rocks a time series record at the lowermost reaches of the river indicates a temporal variation of 87 sr 86 sr values from 0 7101 to 0 7109 with a discharge weighted value of 0 7106 we suggest that temporal variations of the isotopic composition result from changes in the relative contributions from different terrains associated with spatial variability of rainfall within the basin a mixing model based on sr values deduced from basin wide sampling from different seasons yields similar temporal variations of sr isotopic composition compared to experimental data calculation of sr fluxes indicates that the upper reaches contribute 3 times as much as the middle and lower reaches to total sr flux the annual sr flux of the yangtze river to the east china sea is estimated to be 1 9 10 9 mol a 1 which is one magnitude higher than that of the brahmaputra and ganges

watershed reconstruction of a paleocene eocene lake basin using sr isotopes in carbonate rocks provenance studies have used sr isotopes 87 sr 86 sr of silicate source rocks as a link to their eroded basinal equivalents this technique however cannot identify the proportional inputs from different watersheds or define more precisely sedimentation events due to tectonic or climatic change erosion of carbonate rocks dominates the sr input within basin drainage and potentially can be used through 87 sr 86 sr ratios to reconstruct paleohydrology of the entire basin and trace watershed inputs and depositional patterns in continental basins the sr isotopic ratios from waters of the source area allowing for the mixing of shallow groundwater and surface water along the transport path are homogenized in the basinal carbonate sediments mineralogy and diagenesis of carbonate rocks generally do not affect the sr isotopic signal in a near surface system lacking external influence by volcanism eolian dust or deep geothermal waters the 87 sr 86 sr ratios from the source area are directly comparable to those in the receiving continental basin the sr isotopic signal of the paleocene eocene flagstaff formation central utah a carbonate lake deposit in a foreland basin is compared to that of projected source waters draining its thrust front the sevier fold thrust belt freshwater carbonates compose a large portion of the lowermost ferron mountain and uppermost musinia peak members of the formation whereas gypsum and carbonates predominate in the middle cove mountain member previous research had attributed gypsum deposition to the deposition of the middle cove mountain member to either climatic change or unroofing of diapirs of jurassic gypsiferous carbonates to examine more closely the influence of climate versus tectonics on flagstaff sedimentation as well as the efficacy of provenance studies using carbonates we collected rock samples from the three members of the formation on the wasatch plateau of central utah in addition to sampling stream water associated with pennsylvanian permian and jurassic carbonate terrains from the nearby thrust front the 87 sr 86 sr ratios in carbonates and gyprock belonging to the flagstaff formation remained unchanged during deposition the average sr isotope composition of the flagstaff rocks being identical to that of sampled waters draining the projected provenance area there was little change in source rock weathering as the thrust front evolved deposition of gypsum occurred in the basinal lake only during the deposition of the middle cove mountain member despite its constant exposure in the drainage area suggesting a changing balance of tectonic and climatic controls during lake sedimentation the 87 sr 86 sr isotopic studies targeting carbonate rocks and their presumed source waters are a simple but accurate method for reconstructing the paleohydrology of lake basins

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

hydrogeochemistry and strontium isotopes in the arno river basin tuscany italy constraints on natural controls by statistical modeling summary in this paper the chemistry of major and trace elements and for the first time strontium isotopic ratios measured in running waters from the arno river basin tuscany central northern italy and thermal springs discharging in the same hydrographic system are presented and discussed classical graphical methods e g mixing diagrams have here been improved to identify in a correct statistical sample space extreme chemical compositions attributable to the action of geochemical processes and or inherited from specific lithologies namely contributions or components 1 2 and 3 to be used in inverse modeling procedures due to the absence of clear end members a linear least squares problem with non negativity constraints and distances as required for compositional data convex linear mixing was solved by considering the contribution of the most discriminant variables given by the 87 sr 86 sr isotopic ratios and the concentration of ca 2 mg 2 sr and rb following such approach it can be assumed p 2 mg 2 hco 3 radiogenic rich 87 sr 86 sr 0 71274 rb sr 0 039 represents a dominant feature at basin scale with a weight ranging from 69 to 100 much lower percentages are related to component 2 represented by a ca 2 mg 2 so 4 2 facies with intermediate 87 sr 86 sr 0 70874 and low rb sr 2 8 10 4 ratios and component 3 identified by ca 2 hco 3 facies with less radiogenic 87 sr 86 sr 0 70827 and low mg 2 ca 2 0 011 ratios these components are mainly dominated by the dissolution of evaporitic rocks and or mixing with thermal waters in the southern part of the arno river basin and by dissolution of the carbonatic fraction kinetically favored with respect to that of the silicatic minerals in the upper reaches of the main course and its tributaries respectively

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

isotopic and geochemical evidence of palaeoclimate changes in salton basin california during the past 20 kyr 2 87sr 86sr ratio in lake tufa as an indicator of connection between colorado river and salton basin abstract as a part of the colorado river drainage system southern california s salton basin has two major tributaries colorado river and whitewater river interpretations on palaeoclimatic records from the basin strongly depend on the colorado river inflow to the basin in this study we have used the 87sr 86sr ratio in lacustrine deposits to identify the time and duration of the colorado river input our measurements of 87sr 86sr ratios made on water samples collected from salton basin indicate that the 87sr 86sr ratio 0 710169 of the colorado river input is identical to that of salton sea 0 710105 implying little change in the lake water ratio since 1905 when salton sea formed and began receiving water mostly from colorado river and the 87sr 86sr ratio of colorado river is much lower than that of whitewater river 0 715960 these results enable us to trace past changes in the colorado river input using 87sr 86sr in lake carbonates using a two end member mixing model we discuss the major factors that control the 87sr 86sr variation of lake cahuilla which was an ancient lake in the salton basin between 400 and 20 500 yr bp thirty measurements of 87sr 86sr were made on ams 14c dated tufa carbonates in two slabs from lake cahuilla the results show relatively constant 87sr 86sr ratios throughout the past 20 kyr ranging from 0 709944 to 0 710140 the average of these 87sr 86sr ratios 0 710060 0 000049 n 30 is very close to that of the colorado river input our results indicate that 1 the colorado river input was the dominant water source for lake cahuilla at least during 800 20 500 yr bp when the tufa grew in the basin and 2 the provenance of run off to the colorado river did not change significantly during 800 20 500 yr bp hence the palaeoclimatic proxies retrieved from the lake cahuilla tufas in the salton basin can decipher the discharge and flood history of the colorado river under the influence of climate variability in the colorado river drainage basin

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

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

geochemistry of the 2 51 ga old rampur group pelites western himalayas implications for their provenance and weathering the late archean volcano sedimentary succession of the rampur group rg represents the oldest superacrustal rocks exposed in the himalayas the sedimentary component is pelite dominated in the lower part and siliciclastic with associated mafic volcanics dominated in the upper part indicating shallowing of the basin over time the bulk chemistry of the rg pelites shows illite chlorite control that gets diluted with increase in quartz content they have a general similarity with the post archean shales but a slightly higher average sio2 and lower al2o3 contents and severe depletion in cao na2o sr and ba relative to the north american shale composite ree patterns are highly fractionated with la yb n ratio ranging from 8 8 to 18 6 hree show slight fractionation average gd yb n b2 and all the samples have large negative eu anomalies average 0 61 la yb n decrease with increase in al2o3 na2o but lack any relationship with k2o thereby discounting clay mineral control hree have a positive correlation with tio2 th y and nb but not with p2o5 and zr the increase in hree seems likely due to the increased mobilization of hree enriched phase s during intense weathering high zr and th contents and th ni la sc and la yb n ratios as well as sc th sc relations favor a dominantly felsic source with only a minor contribution from mafic rocks the most likely source lithology compatible with the southerly paleocurrent direction and first cycle sediment textural features of the rg sediments appears to be the banded gneissic complex bgc of the northern indian shield the same conclusion is reached when rg data are plotted in al2o3 cao na2o k2o a cn k compositional space the data define a trend which indicates unweathered plagioclase k feldspar source composition similar to that of the bgc pre metasomatized high chemical index of weathering as well as the high plagioclase index of weathering for a majority of the samples conforms to the world wide warm moist climate prevalent during the time of their deposition 2001 elsevier science b v all rights reserved

sr fluxes and isotopic compositions in the headwaters of the yangtze river tongtian river and jinsha river originating from the qinghai tibet plateau abstract water and sediment samples were collected from the headwaters the tuotuo river and chumaer river of the yangtze river tongtian river and jinsha river htjr originating from the qinghai tibet plateau qtp sr and 87 sr 86 sr have been measured to analyze temporal and spatial variation characteristics and determine relative contributions from atmospheric inputs anthropogenic activities and rock weathering these results show that sr in the htjr waters ranges from 1 37 to 11 07 mol l 1 and 87 sr 86 sr from 0 70948 to 0 71409 the headwaters tuotuo river and chumaer river receive 95 of their sr from evaporite dissolution the influence of evaporite decreases gradually downwards from source area as increase in discharge silicate weathering contributes 4 9 28 2 of dissolved sr to the jinsha river mainstream and 11 5 42 4 to the tributaries 87 sr 86 sr ranges from 0 71034 to 0 71177 in the jinsha river mainstream which is higher than those in other reaches of the yangtze river in the jinsha river suture belt granitoids and metamorphic rocks with relatively high 87 sr 86 sr are exposed moreover carbonate weathering is another important source of sr in the jinsha river waters it is estimated that 15 9 46 8 of sr in the mainstream and 37 64 5 of sr in the tributaries are derived from carbonate weathering contribution from atmospheric precipitation to the sr in the htjr is from 0 75 to 6 1 and influence of anthropogenic activities is slight the 87 sr ex flux forcing changes in seawater sr isotopic composition is 1 13 10 6 mol a 1 for the htjr at yibin being far lower than those in the ganges and brahmaputra and merely accounting for 1 36 of the total carried by the global rivers therefore impact of the htjr on steady increase of seawater 87 sr 86 sr ratio since 40 ma may be very small

distinct patterns of chemical weathering in the drainage basins of the huanghe and xijiang river china evidence from chemical and sr isotopic compositions abstract aquatic geochemistry on watershed background helps elucidate the influence of natural processes and anthropogenic activities to the environment the 87sr 86sr ratios and dissolved loads were measured in 35 water samples from the huanghe and xijiang river drainage basins the dissolved loads and 87sr 86sr ratios differed considerably between the two drainage basins the 87sr 86sr ratios of the xijiang river are between 0 70856 and 0 70936 with an average of 0 70894 reflecting weathering of carbonate minerals as the dominant source and anthropogenic pollution as the secondary one especially in the upper reach tributaries while the sr isotopic ratios in the huanghe river range from 0 70986 to 0 71139 averaging 0 71118 that results primarily from evaporite dissolution precipitation contributes to 2 8 and 5 7 to the chemistry of the xijiang and huanghe river respectively evaporite dissolution and silicate weathering account for 79 4 and 11 3 respectively in the huanghe river while carbonate dissolution and silicate weathering account for 75 4 and 14 6 respectively in the xijiang river the chemical weathering rate is 107 6 t km2 yr in the xijiang river drainage basin and 34 2 t km2 yr in the huanghe river drainage basin the co2 consumption budget is 305 2 109 mol yr in the xijiang river drainage basin and 147 9 109 mol yr in the huanghe river drainage basin

sr and 87sr 86sr in the yamuna river system in the himalaya sources fluxes and controls on sr isotope composition abstract sr and 87 sr 86 sr have been measured in the yamuna river headwaters and many of its tributaries yrs in the himalaya these results with those available for major ions in yrs rivers and in various lithologies of their basin have been used to determine their contributions to riverine sr and its isotopic budget sr in the yrs ranges from 120 to 13 400 nm and 87 sr 86 sr from 0 7142 to 0 7932 streams in the upper reaches draining predominantly silicates have low sr and high 87 sr 86 sr whereas those draining the lower reaches exhibit the opposite resulting from differences in drainage lithology 87 sr 86 sr shows significant co variation with sio 2 tds and na k tz indices of silicate weathering in yrs waters suggesting the dominant role of silicate weathering in contributing to high radiogenic sr this is also consistent with the observation that streams draining largely silicate terrains have the highest 87 sr 86 sr analogous to that reported for the ganga headwaters evaluation of the significance of other sources such as calc silicates and trace calcites in regulating sr budget of these rivers and their high 87 sr 86 sr needs detailed work on their sr and 87 sr 86 sr preliminary calculations however indicate that they can be a significant source to some of the rivers it is estimated that on an average 25 of sr in the yrs is derived from silicate weathering in the lower reaches the streams receive 15 of their sr from carbonate weathering whereas in the upper reaches calc silicates can contribute significantly 50 to the sr budget of rivers these calculations reveal the need for additional sources for rivers in the lower reaches to balance their sr budget evaporites and phosphorites are potential candidates as judged from their occurrence in the drainage basin in general precambrian carbonates evaporites and phosphorites dilute the high 87 sr 86 sr supplied by silicates thus making sr isotope distribution in yrs an overall two end member mixing major constraints in quantifying contributions of sr and 87 sr 86 sr from different sources to yrs rivers are the wide range in sr and 87 sr 86 sr of major lithologies limited data on sr and 87 sr 86 sr in minor phases and on the behavior of sr na and ca during weathering and transport the ganga and the yamuna together transport 0 1 of the global sr flux at the foothills of the himalaya which is in the same proportion as their contribution to global water discharge dissolved sr flux from the yamuna and its mobilization rate in the yrs basin is higher than those in the ganga basin in the himalaya a result consistent with higher physical and chemical erosion rates in the yrs

stable isotopes in the source waters of the yamuna and its tributaries seasonal and altitudinal variations and relation to major cations water samples from the yamuna and its tributaries one of the major river systems draining the himalaya have been analysed for their stable oxygen and hydrogen isotopes during three seasons summer monsoon and post monsoon the data show clear seasonal and altitudinal variations waters from higher altitudes and those collected during monsoon season are characterized by relatively depleted isotopic composition regression analysis of d 18 o data of samples collected during summer and monsoon seasons shows that the slope of the best fit lines are nearly identical to those of precipitation at new delhi for the same period the similarity in their slopes suggests that the isotopic composition of precipitation contributing water to these rivers are reasonably well preserved in both monsoon and non monsoon seasons however during the non monsoon period both rainfall and river waters carry signatures of evaporation the deuterium excess in river waters during the three seasons though overlap with each other the values during october are higher this can be understood in terms of recycled moisture contributions to precipitation the altitude effect for 18 o in these waters is determined to be 0 11 per 100 m a factor of about two less than that reported for the ganga source waters from similar altitudinal range the variability in altitude effects in rivers draining the himalaya seems to be controlled by the amount effect associated with the monsoon the significant spatial variability in altitude effect in these river basins which are a few hundred kilometers apart suggests that reconstruction of palaeoelevation in the himalaya based on 18 o altitude gradients would depend critically on its proper assessment in the region this study has established a relationship between total cation abundance and 18 o in waters of the yamuna mainstream total cations corrected for cyclic components double for a 1 4 km decrease in altitude as the yamuna flows downstream

palaeointensity record through the lower mammoth reversal from the waianae volcano hawaii the normal to reverse lower mammoth reversal 3 33 ma has been recorded in several sequences of lava from the waianae volcano the island of oahu hawaii 137 samples from 29 flows from the pu u paheehee section have been the subject of a palaeointensity study using the microwave technique duplicate sister samples from the directional study of herrero bervera and valet earth planet sci lett 171 1999 139 148 were used microwave demagnetisation was carried out on all samples and the directions compared to the published flow mean directions microwave palaeointensity experiments were carried out on all accepted samples using the 8 2 ghz and 14 ghz microwave systems the perpendicular applied field palaeointensity method and a coe analogue method were used eighty four samples from 24 flows gave acceptable palaeointensity results the results indicate that the geomagnetic field was low mean 5 9 1 3 t n 7 prior to the transitional directions during the first stage of the reversal the field remains low results however could only be obtained from three transitional flows the field then strongly recovers with very high intensity 70 t and reversed direction after this the intensity decreases before the field becomes transitional again for a cluster of four flows the field does not reduce as much as previously rather it is about twice the pre reversal intensity for the final section of reversed flows the intensity is more than twice the pre reversal mean value 15 1 5 9 t n 7 whilst some similarities are seen between this reversal and other reversals of different ages and locations there is not enough data at present to say whether there is any systematic behaviour

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

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

a comparison of thermal and microwave palaeomagnetic techniques using lava containing laboratory induced remanence summary a series of laboratory experiments has been carried out using lava from hawaii and australia containing laboratory induced remanence to compare thermal and microwave palaeomagnetic techniques three samples of hawaiian lava containing a known laboratory induced thermal remanence trm were subjected to microwave palaeointensity experiments using the liverpool 8 2 ghz microwave system conventional modified thellier palaeointensity experiments were carried out on the same three lava samples this time containing a known microwave induced thermoremanent magnetisation tmrm both palaeointensity techniques produced the correct intensity value demonstrating the equivalence of trm and tmrm no indications of alteration during the experiment were evident during the microwave experiments whereas alteration was pronounced after heating to 350 c in the thellier experiments demonstrating that alteration during microwave palaeointensity analysis is reduced when compared to thermal techniques in a second set of experiments six samples three hawaiian and three australian lava samples were given a laboratory induced full trm and a secondary perpendicular partial trm ptrm at lower temperatures sister samples were then demagnetised using thermal and microwave methods analysis of the orthogonal vector plots ovps revealed little difference in separating the two components for five out of the six samples for one sample microwave demagnetisation did not clearly distinguish between the two components with the primary component not being resolved until 74 per cent of the moment had been demagnetised compared to just 4 per cent with thermal demagnetisation for this one sample it appears that the microwave unblocking spectra is not equivalent to the thermal unblocking spectra probably due to a combination of microwave demagnetisation processes occurring comparison of the intensity of magnetisation plots during demagnetisation shows that the relationship between temperature and microwave power appears more logarithmic than linear this study demonstrates the validity of the microwave palaeointensity technique and as long as the primary component of magnetisation can be isolated from multicomponent remanence then the microwave palaeointensity technique can be applied

seasonally chemical weathering and co2 consumption flux of lake qinghai river system in the northeastern tibetan plateau the major cation and anion compositions of waters from the lake qinghai river system lqrs in the northeastern tibetan plateau were measured the waters were collected seasonally from five main rivers during pre monsoon late may monsoon late july and post monsoon middle october the lqrs waters are all very alkaline and have high concentrations of tds total dissolved solids compared to rivers draining the himalayas and the southeastern tibetan plateau seasonal variations in the water chemistry show that except the daotang river the tds concentration is high in october and low in july in the lqrs waters the forward models were used to quantify the input of three main rivers buha river shaliu river and hargai river from rain halite carbonates and silicates the results suggest that 1 atmospheric input is the first important source for the waters of the buha river and the shaliu river contributing 36 57 of the total dissolved cations 2 carbonate weathering input and atmospheric input have equal contribution to the hargai river water 3 carbonate weathering has higher contribution to these rivers than silicate weathering and 4 halite is also important source for the buha river the daotang river water is dominated by halite input owing to its underlying old lacustrine sediments the water compositions of the heima river are controlled by carbonate weathering and rainfall input in monsoon season and groundwater input may be important in pre monsoon and post monsoon seasons after being corrected the atmospheric input average co2 drawdown via silicate weathering in the lqrs is 35 103 mol km2 per year with highest in monsoon season lower than himalayas and periphery of tibetan plateau rivers but higher than some rivers draining shields

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

holocene geomagnetic paleointensities a blind test of absolute paleointensity techniques and materials through several decades of research absolute paleointensity estimates have been obtained from a wide range of rocks with varying ages covering the last 3 45 ga years these paleointensity data are crucial to study the past geodynamo and the geological evolution of the earth s deep interior however paleointensity data are often difficult to interpret and on going discussions concerning the past geomagnetic field invariably focus on data reliability and which kind of material and method is best suited for absolute paleointensity experiments in this paper we blind test paleointensity methods and materials using the new geomagia50 database that contains all available experimental information about published paleointensity estimates covering the last 50 000 years our analysis is built on simple comparisons of results obtained from different materials and methodologies to investigate their possible influence on the paleointensity estimate we also study the effect of various numbers of samples and dating accuracies we focus on paleointensity estimates from the last 12 000 years which includes the holocene epoch the advantage of this period is that data have been obtained from a wide array of methodological techniques as well as a wide selection of materials including both natural ones e g lava flows and various archaeological artifacts our main observations are i that well fired archaeological materials bricks potteries clays and ceramics show the best correlation with the rest of the dataset which we interpret to suggest that these data are the most reliable and ii although paleointensity data obtained from lava flows are slightly more scattered there is no evidence for paleointensity data from lavas to be significantly lower or higher than other data irrespective of the methodology c 2007 elsevier b v all rights reserved less

controls on the 87sr 86sr ratio of carbonates in the garhwal himalaya headwaters of the ganges abstract the episodic variation of the seawater 87sr 86sr ratio has been attributed to either variations in the sr flux or the sr isotopic composition of the riverine dissolved load derived from weathering of the continental crust the discovery that himalayan rivers are characterized by high concentrations of dissolved sr concentrations with high 87sr 86sr ratios has raised the possibility that collisional orogens play a critical role in moderating the variations in seawater 87sr 86sr ratios here we describe himalayan carbonates and calc silicates from garhwal the headwaters of the ganges with extreme 87sr 86sr ratios 1 0 elevated sr isotope ratios result from exchange with rb rich silicate material during both himalayan and pre himalayan metamorphic episodes and the carbonates contribute a significant fraction to the ganges 87sr flux particularly elevated 87sr 86sr ratios are found in calc silicates from the deoban formation of the lesser himalaya a detailed traverse of shales and calc silicat

exploring the temporal change in provenance encoded in the late quaternary deposits of the ganga plain abstract temporal analysis of sr isotopes in soil carbonates and sr and nd isotopes in silicate fractions has been carried out in a sedimentary core kalpi core 50 m long raised from the southern bank of the yamuna river ganga plain india the aim of the study is to constrain sediment provenance through comparison with the modern himalayan and peninsular river systems water and bank sediments sr isotopic data in soil carbonates 0 71874 to 0 71410 and sr nd isotopic data in silicate 0 72865 to 0 74544 and 13 9 to 17 2 respectively vary significantly with depth and are indicative of both himalayan and peninsular sources for sediments in the southern ganga plain the positive correlation between 87sr 86sr ratio and 1 sr in soil carbonate and the negative correlation between 87sr 86sr and end in silicate confirm mixing of sediments from these sources variations of 87sr 86sr ratios in soil carbonates show that at 80 and 45 ka the himalaya acted as the major source of sediments in the southern part of the ganga plain the gradual decrease in 87sr 86sr ratios after 80 and 45 ka indicates change in source to peninsular india which is also supported by limited sr and nd isotope data in silicates the change in sediment provenance corresponds well with the available climatic record and is suggestive of strong climatic control in sediment supply with high supply from the himalaya during the interglacial period and peninsular sediments during glacial period

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

chemical weathering outputs from the flood plain of the ganga abstract transport of sediment across riverine flood plains contributes a significant but poorly constrained fraction of the total chemical weathering fluxes from rapidly eroding mountain belts which has important implications for chemical fluxes to the oceans and the impact of orogens on long term climate we report water and bedload chemical analyses from the ganges flood plain a major transit reservoir of sediment from the himalayan orogen our data comprise six major southern tributaries to the ganga 31 additional analyses of major rivers from the himalayan front in nepal 79 samples of the ganga collected close to the mouth below the farakka barrage every two weeks over three years and 67 water and 8 bedload samples from tributaries confined to the ganga flood plain the flood plain tributaries are characterised by a shallow 18o d array compared to the meteoric water line with a low dexcess from evaporative loss from the flood plain which is mirrored in the higher dexcess of the mountain rivers in nepal the stable isotope data confirms that the waters in the flood plain tributaries are dominantly derived from flood plain rainfall and not by redistribution of waters from the mountains the flood plain tributaries are chemically distinct from the major himalayan rivers they can be divided into two groups tributaries from a small area around the kosi river have 87sr 86sr ratios 0 75 and molar na ca ratios as high as 6 tributaries from the rest of the flood plain have 87sr 86sr ratios 0 74 and most have na ca ratios

sr and 87sr 86sr in waters and sediments of the brahmaputra river system silicate weathering co2 consumption and sr flux abstract the brahmaputra is a major river system draining the himalaya the concentration of sr and its 87 sr 86 sr have been measured in dissolved and particulate phases of the brahmaputra and its tributaries in india to trace the sources of dissolved sr dissolved sr ranges from 250 to 1050 nm with 87 sr 86 sr from 0 71298 to 0 75975 the sr data along with the available concentrations of major ions in the samples show that major contributors of sr in the brahmaputra system are the silicates and carbonates of the himalaya and the transhimalaya and carbonates and evaporites of the tibetan basin silicate sr in the brahmaputra river system ranges from 20 to 80 with an average of 45 the silicate component of sr in the brahmaputra system is similar or marginally higher than that in the ganga system due to contribution from the transhimalayan calc alkaline plutonic rocks which have higher concentration of sr evaporites of the tibetan sub basin and hot springs along the indus tsangpo suture could be the other significant contributors to the dissolved sr budget of the brahmaputra contribution from evaporite dissolution decouples the total dissolved sr flux from the tibetan basin from atmospheric co 2 consumption radiogenic sr of the brahmaputra system is derived from the himalayan silicates whereas other sr sources tend to dilute its radiogenic signature the 87 sr 86 sr of the dissolved phase shows significant correlation with indices of silicate weathering indicating that 87 sr 86 sr can serve as a proxy of silicate weathering at their outflow the brahmaputra is less radiogenic 0 72 compared to the ganga 0 73 however the flux of 87 sr from the brahmaputra is similar to that of the ganga

strontium isotopic composition of the po river dissolved load insights into rock weathering in northern italy abstract strontium isotopic composition 87sr 86sr of river water provides insight on the nature of rocks involved in the weathering processes and important constraints for reconstructing silicate versus carbonate weathering in large scale basins new data presented in the context of a geochemical map of the po river basin highlight that the po river water evolves from the upper part of the catchment where 87sr 86sr approaching 0 7097 relates to the weathering of igneous and metamorphic silicate rocks to the middle part where less radiogenic compositions 87sr 86sr 0 7089 are driven by the confluence of the tributaries draining mesozoic carbonate rocks of the south alpine domain and from inflow of apennine streams characterized by less radiogenic sr signatures due to weathering of marly sediments and mafic magmatic rocks down flow the sr isotopic compositions of po river water rises at 0 7091 either by the confluence of the last apennine tributary panaro 87sr 86sr 0 7095 and or by the possible contribution from hyporheic exchanges po river isotopic signatures reveal slightly more radiogenic 87sr 86sr in comparison to other important alpine river systems e g danube rhine and rhone likely suggesting that silicate rocks are comparatively contributing more weathering byproducts in the po basin

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

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

temporal variations in sr and 87sr 86sr of the ganga headwaters estimates of dissolved sr flux to the mainstream the headwaters of the ganga the alaknanda bhagirathi and the ganga were analysed for their dissolved major ions sr and 87sr 86sr on a biweekly to monthly basis over a period of one year to determine their temporal variations and the factors contributing to them the concentrations of major ions and sr show significant seasonal variation with lower values during monsoon period in all the three rivers a similar trend is also observed for 87sr 86sr and na ca na narclr suggesting relatively lower contribution of sr and na from silicates which are more radiogenic in sr during monsoon budget calculations show that silicate derived dissolved sr srs in the river ganga alaknanda and the bhagirathi varied from 10 4 to 27 11 7 3 to 30 12 16 6 to 57 23 of measured sr respectively with lower values during monsoon the relative decrease in silicate erosion compared to carbonate during monsoon can result from several factors these include higher dissolution kinetics of the carbonates lower water rock interaction time and availability of larger area for weathering the annual discharge weighted sr flux derived from the time series data is higher by 20 from that based on peak flow sr and lower by 40 compared to that derived from lean flow sr concentration the area normalized annual flux of dissolved sr from the ganga at rishikesh is about five times its flux at rajshahi bangladesh and a few other major global rivers such as the amazon indicating higher erosion rate over the himalaya copyright 2010 john wiley sons ltd

geologic control of sr and major element chemistry in himalayan rivers nepal our study of the seti river in far western nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology the seti flows through four distinct terranes starting with the tethyan sedimentary series tss and greater himalayan series ghs tss ghs waters display 87 sr 86 sr ratios of 0 73 and high sr and ca consistent with the composition of limestone and marble common in these terranes the 87 sr 86 sr ratio and mg increase markedly as the river passes into the lesser himalayan series lhs where tributaries have 87 sr 86 sr ratios from 0 75 to 1 02 and high sr ca and mg the high mg in lhs waters correlate with high 87 sr 86 sr ratios which we attribute to weathering of highly radiogenic 0 71 0 82 dolostones tributaries to the seti river draining the largely carbonate free dadeldhura thrust sheet dts have ratios near 0 74 but low sr ca and mg and therefore have little impact on seti mainstem chemistry mass balance calculations and camg weathering indices show that carbonate weathering accounts for 70 of total dissolved solids to the seti river sr ca ratios of river waters provide a minimum estimate of the carbonate weathering contribution to sr due to partitioning of sr and ca during incongruent dissolution and reprecipitation of calcite overall we attribute high 87 sr 86 sr ratios in the seti river and its tributaries to the weathering of metacarbonates especially dolostones in the upper nawakhot group which have exchanged sr with silicates during metamorphism our modeling of sr fluxes in the seti river indicates that the tss ghs accounts for 36 39 of the sr the lhs for 40 53 and 8 23 for the dts prior to exposure of lhs rocks at 12 ma tss and ghs carbonates with low 87 sr 86 sr ratios dominated himalayan rivers we attribute the elevated 87 sr 86 sr ratios of himalayan paleorivers during the late miocene and pliocene to exposure and weathering of lhs metacarbonates copyright 2000 elsevier science ltd

typhoon impacts on chemical weathering source provenance of a high standing island watershed taiwan abstract chemical weathering source provenance changes associated with typhoon mindulle 2004 were identified for the choshui river watershed in west central taiwan using radiogenic sr isotope 87 sr 86 sr and major ion chemistry analysis of water samples collected before during and following the storm event storm water sampling over 72 h was conducted in 3 h intervals allowing for novel insight into weathering regime changes in response to intense rainfall events chemical weathering sources were determined to be bulk silicate and disseminated carbonate minerals at the surface and silicate contributions from deep thermal waters loss on ignition analysis of collected rock samples indicate disseminated carbonate can compose over 25 by weight of surface mineralogy but typically makes up 2 3 of watershed rock 87 sr 86 sr and major element molar ratios indicate that typhoon mindulle caused a weathering regime switch from normal flow incorporating a deep thermal signature to that of a system dominated by surface weathering the data suggest release of silicate solute rich soil pore waters during storm events creating a greater relative contribution of silicate weathering to the solute load during periods of increased precipitation and runoff partial depletion of this soil solute reservoir and possible erosion enhanced carbonate weathering lead to increased importance of carbonates to the weathering regime as the storm continues major ion data indicate that complex mica weathering muscovite biotite illite chlorite may represent an important silicate weathering pathway in the watershed deep thermal waters represent an important contribution to river solutes during normal non storm flow conditions sulfuric acid sourced from pyrite weathering is likely a major weathering agent in the choshui river watershed

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

barium in the yamuna river system in the himalaya sources fluxes and its behavior during weathering and transport 1 systematic measurements of ba in waters and bed sediments of the yamuna and many of its tributaries in the himalaya yamuna river system have been carried out dissolved ba in the yamuna river system yrs ranges from 17 to 871 nm streams near the source region draining predominantly granites gneisses have lower abundance of ba 100 nm compared with those in the lower reaches these data coupled with those available for major ion composition of these rivers and their sediments have been used to determine the contributions of silicates and carbonates the two major lithologies in the drainage basin to dissolved ba in yrs in yrs dissolved ba shows significant covariations with na si ca and mg using na as an index it is estimated that silicates are an important source of ba to many of the rivers in a few streams in the lower reaches however they account for only 20 of measured ba carbonate weathering which dominates the major ion composition of yrs rivers contributes on average 30 of dissolved ba together silicates and carbonates roughly balance measured ba in many of the rivers whereas in a few streams ba contributions from additional sources are needed to balance the budget prospective sources include organic matter phosphorites plot of 1 ba versus 87sr 86sr shows a two component mixing trend one with low ba high 87sr 86sr silicates and the other with high ba low 87sr 86sr carbonates phosphorites ba also shows significant positive correlation with dissolved re and so4 a likely explanation for the ba re so4 association is that they are supplied from organic matter phosphorites carbonates assemblages through h2so4 weathering in yrs bed sediments ba shows significant correlation with k and al ba na and ba sr in these sediments are higher than those in granites of the higher himalaya these observations can be explained in terms of 1 differential release of these elements during weathering ba being less mobile because of its association with weathering resistant minerals or 2 nonconservative behavior of ba in rivers resulting in its removal from dissolved to particulate phases either way these results indicate that ba is less mobile relative to na and sr dissolved ba flux from the yrs basin is 5 times more than that from the ganga headwaters a result consistent with higher physical and chemical erosion in the yrs basin the yamuna and the ganga together transport 5 4 106 mol yr 1 of ba out of the himalaya which is 10 of the dissolved ba flux from the ganga at bangladesh roughly the same as their contribution to water discharge the rate of ba mobilization in the yamuna and the ganga basins in the himalaya is a factor of 2 higher than the global average

the indus river system india pakistan major ion chemistry uranium and strontium isotopes the indus river is one of the large river systems draining the himalaya we report in this paper the major ion chemistry sr and u isotope systematics of the indus system particularly its headwaters the results show that 1 on an average about a third of the cations in the waters can be from silicate weathering however most of the ca mg is likely to be from the weathering of carbonates and evaporites 2 the 87sr86sr of the waters ranges between 0 7085 and 0 7595 the higher values 0 72 are typical of the tributaries draining the precambrian granite gneissic terrains the 87sr86sr of the indus main channel throughout its entire stretch shows only minor variations 0 7104 0 7116 the indus transports 8 8 106 mol sr to the arabian sea annually with a 87sr86sr of 0 7111 if our results of sr concentration and 87sr86sr measured at thatta can be considered typical of the indus throughout the year and 3 the u concentration in the indus and its tributaries is generally high 0 37 10 3 g 1 1 the source for the high uranium can be the weathering of granites zones of uranium mineralisation and black shales the indus results when compared with our earlier data on the ganga brahmaputra show that in all these three river systems carbonate weathering is the dominant source of ca mg and hco3 and that u concentrations are high in the case of 87sr86sr the indus waters are less radiogenic however its tributaries draining the precambrian granites gneisses have 87sr86sr in excess of 0 72 similar to that in the rivers of the ganga system the low 87sr86sr of the indus 0 7111 suggests that its contribution to the sr isotope evolution of oceans since the cenozoic is less significant than that of the ganga brahmaputra

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

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

weathering sr fluxes and controls on water chemistry in the lake qinghai catchment ne tibetan plateau strontium sr concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the lake qinghai basin on the north eastern tibetan plateau dissolved sr and 87sr 86sr show ranges of 488 12 240 nmol l and 0 710497 0 716977 respectively these data together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment were used to determine the contributions of sr and its isotopic expense to rivers and lakes our results demonstrate that the chemical components and 87sr 86sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources with the former contributing 72 18 dissolved sr to rivers the difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi arid condition variation in 87sr 86sr ratios places constraint on the sr isotopic compositions of the main tributaries surrounding lake qinghai the water chemistry of the buha river the largest river within the catchment underlain by the late paleozoic marine limestone and sandstones dominates sr isotopic composition of the lake water being buffered by the waters from the other rivers and probably by groundwater however the characteristic chemical composition of the lake itself differs remarkably from the rivers which can be attributed to precipitation of authigenic carbonates low magnesium calcite aragonite and dolomite though this does not impact the sr isotope signature which may remain a faithful indicator in paleo records regarding the potential role of groundwater input within the lake qinghai systems in the water budget and water chemistry we have also determined the sr concentration and 87sr s6sr ratio of groundwater from diverse environments this has allowed us to further constrain the sr isotope systematic of this source a steady state calculation gives an estimate for the groundwater flux of 0 19 0 03 108 m3 yr accounting for about 8 of contemporary lake sr budget copyright 2010 john wiley sons ltd

dissolved rhenium in the yamuna river system and the ganga in the himalaya role of black shale weathering on the budgets of re os and u in rivers and co 2 in the atmosphere extensive measurements of dissolved re and major ion abundances in the yamuna river system yrs a major tributary of the ganga have been performed along its entire stretch in the himalaya from its source near the yamunotri glacier to its outflow at the foothills of the himalaya at saharanpur in addition re analysis has been made in granites and precambrian carbonates some of the major lithologies of the drainage basin these data coupled with those available for black shales in the lesser himalaya allow an assessment of these lithologies contributions to the re budget of the yrs the re concentrations in the yrs range from 0 5 to 35 7 pm with a mean of 9 4 pm a factor of 4 higher than that reported for its global average concentration in rivers dissolved re and cations na k ca mg are strongly correlated in the yrs indicating that they are released to these waters in roughly the same proportion throughout their course the re cations in most of these rivers are one to two orders of magnitude higher than the re na k mg ca measured in granites of the yamuna basin this leads to the conclusion that on average granites crystallines make only minor contributions to the dissolved re budget of the yrs on a basin wide scale though they may be important for rivers with low dissolved re similarly precambrian carbonates of the lesser himalaya do not seem to be a major contributor to dissolved re in these rivers as their re ca mg is much less than those in the rivers the observation that re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite black shale carbonate layers in phosphorite mines are high and that re and so4 are significantly correlated in yrs seems to suggest that the bulk of the dissolved re is derived from black shale carbonaceous sediments material balance considerations based on average re of 30 ng g 1 in black shales from the lesser himalaya require that its abundance in the drainage basin of the yrs needs to be a few percent to yield average re of 9 4 pm furthermore the positive correlation between re and cations would require that these re rich sediments e g black shales and re poor lithologies e g crystallines precambrian carbonates contribute re and cations in roughly the same proportion throughout the drainage basin the available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met the annual fluxes of dissolved re at the base of the himalaya from the yamuna are 150 mol at batamandi and 100 mol at saharanpur compared to 120 mol from the ganga at rishikesh the total flux from the yamuna and the ganga account for 0 4 of the global riverine re flux much higher than their contribution to global water discharge this is also borne out from the mobilization rate of re 1 to 3 g km 2 y 1 in the ganga and yamuna basins in the himalaya compared to the global average of 0 1 g km 2 y 1 black shale weathering can also significantly influence the budgets of os and u in rivers and co2 in rivers and the atmosphere using dissolved re in rivers as a proxy it is estimated that 6 9 108 kg y 1 of black shales are being weathered in the ganga and yamuna basins in the himalaya weathering of such amounts of black shales can account for the reported concentrations of os and u in these rivers furthermore if the weathering results in the conversion of organic carbon in the black shales to co2 it would release 2 105 mol of co2 km 2 y 1 in the yamuna and ganga basins in the himalaya comparable to the co2 consumption from silicate weathering

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

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

submarin hydrothermale entstehung der sedimentaren mangan lagerstatte urkut ungarn abstract a stratiform mn deposit of liassic age was formed in the tethys geosyncline at urkut hungary with rhodochrosite as the predominant mineral 50 among clay minerals goethite is found in the lower part and pyrite in the upper part of the ore bearing layer the close association of fe and mn is due to the fact that the ore was accumulated by submarine volcanogenic processes derivation from terrestrial solutions can be excluded because the different oxidation potentials of fe and mn would have led to a significant separation of these two elements furthermore the co contents and the mn co ratio are higher than in typical ore deposits derived from terrestrial solutions the paragenetic clay minerals are fe rich montmorillonites and celadonites which are respectively formed by the adsorption of silica onto fe hydroxides and mixed fe al gels previously described glauconite is proved to be celadonite due to the absence of detritus and heavy minerals all phases of the deposit are suggested to be chemical precipitates from volcanogenic solutions though volcanic rocks have not been found up to now however it is not necessary to assume a supply of the ore forming elements by initial hydrothermal magmatic solutions because co2 rich waters associated with volcanism are easily able to mobilize and transport both fe and mn from wall rocks upon mixing with marine waters and degassing the eh and ph of the ore solutions are changed besides carbonates sulfides and oxides silicates of different compositions are formed according to the eh ph conditions within the sediment

microwave archaeointensities from peruvian ceramics summary accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization thellier thellier 1959 shaw 1974 by using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample thus avoiding thermal alteration walton et al 1993 incorporation of this new microwave heating technique with the conventional thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from peruvian ceramics and clearly defined how the field strength has varied in peru over the past 2000 years the new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling

chemical weathering of metamorphic rocks from low elevations in the southern himalaya abstract early chemical weathering involving the acid hydrolysis of banded gneisses under warm temperate and subtropical conditions in the likhu catchment of the middle hills of nepal has resulted in the formation in situ of residual soils 2 3 m thickness grading downwards into saprolites that extend to thicknesses exceeding 6 m chemical analyses of bulk samples from three detailed profiles at elevations between 800 and 1000 m above sea level reveals a uniformity of chemical change throughout the weathering sequence within each profile in terms of loss of ca and na however there is also a progressive change between profiles with the more strongly weathered profiles showing almost total loss of ca and na the uniformity of change to depth within profiles is facilitated by the free draining sandy and silty textures of the weathering residues together with the frequent flushing by monsoon rains substantially greater retention of k and mg has occurred in all profiles only subtle decreases in both mgo and k2o are found to occur from the base of the residual soils upwards to the top of the soil these changes in bulk chemistry are consistent with the clay mineralogy and the stream water chemistry analyses it is suggested that the k and mg are preferentially retained in some of the clay minerals illite chlorite palygorskite and hydrobiotite whereas the na and ca are readily leached to the stream waters the general pattern of chemical erosion is consistent with that observed in other warm and humid tectonically active mountain terrains although the widespread formation of kaolinite is less commonly reported in such environments

magnetic field intensity study of the 1960 kilauea lava flow hawaii using the microwave palaeointensity technique summary it is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known in this study two vertical sections 16 m apart have been sampled from the approximately 1 m thick 1960 kilauea lava flow hawaii variations are seen in the rock magnetic and palaeomagnetic properties between and within the two sections indicating that there are small scale lateral and vertical variations in the lava flow the two sections showed dierent responses to microwave palaeointensity analysis section h6001 generally gave ideal linear behaviour on plots of natural remanent magnetization nrm lost against microwave induced thermoremanent magnetization t m rm gained whilst the majority of samples from h6002 showed anomalous two slope behaviour when all plots were interpreted by taking the best fitting line through all points the flow mean intensity for h6001 was 31 6 3 6 mt and that for h6002 was 37 1 6 4 mt compared with the expected intensity of 36 mt additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava and whether it is best to always interpret nrm lost t m rm gained plots by taking the line of best fit regardless of shape

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

seasonal changes in the radiogenic and stable strontium isotopic composition of xijiang river water implications for chemical weathering seasonal changes in strontium sr isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering and help to better constrain the sr isotopic budget of global oceans however such records are scarce here we present a year long time series of both radiogenic and stable sr isotope measurements 87sr 86sr and 88sr from river water at guiping in the middle reaches of the xijiang river south china temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both sr isotopes and major ions in the river water river water 87sr 86sr values range from 0 708487 to 0 710336 with most values being 0 7092 are generally accompanied by high rb sr ratios and low ph and 13c of dissolved inorganic carbo dic and occur during periods of large river flux this indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons seasonal variation in river water 88sr is large from 0 147 to 0 661 with higher 88sr values generally corresponding to higher 87sr 86sr values again low 88sr values 0 3 suggest a dominant contribution from the weathering of carbonate rocks whereas the high 88sr values may represent a contribution from intensive weathering of silicate rocks using the time series data we estimated the flux weighted averages of sr concentration 87sr 86sr and 88sr for the xijiang river to be 1 00 mol l 0 70960 and 0 38 respectively the sr concentration and 87sr 86sr results are close to previous estimates while the 88sr value is amongst the highest recorded for the large rivers of the world and is close to that of seawater our results indicate that large rivers draining through tropical sub tropical regions could play an important role in regulating the stable sr isotopic budget of global oceans

an assessment of the reliability of palaeointensity results obtained from the cretaceous aged suhongtu section inner mongolia china abstract here we present microwave palaeointensity results from 89 sister samples from the study of zhu et al zhu r pan y he h qin h ren s 2008 palaeomagnetism and 40 ar 39 ar age from a cretaceous volcanic sequence inner mongolia china implications for the field variation during the cretaceous normal superchron phys earth planet int 169 59 75 who carried out thellier palaeointensity analysis as part of their integrated palaeomagnetic and 40 ar 39 ar dating study of cretaceous lava from the suhungtu section inner mongolia china additionally a comprehensive rock magnetic investigation has been carried out in order to determine the mineralogy and hence the validity of assuming that the remanence is a thermal remanent magnetisation trm the microwave results are of apparent high quality and give flow mean palaeointensity estimates ranging from 13 to 49 t corresponding to virtual dipole moment vdm estimates ranging from 2 5 to 8 9 10 22 am 2 and an overall mean vdm of 5 5 1 9 10 22 am 2 for the 24 flows aged 110 6 0 1 ma when the microwave results using the perpendicular applied field method with partial microwave thermal remanence pt m rm and pt m rm tail checks are compared to those obtained with the thellier method coe version with ptrm but not tail checks and heating in argon atmosphere differences are seen at the sample flow and palaeomagnetic unit level however the overall means and spread in palaeointensity estimates are consistent some discrepancy is due to the differing sized sample sets and sample inhomogeneity but discrepancy is also interpreted to be due to the differing protocols methodology plus the subjectivity in interpretation considering only those results that are consistent to within 20 the spread in palaeointensity estimates remains there is substantial rock magnetic evidence from progressive heating in air and argon experiments both showing irreversible thermomagnetic behaviour as well as looking at samples under the scanning electron microscope to suggest that maghaemite is present albeit to varying degrees in many of the samples alteration therefore occurred in nature and it is likely that the remanence will have been affected to differing degrees potentially causing underestimates in palaeointensity maghaemite is interpreted to be a remanence carrier where a component of remanence remains after heating to 580 c and loss of ptrm acquisition capacity is found on heating no correlation was found between the estimated palaeointensity microwave or thellier datasets and amount of high temperature remanence or any rock magnetic parameter this could suggest that the palaeointensity estimates are reliable or as seems likely more than one factor such as methodology protocol interpretation chemical remanent magnetisation crm contamination and the geomagnetic field are influencing the palaeointensity estimates in an attempt to remove the influence of palaeointensity protocol and methodology the palaeointensity datasets were reduced to consist only of those results mutually consistent to 20 n 22 no obvious correlation was again seen between the inferred maghaemite contribution and palaeointensity estimate there is therefore no clear evidence for the biasing of results due to crm contamination assuming a simple relationship between biasing and maghaemite contribution and it can thus be inferred that the geomagnetic field was a major influencing factor further studies are however needed to fully elucidate the extent and result of each possible influencing factor and ultimately the reliability of palaeointensity estimates from rocks of this type

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

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

are systematic differences between thermal and microwave thellier type palaeointensity estimates a consequence of multidomain bias in the thermal results a meta analysis which directly compares 13 datasets of microwave and thermal thellier palaeointensity measurements obtained from igneous rocks is reported the results clearly indicate systematic differences in the measurements made using the two approaches the thermal results tend to be higher often by several tens of percent and associated with slightly noisier arai plots additionally in nearly half of the cases considered higher thermal palaeointensity estimates were reported to be calculated from the lowtemperature portions of concave up arai plots while microwave measurements made on specimens from the same core sample or rock unit were derived from more linear arai plots the most plausible explanation for the bulk of these differences appears to be that non ideal behaviour caused by multidomain vortex state and or interacting ferrimagnetic grains is exaggerated in the results of the thermal experiments over their microwave counterparts a detailed investigation of the individual studies concludes that such effects may be adversely affecting some of the measurements thermal and or microwave in 10 of the 13 datasets considered it is probable that these non ideal effects are enhanced in the thermal results over their microwave counterparts at least in part because of the different thellier type protocols that are used in the two types of study the findings of this study suggest that biasing of absolute palaeointensity estimates by multidomain effects may be much more prevalent than previously thought and that this effect might be responsible for certain discrepancies that have been observed in the geomagia50 database they also clearly indicate that in addition to taking the steps they already do to avoid biasing from secondary overprints and thermally induced alteration future absolute palaeointensity studies of

major ion chemistry in the headwaters of the yamuna river system chemical weathering its temperature dependence and co 2 consumption in the himalaya abstract the yamuna river and its tributaries in the himalaya constitute the yamuna river system yrs the yrs basin has a drainage area and discharge comparable in magnitude to those of the bhagirathi and the alaknanda rivers which merge to form the ganga at the foothills of the himalaya a detailed geochemical study of the yrs was carried out to determine i the relative significance of silicate carbonate and evaporite weathering in contributing to its major ion composition ii co2 consumption via silicate weathering and iii the factors regulating chemical weathering of silicates in the basin the results show that the yrs waters are mildly alkaline with a wide range of tds 32 to 620 mg l 1 in these waters the abundances of ca mg and alkalinity which account for most of tds are derived mainly from carbonates many of the tributaries in the lower reaches of the yamuna basin are supersaturated with calcite in addition to carbonic acid sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering silicate weathering in yrs basin contributes on average 25 molar basis of total cations on a basin wide scale silicate weathering however does not seem to be intense in the basin as evident from low si na k in the waters 1 2 and low values of chemical index of alteration cia in bed sediments 60 co2 drawdown resulting from silicate weathering in the yrs basin in the himalaya during monsoon ranges between 4 to 7 105 moles km 2 y 1 this is higher than that estimated for the ganga at rishikesh for the same season the co2 consumption rates in the yamuna and the ganga basins in the himalaya are higher than the global average value suggesting enhanced co2 drawdown in the southern slopes of the himalaya the impact of this enhanced drawdown on the global co2 budget may not be pronounced as the drainage area of the yrs and the ganga in the himalaya is small the co2 drawdown by silicates in the yrs basin is marginally higher than the reported values of co2 release from oxidation of organic rich sediments estimated using re as a proxy this comparison shows the need to constrain co2 sources and sinks better to balance its budget in a regional scale the results also show that silicate weathering rate in the yrs basin is 10 mm ky 1 and on the ganga basin it is 5 mm ky 1 which are several times lower than the carbonate weathering rates the significantly higher silicate weathering rate observed in the yrs basin seems to be governed by rapid physical erosion in this region the apparent activation energy for overall silicate weathering in the yrs basin derived from na and si concentrations and water temperature ranges from 50 to 80 kj mol 1 these values are comparable to those reported for granitoid weathering in natural watersheds and feldspar weathering in laboratory experiments this study brings to light the sources contributing to major ions enhanced chemical weathering rates in the yamuna river basin and interdependence of silicate weathering on physical erosion and temperature