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

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

intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

anthropogenic impacts on mineral weathering a statistical perspective abstract correspondence analysis was adopted as tool for investigating the statistical structure of hydrochemical and weathering datasets of groundwater samples with the main purpose of identifying impacts on mineral weathering caused by anthropogenic activities namely fertilizing of farmlands the hydrochemical dataset comprised measured concentrations of major inorganic compounds dissolved in groundwater namely bicarbonate silica usually by products of chemical weathering chloride sulphate and nitrate typically atmospheric plus anthropogenic inputs the weathering dataset consisted of calculated mass transfers of minerals being dissolved in loess sediments of a region located in sw hungary szigetvar area namely na plagioclase calcite and dolomite and of pollution related concentrations of sodium magnesium and calcium a first run of correspondence analysis described groundwater composition in the study area as a system of triple influence where spots of domestic effluents dominated chemistries are surrounded by areas with agriculture dominated chemistries both imprinted over large regions of weathering dominated chemistries a second run revealed that nitrification of n fertilizers is promoting mineral weathering by the nitric acid reaction anthropogenic pathway in concurrence with the retreating of weathering by carbonic acid natural pathway it also indicated that dolomite and calcite are being players in a dedolomitization process driven by dissolution of gypsum fertilizers and nitrification of n fertilizers

sulfuric acid as an agent of carbonate weathering constrained by δ13cdic examples from southwest china abstract rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric co 2 current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important here we use carbon isotopic evidence and water chemistry of springs and rivers from the beipanjiang river basin guizhou province southwest china to demonstrate that sulfuric acid is also an important agent of rock weathering the 13 c of dissolved inorganic carbon dic in the water samples ranges from 13 1 to 2 4 and correlates negatively to hco 3 ca 2 mg 2 ratios and positively to so 4 2 ca 2 mg 2 ratios these relationships are interpreted as mixing diagrams between two reactions of carbonate weathering using carbonic acid and sulfuric acid as a proton donor respectively mixing proportions show that around 42 of the divalent cations in the spring water from guizhou are originated from the interaction between carbonate minerals and sulfuric acid it is shown that 40 of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin the remaining 60 are derived from the oxidative weathering of sulfide minerals in sedimentary rocks our results show the positive action of sulfuric acid on the chemical weathering of carbonate particularly we show that sulfuric acid generated by coal combustion has increased by almost 20 the weathering rates of carbonate in southwest china this is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases because of the involvement of sulfuric acid in weathering reactions 63 of the alkalinity exported by rivers is derived from carbonate instead of 50 when atmospheric co 2 is the only acid involved in chemical weathering of carbonate in the guizhou province the weathering of carbonate is thus at least transiently a net source of co 2 to the atmosphere when extrapolated at global scale sulfuric acid induced carbonate weathering could counterbalance a significant part of the co 2 consumed by silicate weathering this paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric co 2 level

proterozoic anorthosite granite nain batholith structure and intrusion processes in an active lithosphere scale fault zone northern labrador we present field evidence of the structure and evolution of a typical proterozoic massif type anorthosite the anorthosite forms a batholith composed of numerous plutons and ring complexes intruded episodically in two main sequences each producing anorthositic rocks and monzonite ferrodiorite followed by granite the batholith is located where a lithosphere scale fault zone 50 km wide and extending over 1000 km from greenland to labrador intersected an older continental suture intermittent episodes of mainly sinistral transtension along this gardar voisey s bay fault zone were associated with the generation of a number of pulses of magmatism and controlled the rise of magmas to middle and upper crustal levels between 1363 and 1289 ma both the large and small scale structures and magma intrusion processes are similar to those of many cordilleran batholiths with tabular plutons associated with ring dykes emplaced by cauldron subsidence and basin shaped plutons associated with cone sheets these

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

geology geochemistry and geochronology of fe oxide cu au mineralization associated with şamli pluton western turkey abstract the amli balikesir fe oxide cu au deposit one of several iron cu au deposits in western turkey is hosted by porphyritic rocks of the multi phase amli pluton and metapelitic metadiabasic rocks of karakaya complex two successive mineralization events are recognized in the area as i early magnetite and sulfide and ii late hematite goethite native copper au alteration associated with the mineralization in amli is characterized by four distinct mineralogical assemblages they are in chronological order of formation 1 plagioclase early pyroxene scapolite 2 garnet late pyroxene 3 chlorite epidote and 4 chalcedony calcite alteration geochemical isotopic sr nd o s and geochronological ar ar data from alteration and magmatic rocks suggest a temporal and genetic link between the multiphase amli pluton and the hydrothermal system that controls the fe oxide cu au mineralization 40 ar 39 ar geochronology on hornblende and biotite separates of the amli pluton yielded an age range between 23 20 0 50 and 22 42 0 11 ma overlapping with 40 ar 39 ar age of 22 34 0 59 ma from alteration the close spatial and temporal associations of amli mineralization with porphyritic intrusions pervasive ca rich alteration calcic plagioclase andraditic garnet diopsidic pyroxene scapolite and epidote are considered as common features akin to calcic assemblages in typical iocg deposits besides abundant low ti 0 5 magnetite hematite high cu moderate au up to 8 82 ppm association structural control and lithologic controls of mineralization low s sulfide content chalcopyrite pyrite in the deposit and the derivation of causative magma from subduction modified subcontinental lithospheric mantle under a transpressional to transtensional regime are collectively considered as the features in favor of iocg type mineralization for the amli deposit

new estimates of silicate weathering rates and their uncertainties in global rivers abstract this study estimated the catchment and global scale weathering rates of silicate rocks from global rivers using global compilation datasets from the gems water and hybam these datasets include both time series of chemical concentrations of major elements and synchronous discharge using these datasets we first examined the sources of uncertainties in catchment and global silicate weathering rates then we proposed future sampling strategies and geochemical analyses to estimate accurate silicate weathering rates in global rivers and to reduce uncertainties in their estimates for catchment silicate weathering rates we considered uncertainties due to sampling frequency and variability in river discharge concentration and attribution of weathering to different chemical sources our results showed that uncertainties in catchment scale silicate weathering rates were due mostly to the variations in discharge and cation fractions from silicate substrates to calculate unbiased silicate weathering rates accounting for the variations from discharge and concentrations we suggest that at least 10 and preferably 40 temporal chemical data points with synchronous discharge from each river are necessary for the global silicate weathering rate we examined uncertainties from infrequent sampling within an individual river the extrapolation from limited rivers to a global flux and the inverse model selections for source differentiation for this weathering rate we found that the main uncertainty came from the extrapolation to the global flux and the model configurations of source differentiation methods this suggests that to reduce the uncertainties in the global silicate weathering rates coverage of synchronous datasets of river chemistry and discharge to rivers from tectonically active regions and volcanic provinces must be extended and catchment specific silicate end members for those rivers must be characterized with current available synchronous datasets we suggest that the global silicate weathering rate ca mg silicate weathering flux was 2 17 2 range of 1 59 2 75 10 12 mol yr and the global co 2 consumption rates from silicate weathering was 7 85 5 78 9 93 10 12 mol yr since current synchronous datasets are not available for some rivers in tectonically active regions and highly active volcanic rocks our estimate should be considered as lower limit of estimates including the estimates from volcanic provinces from dessert et al 2003 the global co 2 consumption rates from silicates can be estimated as 11 93 9 86 14 01 10 12 mol yr which is similar to the previous estimates of gaillardet et al 1999

using detrital zircons from river sands to constrain major tectono thermal events of the cathaysia block se china abstract detrital zircons from the minjiang and zhujiang rivers in se china have been analyzed for u pb ages and lu hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the cathaysia block zircon u pb ages show five major populations at 90 250 ma 400 500 ma 0 7 1 2 ga 1 6 2 0 ga and 2 3 2 6 ga proterozoic zircons have hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust however phanerozoic zircons have hf isotopic signatures indicative of reworked or recycled ancient crust crustal growth rates based on the two stage hf model ages of the detrital zircons indicate that 30 and 90 of present crust in the northeastern cathaysia block was formed by 2 5 ga and 1 6 ga respectively whereas

petrochemistry of the south marmara granitoids northwest anatolia turkey post collision magmatic rocks are common in the southern portion of the marmara region kapidag karabiga gonen yenice can areas and also on the small islands marmara avsa pasalimani in the sea of marmara they are represented mainly by granitic plutons stocks and sills within triassic basement rocks the granitoids have ages between late cretaceous and miocene but mainly belong to two groups eocene in the north and miocene in the south the miocene granitoids have associated volcanic rocks the eocene granitoids do not display such associations they are both granodioritic and granitic in composition and are metaluminous calc alkaline medium to high k rocks their trace elements patterns are similar to both volcanic arc and calc alkaline post collision intrusions and the granitoids plot into the volcanic arc granite vag and collision related granite areas colg of discrimination diagrams the have high 87sr 86sr 0 704 0 707 and low 143nd 144nd 0 5124 0 5128 during their evolution the magma was affected by crustal assimilation and fractional crystallization afc nd and sr isotopic compositions support an origin of derivation by combined continental crustal afc from a basaltic parent magma a slab breakoff model is consistent with the evolution of south marmara sea granitoids

weathering and the global carbon cycle geomorphological perspectives abstract the links between the weathering of silicate minerals the global carbon cycle and climate change are complex and involve a whole range of often inter related tectonic climatic geomorphological and biological factors silicate weathering rates are known to have varied through geological time and increasingly sophisticated models now link such variation to the long term carbon cycle and climate change in order to improve the modelling further one key research need is for more and better datasets on weathering and the factors that control it as a contribution to this we review the nature of the weathering carbon cycle system the sources of evidence used to understand it and the challenges that remain in quantifying the feedbacks between weathering and the global carbon cycle we propose that increased understanding of geomorphological diversity of landscapes and processes and especially the dynamic relationships between weathering and erosion will aid clearer portrayal of the links between weathering and the long term carbon cycle

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

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

geochemical and stable isotope studies on natural water in the taroko gorge karst area taiwan chemical weathering of carbonate rocks by deep source co2 and sulfuric acid the geochemical cycle of co2 and the hydrological cycle in the taroko gorge karst area taiwan are discussed using chemical composition data of the natural water together with stable isotope ratios of carbon and oxygen of the water and soil co2 the soil co2 concentration at a depth of 1 m showed seasonal variations with a maximum of 5 2 v v and the minimum of 0 6 v v at three different altitudes ranging from 50 to 2000 m asl the soil temperature is the most important factor controlling the soil co2 concentration in this area the solubility of carbonates in groundwater can be explained by evolution under closed system conditions depending on the soil co2 concentration measured unexpectedly high 13c values of hco3 in groundwater were observed at some springs there was also an equivalent relationship between the sum of the concentration of mg2 and ca2 ions and that of hco3 and so42 ions in their waters these two facts suggest that some deep source co2 and sulfuric acid derived from weathering of pyrite may take part in the chemical weathering of carbonate rocks mainly calcareous schist as well as the soil co2 after the correction for the contribution of sulfuric acid the 13c values of hco3 of groundwater issuing from some springs were still high suggesting the presence of a deep source co2 flux altitude isotope effects were observed for surface water and rainwater in this area and could be expressed as 18o 0 0024h 3 67 h altitude m asl the estimated altitudes of catchment basins of springs using this equation were over 1000 2000 m higher than those of springs the rain falling high in the mountains is supplied with soil co2 dissolves carbonate rocks under closed system conditions penetrates deep underground and comes out again from springs together with the deep source co2 along fault crushing belts

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

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

collision driven slab breakoff magmatism in northwestern anatolia turkey abstract postcollisional eocene magmatism in northwestern anatolia produced two e w trending linear belts of plutons along and north of the izmir ankara erzincan suture zone iaesz whose geochemical features and age relations support a slab breakoff model for their petrogenetic oinevolution the suture zone granitoids szgs in the southern belt have ages around 54 48 ma are intrusive into blueschist rocks of the iaesz and are composed of diorite quartz diorite granodiorite and syenite the marmara granitoids mgs in the northern belt are slightly younger 48 35 ma intrusive into the paleozoic mesozoic crystalline basement rocks of the sakarya continent and composed of monzogranite granite and granodiorite both szgs and mgs have moderately to highly evolved medium to high k calc alkaline compositions and are predominantly metaluminous i type granitoids nd sr isotope systematics documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepacka

carbonate minerals in the global carbon cycle abstract carbonate minerals constitute earth s largest c reservoir this reservoir is considered unimportant to the global c cycle over long periods of time e g 10 6 yrs because it provides balanced sources and sinks of atmospheric co 2 as carbonate minerals precipitate and dissolve from carbonic acid respectively however carbonate mineral reactions may impact the carbon cycle at short time scales 10 2 to 10 5 yrs particularly when atmospheric pco 2 changes by several hundred ppm as exemplified by the paleocene eocene thermal maximum at transitions between glacial interglacial times and over the past century from anthropogenic inputs here i review recent literature about mechanisms in which carbonate minerals may impact the global carbon cycle carbonate mineral dissolution which increases dissolved inorganic carbon dic concentrations may represent a net atmospheric co 2 sink as primary productivity consumes dic resulting in organic c burial in fluvial systems of carbonate terrains alternatively carbonate minerals dissolved by sulfuric and nitric acids may represent an atmospheric source of co 2 with no rapid balancing atmospheric sink sulfuric acid dissolves carbonate minerals of modern carbonate platform sediments and water filled sinkholes and in the deep sea at the base of carbonate platform scarps in terrestrial landscapes sulfuric acid dissolves carbonate minerals of karst terrains hypogene caves and in comminuted glacial sediments nitric acid forms from oxidation of reactive n which has doubled in the past hundred years as humans fix atmospheric n 2 similar to some reactions involving sulfuric acid nitric acid dissolution of carbonate minerals represents a net source of atmospheric co 2 this source is concentrated in fertilized agricultural fields in carbonate terrains each of these processes represents a small flux relative to major c exchanges such as volcanic sources and silicate mineral weathering but collectively they could impact the c cycle at magnitudes similar to these major processes these impacts may increase as humans further alter elemental cycles of s and n

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

the emplacement history of granitic intrusions into the upper crust forceful to passive emplacement of the early miocene solarya pluton nw turkey as a case study abstract post collisional magmatism in western anatolia produced several granitic bodies represented by shallow level intrusions in this study we present field geochronology and geothermo barometry results of the solarya pluton sp nw turkey in order to better understand its emplacement into the different levels of the crust the sp consists of three main plutonic members showing different textural properties the northern part of the plutonic body is represented by k feldspar megacrystalline granodiorite kfmg with distinct porphyritic texture and southern part is made up of microgranite granodiorite mgg displaying microgranular texture whereas haplogranite which displays graphic granophyric textures is represented by a thin aureole between the sp and basement rocks field relations petrography and geothermo barometry studies combined with 40ar 39ar and u pb zircon dating results suggest that different members of the sp were emplaced into different levels of crust with different mechanisms the kfmg 40ar 39ar 23 2 ma u pb 21 8 ma began its emplacement forcefully in the relatively deeper levels in the crust av 1 65 kbar av 797 c 6 1 km depth after this stage mgg 40ar 39ar 22 6 ma u pb 21 2 ma was passively emplaced into the shallow levels av 0 69 kbar av 745 c 2 4 km depth via cauldron subsidence and in the latter stages the sheet intrusive rocks haplogranite 40ar 39ar 21 6 ma and hypabyssal association were emplaced into the ring faults at 1 5 km depth forceful to passive emplacement of the sp into the upper crust occurred under aegean extensional tectonics our study contributes to examination of the granite ascent and emplacement within other extensional provinces worldwide

water geochemistry of rivers draining karst dominated regions guangxi province south china implications for chemical weathering and role of sulfuric acid abstract guangxi province located in south china is a typical karst region affected by acid depositions for a couple of decades water samples from the major river basins in this region were collected and the chemical compositions were measured with a main purpose to quantify chemical weathering rates and associated co2 budget the average total dissolved solids tds of the river waters 232 mg l are comparable with other karstic rivers the major ion compositions of the river waters are characterized by the dominance of ca2 mg2 hco3 and are significantly rich in so42 the chemical compositions of the river waters indicate that four major reservoirs atmospheric anthropogenic carbonate and silicate inputs contribute to the dissolved loads the carbonate chemical weathering rates range from 61 4 t km2 yr for the qingshuihe river basin to 93 3 t km2 yr for the zuojiang river basin the silicate chemical weathering rates range from 2 9 t km2 yr for the qingshuihe river basin to 7 9 t km2 yr for the liujiang river basin the co2 consumption rates by carbonate weathering range from 559 103 mol km2 yr for the qingshuihe river basin to 817 103 mol km2 yr for the zuojiang river basin the co2 consumption rates by silicate weathering range from 19 103 mol km2 yr for the zuojiang river basin to 85 103 mol km2 yr for the liujiang river basin sulfuric acid is involved as a proton donor in weathering reactions and about 9 15 of the chemical weathering rates of the river basins are sulfuric acid induced the co2 consumption rates are only 85 91 of the value when assuming carbonic acid provides all the protons in the weathering reactions the co2 released from sulfuric acid induced carbonate weathering would exceed the co2 consumed by silicate weathering making the river basins in guangxi net co2 sources on geological timescales the total net co2 releasing flux is approximately 15 7 109 mol yr 0 19 1012 gc yr this result quantitatively highlights the fact that co2 budget by chemical weathering will be largely modified by sulfuric acid especially in seriously acid deposition affected region

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

time space relationships among structural and metamorphic aureoles related to granite emplacement a case study from the serre massif southern italy tectonic and thermal perturbations related to emplacement of granodiorite in the upper continental crust have been investigated in the late hercynian basement exposed in southern calabria italy here the structural aureole is marked by the presence of a major rim fold adjacent to the intrusive contact for a length of at least 20 km geometrical analysis of the structural aureole and related foliations lineations and crenulations reveals that the perturbed zone is at least 3000 m wide and characterized by an open synform trending nearly parallel to the intrusive contact this pattern is compatible with a laccolith like mode of magma emplacement related to the accretion of the pluton that shouldered weak phyllitic and slaty wall rocks the metamorphic aureole about 1800 m wide is characterized by biotite cordierite and andalusite that appear sequentially in spotted schists and hornfelses approaching the intrusive contact the peak assemblage equilibrated between 535 and 590 c at pressures between 175 and 200 mpa confirmed by al in hornblende barometry on granodiorite microstructural analysis allowed the inference of a time lag between the thermal and tectonic perturbations with the aid of thermal modelling it was possible to quantify the time required to reach the peak temperature at a distance from the intrusive contact where cordierite spots and andalusite porphyroblasts clearly overprint crenulations this estimate represents the time limit to accomplish deformation in the inner portion of the aureole and thus indicates a minimum strain rate of 4 10 14 s 1 within the country rocks during granodiorite intrusion

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

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

chemical weathering under mid to cool temperate and monsoon controlled climate a study on water geochemistry of the songhuajiang river system northeast china abstract for the first time the river water geochemistry of the songhuajiang basin the third largest river system in china has been studied in order to understand chemical weathering and associated co2 consumption rate in a mid to cool temperate and monsoon controlled climatic zone the major ion compositions of the river waters are characterized by the dominance of ca2 and hco 3 accounting for 46 and 74 of major cations and anions respectively the average total dissolved solids tds 116 mg l 1 and total cation concentration tz 1388 eq l 1 of the river waters are similar to those of global major rivers the chemical weathering rates of carbonate silicate and evaporites in the whole songhuajiang basin are estimated to be approximately 5 15 2 23 and 0 40 t km 2 a 1 respectively the total rock weathering rate for the whole songhuajiang basin is approximately 7 78 t km 2 a 1 which is at the lower end of the spectrum for global major rivers and is comparable with that of the amur and the congo zaire river the estimated co2 consumption rates for the whole songhuajiang basin are 53 4 103 mol km 2 a 1 and 66 6 103 mol km 2 a 1 by carbonate and silicate weathering respectively as a sub basin the 2nd songhuajiang has the highest 18 9 t km 2 a 1 while the nenjiang river basin has the lowest total rock weathering rate 5 03 t km 2 a 1 which indicates important controls of regional climate and lithology compared to the large rivers of china total rock weathering rates increase from north to south supporting the idea that the climate acts as major control on global chemical weathering the co2 consumption rate by silicate weathering within the whole songhuajiang river basin though under mid to cool temperate climate is in the same order of magnitude as that of huanghe 82 4 103 mol km 2 a 1 and is not much lower than that of changjiang 112 103 mol km 2 a 1 which suggests that the role of songhuajiang river weathering in long term climate change cannot be neglected compared to those of the large rivers of china

flow lobes in granite the determination of magma flow direction in the trawenagh bay granite northwestern ireland using anisotropy of magnetic susceptibility anisotropy of magnetic susceptibility ams has been determined from 152 sites over the 64 km2 trawenagh bay granite part of the 400 ma caledonian donegal batholith microscopic observations thermomagnetic analyses high field torque magnetometry and heating experiments demonstrate that the ams fabric is carried by biotite with varying amounts of mimetic magnetite in the biotite cleavage planes the ams fabric is interpreted as a flow fabric because microstructures indicate magmatic state deformation it defines large scale macroscopic flow features flow lobes in this weakly deformed granite at pluton scale the data set shows a gentle westward plunging lineation at a smaller scale many lobate magnetic foliation patterns can be discerned in which the magnetic lineation is usually symmetrically disposed about the long axes of the lobes in three dimensions the lobes are tongue like 1500 m wide subunit scale and elongated east west parallel with the general lineation they close consistently westward and younger lobes in the east appear to deflect older lobes in the west the trawenagh bay granite is west of a major synplutonic shear zone that hosts the main donegal granite pluton these structures are interpreted as frozen flow lobes and indicate that the magma flowed in a westward direction from within the active shear zone of the main donegal granite into the weakly deformed wall rock trawenagh bay granite intra unit pulses or surges have long been suspected in granite plutons however this study reports the most detailed description of such structures to date

chemical weathering of carbonates and silicates in the han river basin south korea abstract a detailed investigation of the fluvial geochemistry of the han river system allows to estimate the rates of chemical weathering and the consumption of co 2 the han river drains approximately 26 000 km 2 and is the largest river system in south korea in terms of both water discharge and total river length it consists of two major tributaries the north han river nhr and the south han river shr distinct differences in basin lithology silicate vs carbonate between the nhr and shr provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality the concentrations of major elements and the sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the han river system in both 2000 and 2006 the concentrations of dissolved loads differed considerably between the nhr and shr compared with the shr the nhr had much lower total dissolved solids tds sr and major ion concentrations but a higher si concentration and 87 sr 86 sr ratio a forward model showed that the dissolved loads in the nhr came primarily from silicate weathering 55 11 with a relatively small portion from carbonates 30 14 whereas the main contribution to the dissolved loads in the shr was carbonate weathering 82 3 with only 11 4 from silicates these results are consistent with the different lithologies of the two drainage basins silicate rocks in the nhr versus carbonate rocks in the shr sulfuric acid derived from sulfide dissolution in coal containing sedimentary strata has played an important role in carbonate weathering in the shr basin unlike in the nhr basin the silicate weathering rate swr was similar between the nhr and shr basins but the rate of co 2 consumption in the shr basin was lower than in the nhr basin due to an important role of sulfuric acid derived from pyrite oxidation

the late miocene mediterranean atlantic connections through the north rifian corridor new insights from the boudinar and arbaa taourirt basins northeastern rif morocco new data from the neogene boudinar and arbaa taourirt basins northeastern morocco provide constraints on the late miocene evolution of the north rifian corridor the chronostratigraphy of these basins is clarified on the basis of biostratigraphic planktonic foraminifers calcareous nannoplankton and radio isotope ages marine sedimentation in the boudinar basin began during the early tortonian at 10 ma and persisted until the late early messinian at 6 1 ma in the arbaa taourirt basin it occurred between the late tortonian and the earliest messinian paleoenvironmental data benthic foraminifera and pollen grains record a major drowning in association with extensive tectonism in the boudinar basin during the early messinian 7 2 ma synchronously there was a major sedimentological change in the arbaa taourirt basin with progradation of conglomerates and sandstones over late tortonian marls large scale cross bedded sandstones indicate paleo currents flowing from the atlantic ocean toward the mediterranean sea during the late early messinian a shallowing trend occurred culminating with the progradation of reefal carbonates our findings indicate that the north rifian corridor opened at 7 2 ma ensuring atlantic mediterranean connections the corridor was progressively restricted during the late early messinian with complete closure by 6 1 ma the results of this study thus question existing hypotheses for the timing and nature of atlantic mediterranean connections during the late messinian

chemical weathering and associated co2 consumption in six major river basins south korea abstract we report the chemical strontium sr and sulfur s isotopic compositions of water samples collected from six major south korean rivers to investigate seasonal and spatial variations in water chemistry and to estimate the chemical weathering rates and associated co 2 consumption overall the chemical compositions of river water exhibited significant temporal and spatial variations the magnitude of which varied depending on river size and geology the 87 sr 86 sr ratios and 34 s values of the rivers varied only spatially in close relation to basin lithology a mass balance calculation indicated that the dissolved loads of the six rivers were controlled by atmospheric 4 3 18 4 anthropogenic 6 0 27 2 and chemical weathering inputs 66 1 83 3 the average rates of carbonate weathering by sulfuric scw and carbonic acids ccw and silicate weathering by sulfuric ssw and carbonic acids csw were 4 50 and 11 0 t km 2 yr and 5 77 and 10 8 t km 2 yr respectively the associated mean co 2 consumption rates by ccw and csw were 312 10 3 and 471 10 3 mol km 2 yr respectively the calculated chemical weathering rates were closely related to runoff and the associated co 2 consumption rates tended to be higher in summer than in winter this study highlights the role of sulfuric acid in chemical weathering suggesting that it should be carefully considered in studies of co 2 consumption rate

chemical weathering processes in the yalong river draining the eastern tibetan plateau china abstract to better understand chemical weathering and controlling processes in the yalong river of the eastern tibetan plateau this study presents major ion concentrations and stable isotopes of the dissolved loads the isotopic compositions 13c dic 34s and 18o so4 of the dissolved loads are very useful to quantify solute sources and define the carbon budget related with chemical weathering in riverine systems the isotopic composition of sulphate demonstrates that most of the sulphate is derived from sulphide oxidation particularly in the upper reach of the yalong river the correlations between 13c dic water chemistry and isotopes of sulphate suggest that the carbon dynamics are mainly affected by carbonate weathering by sulphuric acid and equilibration processes approximately 13 of the dissolved inorganic carbon in the yalong river originates from carbonate weathering by strong acid the co2 consumption rates are estimated to be 2 8 105 mol km2 yr and 0 9 105 mol km2 yr via carbonate and silicate weathering in the yalong river respectively in this study the influence of sulphide oxidation and metamorphic co2 on the carbon budget is estimated for the yalong river draining the eastern tibetan plateau

characteristics of carbonate evaporite and silicate weathering in huanghe river basin a comparison among the upstream midstream and downstream abstract to systematically study chemical weathering in the entire huanghe river basin we divided the basin into three parts with significant differences in geology and climate we collected 38 water samples from the main channel and its main tributaries spread between the upstream above lanzhou midstream from lanzhou to huayuankou and downstream from huayuankou up to river mouth segments of the river the concentrations of major elements and h o isotopic compositions were obtained from the samples and the total dissolved solids tds and co2 consumption budget were calculated from the aggregated data of each of the three segments the results demonstrate that the tds are mainly derived from carbonate weathering in upper huanghe river evaporite dissolution is predominately occurred in the midstream and there is almost no additional contribution from rock weathering in the downstream an increasing trend of co2 consumption rate by silicate weathering is observed from 0 14 105 mol km2 yr in the upstream to 5 62 105 mol km2 yr in the downstream and the budget of co2 consumption by silicate weathering is estimated to be 26 2 109 mol yr in contrast the co2 consumption rate by carbonate weathering decreases from 3 04 105 mol km2 yr in the upstream to near zero in the downstream and the budget of co2 consumption is estimated to be 100 5 109 mol yr as a whole in the entire huanghe river basin the co2 consumption budget and tds yield are estimated to be 126 7 109 mol yr and 27 5 106 t yr respectively these results indicate that evaporite dissolution in the midstream is responsible for the high tds in the huanghe river basin while carbonate weathering in the upstream plays the most significant role in co2 consumption

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

chemical weathering in the three rivers region of eastern tibet abstract three large rivers the chang jiang yangtze mekong lancang jiang and salween nu jiang originate in eastern tibet and run in close parallel over 300 km near the eastern himalayan syntaxis seventy four river water samples were collected mostly during the summer season from 1999 to 2004 their major element compositions vary widely with total dissolved solids tds ranging from 31 to 3037 mg l reflecting the complex geologic makeup of the vast drainage basins the major ion distribution of the main channel samples primarily reflects the weathering of carbonates evaporite dissolution prevails in the headwater samples of the chang jiang in the tibetan plateau interior as evidenced by the high tds 928 and 3037 mg l and the na cl dominant major element composition local tributary samples of the mekong and salween draining the lincang batholith and the tengchong volcano show distinctive silicate weathering signatures we used five reservoirs rain halite sulfate carbonate and silicate in a forward model to calculate the contribution from silicate weathering to the total dissolved load and to estimate the consumption rate of atmospheric co 2 by silicate weathering carbonate weathering accounts for about 50 of the total cationic charge tz in the samples of the mekong and the salween exiting the tibetan plateau in the exit sample of the chang jiang 45 of tz is from halite dissolution inherited from the extreme headwater tributaries in the interior of the plateau and carbonates contribute only 26 to the tz the net rate of co 2 consumption by silicate weathering is 103 121 10 3 mol km 2 year 1 lower than the rivers draining the himalayan front gis based analyses indicate that runoff and relief can explain 52 of the spread in the rate of atmospheric co 2 drawdown by silicate weathering but other climatic temperature precipitation potential evapotranspiration and geomorphic elevation slope factors also show collinearity only qualitative conclusions can be drawn for the significance of lithology due to lack of digitized lithologic information the effect of the peculiar drainage pattern due to tectonic forcing is not readily apparent in the major element composition or in increased chemical weathering rates the 87 sr 86 sr ratios and the silicate weathering rates are in general lower in the three rivers than in the rivers draining the himalayan front

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

water geochemistry of the qiantangjiang river east china chemical weathering and co2 consumption in a basin affected by severe acid deposition abstract the chemical composition of the qiantangjiang river the largest river in zhejiang province in eastern china was measured to understand the chemical weathering of rocks and the associated co2 consumption and anthropogenic influences within a silicate dominated river basin the average total dissolved solids tds 113 mg l 1 and total cation concentration tz 1357 eq l 1 of the river waters are comparable with those of global major rivers ca2 and hco3 followed by na2 and so42 dominate the ionic composition of the river water there are four major reservoirs carbonates silicates atmospheric and anthropogenic inputs contributing to the total dissolved load of the investigated rivers the dissolved loads of the rivers are dominated by both carbonate and silicate weathering which together account for about 76 3 of the total cationic load origin the cationic chemical weathering rates of silicate and carbonate for the qiantangjiang basin are estimated to be approximately 4 9 ton km 2 a 1 and 13 9 ton km 2 a 1 respectively the calculated co2 consumption rates with the assumption that all the protons involved in the weathering reaction are provided by carbonic acid are 369 103 mol km 2 a 1 and 273 103 mol km 2 a 1 by carbonate and silicate weathering respectively as one of the most severe impacted area by acid rain in china h2so4 from acid precipitation is also an important proton donor in weathering reactions when h2so4 is considered the co2 consumption rates for the river basin are estimated at 286 103 mol km 2 a 1 for carbonate weathering and 211 103 mol km 2 a 1 for silicate weathering respectively the results highlight that the drawdown effect of co2 consumption by carbonate and silicate weathering can be largely overestimated if the role of sulfuric acid is ignored especially in the area heavily impacted by acid deposition like qiantangjiang basin the actual co2 consumption rates after sulfuric acid weathering effect deduction is only about 77 of the value calculated with the assumption that carbonic acid donates all the protons involved in the weathering reaction

dissolved load of the loire river chemical and isotopic characterization the loire river with one of the largest watersheds in france has been monitored just outside the city of orleans since 1994 physico chemical parameters and major and trace elements were measured between 2 day and 1 week intervals according to the river flow the sampling site represents 34 of the total loire watershed with 76 silicate rocks and 24 carbonate rocks elements are transported mainly in the dissolved phase with the ratio of total dissolved salts tds to suspended matter sm ranging between 1 6 and 17 4 chemical weathering of rocks and soils are thus the dominant mechanisms in the loire waters composition the highest tds sm ratios are due to dissolved anthropogenic inputs the database shows no link between no3 content and river flow the na k mg2 so42 and cl concentrations are seen to decrease with increasing discharge in agreement with a mixing process involving at least two components the first component during low flow is concentrated and may be related with input from the groundwater and sewage station water the second component during high flow is more dilute and is in agreement with bedrock weathering and rainwater inputs a geochemical behaviour pattern is also observed for hco3 and ca2 species their concentrations increase with increasing discharge up to 300 m3 s after which they decrease with increasing discharge the sr isotopic composition of the dissolved load is controlled by at least five components a series of natural components represented by a waters draining the silicate and carbonate bedrock b groundwater and c rainwaters and two kinds of anthropogenic components the aim of this study is to describe the mixing model in order to estimate the contribution of each component finally specific export rates in the upper loire watershed were evaluated close to 12 t year 1 km 2 for the silicate rate and 47 t year 1 km 2 for the carbonate rate

impact of nitrogen fertilizers on the natural weathering erosion processes and fluvial transport in the garonne basin knowledge of the impact of n fertilizers on the weathering erosion processes of soils in intensively cultivated regions is of prime importance nitrification of nh4 fertilizers produces hno3 in the basin of the garonne river enhancing soil degradation their influence on the weathering rates was determined by calculating the consumption rate of atmospheric soil co2 by soil weathering and erosion and its contribution to the total dissolved riverine hco3 this contribution was found to be less than 50 which corresponds normally to a complete carbonate dissolution by carbonic acid suggesting that part of the alkalinity in the river waters is due to carbonate dissolution by an acid other than carbonic acid probably hno3

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

tectonic significance of synextensional ductile shear zones within the early miocene alacamdag granites northwestern turkey synextensional granitoids may have significant structural features leading to the understanding of the evolution of extended orogenic belts one of the highly extended regions the aegean region includes a number of metamorphic core complexes and synextensional granitoids that developed following the alpine collisional events the alacamdag area in northwestern turkey is one of the key areas where miocene granites crop out along the boundary of various tectonic units structural data from the early miocene alacamdag granites demonstrated two different deformation patterns that may provide insights into the development of granitic intrusions and metamorphic core complexes 1 steeply dipping ductile shear zones caused emplacement of syn tectonic granite stocks they include kinematic indicators of a sinistral top to the sw displacement this zone has also juxtaposed the izmir ankara zone and the menderes massif in the west and east respectively 2 gently dipping ductile shear zones have developed within the granitic stocks that intruded the schists of the menderes massif on the structurally lower parts kinematic data from the foliated granites indicate a top to the ne displacement which can be correlated with the direction of the hanging wall movement documented from the simav and kazdag metamorphic core complexes the gently dipping shear zones indicate the presence of a detachment fault between the menderes massif and the structurally overlying izmir ankara zone mesoscopic to map scale folds in the shallow dipping shear zones of the alacamdag area were interpreted to have been caused by coupling between ne sw stretching and the accompanying nw se shortening of ductilely deformed crust during early miocene times one of the ne trending shear zones fed by granitic magmas was interpreted to form the northeastern part of a sinistral wrench corridor which caused differential stretching between the cycladic and the menderes massifs this crustal scale wrench corridor the izmir balikesir transfer zone may have controlled the asymmetrical and symmetrical extensions in the orogenic domains the combination of the retreat of the aegean subduction zone and the lateral slab segmentation leading to the sinistral oblique slip tearing within the eurasian upper plate appears to be a plausible mechanism for the development of such extensive ne trending shear zones in the aegean region

emplacement and magnetic fabrics of rapakivi granite intrusions within wiborg and aland rapakivi granite batholiths in finland abstract anisotropy of magnetic susceptibility ams studies were carried out in two areas in finland the ruotsinpyhtaa intrusion within the wiborg rapakivi granite batholith and the saltvik intrusions within the aland rapakivi granite batholith the main aim of this study was to understand the emplacement history of these mid proterozoic rapakivi granites aeromagnetic images reveal structures of ca 5 10 km intrusions that build up the large rapakivi granite batholiths of aland and wiborg magnetic susceptibility data from the database of the geological survey of finland including more than 1700 samples from the wiborg rapakivi batholith and almost 900 samples from the aland rapakivi batholith were compared with measurements from the present study the mean susceptibility is ca 1500 si for the wiborg batholith and ca 10 000 si for the aland batholith samples taken for this study demonstrate that the mean value for the ruotsinpyhtaa intrusion is ca 1200 si and for the saltvik intrusions ca 24 000 si thermomagnetic measurements reveal that the magnetic susceptibility is mainly derived either from paramagnetic minerals or from magnetite the absence of solid state deformation features such as breccia or contact deformation indicates a cauldron type subsidence emplacement the ams measurements from ruotsinpyhtaa confirm these proposals with concentric gently dipping magnetic foliations that support a ring complex structure above a piston type subsidence system the saltvik area consists of a number of smaller elliptical intrusions of different rapakivi granites forming a multiple intrusive complex the magnetic fabric shows a general westward dipping of the pyterlite and eastward dipping of the contiguous even grained rapakivi granite which indicates a central inflow of magma batches towards the east and west resulting from a laccolitic emplacement of magma batches while the main mechanism for space creation was derived from subsidence

the relationship between forceful and passive emplacement the interplay between tectonic strain and magma supply in the rosses granitic complex nw ireland the rosses granitic complex nw ireland part of the late caledonian c 400 ma donegal batholith provides the opportunity to study the interplay between relative tectonic strain and magma supply rates in the wall of a major tectonic shear zone anisotropy of magnetic susceptibility ams measurements structural analysis and examination of key intrusive relationships were used to assess the accommodation of magma associated deformation and magma flow pathways in this complex in this case the varying emplacement styles switching from forceful to passive indicate that relative tectonic strain and magma supply rates were not constant in the earliest component a suite of microgranite sheets ams reveals subtle fabrics discordant to the sheet margins and is interpreted as post emplacement deformation fabrics the concordance of these fabrics to the next component of the complex the main pluton g1 and g2 monzogranite indicates that this deformation was caused by the forceful emplacement of the pluton ams fabrics in g1 and g2 reveal a dome shaped foliation with an east west lineation indicating an east west oriented magma transport direction outcrops of small stocks or cupolas similar to g2 east of the main pluton link it to similar lithologies in the main donegal granite further to the east via a partially exposed lateral feeder this suggests east to west emplacement the next component a suite of subvertical porphyritic felsite dykes is shown from ams and visible shearing fabrics to have been emplaced passively under east west tension the final component comprises g3 and g4 of the main pluton which passively cut all earlier components and contains significant amounts of aplite pegmatite and greisen these are interpreted to be cupolas or stocks emanating from an unexposed sheet probably similar in composition and mode of emplacement to g1 and g2 thus a general model is put forward where initially forceful subhorizontal sheets extending laterally from the nearby main donegal granite shear zone gave way to passive emplacement where the roofs of these and subjacent sheets failed the control on siting of the complex can be related to lower crustal structures which control upper crustal shear zones the reason for the switch in emplacement style is suggested to be due to a waning magma supply in a tectonic strain field where the extensional component was oriented east west the waning magma supply then possibly due to switching of the site of emplacement of magma supplied by the main donegal granite shear zone to another member of the donegal batholith the trawenagh bay granite

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering