chemical weathering rates and atmospheric soil co2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil abstract chemical weathering rates and atmosphere soil co 2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil were evaluated using the chemical composition of surface waters and fresh rocks and soil horizon c in the upper sorocaba river basin surface water samples were collected between june 2009 and june 2010 and analyses were performed to assess ph electrical conductivity ec temperature and total dissolved solids tds including na k ca 2 mg 2 cl so 4 2 po 4 3 no 3 and sio 2 fresh rocks and c horizon samples were also collected taking into account their geological context abundance and spatial density to analyze major elements and mineralogy the concentration of tds and dissolved cations anions and silica increased during the dry period in relation to the wet period and the same behavior was observed for ph ec and temperature after corrections of anthropogenic contributions ca 21 t km 2 yr and atmospheric inputs ca 19 t km 2 yr the annual flux due to chemical weathering involving the igneous and metamorphic rocks was ca 29 t km 2 yr the co 2 atmospheric soil consumption in the upper sorocaba river basin was ca 0 2 10 6 mol km 2 yr and when extrapolated to the entire mantiqueira orogenic belt accounted an estimated consumption of 0 07 10 12 mol yr representing 0 6 of the total co 2 consumption flux derived from global average silicate weathering the chemical weathering rates of igneous and metamorphic rocks in the upper sorocaba river basin were estimated at 15 m my respectively the main weathering process in this watershed was the monossialitization with partial hydrolyses of bedrock minerals except quartz which was not weathered and remained in the soil profile the annual specific flux derived from igneous and metamorphic rocks at upper sorocaba river basin could be compared with watersheds in tropical climates however this value is higher than in other north american european asian and african granitoid watersheds and lower than in montane watersheds

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

chemical weathering of a marine terrace chronosequence santa cruz california i interpreting rates and controls based on soil concentration depth profiles abstract the spatial and temporal changes in element and mineral concentrations in regolith profiles in a chronosequence developed on marine terraces along coastal california are interpreted in terms of chemical weathering rates and processes in regoliths up to 15 m deep and 226 kyrs old quartz normalized mass transfer coefficients indicate non stoichiometric preferential release of sr ca na from plagioclase along with lesser amounts of k rb and ba derived from k feldspar smectite weathering results in the loss of mg and concurrent incorporation of al and fe into secondary kaolinite and fe oxides in shallow argillic horizons elemental losses from weathering of the santa cruz terraces fall within the range of those for other marine terraces along the pacific coast of north america residual amounts of plagioclase and k feldspar decrease with terrace depth and increasing age the gradient of the weathering profile bs is defined by the ratio of the weathering rate r to the velocity at which the profile penetrates into the protolith a spreadsheet calculator further refines profile geometries demonstrating that the non linear regions at low residual feldspar concentrations at shallow depth are dominated by exponential changes in mineral surface to volume ratios and at high residual feldspar concentrations at greater depth by the approach to thermodynamic saturation these parameters are of secondary importance to the fluid flux qh which in thermodynamically saturated pore water controls the weathering velocity and mineral losses from the profiles long term fluid fluxes required to reproduce the feldspar weathering profiles are in agreement with contemporary values based on solute cl balances qh 0 025 0 17 m yr 1 during saturation controlled and solute limited weathering the greater loss of plagioclase relative to k feldspar is dependent on the large difference in their respective solubilities instead of the small difference between their respective reaction kinetics the steady state weathering rate under such conditions is defined as r q h m sol m total 1 s v b s the product of qh and the ratio of solubilized to solid state feldspar msat mtotal define the weathering velocity the weathering gradient bs reflects the kinetic rate of reaction where sv is the volumetric surface area of the residual feldspar both this rate expression and the spreadsheet calculations produce similar plagioclase weathering rates r 5 14 10 16 mol m 2 s 1 which agree with those reported for other environments of comparable climate and age weathering dependent concentration profiles are commonly described in literature the present paper provides methods by which these data can yield a more fundamental understanding of the weathering processes involved

chemical overprinting of magmatism by weathering a practical method for evaluating the degree of chemical weathering of granitoids abstract quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology and many weathering indices based on whole rock chemistry have been proposed however most classical indices are of limited application to granitoids in a wide area because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis the chemical evolution produced during rock weathering therefore overprints pre existing magmatic chemical variation this problem can cause many classical weathering indices to yield misleading results this study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index the method is based on a bivariate plot of the magmatic chemical variation mcv in granitoids and the degree of chemical weathering dcw the mcv axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering in this study tio 2 contents are utilized for the mcv the dcw axis is fundamentally defined by the ratios of more mobile to less mobile elements during weathering and hence many classical indices can be applied the improved value of the degree of chemical weathering dcw i for a weathered rock is derived by dcw i s mcv cv mcv 1 dcw 1 where mcv 1 is the measured composition e g tio 2 content of the weathered rock dcw 1 denotes the ratios of more mobile to less mobile elements of the weathered rock the s parameter is the slope of the least square linear regression for fresh granitoids in the mcv dcw relationship mcv cv is a correction factor which is given by the average point on the mcv axis e g average tio 2 of the fresh rocks this method is useful for evaluating the degree of weathering of various granitoids and enhances the practical application of many weathering indices

chemical weathering of crystalline rocks in contrasting climatic conditions using geochemical proxies an overview abstract weathering profiles of granitoid rocks from the sila massif southern italy have been studied to characterize weathering processes that affect this area chemical weathering indices of the sila massif weathered granitoids were compared to those of different areas of the world characterized by different climates malaysia puerto rico georgia china nigeria colorado switzerland and sweden to decipher their weathering characteristics the geochemical indices show values of cia chemical index of alteration ranging from 55 to 97 ciw chemical index of weathering ranging from 60 to 100 pia plagioclase index of alteration ranging from 55 to 100 wip weathering index of parker ranging from 7 to 64 and rr ruxton ratio ranging from 2 14 to 3 96 all these geochemical proxies closely resemble each other and show variations mainly related to the different climatic and tectonic settings malaysia and puerto rico granitoids showing high cia values respectively 97 and 95 on average underwent very intensive chemical weathering alteration georgia china and nigeria showing medium high cia values respectively 86 90 and 92 on average underwent moderate intensive chemical weathering alteration southern italy and colorado granitoids showing medium low cia values 68 on average underwent moderate weak chemical weathering alteration whereas switzerland and sweden granitoids showing low cia values respectively 58 and 55 on average underwent weak chemical weathering alteration those values are mainly related to the climatic conditions in term of temperature and precipitation of each area cia vs climate histograms display a shift towards higher cia values with increasing of warm humidity tropical conditions whereas granitoids weathered under conditions inferred to be cold arid polar climate show lower cia values

element mobilization and redistribution under extreme tropical weathering of basalts from the hainan island south china abstract chemical weathering of rocks has substantial influence on the global geochemical cycle in this paper the geochemical profile of a well developed basalt weathering profile 15 m thick including soil saprolite semi weathered rock and fresh basalt on the island of hainan south china was presented the soil and saprolite samples from this profile are characterized by high al2o3 and fe2o3 concentrations up to 32 3 and 28 5 respectively the mineral assemblage is dominated by kaolinite fe oxides hydroxides and gibbsite or boehmite indicating extensive desilicate and ferrallitic weathering the acidic and organic rich environment in the soil horizon may have promoted elemental remobilization and leaching the strongest sio2 depletion and al2o3 enrichment at about 2 4 m deep indicate that the main kaolinite hydrolysis and gibbsite formation occurred near the soil saprolite interface the mild sr reconcentration at about 3 9 m and 7 1 m deep may be attributed to secondary carbonate precipitation mn oxides hydroxides precipitated at 6 1 m deep accompanied by the strongest enrichment of ba and co uranium is mildly enriched in the middle part about 7 1 m and 9 1 m deep of the weathering profile and the enrichment may have been caused by the decomposition of uranyl carbonates or the accumulation of zircon immobile element i e zr hf nb ta th and ti distributions at different depths are mainly controlled by secondary fe oxides hydroxides and follow the stability sequence of nb ta th zr hf ti the limited thickness 15 cm of the semi weathered basalt horizon at the rock regolith interface 15 28 m deep suggests that plagioclase and pyroxene are readily altered to kaolinite smectite and fe oxides under tropical climate the marked enrichment of transitional metals such as cu zn ni and sc along the rock regolith interface may have associated mainly with increasing ph values as well as the dissolution of primary apatite and formation of secondary phosphates our findings highlight the importance of secondary phosphates in the redistribution of transition metals and in the possible mg cu and ni isotopic fractionation under extreme weathering of basalt in tropic climate

geochemistry of paleoproterozoic black shales from the intracontinental cuddapah basin india implications for provenance tectonic setting and weathering intensity abstract the cuddapah supergroup is one of the series of thick proterozoic sedimentary sequences developed on archean cratonic peninsular india the stratigraphically higher cumbum formation includes well preserved and unweathered black shales that include marine facies recording lower greenschist facies metamorphism in multielement normalized diagrams conservative elements ti al ree sc co plot parallel and close to post archean upper continental crust pa ucc small variations in absolute concentrations of conservative elements covary with fe2o3 content which ranges from 1 6 11 wt accordingly those concentrations are controlled by hydrothermal leaching or additions of fe consistent with reduced fluids reflected in variable eu anomalies in th sc vs sc co ordinates these shales trend to slightly lower sc but greater th sc than either pa ucc or average proterozoic shale cratonic lithologies such as tonalite clasts or detrital gold are not represented in basal conglomerates and ree systematics and low al2o3 yb th yb and zr sm ratios rule out a significant tonalite component in the source consequently both sedimentary and geochemical evidences endorse an extra cratonic provenance the best compositional fit is to average paleoproterozoic andean type continental margin granite with 10 of closepet type granite contributing to the excess zr and ree an active continental margin provenance is also consistent with the th sc zr discriminant diagram of siliciclastic sedimentary rocks the chemical index of alteration cia corrected for diagenetic addition of k is 85 100 indicative of intense weathering of the catchment compared to a range of mean values of 70 88 at 1 8 ga shales are variably enriched in v cr ni relative to pa ucc consistent with the established kerogen transition metal association the cuddapah supergroup may have evolved as a foreland basin to the 2 1 1 8 ga central indian tectonic zone with its associated granites evolving into an intracontinental basin connected to the ocean given the marine kerogen v ni association this scenario is similar to the paleoproterozoic mcarther river australia and athabasca canada basins which evolved from foreland basins respectively to the barrumundi and trans hudson orogens collectively as part of assembly of the proposed paleoproterozoic supercontinent columbia

ree and other trace elements in a granitic weathering profile from serre southern italy abstract ree v cr ni rb sr y zr and nb behaviour in a granitic weathering profile in southern italy is studied in the saprolites of the considered profile depletion of v cr ni rb sr zr and nb is observed this is quite remarkable for sr and cr whereas ree and y are enriched in the more altered portion of the profile and especially in its m fraction such enrichment is associated with the lree hree fractionation and the positive ce anomaly the former results from an increased solubility of hree in a non acid environment as well as from the removal of the hree rich phases from the residual component the latter is related to the redox chemistry of ce which as ceo 2 is less soluble than the other ree no analogy is observed between the behaviour of ce and fe mn and cr saprolites also exhibit a negative eu anomaly which is mostly inherited from the parental material finally the influence of accessory minerals in the ree distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes this is especially true in the parent material sediment relationships

shield effect on continental weathering implication for climatic evolution of the earth at the geological timescale abstract a model sensitivity study is performed in order to explore the impact of the development of thick weathering profiles in the equatorial area on the geological evolution of climate long term climatic evolution is driven by the balance existing between solid earth degassing and continental silicate weathering the co 2 consumption through continental silicate weathering is here calculated as a function of climate based on the correlation existing with mean annual continental runoff for large drainage basins these correlations appear to be dependent on the climatic regime under mid latitude temperate climate the silicate weathering is 5 times more sensitive to continental runoff than in the warm humid equatorial belt these correlations emphasize the role of the thick weathering profiles existing in equatorial area shielding the bedrock from further weathering we use this set of relationships between runoff and silicate weathering as a function of the geoclimatic zone to explore the impact of this shield effect on the mesozoic evolution of climate using the geoclim model compared to previous work we suggest that atmospheric co 2 was generally underestimated in the past evidencing a complex interplay between the paleogeographic setting and the shield effect particularly calculated atmospheric co 2 during the early middle jurassic rises up to 1600 ppmv while it was limited to 700 ppmv when shield effect was neglected corresponding to a global warming of more than 4 c this study emphasizes the need for the building up of numerical models describing the growth of the weathering profiles that can be coupled to vegetation and climate models to investigate biogeochemical cycle and climate evolution even at the geological timescale

deformation of chromite s e m investigations abstract the scannning electron microscope operated in the back scattered electron mode has been applied in a microstructural analysis of chromites samples from the oman vourinos greece and tiebaghi new caledonia ophiolites displaying a variety of mantle flow and emplacement structures have been examined and compared with undeformed chromite from the bushveld intrusion and deformed chromite from the high grade metamorphic fiskenaesset complex channelling contrast and electron channelling patterns provide information on grain boundaries subgrains inclusions and cracks as well as defects in the chromite lattice these microstructures suggest that dislocation mechanisms are active in chromite deforming under mantle conditions recovery is quick whereas nucleation is slow and accordingly recrystallization of chromite occurs by migration of grain boundaries driven either by strain energy or by interfacial energy increasing the grain size during deformation dislocation mechanisms however only provide a secondary mode of deformation compared to brittle fracturing and passive rotation of chromite grains and fragments in the weaker silicate matrix diffusion accommodated flow may also be significant

sr isotopes as a tracer of weathering processes and dust inputs in a tropical granitoid watershed luquillo mountains puerto rico abstract sr isotope data from soils water and atmospheric inputs in a small tropical granitoid watershed in the luquillo mountains of puerto rico constrain soil mineral development weathering fluxes and atmospheric deposition this study provides new information on pedogenic processes and geochemical fluxes that is not apparent in watershed mass balances based on major elements alone 87sr 86sr data reveal that saharan mineral aerosol dust contributes significantly to atmospheric inputs watershed scale sr isotope mass balance calculations indicate that the dust deposition flux for the watershed is 2100 700 mg cm 2 ka 1 nd isotope analyses of soil and saprolite samples provide independent evidence for the presence of saharan dust in the regolith watershed scale sr isotope mass balance calculations are used to calculate the overall short term chemical denudation velocity for the watershed which agrees well with previous denudation rate estimates based on major element chemistry and cosmogenic nuclides the dissolved streamwater sr flux is dominated by weathering of plagioclase and hornblende and partial weathering of biotite in the saprock zone a steep gradient in regolith porewater 87sr 86sr ratio with depth from 0 70635 to as high as 0 71395 reflects the transition from primary mineral derived sr to a combination of residual biotite derived sr and atmospherically derived sr near the surface and allows multiple origins of kaolinite to be identified

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

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

variations of sr nd hf isotopic systematics in basalt during intensive weathering abstract the sr nd hf isotopic compositions of both saprolites and parent rocks of a profile of intensively weathered neogene basalt in hainan south china are reported in this paper to investigate changes of isotopic systematics with high masses the results indicate that all these isotopic systematics show significant changes in saprolites compared to those in corresponding parent rocks the 87 sr 86 sr system was more seriously affected by weathering processes than other isotope systems with e sr drifts 30 to 70 away from those of the parent rocks in the upper profile 2 2 m the sr isotopes of the saprolites show an upward increasing trend with e sr changing from 50 at 2 2 m to 70 at 0 5 m accompanying a upward increasing of sr concentrations from 10 g g to 25 g g as nearly all the sr of the parent rock has been removed during intensive weathering in this profile the upward increasing of sr concentrations in the upper profile suggests import of extraneous sr rainwater in this region which enriches in sr up to 139 g l from seawater may be the important extraneous source thus the sr isotopes of the saprolites in the upper profile may be mainly influenced by import of extraneous materials and the sr isotopic characteristics may not be retained in contrast the e nd and e hf of the saprolites drift only 0 2 6 and 0 3 7 away from the parent rocks respectively the negative drifts of the e nd and e hf are coupled with nd and hf losses in the saprolites i e larger proportions of nd and hf loss correspond to lower e nd and e hf compared with the relative high nd and hf concentrations of the saprolites the contributions of extraneous nd and hf both from wet and dry deposits of aeolian input are negligible thus the e nd and e hf changes in the profile are mainly resulted from consecutive removal of the nd and hf calculation indicates that the 143 nd 144 nd and 176 hf 177 hf ratios in saprolites are all significantly lower than their initial values in the parent rock simply removing part of the nd and hf by incongruent decomposing some of the minerals may not account for this fractionation should be happen which 143 nd and 176 hf may be preferentially removed from the profile relative to 144 nd and 177 hf during intensive chemical weathering resulting in lower 143 nd 144 nd and 176 hf 177 hf ratios in saprolites relative to the parent rock even though details for this process is not known a positive correlation is observed between the e nd and e hf of the saprolites interestingly the saprolites with a net loss of nd and hf in the upper profile show good positive correlation and the regression line parallels the terrestrial array by contrast saprolites with a net gain of nd and hf in the lower profile generally show higher e hf values at a given e nd value and the regression line between these e nd and e hf appears to parallel the seawater array this supports the hypothesis that the contribution of continental hf from chemical weathering release is the key to the obliquity of the seawater array away from the terrestrial array of the global e nd and e hf correlation our results also indicate that caution is needed when using e sr e nd and e hf to trace provenances for sediments and soils

mineral weathering and elemental transport during hillslope evolution at the susquehanna shale hills critical zone observatory located in the uplands of the valley and ridge physiographic province of pennsylvania the susquehanna shale hills critical zone observatory ssho is a tectonically quiescent first order catchment developed on shales of the silurian rose hill formation we used soil cores augered at the highest point of the watershed and along a subsurface water flowline on a planar hillslope to investigate mineral transformations and physical chemical weathering fluxes about 25 m of bedrock was also drilled to estimate parent composition depletion of carbonate at tens of meters of depth in bedrock may delineate a deep carbonate weathering front overlying this extending from 6 m below the bedrock soil interface up into the soil is the feldspar dissolution front in the soils depletion profiles for k mg si fe and al relative to the bedrock define the illite and chlorite reaction fronts when combined with a cosmogenic nuclide derived erosion rate on watershed sediments these depletion profiles are consistent with dissolution rates that are several orders of magnitudes slower for chlorite 1 5 10 17 mol m 2 s 1 and illite 2 9 10 17 mol m 2 s 1 than observed in the laboratory mineral reactions result in formation of vermiculite hydroxy interlayered vermiculite and minor kaolinite during weathering exchangeable divalent cations are replaced by al as soil ph decreases the losses of mg and k in the soils occur largely as solute fluxes in contrast losses of al and fe are mostly as downslope transport of fine particles physical erosion of bulk soils also occurs results from a steady state model demonstrate that physical erosion accounts for about half of the total denudation at the ridgetop and midslope positions chemical weathering losses of mg na and k are higher in the upslope positions likely because of the higher degree of chemical undersaturation in porewaters chemical weathering slows down in the valley floor and al and si even show net accumulation the simplest model for the hillslope that is consistent with all observations is a steady state clay weathering limited system where soil production rates decrease with increasing soil thickness

regolith mass balance inferred from combined mineralogical geochemical and geophysical studies mule hole gneissic watershed south india the aim of this study is to propose a method to assess the long term chemical weathering mass balance for a regolith developed on a heterogeneous silicate substratum at the small experimental watershed scale by adopting a combined approach of geophysics geochemistry and mineralogy we initiated in 2003 a study of the steep climatic gradient and associated geomorphologic features of the edge of the rifted continental passive margin of the karnataka plateau peninsular india in the transition sub humid zone of this climatic gradient we have studied the pristine forested small watershed of mule hole 4 3 km2 mainly developed on gneissic substratum mineralogical geochemical and geophysical investigations were carried out i in characteristic red soil profiles and ii in boreholes up to 60 m deep in order to take into account the effect of the weathering mantle roots in addition 12 electrical resistivity tomography profiles ert with an investigation depth of 30 m were generated at the watershed scale to spatially characterize the information gathered in boreholes and soil profiles the location of the ert profiles is based on a previous electromagnetic survey with an investigation depth of about 6 m the soil cover thickness was inferred from the electromagnetic survey combined with a geological pedological survey taking into account the parent rock heterogeneity the degree of weathering of each of the regolith samples has been defined using both the mineralogical composition and the geochemical indices loss on ignition weathering index of parker chemical index of alteration comparing these indices with electrical resistivity logs it has been found that a value of 400 ohm m delineates clearly the parent rocks and the weathered materials then the 12 inverted ert profiles were constrained with this value after verifying the uncertainty due to the inversion procedure synthetic models based on the field data were used for this purpose the estimated average regolith thickness at the watershed scale is 17 2 m including 15 2 m of saprolite and 2 m of soil cover finally using these estimations of the thicknesses the long term mass balance is calculated for the average gneiss derived saprolite and red soil in the saprolite the open system mass transport function indicates that all the major elements except ca are depleted the chlorite and biotite crystals the chief sources for mg 95 fe 84 mn 86 and k 57 biotite only are the first to undergo weathering and the oligoclase crystals are relatively intact within the saprolite with a loss of only 18 the ca accumulation can be attributed to the precipitation of caco3 from the percolating solution due to the current and or the paleoclimatic conditions overall the most important losses occur for si mg and na with 286 106 mol ha 62 of the total mass loss 67 106 mol ha 15 of the total mass loss and 39 106 mol ha 9 of the total mass loss respectively al fe and k account for 7 4 and 3 of the total mass loss respectively in the red soil profiles the open system mass transport functions point out that all major elements except mn are depleted most of the oligoclase crystals have broken down with a loss of 90 the most important losses occur for si na and mg with 55 106 mol ha 47 of the total mass loss 22 106 mol ha 19 of the total mass loss and 16 106 mol ha 14 of the total mass loss respectively ca al k and fe account for 8 6 4 and 2 of the total mass loss respectively overall these findings confirm the immaturity of the saprolite at the watershed scale the soil profiles are more evolved than saprolite but still contain primary minerals that can further undergo weathering and hence consume atmospheric co2

pedogenic translocation of fe in modern and ancient vertisols and implications for interpretations of the hekpoort paleosol 2 25 ga abstract many interpretations of oxygen levels in the precambrian atmosphere use interpretations of fe distributions measured in paleosols this article addresses the current lack of knowledge concerning baseline fe translocations in modern soil analogs for the 2 25 ga hekpoort paleosol at waterval onder south africa as well as the lack of understanding of diagnostic petrographic features related to fe translocation preserved in the precambrian paleosols petrographic features related to fe translocations include redox related fe depletions and enrichments and possibly fe mn nodules which compare favorably with similar pedogenic features in paleozoic paleo vertisols and modern analog vertisols additionally preservation of sepic plasmic microfabrics in the hekpoort paleosol which are characteristic of clay soils experiencing shrink swell supports previous paleo vertisol interpretations total fe losses in vertisols are 10 50 losses increase with increasing soil age and with increasing mean ann

behavior of redox sensitive elements during weathering of granite in subtropical area using x ray absorption fine structure spectroscopy abstract the variation in chemical compositions of regolith along a weathering profile developed on a granite substrate in jiangxi province in southern china was investigated in this paper with the aim to characterize the speciation of redox sensitive elements and to evaluate their mobility and redistribution during chemical weathering mass balance calculations indicate titanium ti is the most immobile element in this weathering profile a new method x ray absorption fine structure xafs spectroscopy was used to determine the speciation of fe and mn along the profile fe k edge x ray absorption near edge structure xanes spectra show fe in saprolith is stabilized mainly in the state of fe iii suggesting fe is as immobile as conservative elements during granite weathering mn k edge xanes spectra show mn iii iv oxides are reduced to mn ii in surface soil where soil organic matter som acts as an important reductant although ce co and v were unable to be analysed by xafs their concentrations have significant correlations with that of mn indicating that the mobilization and redistribution of ce co and v may also be governed by redox condition all in all the results suggest that redox process impacts significantly on the redistribution of mn ce co and v along the profile the successful application of xafs in the study on migration of redox sensitive elements during granite chemical weathering has provided valuable information for the understanding and evaluating the geochemical behavior of elements in the environment

the assessment of weathering stages in granites using an ec ph meter the weathering of granite encompasses a wide range extending from slightly weathered rock to saprolite to soil although many different methods are available for quantifying the amount of chemical or physical weathering in granites dissolution rate as a method for estimating the degree of chemical weathering in these rocks was not thoroughly investigated this study sought to identify a method for quantifying weathering stages in granite based on both the chemical and physical properties of the rock using the weathering profile of granites from two quarries in the chugoku region of western japan a simple dissolution experiment measured with an electrical conductivity meter for 10 min recorded the differences in dissolution rates which reflects the chemical weathering stages in granites the combination of the dissolution rate and the p wave velocity produces a diagram that gives the chemical and physical properties of the weathered rock body in a single chart

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

chemical transfers along slowly eroding catenas developed on granitic cratons in southern africa abstract a catena is a series of distinct but co evolving soils arrayed along a slope on low slope slowly eroding catenas the redistribution of mass occurs predominantly as plasma the dissolved and suspended constituents in soil water we applied mass balance methods to track how redistribution via plasma contributed to physical and geochemical differentiation of nine slowly eroding 5 mm ky 1 granitic catenas the catenas were arrayed in a 3 3 climate by relief matrix and located in kruger national park south africa most of the catenas contained at least one illuviated soil profile that had undergone more volumetric expansion and less mass loss and these soils were located in the lower halves of the slopes by comparison the majority of slope positions were eluviated soils from the wetter climates 550 and 730 mm precipitation yr 1 generally had undergone greater collapse and lost more mass while soils in the drier climate 470 mm yr 1 had undergone expansion and lost less mass effects of differences in catena relief were less clear within each climate zone soil horizon mass loss and strain were correlated as were losses of most major elements illustrating the predominant influence of primary mineral weathering nevertheless mass loss and volumetric collapse did not become extreme because of the skeleton of resistant primary mineral grains inherited from the granite colloidal clay redistribution as traced by the ratio of ti to zr in soil suggested clay losses via suspension from catena eluvial zones thus illuviation of colloidal clays into downslope soils may be crucial to catena development by restricting subsurface flow there our analysis provides quantitative support for the conceptual understanding of catenas in cratonic landscapes and provides an endmember reference point in understanding the development of slowly eroding soil landscapes

soil chemistry and shale weathering on a hillslope influenced by convergent hydrologic flow regime at the susquehanna shale hills critical zone observatory soil chemistry data major and rees are presented from a swale transect for comparison to similar measurements on a planar transect published previously for the susquehanna shale hills critical zone observatory similar reaction fronts are observed plagioclase dissolution is indicated by na and ca depletion and a negative eu anomaly clay dissolution followed by particle loss is accompanied by depletion of mg k fe al and si however in contrast to the planar transect soils along the swale transect especially in the topographically depressed site do not show smooth elemental profiles this documents both residuum soils and accumulation of colluvium sediments the soils in the swale transect are thicker and on average wetter than those along the planar transect however the ce anomaly observed in the swale soils is consistent with a generally oxic environment thus preferential flowpaths are an important mechanism for water transport preventing swale soils from water saturation

adsorption of rees on kaolinite and halloysite a link to the ree distribution on clays in the weathering crust of granite abstract the clay minerals kaolinite and halloysite are dominant hosts for rare earth elements rees in the weathered crust elution deposited ree deposits however the accumulation of rees on kaolinite and halloysite has not been systematically compared in this study the adsorption of complete ree series on kaolinite and halloysite was investigated under different ph levels and ionic strengths which was linked to the enrichment and fractionation of rees within the clay fraction of a typical weathered crust elution deposited ree deposit at low ionic strength the adsorption of rees on kaolinite and halloysite increased with increase in ph with some noticeable fluctuation observed on halloysite at high ph all the rees were adsorbed to a similar extent without apparent fractionation except for the slight enrichment of heavy rees hrees at high ph at high ionic strength ree adsorption exhibited a linear increase with the increase in ph particularly at high ph with hrees being preferentially adsorbed compared to halloysite kaolinite possessed a higher specific surface area ssa normalized adsorption capacity towards rees these observed adsorption characteristics could possibly explain the distribution of rees in the clay fraction along the ree deposit the decrease of ion exchangeable ree content with depth was significant for kaolinite while the ree fractionation was ascribed to the selective adsorption of hrees on both kaolinite and halloysite the enrichment and fractionation mechanism of rees on kaolinite and halloysite were also discussed in terms of the surface chemistry and morphology of the clay minerals and the variations of chemical properties across the ree group

regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory abstract in the critical zone where rocks and life interact bedrock equilibrates to earth surface conditions transforming to regolith the factors that control the rates and mechanisms of formation of regolith defined here as material that can be augered are still not fully understood to quantify regolith formation rates on shale lithology we measured uranium series u series isotopes 238 u 234 u and 230 th in three weathering profiles along a planar hillslope at the susquehanna shale hills observatory ssho in central pennsylvania all regolith samples show significant u series disequilibrium 234 u 238 u and 230 th 238 u activity ratios range from 0 934 to 1 072 and from 0 903 to 1 096 respectively these values display depth trends that are consistent with fractionation of u series isotopes during chemical weathering and element transport i e the relative mobility decreases in the order 234 u 238 u 230 th the activity ratios observed in the regolith samples are explained by i loss of u series isotopes during water rock interactions and ii re deposition of u series isotopes downslope loss of u and th initiates in the meter thick zone of bedrock that cannot be augered but that nonetheless consists of up to 40 clay silt sand inferred to have lost k mg al and fe apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m myr to 17 m myr with increasing regolith thickness from the ridge top to the valley floor with increasing distance from the ridge top toward the valley apparent equivalent regolith residence times increase from 7 kyr to 40 kyr given that the ssho experienced peri glacial climate 15 kyr ago and has a catchment wide averaged erosion rate of 15 m myr as inferred from cosmogenic 10 be we conclude that the hillslope retains regolith formed before the peri glacial period and is not at geomorphologic steady state both chemical weathering reactions of clay minerals and translocation of fine particles colloids are shown to contribute to mass loss of u and th from the regolith consistent with major element data at ssho this research documents a case study where u series isotopes are used to constrain the time scales of chemical weathering and regolith production rates regolith production rates at the ssho should be useful as a reference value for future work at other weathering localities

chemical characters of volcanic rocks from andaman ophiolite india two parallel belts of late mesozoic ophiolitic rocks occur along the outer arc ridge and inner volcanic line of the indonesian arc system the northernmost occurrence along the outer arc ridge is in the andaman group of islands where ophiolitic rocks occur as dismembered slices emplaced over eocene to oligocene turbidites volcanic members of the ophiolitic suite occur in two thrust slices one consisting only of pillow basalts while the other is made up of basalts basaltic andesites and acid differentiates certain chemical characters of the basaltic components are comparable to mar basalts at 45 n on the basis of comparable ree patterns and the presence of appreciable volumes of acid differentiates they are further suggested to represent marginal basin crust variable la ce n and la sm n ratios in these basalts are interpreted in terms of a heterogeneous source the basaltic melts have undergone extensive fractional crystallization of clinopyroxene olivine and plagioclase to produce basaltic andesite and acid volcanic rocks between the parent and the differentiates there is no appreciable change in ce yb n ratio or hree abundance level suggesting low pressure fractionation in a shallow magma chamber possibly beneath a slow spreading centre

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

joint imaging by teleseismic converted and multiple waves and its application in the indepth iii passive seismic array 1 a joint imaging by teleseismic converted and multiple phases is put forward to image the crustal structure beneath the indepth iii passive seismic profile in the central tibet a depth dependent vp vs ratio is adopted to map common conversion point ccp via a vp vs scanning and stacking approach our new crustal image shows that the crust is divided into two sections with different moho depth distributions and amplitudes with the boundary nearby the bangong nujiang suture bns a negative p to s amplitude band is located in the upper to middle crust indicating a low velocity zone possibly caused by partial melting beneath the negative amplitude band the average crustal vp vs ratio estimated by our joint imaging method is higher than previous study but is consistent with a partial melting middle to lower crust implied by many other results

distribution of rare earth elements and oxyhydroxide phases within a weathered felsic igneous profile in hong kong abstract variation in type and abundance of oxyhydroxide phases and the fractionation of rare earth elements ree within a weathered felsic pyroclastic profile in hong kong were investigated in order to assess the key factors and micro environmental conditions controlling their distribution during weathering at rock and mineral scales three types of oxyhydroxide phases fe mn and ce rich were recognized based on their most abundant elements the fe rich types appeared in all samples at different stages of weathering the mn rich types however were limited to samples at advanced stages of weathering while the ce rich types were found solely in samples from oxyhydroxide rich zones fractionation of ree likely started at the early stages of weathering but became evident only at the advanced stages characteristics of ree patterns especially the direction negative or positive and extent of ce anomalies correlated very well with the appearance and abundance of mn oxyhydroxides and were attributed to the co existence of distinct micro environmental conditions within the profile these conditions resulted from two major competing processes leaching and fixation and oxidation precipitation and reduction dissolution which operated simultaneously within the profile at any given stage of weathering

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

the use of cation packing index for characterizing the weathering degree of granitic rocks the weathering state and weatherability of rocks are highly important for engineering geology projects and the use of rocks as building stones the weathering state of rocks can be described by various chemical and petrographical weathering indices to determine weathering state of a rock considerable amount of chemical analyses is required weatherability of rocks depends on not only their mineral composition but also the number of cation replaceable with hydrogen in a mineral in this study the use of the k value cation packing index is defined as the number of cation in a mole for characterizing the degree of weathering of granitic rocks is investigated for the purpose of the study the kurtun granitic rocks are selected as the material of the study the study contains three main stages and these are field investigations laboratory studies and regression analyses during the field studies in situ weathering descriptions and sampling are carried out the samples are subjected to chemical and petrographic analyses and physical and mechanical tests at the final stage of the study a series of regression analyses between the cation packing index and other properties of the samples are performed the results show that the k value can be used as a weathering indicator when compared with the other chemical weathering indices the k value can be used as a weathering index without chemical analyses because it can be determined by mineralogical analyses

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

mobilization and re distribution of major and trace elements during extreme weathering of basalt in hainan island south china major trace and organic elements of a laterite profile developed on neogene basalts in northern hainan island south china were reported in this paper the aim of which was to investigate element mobilization and re distribution during extreme weathering the results indicate that most of the elements have been mobilized and transferred downwards along the profile by aqueous solution organic matter om can significantly improve the transport of insoluble elements among all the elements th is the least mobile as for the general conservative elements during incipient chemical weathering such as fe ti zr hf nb and ta the removals are up to 20 40 in the upper profile however these elements behave as conservatively as th in the lower profile in the middle profile oxic environment occurs accompanied with significant om decomposition the mn and ce transferred downward are readily oxidized into insoluble mn iv and ce iv and precipitate in the oxic front important om decomposition decreases the capacity of transfer of insoluble elements in aqueous solution consequently al significantly precipitates in the oxic front and rees with the exception of ce precipitate largely in the omdepleted layers co and u are also concentrated in the oxic front in association with mn and ce respectively however cr shows a negative correlation with mn because its response to redox condition changes is reversed from that of mn mn oxides hydroxides fe oxides hydroxides and secondary phosphate minerals other than clay minerals are potential hosts for rees except for ce in the profile rees with high concentrations in the profile seem closely associated with mn oxides hydroxides remarkable highly correlated ce and gd anomalies are observed in the profile ce anomalies are caused by ce precipitation in the oxic environment and successive decomposition of organic matter gd anomalies are likely to have resulted from lower stability constants of gd om complexes compared to those of neighboring rees the overall elemental behaviors in this profile suggest that organic matter plays a very important role in the mobilization and re distribution of the elements during extreme weathering

how accurate are rivers as gauges of chemical denudation of the earth surface examination of the behavior of oxygen and hydrogen during weathering reactions shows that river dissolved load although widely used is an imperfect tracer of chemical denudation at the current state of knowledge none of the metrics for river total dissolved loads such as the silicate derived total dissolved solids tds sil ca 2 mg 2 na k sio 2 converted or not to equivalent oxides account in a mechanistic manner for the transfer of oxygen and hydrogen between the solid and fluid phase during weathering reactions we assess that chemical denudation derived from tds sil will significantly overestimate the true chemical denudation for weathering of ca feldspar to kaolinite whereas weathering of water rich sedimentary rocks will be characterized by an underestimation of chemical denudation by tds sil for a handful of field sites we estimate that the bias is lower than 10 the sign and extent of the bias depends on the nature of bedrock and on weathering conditions altogether our analysis questions the broadly accepted concept of chemical denudation rate

in situ and experimental evidence for acidic weathering of rocks and soils on mars experimental data for alteration of synthetic martian basalts at ph 0 1 indicate that chemical fractionations at low ph are vastly different from those observed during terrestrial weathering rock surface analyses from gusev crater are well described by the relationships apparent from low ph experimental alteration data a model for rock surface alteration is developed which indicates that a leached alteration zone is present on rock surfaces at gusev this zone is not chemically fractionated to a large degree from the underlying rock interior indicating that the rock surface alteration process has occurred at low water to rock ratio the geochemistry of natural rock surfaces analyzed by apxs is consistent with a mixture between adhering soil dust and the leached alteration zone the chemistry of rock surfaces analyzed after brushing with the rat is largely representative of the leached alteration zone the chemistry of rock surfaces analyzed after grinding with the rat is largely representative of the interior of the rock relatively unaffected by the alteration process occurring at the rock surface elemental measurements from the spirit opportunity pathfinder and viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low ph low water to rock ratio alteration relationships developed for gusev rocks soils are affected principally by mobility of fe and mg consistent with alteration of olivine bearing basalt and subsequent precipitation of fe and mg bearing secondary minerals as the primary control on soil geochemistry copyright 2006 by the american geophysical union

the paleoproterozoic baraboo paleosol revisited quantifying mass fluxes of weathering and metasomatism chemical climofunctions and atmospheric pco2 in a chemically heterogeneous protolith abstract the paleoproterozoic baraboo paleosol is the most chemically mature precambrian paleosol in the lake superior region having formed under the influence of a warm humid climate in a region of subdued topography we have determined the chemical variability among six samples of granitic protolith and found that such variability is inherited in the weathering profile to minimize the effect of sample heterogeneity on various geochemical calculations transformed compositions of saprolite and regolith were generated by obtaining linear least squares fits to the concentrations of sio2 tio2 al2o3 and zr through the weathering profile and summing the totals to 100 fortunately use of measured or transformed compositions makes little difference in calculation of mass fluxes however transformed compositions allow for clearer comparisons among paleosols and are essential for determining certain paleosol parameters such as chemical depletion fraction calculations of total and reduced mass fluxes chemical index of alteration feldspar index of weathering and chemical depletion fraction demonstrate that the baraboo paleosol is chemically more mature than the paleoproterozoic pronto and cambrian timna paleosols but less mature than modern subtropical and tropical soils estimates of mean annual temperature matppm and mean annual precipitation mapppm for baraboo are 14 3 19 2 9 4 c and 1177 1695 658 mm yr 1 confirming the previous interpretation of a warm humid climate although the level of atmospheric pco2 is poorly constrained due to the uncertainty in duration of weathering and possibility of regolith removal by erosion pco2 is calculated to be 4 8 pre industrial atmospheric level 280 ppm for 100 000 years of weathering which is consistent with the pco2 level at 1 7 ga predicted by the weak sun model

deep weathering along a granite ridgeline in a subtropical climate abstract bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11 meter profile weathering on a granite ridgeline under subtropical climate conditions in south china the weathering sequence is delineated by mineralogy and major element variations apatite biotite hornblende and plagioclase dissolve early during weathering resulting in nearly 100 ca and na loss and significant mg fe and p depletion at depth the k feldspar reaction front begins at the depth of depletion of plagioclase leading to a loss of 80 of the k at the land surface near the bottom of the ridgeline and almost 100 at the top dissolution of quartz and other silicates releases about 60 of si in the profiles kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer the soil horizon upper 100 cm is the zone dominated by pedogenic processes including active biological activity physical erosion and influx of high concentrations of atmospheric components especially co2 and o2 the pedogenic processes are characterized by low ph 4 54 to 5 85 high clay content kaolinite 6 16 wt gibbsite 2 8 wt and total organic carbon content 0 13 3 93 and intensive fracturing and dissolution of quartz and k feldspar compared with the lower horizons accumulation of organic material and resistant minerals downslope is attributed to down ridge movement of water termed here interflow and weathering products in the uppermost 100 cm down the ridgeline using a mass balance model calculation for the catena that assumes steady state soil thickness at all sites the bottom profile shows the highest apparent total chemical weathering loss rate 14 g m 2 y 1 whereas the middle position shows the highest physical erosion loss rate 44 g m 2 y 1 sio2 accounts for about 84 of the chemical weathering outflux from the soil horizons along the ridgeline hillslope chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite this study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena

significance of chromian spinels from the mantle sequence of the andaman ophiolite india paleogeodynamic implications abstract the mantle section of the andaman ophiolite between rutland island in the south and north andaman in the north has been studied the restitic peridotite of rutland island is comprised of depleted harzburgite to clinopyroxene bearing harzburgite whereas that in middle and north andaman is mostly less depleted lherzolite dominated mantle chromian spinels from the mantle section of the andaman ophiolite belong to four major groups group 1 spinels from rutland chromitite pods characterized by high cr cr cr a1 atomic ratio 0 71 group 2 spinels from north andaman chromitite pods with two subgroups 2a characterized by high cr 0 70 0 79 and 2b characterized by medium cr 0 48 0 51 and high mg mg mg fe 2 atomic ratio 0 74 0 77 group 3 residual accessory grains from rutland peridotite characterized by medium cr 0 37 0 55 and low mg 0 41 0 54 and group 4 residual accessory grains from middle and north andaman peridotites characterized by low cr 0 09 0 23 and high mg 0 71 0 81 group 1 chromian spinels of rutland island and group 2a of north andaman are likely to have crystallized from boninitic melts formed by relatively high degrees of partial melting whereas group 2b varieties from north andaman are from tholeiitic melts formed by lower degrees of melting the chemistry of the residual accessory chromian spinels groups 3 and 4 suggests that the mantle peridotites of rutland island towards the south are similar to fore arc peridotites of suprasubduction zone environments whereas those of north andaman are less depleted this spatial and or temporal directional change in spinel compositions may reflect variations linked to the melting history where the same sliver of oceanic mantle underwent different styles of melting in different tectonic settings at different points in time the coexistence of both chromitite types with high and low cr spinels in the same area from north andaman possibly reflects temporal variations of separate melt intrusions produced through specific melting stages it is inferred that a similar geodynamic setting to the present day also existed during the cretaceous period with a fore arc at rutland island and a back arc towards the north at north andaman

nature of ophiolite occurrences along the eastern margin of the indian plate and their tectonic significance upper mesozoic to lower eocene ophiolitic rocks occur in two parallel belts along the eastern margin of the indian plate the eastern belt passes through central burma sumatra and java and coincides with a zone of gravity highs resulting from steeply dipping mafic rocks it denotes the locus of the subduction where these ophiolites were accreted just prior to middle eocene time in contrast the western belt which passes through nagaland manipur western burma and andaman is flanked to the east by a negative gravity anomaly zone in it the ophiolites occur as rootless subhorizontal bodies tectonically overlying eocene oligocene flysch sedimentary rocks they are inferred to be nappes that propagated westward from the eastern belt during late oligocene terminal collision of the indian and eurasian continental blocks ophiolite occurrences in andaman and mentawai islands belonging to the western belt are generally linked with active subduction west of the island arc this subduction began only in late miocene time and thus it could not have produced the ophiolites which had been emplaced on land much earlier

enrichment of ion exchangeable rare earth elements by felsic volcanic rock weathering in south china genetic mechanism and formation preference abstract felsic volcanic rocks are an important source for generating ion adsorption type rare earth element ree resources to better understand the supergene enrichment of rees related to felsic volcanic rock weathering this study conducted an investigation of indosinian felsic volcanic rocks from guangxi southwest china which have been subjected to deep weathering the weathering has formed large areas of thick regolith with the potential to host ion adsorption type ree mineralization the felsic volcanic rocks belong to the dacite rhyolite series and are peraluminous high k calc alkaline and ree rich 325 376 ppm abundant ree bearing accessory minerals are present in the felsic volcanic rocks including titanite average ree 15 1 wt allanite average ree 14 9 wt and apatite average ree 1510 ppm and these three minerals contain an estimated 88 7 of the whole rock rees content significant ree enrichment is present in the felsic volcanic rock derived regolith a typical rhyolite derived regolith profile has ree contents that increase from 376 ppm in the rhyolite to 1737 ppm in the regolith representing an almost five fold enrichment due to weathering the rees in the regolith are present in an ion exchangeable form irees which accounts for 52 87 of the total rees present trees the occurrence of irees is closely linked to clay minerals showing an affinity in the order halloysite kaolinite illite continuous operations of rees by an eluviation illuviation process from the source minerals titanite allanite apatite to sink minerals kaolinite halloysite illite results in an iree enriched zone in the middle and lower parts of the rhyolitic regolith notably besides the studied indosinian felsic volcanic rocks there are multi epochs of such lithology outcropped in south china their related irees mineralizations however are preferentially developed in the weathered terrains of early yanshanian and indosinian felsic volcanic rocks and not in those of the yanshanian and late yanshanian felsic volcanic rocks a comparison of the mineralized and barren units indicates that the irees mineralization hosted in felsic volcanic rocks regolith is controlled by some key endogenic and exogenic ore forming factors high initial ree concentrations in the unaltered felsic volcanic rocks a suitable climate and a relatively quiescent tectonic setting are favorable for the formation and preservation of irees mineralization

how mineralogy and slope aspect affect ree release and fractionation during shale weathering in the susquehanna shale hills critical zone observatory abstract to understand the factors that control rare earth elements ree release and fractionation during shale weathering we investigate the ree contents in solid bedrock regolith stream sediments and natural waters stream and pore waters from a first order catchment developed entirely on gray shales in central pennsylvania usa up to 65 of the ree relative to parent bedrock is depleted from the weathering profiles in the acidic and organic rich soils due to chemical leaching in addition newly formed fine particles were also lost along with the down slope movement of soil waters weathering profiles on the south facing slope show less depletion of ree than those on the north facing slope 33 vs 45 on average we hypothesize that the different degrees of ree depletion on the two transects reflect a history of different chemical weathering rates and possible different surface erosion rates controlled by contrasting slope aspect induced microclimate conditions in addition weathering profiles natural waters and sequential extractions all show a preferential removal of middle ree up to 22 more relative to light ree and heavy ree during shale weathering due to preferential release of mree from rhabdophane furthermore the long term phosphate mineral dissolution rates e g rhabdophane were estimated at 10 15 to 10 14 mol m 2 s 1 under field conditions based on ree depletion profiles strong positive ce anomalies average ce ce n value 1 79 observed in the regolith stream sediments and regolith extractions point to the fractionation and preferential precipitation of ce as compared to other ree due to the generally oxidizing conditions during release transport and redistribution of ree in the surface and subsurface environments positive eu anomalies average eu eu n value 1 30 observed in the natural waters of the catchment are attributed to weathering of plagioclases in the shale bedrock this study highlights the use of ree as natural tracers for low temperature geochemical processes

quantification of chemical weathering rates across an actively eroding hillslope abstract chemical weathering rates for landscapes are difficult to quantify because the timescales over which weathering occurs are often unknown in this study we use timescales defined by prior cosmogenic nuclide analyses and a suite of geochemical measurements to calculate weathering rates in saprolite and soil and to determine how these rates vary across an eroding hillslope we also estimate the relative contributions of solute and erosional mass loss to landscape lowering analyses were conducted on a soil mantled hillslope developed on a granodiorite pluton in southern nsw australia mass loss in solution accounts for 35 to 55 of the total mass loss from the hillslope saprolite close to the soil saprolite boundary is less weathered at the ridge than at distance from the ridge the calculated flux of silica from the saprolite is 5 tons km 2 yr 1 and does not vary with distance from the ridge or overlying soil thickness the assumption of steady state but spatially variable erosion rates with a temporally constant thickness of soil and saprolite allows us to calculate the downslope variation in the rate of solute losses soil silica weathering rates initially increase from 12 tons km 2 yr 1 at the ridge crest to 20 tons km 2 yr 1 on the convex region of the hillslope and then decrease to 13 tons km 2 yr 1 by the time soils have been transported 45 50 m soils closer to the surface are more weathered than deeper soils this geochemical stratification suggests that the soil column does not become thoroughly vertically mixed as soils move down slope dependence of solute loss on transport distance may explain the previously noted discrepancy between the observed soil thickness and that predicted based on curvature variation of solute loss with transport distance may also contribute to the linear dependence of soil thickness on distance from the ridge

investigation of in situ weathering of quartz diorite bedrock in the rio icacos basin luquillo experimental forest puerto rico abstract the rio icacos basin in puerto rico is the site of the highest measured chemical solute fluxes for a catchment on granodiorite this is partly attributable to high annual rainfall 4300 mm high average temperature 23 c and moderate relief the bulk of these fluxes is contributed by dissolution of plagioclase and amphiboles in zones of partially weathered rock 0 5 1 5 m thick underlying saprolite these zones are characterized by systems of onion skin rindlets each 3 10 cm thick in which porosity development is dominated by weathering of plagioclase to kaolinite fe bearing aluminosilicate minerals hornblende augite and biotite persist in the weathered rock after plagioclase has weathered to completion but hornblende and augite disappear between the porous rindlet systems and saprolite a new watershed scale solute mass balance corroborates earlier studies and yields an overall reaction stoichiometry that closely resembles complete weathering of the rock except quartz and biotite to kaolinite and fe3 oxides our findings indicate that steady state assumptions are reasonable and useful in studying weathering at this site estimated steady state sediment yields based on net solute fluxes and average bedrock composition of 3 24 10 9 to 3 60 10 9 kg m 2 s 1 are smaller than measured values indicating that sediment generation is currently accelerated with respect to steady state however sediment generation has recently been closer to steady state since weathering within the rindlet systems occurs on multiple fronts moving upward and downward two new steady state conceptual models are developed to account for 1 multiple parallel weathering fronts and 2 differential rates of advance of weathering fronts due to porosity development based on these models in situ weathering rates for plagioclase at two sample locations of 2 7 10 15 and 5 0 10 15 mol na g 1 s 1 are calculated values comparable to bet surface area normalized rates of 2 7 10 16 to 5 0 10 15 mol na m 2 s 1

learning to read the chemistry of regolith to understand the critical zone the base of the critical zone includes the mantle of altered soil and rock regolith that changes in response to chemical physical and biological processes occurring at earth s surface these processes are recorded in the chemistry of the regolith and this long term record can often be deciphered for example on eroding ridgetops where flows are generally downward for water and upward for earth material element concentrations vary with depth to constitute depletion addition depletion enrichment and biogenic profiles models can be used to explore the records of mineral dissolution atmospheric input coupled dissolution precipitation and biolifting documented in these profiles these models enable interpretation of the effects of time climate rates of erosion and human and other biotic impacts on the profile patterns by testing quantitative models against the long term record of information in regolith we will learn to project changes arising from human and natural perturbations of the critic

collision related fore arc and back arc evolution of the northern sunda arc abstract comparison with other arc systems suggests that in the fore arc area of the northern sunda arc emplacement of chromite and jadeite bearing serpentinite melange diapirs and deposition of olistostromes were caused by campanian collision with a continental fragment since underthrust eastwards beneath the arc the age and position of east directed thrusts and associated tin granites in the continental back arc area implies that thrusting and generation of granites were genetically related to the collision and that the back thrusts were coupled to the fore arc thrusts by a decollement beneath the fore arc basin and magmatic arc subsidence and sedimentation in the fore arc basin succeeded collision and rise of the back arc shan plateau possibly resulted from late cenozoic relaxation of collision related compressive stress