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

kinetically limited weathering at low denudation rates in semiarid climatic conditions biogeochemical cycling within the critical zone depends on the interactions between minerals and fluids controlling chemical weathering and physical erosion rates in this study we explore the role of water availability in controlling soil chemical weathering in semiarid climatic conditions weathering rates and intensities were evaluated for nine soil profiles located on convex ridge crests of three mountain ranges in the spanish betic cordillera we combine a geochemical mass balance with 10be cosmogenic nuclides to constrain chemical weathering intensities and long term denudation rates as such this study presents new data on chemical weathering and 10be derived denudation for understudied semiarid climate systems in the betic cordillera chemical weathering intensities are relatively low 5 to 30 of the total denudation of the soil and negatively correlated with the magnitude of the water deficit in soils chemical mass losses are inversely related to denudation rates 14 109 mm kyr and positively to soil thickness 14 58 cm these results are consistent with kinetic limitation of chemical weathering rates a worldwide compilation of chemical weathering data suggests that soil water balance may regulate the coupling between chemical weathering and physical erosion by modulating soil solute fluxes therefore future landscape evolution models that seek to link chemical weathering and physical erosion should include soil water flux as an essential driver of weathering

in situ major and trace element compositions of apatite from the yangla skarn cu deposit southwest china implications for petrogenesis and mineralization abstract the yangla copper deposit is a rare triassic intrusion related cu skarn system in the central part of the jinshajiang tectonic belt central sanjiang orogenic belt southwest china major and trace element compositions of apatites from ores fertile calc alkaline intrusions and its mafic microgranular enclaves and barren calc alkaline intrusions from the yangla skarn copper deposit were measured by electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry results indicate that apatites grown within ores fertile intrusions and its enclaves show similar features but are different from that grown within barren intrusions apatite from fertile intrusions has higher ca and correspondingly lower total trace element contents which partition onto the ca sites relative to that from barren intrusions apatites from the barren intrusions have high f and low cl contents and correspondingly high f cl ratios which may have resulted from the assimilation of sediment apatites from fertile intrusions show relatively high cl and low f contents which may reflect crystallization from magmas with high water contents redox sensitive elements in apatite can be used as indicators of the oxidation state of magmas apatites from the barren intrusion have lower v and as contents higher mn fe and u contents and more pronounced negative eu anomalies than those from fertile intrusion indicating that the barren magma was more reduced consistent with its lower whole rock fe2o3 feo and zircon ce4 ce3 ratios these findings demonstrate that apatites are effective in distinguishing fertile from barren intrusions and can be used as a robust tool in mineral exploration

bajo de la alumbrera copper gold deposit stable isotope evidence for a porphyry related hydrothermal system dominated by magmatic aqueous fluids alteration zones at the gold rich bajo de la alumbrera porphyry copper deposit in northwestern argentina are centered on several porphyritic intrusions they are zoned from a central copper iron sulfide and gold mineralized potassic biotite k feldspar quartz core outward to propylitic chlorite illite epidote calcite assemblages a mineralized intermediate argillic alteration assemblage chlorite illite pyrite has overprinted the potassic alteration zone across the top and sides of the deposit and is itself zoned outward into phyllic quartzinuscovite illite pyrite alteration this study contributes new data to previously reported delta 18 o and delta d compositions of fluids responsible for the alteration at bajo de la alumbrera and the data are used to infer likely ore forming processes measured and calculated delta 18 o and delta d values of fluids 8 3 to 10 2 and 33 to 81 parts per thousand respectively confirm a primary magmatic origin for the earliest potassic alteration phase lower temperature potassic alteration formed from magmatic fluids with lower delta d values down to 123 parts per thousand these depleted compositions are distinct from meteoric water and consistent with degassing and volatile exsolution of magmatic fluids derived from an underlying magma variability in the calculated composition of fluid associated with potassic alteration is explained in terms of phase separation or boiling if copper iron sulfide deposition occurred during cooling as proposed elsewhere this cooling was largely a result of phase separation magmatic water was directly involved in the formation of overprinting intermediate argillic alteration assemblages at bajo de la alumbrera calculated delta 18 o and delta d values of fluids associated with this alteration range from 4 8 to 8 1 and 31 to 71 per mil respectively compositions determined for fluids associated with phyllic alteration 0 8 to 10 2 and 31 to 119 parts per thousand overlap with the values determined for the intermediate argillic alteration we infer that phyllic alteration assemblages developed during two stages the first was a high temperature 400 degrees 300 degrees c stage with d depleted water delta d 66 to 119 parts per thousand this compositional range may have resulted from magma degassing and or the injection of new magmatic water into a compositionally evolved hydrothermal system the isotopic variations also can be explained by increased fluid rock interaction the second stage of phyllic alteration occurred at a lower temperature similar to 200 degrees c and variations in the modeled isotopic compositions imply mixing of magmatic and meteoric waters ore deposition that occurred late in the evolution of the hydrothermal system was probably associated with further cooling of the magmatic fluid in part caused by fluid rock interaction and phase separation changing ph and or oxygen fuoracity may have caused additional ore deposition the ingress of meteoric water appears to postdate the bulk of mineralization and occurred as the system at bajo de la alumbrera waned

chemical weathering of mafic rocks in boreal subarctic environment northwest russia under influence of glacial moraine deposits abstract chemical weathering of mafic rocks represents substantial sink of atmospheric co2 yet the mechanismes of this process in high latitude regions are poorly understood this work addresses geochemical migration and partitioning of major and trace elements between rock soil and surface waters during chemical weathering of mafic rocks and soil formation under the influence of a glacial moraine in the northwestern russian subarctic we used multidisciplinary approach which included major and trace element chemical analysis sr isotopic measurements and mineralogical structural and microscopic investigations quaternary pleistocene deposits were observed even in the deepest horizons of soil profiles and confirm a strong moraine influence as most soils showed podzolic features chemical and sr isotopic analyses revealed a strong impact of the moraine on soil chemistry and mineralogy mineralogical studies showed the presence of non aeolian quartz and zircon in soils which were not linked to the nature of the parental rocks i e mafic and felsic at the same time we observed the presence of etch pit corrosion on the surface of zircons and feldspars and a newly formed matter adjacent to the surface of primary phases the chemical index of alteration cia showed weak or no weathering of rocks within the soil profile and the weathering intensity scale confirmed the felsic chemical composition of soils developed over mafic and ultramafic rocks analysis of sr radiogenic isotopes demonstrated preferential removal of easily weatherable and less radiogenic minerals over the full depth of soil profile and a more radiogenic signature of the granitic moraine compared to mafic and felsic bedrocks the composition of most surface waters reflected the weathering of silicate rocks but did not allow for distinguishing purely mafic source the chemical weathering rates of ultramafic rocks were calculated to be higher than those for the granitic till but the moraine depositions which dominate this region hide evidence of the real weathering process this could be due to retention of mg and ca in soil due to precipitation of secondary phases such as mg vermiculite or divalent cation adsorption on mineral organic or organo mineral phases as a result weathering rates estimated for the olivinite rock appear to be lower than the weathering rates of mafic rocks reported in other boreal and subarctic regions overall the felsic moraine deposits are capable to sizably decrease the weathering intensity of mafic rocks which should be taken into account for chemical weathering modelling of high latitude regions subjected to glaciation in the past

generation of the early cenozoic adakitic volcanism by partial melting of mafic lower crust eastern turkey implications for crustal thickening to delamination abstract early cenozoic 48 50 ma adakitic volcanic rocks from the eastern pontides ne turkey consist of calc alkaline and high k calc alkaline andesite and dacite with sio2 contents ranging from 56 01 to 65 44 wt this is the first time that early eocene volcanism and adakites have been reported from the region the rocks are composed of plagioclase amphibole quartz and mg rich biotite they have high and low mg values ranging from 55 to 62 and 13 to 42 respectively high mg rocks have higher ni and co contents than low mg samples the rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements depletions in nb ta and ti and have high la yb and sr y ratios their relative high isr 0 70474 0 70640 and low end 50 ma values 2 3 to 0 8 are inconsistent with an origin as partial melts of a subducted oceanic slab combined major and trace element and sr nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region where a transition from a collision to an extension stage has created thickening and delamination of the pontide mafic lower crust at 50 ma the high mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle and its subsequent interaction with the mantle peridotite during upward transport leaving garnet as the residual phase elevates the mgo content and mg of the magmas whereas low mg magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling which supplies heat flux to the lower crust the data also suggest that the mafic lower continental crust beneath the region was thickened between the late cretaceous and the late paleocene and delaminated during late paleocene to early eocene time which coincides with the initial stage of crustal thinning caused by crustal extensional events in the eastern pontides and rules out the possibility of an extensional regime before 50 ma in the region during the late mesozoic to early cenozoic

a multidisciplinary approach to investigate weathering processes affecting gneissic rocks calabria southern italy abstract the paper focuses on the weathering processes affecting gneissic rocks of the western sila grande massif calabria italy through the development of an interdisciplinary research based on field studies and investigations minero petrographical analyses and geochemical modeling both physical and chemical weathering affect gneissic rocks of the study area where the combination of tectonic and past climatic conditions played an important key role in the development of complex and deep weathering profiles field surveys and cut slope analyses highlight articulated and complex geometric relationships between various classes of weathering i e out of sequence weathering horizons giving rise to a partial or even complete inversion of the normal weathering profile the weathering profile has turned out particularly intense as classes iv v and vi are widespread among the class vi the colluvial soils are prominent in comparison whit the residual soils borehole logs that confirm the intensity and complexity of weathering profiles in deep allow to estimate the presence of weathered rocks to be at least 70 m in thicknesses the main mineralogical modifications linked to weathering processes concern the partial transformation of biotite and the partial destruction of feldspars mainly plagioclases associated with the neoformation of secondary mineralogical phases clay minerals and fe oxides neoformed clay minerals such as sericite illite and mixed layer phases and ferruginous products replaced feldspars and biotite during the most advanced weathering stage results of xrd analyses and geochemical modelling provide a good indication on the secondary mineral assemblage due to the increase of the weathering intensity form class iii to class vi that reflects the different contributions of chemical elements provided by dissolution of silicate minerals into the surrounding groundwater system the chemical composition of the studied rock samples and the oxides variations suggest a removal of some alkali na and k and alkaline earth ca and mg into solution as a consequence of weathering reactions the chemical analysis and the weathering indices cia pia ciw and ciw show a marked alteration process with ferromagnesian minerals and feldspars probably dissolved and leached into the surrounding groundwater system the co2 controlled dissolution of plagioclase appears to be the most important reaction during chemical weathering the progressive dissolution results then dominated by biotite followed by a minor amounts k feldspar chlorite and garnet whereas the sillimanite shows a neglectable amounts the secondary solid phases observed during the geochemical modeling illite followed by vermiculite ferrihydrite and saponite are similar to those found in this natural system the proposed approach could be used to characterize weathered crystalline rocks and related weathering profiles in similar geological setting and the obtained results represent a key point for the evaluation of the control exerted by weathering on landscape evolution under current environmental settings in terms of sediment generation soil erosion rates and mass movements and for the mechanical characterization of weathering profiles for engineering geological purposes

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

subduction modified mantle derived triassic high mg andesites in the sanjiang tethys eastern tibet abstract andesites in the yangla district of the sanjiang tethys eastern tibet are characterized by relatively high mgo and with rich large ion lithophile elements liles indicating similarities to typical high mg andesites formed in continental collisional zones zircon u pb age of 232 1 ma for these andesites shows that they occurred synchronously with the regionally widespread late middle triassic granitoids and bimodal volcanic rocks primitive mantle normalized spidergrams for these andesites show depletion in high field strength elements hfses with sr nd pb isotopic compositions that are comparable to both arc and morb like high mg rocks generated from subduction modified sources modelling results suggest that an input of 20 sediment derived melts into mantle derived melts could be possibly responsible for the sr nd isotopic characteristic of these andesites morb and arc like compositions likely indicate a metasomatized mantle wedge modified by subduction processes during the closure of the paleo tethys ocean and subsequent continental collision it is speculated that the late middle to late triassic intra continental re activation associated with regional tectonic collapse and thermal relaxation triggered the melting of this previously subduction modified mantle leading to the formation of the high mg andesites in the yangla district

silicate weathering of soil mantled slopes in an active alpine landscape abstract despite being located on high steep actively uplifting and formerly glaciated slopes of the swiss central alps soils in the upper rhone valley are depleted by up to 50 in cations relative to their parent bedrock this depletion was determined by a mass loss balance based on zr as a refractory element both holocene weathering rates and physical erosion rates of these slopes are unexpectedly low as measured by cosmogenic 10be derived denudation rates chemical depletion fractions cdf range from 0 12 to 0 48 while the average soil chemical weathering rate is 33 15 t km 2 yr 1 both the cosmogenic nuclide derived denudation rates and model calculations suggest that these soils have reached a weathering steady state since deglaciation 15 ky ago the weathering signal varies with elevation and hillslope morphology in addition the chemical weathering rates decrease with elevation indicating that temperature may be a dominant controlling factor on weathering in these high alpine basins model calculations suggest that chemical weathering rates are limited by reaction kinetics and not the supply rate of fresh material we compare hillslope and catchment wide weathering fluxes with modern stream cation flux and show that high relief bare rock slopes exhibit much lower chemical weathering rates despite higher physical erosion rates the low weathering fluxes from rocky rapidly eroding slopes allow for the broader implication that mountain building while elevating overall denudation rates may not cause increased chemical weathering rates on hillslopes in order for this sediment to be weathered intermediate storage for instance in floodplains is required

the role of the mantle in the genesis of tin deposits and tin provinces of eastern australia initial nd isotope data for the four granites related to the ardlethan sn deposit in the wagga sn belt of the central lachlan fold belt of eastern australia range from 11 6 to 2 1 increasing with increasing fractionation the four granites beneath the renison tin mine in western tasmania range from 6 1 to 3 9 the data clearly establish the presence of light rare earths of mantle origin in the fractionated granites associated with the ardlethan porphyry sn deposits and hint at the same relationship for the renison granites though in this case the mineralizing pluton is probably yet to be discovered sulfur and carbon isotope data from the ardlethan and renison ores and from similar deposits in tasmania suggest that mantle volatiles played a significant role in the genesis of sn granites and deposits mantle input may have occurred either by mixing of crustal and mantle melts or metasomatism by mantle derived fluids

climate driven processes of hillslope weathering climate controls erosion and weathering on soil mantled landscapes through diverse processes that have remained diffi cult to disentangle due to their complex interactions we quantify denudation soil and saprolite weathering and soil transport near the base and crest of the western slope of the sierra nevada to examine how large differences in climate affect these processes depth profi les of fallout radionuclides and fi eld observations show relative differences in erosion and weathering processes at these two climatically diverse sites and our data suggest fundamentally different patterns of soil production and transport mechanisms biotically driven soil transport at low elevation and surface erosion driven by overland fl ow at high elevation soil production rates from cosmogenic 10 be decrease from 31 3 to 13 6 m ma with increasing soil depth at low elevation but show uncertain depth dependence at the high elevation site our data also show a positive correlation between physical erosion and saprolite weathering at both sites highly weathered saprolites are overlain by weakly weathered and rapidly eroding soils while chemically less depleted saprolites are overlain by slowly eroding more weathered soils our data are among the fi rst to quantify the critical role of saprolite weathering in the evolution of actively eroding upland landscapes and our results provide quantitative constraints on how different climates can shape hillslopes by driving processes of erosion and weathering

silicon isotope variations accompanying basalt weathering in iceland abstract this study presents the si isotope compositions of the dissolved phase of twenty rivers from across iceland the high resolution nu plasma 1700 mc icp ms was used to provide interference free 30 si 28 si ratios with an average limiting precision of 0 04 30 si the si isotope composition ranges from 0 08 to 1 46 30 si averaging 0 63 0 38 1 sd this is only slightly lighter than the recently reported mean of 0 84 0 19 for high precision measurements of swiss rivers but is significantly lighter than compositions reported for some other rivers the si isotope composition varies slightly with the amount of glacial cover which provides evidence that the continental si input to the oceans may be climatically controlled and thus likely to vary over glacial interglacial cycles after correction for the dissolution of trace amounts of calcite in one region a correlation is found between 30 si and ca si this is consistent with the measured basaltic composition and indicates isotopic fractionation during si removal from the dissolved phase by calculating the fraction of si that is removed from the dissolved phase into secondary phases it is possible to use the riverine si flux si denudation rate to calculate the initial dissolution rate of si within these catchments from this study we estimate that the total amount of si being dissolved by primary weathering of iceland is 3 million tons per yr however only 50 of this si is released into the rivers and contributes to denudation using the si isotope composition and the si fraction removed it is possible to model the si isotope fractionation as either a rayleigh type fractionation or a steady state system both yield similar fractionation factors of about 1 5 30 si implying only one underlying fractionation process that is controlled by external parameters such as runoff furthermore rivers that follow a steady state fractionation model are associated with higher si dissolution rates and lower 30 si values indicating an inverse relationship between weathering rates and dissolved riverine si isotope composition

natural and anthropogenic controls on soil erosion in the internal betic cordillera southeast spain soil erosion in southeast spain is a complex process due to strong interactions between biophysical and human components significant progress has been achieved in the understanding of soil hydrological behavior despite the fact that most investigations were focused on the experimental plot scale although experimental plots allow exploring the effect of multiple biophysical and anthropogenic factors they provide limited insights in the combined effect of all factors acting together at the landscape scale in this study area specific sediment yields ssy have been estimated based on the volume of sediment trapped behind 36 check dams in the southeast of spain low ssy values were reported mean 1 40 t ha 1 year 1 median 0 61 t ha 1 year 1 ssy variability could be explained for 67 by catchment characteristics such as drainage area soil characteristics land cover average catchment slope and annual rainfall the low ssy values are probably caused by the agricultural abandonment that occurred over the past decades and allowed the recovery of natural vegetation furthermore our results suggest that the soils have eroded in the past to such an extent that nowadays not much sediment is detached by overland flow due to residual enrichment of clay and stones also sediment is to a large extent trapped locally in the catchment as indicated by the negative relationship between ssy and catchment area c 2011 elsevier b v all rights reserved

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

sample size for determination of coarse fragment content in a stony soil abstract particle size analysis of soils containing coarse fragments requires sufficient amounts of soil material we tried to quantify the sample volume for coarse fragment measurements in a rendzina soil with more than 50 coarse fragment content a monolith of 50 cm 80 cm was excavated to a depth of 160 cm hardened with an epoxy resin and cut into six cross sections the coarse fragment contents were determined on the cross sections by counting the aerial fractions belonging to the fine earth fine gravel and gravel classes additionally 24 samples with a volume of 3 2 to 4 5 1 were sieved to determine the coarse fragment content the contents estimated from the cross sections equalled the contents measured with particle size analysis the data were evaluated in terms of the representative elementary area and volume the coarse fragment content as a function of the sampling size exhibited the features of the representative elementary volume graph the side length of the representative elementary area ranged from 11 to 19 cm the estimated representative elementary volume ranged from 400 to 2 100 cm 3

weathering dust and biocycling effects on soil silicon isotope ratios abstract silicon isotope ratios 30si of bulk mineral materials in soil integrate effects from both silicon sources and processing here we report 30si values from a climate gradient of hawaiian soils developed on 170 ka basalt and relate them to patterns of soil chemistry and mineralogy the results demonstrate informative relationships between the mass fraction of soil si depletion and 30si in upper 1 m deep soil horizons generally correlate with the isotope fractionation predicted by a study of dissolved si in basalt watershed rivers and driven by preferential 28si removal from the dissolved phase during precipitation in contrast after correcting for the influence of dust secondary mineral si depletion and 30si values in shallow

slope gradient controls soil thickness and chemical weathering in subtropical brazil understanding rates and timescales of regional soilscape evolution through a combination of field data and modeling

petrology of the intrusive rocks within the sungun porphyry copper deposit azerbaijan iran abstract the sungun intrusive complex hosting the sungun porphyry copper stock is located about 75 km north west of ahar in azarbaijan province and intruded along the sungun anticline into cretaceous limestone and eocene tuff and agglomerate of andesitic to trachytic composition based on the petrography and geochemistry it is suggested that the sungun deposit as a composite stock comprising an early monzonite quartzmonzonite and a later diorite granodiorite phase the parental magma was a medium to high k andesite or diorite initially contained 3 wt h2o and was generated in a continental arc setting the high level emplacement of this magma led to its saturation with h2o and the exsolution of fluids at an early stage of crystallization and subsequently mo and then cu mineralization based on the major and trace element geochemistry especially the behaviour of the immobile trace elements y zr and nb fractional crystallization is suggested as the process that produced the present intrusive rocks the degree of fractionation was estimated using the rayleigh fractionation equation relating the concentration of zr nb and y in the least evolved sample to the concentrations of these elements in progressively more evolved samples the results of these calculations indicate that the compositions of the various rock types can be explained by up to 24 fractionation of ferromagnesian minerals e g pyroxene and amphibole of the diorite magma to produce the more evolved monzonite quartz monzonite suite

silicon isotopes in allophane as a proxy for mineral formation in volcanic soils abstract weathering of basaltic ash in volcanic areas produces andosols rich in allophane and ferrihydrite since the rate of mineral formation is very useful in climate and geochemical modelling this study investigates si isotope compositions of allophane as a proxy for mineral formation allophane formed in contrasting conditions in five icelandic soil profiles displays silicon isotope signatures lighter than the basalt in less weathered soils 0 64 0 15 and heavier in more weathered organic rich soils 0 23 0 10 the fate of the dissolved si in those volcanic soils strongly depends on al availability in organic rich soils most of al is humus complexed and the results support that si precipitates as opaline silica by super saturation leaving an isotopically heavier dissolved si pool to form allophane with uncomplexed al this study highlights that si isotopes can be useful to record successive soil processes involved in mineral formation which is potentially useful in environmental paleo reconstruction

bulk composition of northern african dust and its source sediments a compilation abstract this paper presents a review of bulk compositional data of northern african dust and its potential source sediments and includes elemental isotope and mineralogical data northern african dust represents about one half of the total global atmospheric mineral dust burden and its uplift transport and deposition have strong impacts on climate and various terrestrial and marine ecosystems the chemical data set shows that an average northern african dust exhibits comparable si fe and mn contents with respect to the average composition of the upper continental crust is slightly depleted in the alkali metals k and na and enriched in ti and p however the complete data set yields clear evidence that northern african dust and its source sediments are compositionally heterogeneous on a regional scale and that this heterogeneity can be used to differentiate between major potential source areas on the basis of so called source markers an evaluation of these compositional fingerprints shows that the following parameters and especially their combination are effective in the discrimination of the most active source areas in northern africa ratio of ca mg fe wt calcite or carbonate content palygorskite occurrence and abundance illite kaolinite ratio nd 0 value and 87sr 86sr ratio for example the data set corroborates previous ideas which assign carbonate illite and palygorskite rich mineral dusts to north west ern source regions because most of the above listed source markers do not change substantially during transport even far traveled dusts may be assigned to specific potential source areas in northern africa some limitations of the presented data set are also discussed our compilation reveals some substantial gaps in the knowledge of the composition of source sediments and mineral dusts from important potential source areas that should be filled in the future the here compiled data set can be used as a reference frame when incorporating the composition of source sediments e g mineralogy into global or regional dust transport models and can be compared with source analysis by remote sensing or back trajectory analysis however source apportionment studies supported by our data set will not only be useful for actual dust samples but will also be helpful for the understanding of paleo wind directions and hence paleo climatological conditions through the investigation of quaternary eolian sediments deposited in and around northern africa

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

geochemistry and s pb isotope of the yangla copper deposit western yunnan china implication for ore genesis abstract the yangla copper deposit situated in the middle section of jinshajiang tectonic belt between zhongza zhongdian block and changdu simao block is a representative and giant copper deposit that has been discovered in jinshajiang lancangjiang nujiang region in recent years there are coupled relationships between yangla granodiorite and copper mineralization in the yangla copper deposit five molybdenite samples yielded a well constrained 187 re 187 os isochron age of 233 3 3 ma the metallogenesis is therefore slightly younger than the crystallization age of the granodiorite s pb isotopic compositions of the yangla copper deposit indicate that the ore forming materials were derived from the mixture of upper crust and mantle also with the magmatic contributions in the late early permian the jinshajiang oceanic plate was subducted to the west resulting in the formation of a series of gently dipping thrust faults in the jinshajiang tectonic belt meanwhile accompanied magmatic activities in the early late triassic which was a time of transition from collision related compression to extension in the jinshajiang tectonic belt the thrust faults were tensional it would have been a favorable environment for forming ore fluids the ascending magma provided a channel for the ore forming fluid from the mantle wedge after the magma arrived at the base of the early stage yangla granodiorite the platy granodiorite at the base of the body would have shielded the late stage magma from the fluid the magma would have cooled slowly and some of the ore forming fluid in the magma would have entered the gently dipping thrust faults near the yangla granodiorite resulting in mineralization

magma mixing and gold mineralization in the maevatanana gold deposit madagascar abstract the maevatanana gold deposit in madagascar is hosted by archean metamorphic rocks in quartz sulfide veins that are structurally controlled by nnw sse trending shear zones fluid inclusion data show that the trapping conditions in quartz range from 0 87 to 2 58 kbar at temperatures of 269 362 c laser raman spectroscopy confirms that these inclusions consist of co 2 so 2 and h 2 o the 34 s values of the pyrites range from 1 7 to 3 6 with an average of 2 25 supporting a magmatic origin noble gases he ne ar ke xe are chemically inert thus will not be involved in chemical reactions during geological processes also due to the low concentration of he in the atmosphere and the low solubility of he in aqueous fluids the atmosphere derived he is unlikely to significantly affect he abundances and isotopic ratios of crustal fluids ensures that he production should have the typical crust 3 he 4 he ratios the 3 he 4 he ratios of fluid inclusions in pyrite from the deposit range from 0 06 to 0 12 ra while the 40 ar 36 ar ratios range from 6631 to 11441 we infer that the ore forming fluids could have been exsolved from a granitic magma the oxygen and hydrogen isotope compositions of the ore forming fluids 1 5 18 o h2o 7 8 72 d 117 indicate they were derived from a granitic magma four pyrite samples from the gold deposit yield a precise re os isochron age of 534 13 ma given that the post collisional granites in northern and central madagascar were derived by melting of sub continental lithospheric mantle and formed between 537 and 522 ma we can state that the gold metallogenesis was coeval with the crystallization age of these parental magmas these data could be accounted for the formation of the maevatanana gold deposit first the shear zones hosting the deposit formed around 2 5 ga when the madagascan micro continental blocks collided with other continental blocks triggering large scale tectono magmatic activity and forming nnw sse trending shear zones the gold mineralization at maevatanana is coeval with the crystallization age of the cambrian post collisional a type granitoid plutons in northern and central madagascar implying that this deposit is associated with extensional collapse of the east african orogen this extension in turn induced asthenospheric upwelling melting of sub continental lithospheric mantle these magmas underplated the lower crust generating voluminous granitic magmas by partial melting of the lower crust the mixing magma during tectono thermal reactivation of the east african orogen produced large volumes of volatiles that extracted gold from the granitic magma and produced au s complexes e g au hso 3 2 the shear zones which were then placed under extensional collapse of the east african orogen in the cambrian formed favorable pathways for the magmatic ore forming fluids these fluids then precipitated gold sulfides that form the maevatanana gold deposit

micrometer silicon isotope diagnostics of soils by uv femtosecond laser ablation this study presents the first si isotope data of the principle si pools in soils determined by a uv femtosecond laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer mc icp ms this method reveals accurate and precise si isotope data on bulk materials and at high spatial resolution on the mineral scale the following si pools have been investigated a the si source to soils on all major silicate minerals on thin sections from bedrock fragments in the soil profiles b bulk soils particle size 2 mm after fusion to glass beads with an iridium strip heater or pressed into powder pellets c separated clay fractions as pressed powder pellets and e separated phytoliths as pressed powder pellets multiple analyses of three rock standards bhvo 2 agv 1 and rgm 1 as fused glass beads and as pressed powder pellets reveal 30si values within the expected range of igneous rocks the mpi ding reference glass kl2 g exhibits the same si isotope composition after remelting by an iridium strip heater showing that this technique does not alter the isotope composition of the glass we used this approach to investigated two immature cambisols developed on sandstone and paragneiss in the black forest germany respectively bulk soils show a largely uniform si isotope signature for different horizons and locations which is close to those of primary quartz and feldspar with 30si values around 0 4 soil clay formation is associated with limited si mobility which preserves initial si isotope signatures of parental minerals an exception is the organic horizon of the paragneiss catchment where intense weathering leads to a high mobility of si and significant negative isotope signatures as low as to 1 00 in bulk soils biogenic opal in the form of phytoliths exhibits negative si isotope signatures of about 0 4 these results demonstrate that uv femtosecond laser ablation mc icp ms provides a tool to characterize the si isotope signature of the principle si pools left behind after weathering and si transport have altered soils these results can now serve as a fingerprint of the residual solids that can be used to explain the isotope composition of dissolved si in soil solutions and river water which is mostly enriched in the heavy isotopes

possible correlation between a mantle plume and the evolution of paleo tethys jinshajiang ocean evidence from a volcanic rifted margin in the xiaru tuoding area yunnan sw china abstract several paleozoic sutures in southwestern china provide a record of the history of the paleo tethys ocean whose birth and final closure are associated with the breakup and assembly of gondwanaland recent studies indicate that there are widespread oib type mafic volcanic rocks within these suture zones and intervening terranes this paper examines the geology and geochemistry of volcanic rocks in the xiaruo tuoding area a remnant passive margin succession of the jinshajiang paleo tethyan ocean the sedimentary and volcanic stratigraphy of this area is interpreted as a seaward dipping margin with a few continentward dipping normal faults the available geochemistry of these volcanic rocks suggest that they are oib like basalts characterised by sio 2 42 78 50 46 wt high tio 2 contents tio 2 2 2 3 55 wt moderate mgo 4 15 6 49 wt mg 0 37 0 50 high ti y ratios mostly 450 large ion lithosphere elements enrichment high strength field elements and rare earth elements with la nb 1 04 1 39 ce yb 18 38 30 sm yb 2 16 3 52 87 sr 86 sr i 0 705350 0 707867 and nd t 1 43 1 90 these geochemical and isotopic signatures are generally similar to those of the emeishan flood basalts which together with stratigraphic constraints demonstrate that these volcanics were formed in a volcanic rifted margin probably associated with a mantle plume a new model is proposed to interpret the evolution of the jinshajiang paleo tethyan ocean and its possible relationship to the emeishan mantle plume in this model we argue that the opening of the jinshajiang paleo tethyan ocean in the carboniferous was caused by a mantle plume the mantle plume was active to the east along the western margin of the yangtze craton between 300 and 260 ma from which the voluminous emeishan flood basalts were erupted at 260 ma the closure of the jinshajiang ocean occurred since the middle permian continuous westward subduction generated the jiangda weixi magmatic arc to the west of the jinshajiang suture this subduction also partly destroyed and or tectonically sliced the volcanic rifted margin some seaward dipping volcanic sedimentary sequences on the east flank of the jinshajiang ocean were preserved but are strongly deformed

impact of low denudation rates on soil chemical weathering intensity a multiproxy approach abstract quantifying the influence of denudation i e physical erosion and chemical weathering on soil weathering intensity is an important component for a comprehensive understanding of element biogeochemical cycles the relation between the weathering intensity and the denudation rate is not clear and requires further investigation in a variety of climatic and erosional settings here in the betic cordillera southern spain we assess the soil chemical weathering intensity with a multiproxy approach combining different indicators of chemical weathering of the soil the total reserve in bases trb the content in fe oxides the quartz and clay content the soil cation exchange capacity cec and the silicon si isotope composition of the clay sized fraction our multiproxy approach demonstrates that in this semi arid environment at low denudation rates an increasing denudation rate decreases the soil weathering intensity whereas si mobility remains limited our results converge with previous conclusions based on chemical mass balance methods in the same geological setting mass balance methods and particularly chemical depletion fractions cdf are based on the immobility of a refractory element commonly zirconium zr relative to major cations in soils interestingly our study suggests that a weathering index such as the trb may provide a useful complement to assess soil chemical weathering intensity in eroding landscapes where the application of chemical mass balances may be hampered by potential zr mobility in the soil or by heterogeneity of zr concentrations in the bedrock

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

geology fluid inclusions and geochemistry of the zhazixi sb w deposit hunan south china abstract the zhazixi sb w deposit in the xuefeng uplift south china exhibits a unique metal association of w and sb where the w orebodies are hosted by interlayer fractures and the sb orebodies are contained within nw trending faults this study proposes that the w and sb mineralization took place in two separate periods the mineral paragenesis of the w mineralization reveals a mass of quartz scheelite and minor calcite the mineral assemblage of the sb mineralization developed after w mineralization and consists of predominantly quartz and stibnite and small amounts of native sb berthierite chalcostibnite pyrite and chalcopyrite fluid inclusions in quartz and coexisting scheelite are dominated by two phase liquid rich aqueous inclusions at room temperature microthermometric studies suggest that ore forming fluids for w mineralization are characterized by moderate temperatures 170 270 c low salinity 3 7 wt nacl equiv low density 0 75 0 95 g cm 3 and moderate to high pressure 57 2 99 7 mpa and these fluids experienced a cooling and dilution evolution during w mineralization ore forming fluids for sb mineralization are epithermal types with low temperatures 150 230 c low salinity 4 6 wt nacl equiv moderate density 0 82 0 94 g cm 3 and high pressure 42 2 122 5 mpa and these fluids display an evident decline in homogenization temperature during sb mineralization laser raman analyses of the vapor phase indicate that the ore forming fluids for both w and sb mineralization contain a small amount of co 2 the ore forming fluids for sb mineralization are identified as predominantly originating from the continental crust as suggested by the low 3 he values 0 009 10 12 cc stp g and 3 he 4 he ratios 0 002 0 056 ra as well as high 36 ar values 1 93 10 9 cc stp g and 40 ar 36 ar ratios 909 5 2279 7 the source of s is identified to be the neoproterozoic wuqiangxi formation as traced by the 34 s v cdt values of stibnite 3 1 9 4 the 208 pb 204 pb 37 643 40 222 207 pb 204 pb 15 456 15 681 and 206 pb 204 pb 17 093 20 042 ratios suggest a mixture of lower crustal and supracrustal pb sources it is thus concluded that the ore genesis of the zhazixi sb w deposit is related to the intracontinental orogeny during the early mesozoic fluid mixing is considered to be the critical mechanism involved in w mineralization whereas a fluid cooling process is responsible for sb mineralization furthermore the absence of au is attributed to the low a s content in sb mineralizing fluids

zircon u pb ages hf o isotopes and whole rock sr nd pb isotopic geochemistry of granitoids in the jinshajiang suture zone sw china constraints on petrogenesis and tectonic evolution of the paleo tethys ocean the jinshajiang suture zone located in the eastern part of the tethyan tectonic domain is noticeable for a large scale distribution of late jurassic to triassic granitoids these granitoids were genetically related to the evolution of the paleo tethys ocean beiwu linong and lunong granitoids occur in the middle zone of the jinshajiang suture zone and possess similar geochemical features indicating that they share a common magma source sims zircon u pb dating reveals that the beiwu linong and lunong granitic intrusions were emplaced at 233 9 1 4 ma 2 233 1 1 4 ma 2 and 231 0 1 6 ma 2 respectively all of these granitoids are enriched in abundances of si sio2t 65 2 73 5 wt and large ion lithophile elements liles but depleted in high field strength elements contents hfses e g nb ta and ti in addition they have low p2o5 contents 0 06 0 11 wt a cnk values molecular al2o3 cao na2o k2o mostly 1 1 and 10 000 ga al ratios 1 7 2 2 consistent with the characteristics of i type granites in terms of isotopic compositions these granitoids have high initial 87sr 86sr ratios 0 7078 0 7148 pb isotopic compositions 206pb 204pb t 18 213 18 598 207pb 204pb t 15 637 15 730 and 208pb 204pb t 38 323 38 791 zircon 18o values 7 3 9 3 and negative end t values 5 1 to 6 7 suggesting they were predominantly derived from the continental crust their nb ta ratios average value 8 6 are consistent with those of the lower continental crust lcc however variable ehf t values 8 6 to 2 8 and the occurrences of mafic microgranular enclaves mmes suggest that mantle derived melts and lower crustal magmas were involved in the generation of these granitoids moreover the high pb isotopic ratios and elevated zircon 18o values of these rocks indicate a significant contribution of the upper crustal composition we propose a model in which the beiwu linong and lunong granitoids were generated under a late collisional or post collisional setting it is possible that this collision was completed before late triassic decompression induced mantle derived magmas to be underplated and provided the heat for the anatexis of the crust hybrid melts including mantle derived and the lower crustal magmas were then generated the hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rock assimilation such three component mixing magma source and subsequent fractional crystallization could be responsible for the formation of the beiwu linong and lunong granitoids

δ30si systematics in a granitic saprolite puerto rico granite weathering and clay mineral formation impart distinct and interpretable stable si isotope 30 si signatures to their solid and aqueous products within a saprolite clay minerals have 30 si values 2 0 more negative than their parent mineral and the 30 si signature of the bulk solid is determined by the ratio of primary to secondary minerals mineral specific weathering reactions predominate at different depths driving changes in differing 30 si pore water values at the bedrock saprolite interface dissolution of plagioclase and hornblende creates 30 si pore water signatures more positive than granite by up to 1 2 these reactions are the main contributor of si to stream water and determine its 30 si value throughout the saprolite biotite weathering releases si to pore waters but kaolinite overgrowth formation modulates its contribution to pore water si the influence of biotite on 30 si pore water is greatest near the bedrock where biotite derived si mixes with bulk pore water prior to kaolinite formation higher in the saprolite biotite grains have become more isolated by kaolinite overgrowth which consumes biotite derived si that would otherwise influence 30 si pore water because of this isolation which shifts the dominant source of pore water si from biotite to quartz 30 si pore water values are more negative than granite by up to 1 3 near the top of the saprolite

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

mineralogy and genesis of planosols under a semi arid climate borborema plateau ne brazil abstract planosols such as those found on the borborema plateau ne brazil form an important class of moderately weathered soils that support subsistence agriculture in underdeveloped regions of africa asia and south america despite its socioeconomic importance the genesis of this soil class has not yet been fully elucidated this study was conducted with the aim of improving knowledge about the genesis of planosols under a semi arid climate three planosol profiles on the borborema plateau in ne brazil were collected classified and described morphologically and the main physical and chemical attributes the pedogenetic forms of iron oxides and the mineralogical compositions of the sand silt and clay fractions were determined the results indicate that a parent materials richer in feldspar and biotite favor the formation of planosols with a higher clay content b the dissolution of primary minerals and the formation of clay minerals known as the argillation process are fundamental for the genesis of bt horizons c depth drainage deficiency leads to hydromorphism an associated gray color and the formation of mottles and d monosialitization and bisialitization processes kaolinite formation and the formation of 2 1 clay minerals respectively prevail in planosols located within landscape positions that have good and poor drainage respectively in addition the present study shows that planosols under a semi arid climate can have a clay fraction consisting predominantly of kaolinite and mineralogical alteration pathways similar to those described in soils under an analogous climate and geology in northwest africa this refutes classical theories that soils with 2 1 clay minerals prevail in warmer and drier regions this study thus provides greater knowledge about the attributes of planosols in dry and poor regions and can be used as a reference in studies on the sustainable use and management of such soils

simultaneous measurement of sulfur and lead isotopes in sulfides using nanosecond laser ablation coupled with two multi collector inductively coupled plasma mass spectrometers abstract we herein report the coupling of a nanosecond laser ablation system with a large scale multi collector inductively coupled plasma mass spectrometer nu1700 mc icpms np 1700 and a conventional nu plasma ii mc icpms np ii for the simultaneous laser ablation and determination of in situ s and pb isotopic compositions of sulfide minerals we found that the required aerosol distribution between the two spectrometers depended on the pb content of the sample for example for a sulfide containing 100 3000 ppm pb the aerosol was distributed between the np 1700 and the np ii spectrometers in a 1 1 ratio while for lead contents 3000 and

coupling chemical weathering with soil production across soil mantled landscapes soil covered upland landscapes constitute a critical part of the habitable world our understanding of how they evolve as a function of different climatic tectonic and geological regimes is important across a wide range of disciplines and depends in part on understanding the links between chemical and physical weathering processes extensive previous work has shown that soil production rates decrease with increasing soil column thickness but chemical weathering rates were not measured here we examine a granitic soil mantled hillslope at point reyes california where soil production rates were determined using in situ produced cosmogenic nuclides 10be and 26al and we quantify the extent as well as the rates of chemical weathering of the saprolite from beneath soil from across the landscape we collected saprolite samples from the base of soil pits and analysed them for abrasion ph as well as for major and trace elements by x ray fluorescence spectroscopy and for clay mineralogy by x ray diffraction spectroscopy our results show for the first time that chemical weathering rates decrease with increasing soil thickness and account for 13 to 51 per cent of total denudation we also show that spatial variation in chemical weathering appears to be topographically controlled weathering rate decreases with slope across the divergent ridge and increases with upslope contributing area in the convergent swale furthermore to determine the best measure for the extent of saprolite weathering we compared four different chemical weathering indices the vogt ratio the chemical index of alteration cia parker s index and the silicon aluminium ratio with saprolite ph measurements of the cia were the most closely correlated with saprolite ph showing that weathering intensity decreases linearly with an increase in saprolite ph from 4 7 to almost 7 data presented here are among the first to couple directly rates of soil production and chemical weathering with how topography is likely to control weathering at a hillslope scale copyright 2006 john wiley sons ltd

stable silicon isotopes of groundwater feldspars and clay coatings in the navajo sandstone aquifer black mesa arizona usa abstract we present some of the first analyses of the stable isotopic composition of dissolved silicon si in groundwater the groundwater samples were from the navajo sandstone aquifer at black mesa arizona usa and the si isotope composition of detrital feldspars and secondary clay coatings in the aquifer were also analyzed silicon isotope compositions were measured using high resolution multi collector inductively coupled mass spectrometry hr mc icp ms nu1700 nuplasma hr the quartz dominated bulk rock and feldspar separates have similar 30 si of 0 09 0 04 and 0 15 0 04 95 sem respectively and clay separates are isotopically lighter by up to 0 4 compared to the feldspars from isotopic mass balance considerations co existing aqueous fluids should have 30 si values heavier than the primary silicates positive 30 si values were only found in the shallow aquifer where si isotopes are most likely fractionated during the dissolution of feldspars and subsequent formation of clay minerals however 30 si decreases along the flow path from 0 56 to 1 42 representing the most negative dissolved si isotope composition so far found for natural waters we speculate that the enrichment in 28 si is due to dissolution of partly secondary clay minerals and low temperature silcretes in the navajo sandstone the discovery of the large range and systematic shifts of 30 si values along a groundwater flow path illustrates the potential utility of stable si isotopes for deciphering the si cycling in sedimentary basins tracing fluid flow and evaluating global si cycle

the timing origin and t fo2 crystallization conditions of long lived magmatism at the yangla copper deposit sanjiang tethyan orogenic belt implications for post collisional magmatic hydrothermal ore formation abstract an integrated study involving zircon geochronology hf isotopic characteristics and trace elements combined with detailed field investigation was carried out for the felsic magmatic system in the yangla skarn copper deposit area in the sanjiang orogenic belt southwestern china the intrusive units are composed of syn mineralized dioritic enclaves granodiorite quartz monzonite porphyry 238 230 ma and granite stocks and monzogranite dikes 223 ma bracketing a time span of ca 15 myr the uniform hf isotope characteristics during an 15 myr period suggest a primary control of the isotopic signature by a stable long lived hot reservoir in the deep lithosphere the occurrence of mafic enclaves and the identical intermediate initial ehf values 5 9 to 1 7 of granodiorite granite and monzogranite suggest that the felsic magmatic system was produced by remelting of neoproterozoic lower crustal rocks that mixed with minor amounts of mantle derived melts application of comprehensive indices of zircons such as th u zr hf t ti in zircon and ce nd implies that 1 mafic melt injected into felsic magma during the early stage from which the granodiorite and dioritic enclaves formed 2 progressive evolution from granodiorite to quartz monzonite porphyry with addition of crustal components as revealed by the positive correlation between ehf and th u 3 the incorporation of the crustal component into the residual magma from which quartz monzonite porphyry formed reduced the f o2 of the mineralized and barren quartz monzonite porphyry and settled much of dense sulfides out at depth and 4 another discrete reduced magma pulse from which the granite and monzogranite dikes crystallized at slightly higher ti in zircon model temperatures suggesting a slightly more reduced condition of the hidden intrusive portion of magma chamber in general the magmatic system is interpreted to be related to post collisional lithospheric extension after slab break off the cu s and water of the felsic magmas were mainly derived from the recycling of neoproterozoic hydrous arc lower crustal rocks triggered by asthenospheric upwelling

relating the spatial variability of chemical weathering and erosion to geological and topographical zones abstract the relationship between the spatial variability of soil elements weathering and erosion rates can be very complex topography abruptly changing elevation gradients and slopes of varying geological composition exert an important influence on weathering trajectories and erosion this complex interconnectivity is only rarely addressed in weathering studies the main objectives of this investigation are therefore to relate weathering and erosion to various and geomorphic units in a dry alpine and threshold landscape having steep slopes kan catchment tehran province iran a number of common weathering indices were tested using a genetic algorithm the best indices are the k na ti ratio the wip weathering index according to parker and the pi product index according to ruxton however the recently suggested 4si m r2 and m f wmin systems discriminate weathering trends more accurately our results show that these soils have a low to moderate weathering stage weathering trajectories point to the active formation of kaolinite and oxyhydroxides river sediments are slightly more weathered and contain the most weathered topsoils and suggest erosion in the catchment is predominantly due to topsoil removal chemical weathering is influenced by the dominant geomorphic units unconsolidated deposits of the quaternary and solid bedrock and landform features combination of altitude and slope aspect does not appear to have a significant impact on weathering denudation erosion rates were determined using meteoric 10be since the fluvial sediments did not contain enough quartz for in situ 10be analyses this procedure has higher uncertainties due to difficulties in estimating the depositional flux of meteoric 10be due to tectonic uplift the erosion rates are very high to maintain a soil layer soil production rates must be also high although annual precipitation is relatively low slope and soil dynamics seem particularly high which leads to a fast turnover of the soil material and maintains the weathering intensity at a rather low to intermediate level

geochemical evidence for origin of magma mixing for the triassic monzonitic granite and its enclaves at mishuling in the qinling orogen central china abstract whole rock major trace elements and sr nd isotopes mineral chemistry and zircon u pb and lu hf isotope compositions are reported for i type monzogranite and its mafic microgranular enclaves from the triassic mishuling granite in the qinling orogen central china zircon u pb dating yields an age of 212 5 ma for the mafic enclaves and 213 3 ma for the host monzogranite whole rock major trace elements sr nd isotopes and zircon hf isotopes preclude simple crystal fractionation or restite unmixing for a genetic link between the enclaves and the monzogranite mixing between mafic and felsic magmas is compatible with the geochemical data the monzogranite displays an enriched lile and lree pattern high 87sr 86sr i ratios of 0 7068 to 0 7071 and low end t values of 9 2 to 5 7 suggesting a crustal origin its high mg 47 6 to 50 7 cr and ni contents clearly indicate its derivation from mafic refractory lower crust most of the zircons in the monzogranite have negative ehf t values of 12 5 to 0 1 and two stage hf model ages of 1049 to 1683 ma and some zircons in the host monzogranite have positive ehf t values of 0 3 to 4 8 and single stage hf model ages of 665 to 845 ma this indicates that the monzogranite is most likely to be formed by partial melting of a proterozoic lower continental crust the mafic enclaves have fine grained igneous textures and contain abundant acicular apatite that indicates rapid cooling they also have a high 87sr 86sr i ratio of 0 7071 and a low end t value of 6 5 suggesting a derivation from ancient subcontinental lithosphere mantle sclm zircons in the mafic microgranular enclaves have ehf t values of 1 6 to 5 1 and single stage hf model ages of 700 to 910 ma suggesting a possible origin from partial melting of the neoproterozoic sclm that may form in association with contemporaneously supercontinental rifting in the south china block therefore the mishuling i type granite may form by anatexis of meso neoproterozoic lower crust with mixing between the mafic and felsic magmas in particular we interpret the positive ehf t values as being derived from reworking of neoproterozoic juvenile lithosphere in response to tectonic extension in the late stage of the triassic continental collision between the south china block and the north china block

patterns and average rates of late neogene recent uplift of the betic cordillera se spain abstract the facies distribution in the sedimentary units infilling a series of neogene basins has been used to reconstruct the relief generation and uplift across the internal zone of the betic cordillera in southern spain uplift amounts and average rates can be estimated using the current elevation of the outcrops of well dated deposits indicative of ancient sea level positions coral reefs and coastal conglomerates record the initial development of emergent betic relief during the langhian continental and marginal marine deposits indicate the existence of a large island centred on the present sierra nevada sierra de los filabres chain by the end of the middle miocene the precursor of the sierra nevada sierra de los filabres chain originally part of this large island remained emerged whilst the surrounding areas were re invaded by the sea during the early tortonian at the end of the tortonian the inland basins granada and guadix basins became continental while the sierras de la contraviesa sierra de gador and sierra alhamilla emerged separating the alboran basin from the alpujarra tabernas and sorbas basins which became narrow passages of the mediterranean sea in contrast the sierra cabrera emerged during the late messinian suggesting a progressive uplift from west to east of the sierras south of the sierra nevada sierra de los filabres chain during the pliocene only the low areas closest to the present day coast remained as marine basins and progressively emerged throughout this stage the highest average uplift rate recorded is 280 m ma for the sierra de gador although the average uplift rates of upper neogene coastal marine rocks since depositon have maximum values of approximately 200 m ma most of the uplift of the betic mountains took place before the early pliocene the recorded uplift of neogene rocks was highest at the margins of western sierra nevada where peaks higher than 3000 m occur the average rates of uplift were lower to the east of this major relief the main sierras and depressions in the present day landscape correspond respectively to the emergent land in which uplift was concentrated and to the marine basins that existed before the final emergence of the region the altitude of the sierras reflects the time at which they became emergent the highest mountains being the first to rise above sea level

the silicon isotope composition of the upper continental crust the upper continental crust ucc is the major source of silicon si to the oceans and yet its isotopic composition is not well constrained in an effort to investigate the degree of heterogeneity and provide a robust estimate for the average si isotopic composition of the ucc a representative selection of well characterised continentally derived clastic sediments have been analysed using high precision mc icpms analyses of loess samples define a narrow range of si isotopic compositions 30si 0 28 to 0 15 this is thought to reflect the primary igneous mineralogy and predominance of mechanical weathering in the formation of such samples the average loess 30si is 0 22 0 07 2 s d identical to average granite and felsic igneous compositions therefore minor chemical weathering does not resolvably affect bulk rock 30si and loess is a good proxy for the si isotopic composition of unweathered crystalline continental crust the si isotopic compositions of shales display much more variability 30si 0 82 to 0 00 shale si isotope compositions do not correlate well with canonical proxies for chemical weathering such as cia values but do correlate negatively with insoluble element concentrations and al si ratios this implies that more intensive or prolonged chemical weathering of a sedimentary source with attendant desilicification is required before resolvable negative si isotopic fractionation occurs shale 30si values that are more positive than those of felsic igneous rocks most likely indicate the presence of marine derived silica in such samples using the data gathered in this study combined with already published granite si isotope analyses a weighted average composition of 30si 0 25 0 16 2 s d for the ucc has been calculated

post collisional crustal extension setting and vhms mineralization in the jinshajiang orogenic belt southwestern china abstract the jinshajiang orogenic belt job of southwestern china located along the eastern margin of the himalayan tibetan orogen includes a collage of continental blocks joined by paleozoic ophiolitic sutures and permian volcanic arcs three major tectonic stages are recognized based on the volcanic sedimentary sequence and geochemistry of volcanic rocks in the belt westward subduction of the paleozoic jinshajiang oceanic plate at the end of permian resulted in the formation of the chubarong dongzhulin intra oceanic arc and jamda weixi volcanic arc on the eastern margin of the changdu continental block collision between the volcanic arcs and the yangtze continent block during early middle triassic caused the closing of the jinshajiang oceanic basin and the eruption of high si and al potassic rhyolitic rocks along the permian volcanic arc slab breakoff or mountain root delamination under this orogenic belt led to post collisional crustal extension at the end of the triassic forming a series of rift basins on this continental margin arc significant potential for vhms deposits occurs in the submarine volcanic districts of the job mesozoic vhms deposits occur in the post collisional extension environment and cluster in the late triassic rift basins

weak influences of climate and mineral supply rates on chemical erosion rates measurements along two altitudinal transects in the idaho batholith 1 chemical weathering promotes regolith production physical erosion nutrient supply and drawdown of atmospheric co2 although mineral dissolution rates show dependences on temperature and moisture in theoretical models and laboratory experiments effects of climate on chemical erosion rates in nature remain uncertain in part because variations in physical erosion rates and lithology can obscure climatic signals in chemical erosion rate measurements here we present new estimates of millennial scale chemical and physical erosion rates along two altitudinal transects in the idaho batholith our measurements suggest that chemical erosion rates and the extent of regolith chemical alteration are insensitive to mean annual regolith temperature even though the study sites span a wide range in temperatures 4 8 c 10 9 c these data also suggest that rates of chemical erosion and the extent of regolith chemical alteration are weakly correlated with the annual duration of high regolith moisture conditions lastly our measurements show that the sampled regoliths tend to grow more chemically weathered with increasing regolith residence time implying that weathering at these sites is primarily limited by mineral dissolution kinetics rather than mineral supply rates to the regolith the lack of strong control by mineral supply means that chemical erosion rates at these sites could potentially vary in response to climatic factors such climatically driven variation in chemical erosion rates is not obvious in our data however instead our measurements suggest that chemical erosion rates at these sites are insensitive to mean annual regolith temperature and only weakly dependent on the length of the wet season

coupling uranium series and 10be cosmogenic radionuclides to evaluate steady state soil thickness in the betic cordillera abstract on earth the critical zone is the near surface environment where interactions between the atmosphere lithosphere hydrosphere and biosphere take place the development of the regolith mantle is controlled by the downwards propagation of the weathering front into the bedrock and denudation at the surface of the regolith by mass movements water and wind erosion when the removal of surface material is approximately balanced by the production of weatherable material at the bottom of the regolith profile the soil system is assumed to be in steady state although recent literature on chemical weathering often assumes that soils have a steady state thickness the concept has rarely been validated with empirical field data in this study we present and compare analytical data from two independent isotopic techniques in situ produced cosmogenic nuclides and u series disequilibria to constrain soil development under semi arid climatic conditions three soil profiles were sampled across the betic ranges at the ridge crest of zero order catchments with distinct topographic relief hillslope gradient and 10be derived denudation rate soil production rates determined based on u series isotopes 238u 234u 230th and 226ra are of the same order of magnitude as 10be derived denudation rates suggesting steady state soil thickness in two out of three sampling sites our results show the potential of a combined u series disequilibria and in situ 10be isotope approach to evaluate steady state soil thickness our study also illustrates the frontiers in applying u series disequilibria to track soil production in environments characterized by weak soil development

experimental evidence for mobility of zr and other trace elements in soils a soxhlet extraction was carried out over a period of 27 d on a column comprising 3 cm of quartz overlain by 4 cm of soil from the b horizon and then 1 cm of soil from the a horizon of a granitic podzol major and trace elements were leached from the column and accumulated in a reservoir at the base of the column total loss of elements from the soil over the course of the experiment ranged from 0 002 to 1 wt with major elements and the light and heavy rare earth elements ree showing the largest percentage losses zirconium 0 002 and then al 0 008 showed the lowest percentage loss the light ree were leached out of the soil preferentially to the mid ree all elements showed accumulation by a factor of 2 to 11 in the quartz layers at the base of the column particularly in the upper first 1 cm of the quartz major elements were leached from the column at a rate of 0 02 to 0 59 mol h 1 whereas zr nd sm gd dy rb and sr were leached at the rate of 0 5 to 30 10 6 mol h 1 concentrations of other ree in the reservoir increased over the duration of the experiment but they were poorly correlated with time so leaching rates were not calculated normalization of the major element leaching rates to take into account the constant flushing of water through the column the average annual rainfall in the allt a mharcaidh catchment in scotland from where the soil was sampled and the cross sectional area of the soil in the column together with the temperature of the soil in the column 70 c compared with the average annual temperature of the allt a mharcaidh catchment 5 7 c gave major element release rates from the soil of 0 002 to 0 97 meq m 2 yr 1 depending on the choice of ea the dissolution activation energy which are generally less than those measured in the field of 0 1 to 40 9 meq m 2 yr 1 calculations showed that despite the redistribution and loss of zr from the column assumptions of zr mobility would have had a negligible effect on calculated element release rates of na ca fe and mg however significant underestimates of the release of k 5 ti 57 al 5 and si 10 as well as some trace elements e g nd 23 rb 54 sr 24 would have occurred concentrations of ca and sr leached from the column correlated well rsq 0 93 p 0 01 supporting the idea of the use of sr release as a proxy for ca release in weathering rate calculations the release rates and percentage loss of ree from the soil varied between elements indicating that ree distribution patterns of rocks and soils may not be preserved in drainage waters

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

silicon isotopes record dissolution and re precipitation of pedogenic clay minerals in a podzolic soil chronosequence by providing the largest part of the reactive surface area of soils secondary minerals play a major role in terrestrial biogeochemical processes the understanding of the mechanisms governing neo trans formation of pedogenic clay minerals in soils is therefore of the utmost importance to learn how soils evolve and impact the chemistry of elements in terrestrial environments soil forming processes governing the evolution of secondary aluminosilicates in podzols are however still not fully understood the evolution of silicon si isotope signature in the clay fraction of a podzolic soil chronosequence can provide new insight into these processes enabling to trace the source of si in secondary aluminosilicates during podzol forming processes characterized by the mobilization transport and precipitation of carbon metals and si the si isotope compositions in the clay fraction comprised of primary and secondary minerals document an increasing light 28 si enrichment and depletion with soil age respectively in illuvial b horizons and eluvial e horizon the mass balance approach demonstrates that secondary minerals in the topsoil eluvial e horizons are isotopically heavier with 30 si values increasing from 0 39 to 0 64 in c a 200years while secondary minerals in the illuvial bhs horizon are isotopically lighter 30 si 2 31 compared to the original unweathered secondary minerals in bc horizon 30 si 1 40 the evolution of si isotope signatures is explained by the dissolution of pedogenic clay minerals in the topsoil which is a source of light 28 si for the re precipitation of new clay minerals in the subsoil this provides consistent evidence that in strong weathering environment such as encountered in podzols si released from secondary minerals is partially used to form tertiary clay minerals over very short time scales ca 300years our dataset demonstrates the usefulness to measure si isotope signatures in the clay fraction to discern clay mineral changes e g neoformation versus solid state transformation during soil evolution this offers new opportunity to better understand clay mineral genesis under environmental changes and the short term impact of the dissolution and re precipitation of pedogenic clay minerals on soil fertility soil carbon budget and elemental cycles in soil plant systems 2014 elsevier b v

the jinshajiang ailaoshan suture zone china tectonostratigraphy age and evolution abstract the jinshajiang suture zone is important for enhancing our understanding of the evolution of the paleo tethys and its age tectonic setting and relationship to the ailaoshan suture zone have long been controversial based on integrated tectonic biostratigraphic chemostratigraphic and isotope geochronological studies four tectono stratigraphic units can be recognized in the jinshajiang suture zone the eaqing complex the jinshajiang ophiolitic melange the gajinxueshan group and the zhongxinrong group isotope geochronology indicates that the redefined eaqing complex composed of high grade metamorphic rocks might represent the metamorphic basement of the jinshajiang area or a remnant micro continental fragment eaqing complex protolith rocks are pre devonian and probably of early middle proterozoic age and are correlated with those of the ailaoshan complex two zircon u pb ages of 340 3 and 294 3 ma separately dated from the shusong and xuitui plagiogranites within the ophiolitic assemblage indicate that the jinshajiang oceanic lithosphere formed in latest devonian to earliest carboniferous times the oceanic lithosphere was formed in association with the opening and spreading of the jinshajiang oceanic basin and was contiguous and equivalent to the ailaoshan oceanic lithosphere preserved in the shuanggou ophiolitic melange in the ailaoshan suture zone the latter yielded a u pb age of 362 41 ma from plagiogranite the re defined gajinxueshan and zhongxinrong groups are dated as carboniferous to permian and latest permian to middle triassic respectively on the basis of fossils and u pb dating of basic volcanic interbeds the gajinxueshan group formed in bathyal slope to neritic shelf environments and the zhongxinrong group as bathyal to abyssal turbidites in the jinshajiang ailaoshan back arc basin latest permian earliest middle triassic synorogenic granitoids with ages of 238 18 and 227 5 255 8 ma respectively and an upper triassic overlap molasse sequence indicate a middle triassic age for the jinshajiang ailaoshan suture formed by collision of the changdu simao block with south china

chemical weathering response to tectonic forcing a soils perspective from the san gabriel mountains california abstract what controls the chemical weathering of soils in tectonically active landscapes recent field and modeling studies suggest that tectonic forcing and associated increases in erosion rates may either promote or hinder soil chemical weathering these competing trajectories are dependent on two primary controls the availability of fresh minerals and their residence time on the landsurface here we explore rates and extents of soil weathering in the san gabriel mountains of california where previous work has measured clear tectonic fingerprints on rates of long term exhumation hillslope erosion and landscape morphology we quantify chemical weathering across this landscape by elemental analysis of soils saprolites and bedrock on six sites that bracket the low gradient hillslopes of the relict upland plateau and the high gradient hillslopes at the margins of the tectonically driven incising landscape average chemical depletion fractions which measure weathering losses from soil relative to unweathered parent material decrease with increasing elevation and decreasing temperature reflecting a combination of climate influence and potential dust inputs from the mojave desert weathering fluxes from non dust affected sites with similar elevations climates and lithology correlate with both erosion rates and hillslope gradient on low gradient hillslopes 25 weathering intensities and rates both decrease as erosion rates increase and soils thin at the highest denudation rates 300 t km 2 y 1 saprolite production is outpaced and soils are produced directly from fractured rock these patterns are consistent with those predicted by a previously published model for denudation weathering relationships based on mineral weathering kinetics variable weathering extents in soils indicate that weathering in the sgm is largely kinetically limited this study is the first to quantify decreases in both rates and extents of soil chemical weathering with increasing erosion rates and suggests tectonic uplift in rapidly eroding and incising landscapes may not stimulate increased silicate weathering

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

carbon oxygen isotopic geochemistry of the yangla cu skarn deposit sw china implications for the source and evolution of hydrothermal fluids abstract the yangla cu deposit is the largest cu skarn deposit in the jinshajiang tectonic belt based on the detailed observation of crosscutting relationships three mineralization stages i e pre ore ore and supergene have been identified in the yangla deposit the pre ore stage is dominated by prograde skarn the ore stage is characterized by the precipitation of hydrous silicate minerals fe oxides fe cu mo sulfides quartz and calcite whose mineral assemblages were formed in the early and late sub ore stages the early sub ore stage is marked by retrograde alteration with the deposition of hydrous silicate minerals e g actinolite epidote and chlorite fe oxides abundant fe cu mo sulfides quartz and minor calcite whilst the late sub ore stage associated with silicic and carbonate alteration is represented by widespread thick quartz or calcite veins with disseminated pyrite chalcopyrite galena and sphalerite we present new carbon oxygen c o isotopic compositions of the ore hosting marble and hydrothermal calcite of this deposit the hydrothermal calcite in the yangla deposit was precipitated from both the early and late sub ore stages calcite i from the early sub ore stage is anhedral and occurs as spot in the skarn or locally replaces the skarn minerals calcite ii from the late sub ore stage is distinguished by being coarse grained subhedral to euhedral and its occurrence in thick veins calcite i contains lower 13 c pdb 7 0 to 5 0 and 18 o smow 7 2 to 12 7 than calcite ii 13 c pdb 4 5 to 2 3 18 o smow 10 7 to 19 4 in the 13 c pdb vs 18 o smow diagram the calcite i and calcite ii data fall close to the igneous carbonatite field and between the fields of igneous carbonatite and marine carbonates respectively this suggests a dominantly magmatic origin for the early sub ore fluids and there might have been increasing carbonate wall rock involvement towards the late sub ore stage the ore hosting marble 13 c pdb 4 8 to 0 3 18 o smow 10 2 to 23 9 also shows a positive 13 c pdb vs 18 o smow correlation which is interpreted to reflect the decreasing alteration intensity during the interactions between the hydrothermal fluids and ore hosting carbonates simulated calculation suggests that both the calcite i and calcite ii precipitated at 350 c to 250 c and 250 c to 150 c respectively we proposed that co 2 degassing and water rock interactions were likely the two major processes that precipitated the calcite and led to the observed c o isotopic features of the yangla cu deposit

evaluation of laboratory dolomite core sample size using representative elementary volume concepts the adequacy for laboratory testing of four dolomite cores from the culebra dolomite of the rustler formation at the waste isolation pilot plant near carlsbad new mexico were evaluated using representative elementary volume rev theory gamma ray computerized tomography created three dimensional grids of bulk density and macropore index over volumes from 1 4 10 7 to 1 6 l three different methods for both volume averaging and rev analysis were applied and compared both density and macropore index converged to single values with increasing volume which meets the most common qualitative definition of a rev statistical test results for the relatively homogeneous samples indicate that volumes larger than 1 to 7 ml have constant properties contrarily a highly varied sample required 250 and 373 ml to achieve invariant density and macropore characteristics respectively prismatic volume averaging was found to be better than slice averaging while a qualitative test for the rev provided similar results as a rigorous statistical method all cores were larger than the rev but were significantly different from one another this implies that multiple cores are necessary to determine the entire range of transport properties within the rock

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

late triassic granitic magmatism in the eastern qiangtang eastern tibetan plateau geochronology petrogenesis and implications for the tectonic evolution of the paleo tethys abstract triassic granites are widely exposed in the central qiangtang northern tibetan plateau they therefore made an important contribution to the growth of the tibetan plateau in this paper we present zircon u pb dating and hf isotopic results and whole rock elemental and sr nd isotopic analyses of the dongdashan dds batholith in the central qiangtang in order to understand their petrogenesis and tectonic setting la mc icp ms zircon u pb results show that the dds batholith was emplaced at 220 3 0 7 ma all the granites in the dds possess high a cnk values 1 0 and display peraluminous characteristics similar to s type granite their strongly fractionated ree patterns la yb n 6 98 13 9 with conspicuous negative eu anomalies eu eu 0 51 0 67 together with negative e nd t and e nd t values and depleted nd and hf model ages suggest that the dds granitic magma had a dominantly crustal source likely the paleoproterozoic basement i e the ningduo and caoqu group metasediments in the area in combination with regional studies our new geochemical data and geochronological results demonstrate that the late triassic magmatism was generated in a post collisional tectonic setting the spatial distribution pattern of the mesozoic igneous rocks coupled with the exhumation of high pressure metamorphic rocks in the central qiangtang favors a slab breakoff model which resulted in post collisional extension and asthenospheric upwelling that induced large scale partial melting of the middle lower crust to produce voluminous amounts of felsic magma therefore the occurrence of the late triassic post collisional magmatism and particularly the exhumation of high pressure eclogites and blueschists as well as their presence in the lowermost portion of the late triassic volcanoclastics in the qiangtang basin clearly indicate that the final closure of the of paleo tethys ocean and associated continent continent collision between the gondwana derived western qiangtang and eastern qiangtang terranes had not been completed until the early mid triassic

denudation rates and tectonic geomorphology of the spanish betic cordillera abstract the tectonic control on landscape morphology and long term denudation is largely documented for settings with high uplift rates relatively little is known about the rates of geomorphic response in areas of low tectonic uplift here we evaluate spatial variations in denudation of the spanish betic cordillera based on cosmogenic 10be derived denudation rates denudation rates are compared to published data on rock uplift and exhumation of the betic cordillera to evaluate steady state topography the spatial patterns of catchment wide denudation rates n 20 are then analysed together with topographic metrics of hillslope and channel morphology catchments draining the betic ranges have relatively low denudation rates 64 54 mm kyr 1 but also show large variation as they range from 14 to 246 mm kyr 1 catchment wide denudation is linearly proportional to the mean hillslope gradient and local relief despite large spatial variation in denudation the magnitude and spatial pattern of denudation rates are generally consistent with longer term local uplift rates derived from elevated marine deposits fission track measurements and vertical fault slip rates this might be indicative of a steady state topography where rock uplift is balanced by denudation

variations of δ30si and ge si with weathering and biogenic input in tropical basaltic ash soils under monoculture in soils silicon released by mineral weathering can be retrieved from soil solution through clay formation si adsorption onto secondary oxides and plant uptake thereby impacting the si isotopic signature and ge si ratio of dissolved si dsi exported to rivers here we use these proxies to study the contribution of biogenic si bsi in a soil plant system involving basaltic ash soils differing in weathering degree under intensive banana cropping delta si 30 and ge si ratios were determined in bulk soils 2 mm sand 50 2000 mu m silt 2 50 mu m amorphous si asi 2 50 mu m and clay 2 mu m fractions delta si 30 by mc icp ms nu plasma in medium resolution operating in dry plasma with mg doping delta si 30 vs nbs28 0 12 parts per thousand 2 sigma sd ge si computed after determination of ge and si concentrations by hr icp ms and icp aes respectively components of the asi fraction were quantified by microscopic counting phytoliths diatoms ashes compared to fresh ash delta si 30 0 38 parts per thousand ge si 2 21 mu mol mol 1 soil clay fractions 2 mu m were enriched in light si isotopes and ge with increasing weathering degree delta si 30 decreased from 1 19 to 2 37 parts per thousand and ge si increased from 4 10 to 5 25 mu mol mol 1 sand and silt fractions displayed delta si 30 values close to fresh ash 0 33 parts per thousand or higher due to saharian dust quartz deposition whose contribution was evaluated by isotopic mass balance calculation si isotopic signatures of bulk soils 2 mm were strongly governed by the relative proportions of primary and secondary minerals the bulk soil si isotopic budget could be closed indicating that all the phases involved were identified microscopic counting highlighted a surface accumulation of banana phytoliths and a stable phytolith pool from previous forested vegetation delta si 30 and ge si values of clay fractions in poorly developed volcanic soils isotopically heavier and ge depleted in surface horizons support the occurrence of a dsi source from banana phytolith dissolution available for si sequestration in clay sized secondary minerals clay minerals formation and si adsorption onto fe oxide in the soil plant system delta si 30 and ge si are thus highly relevant to trace weathering and input of dsi from phytoliths in secondary minerals although not quantifying the net input of bsi to dsi c 2009 elsevier ltd all rights reserved

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

silicon isotopes and the tracing of desilication in volcanic soil weathering sequences guadeloupe abstract silicon si stable isotopes have the potential to become a useful weathering proxy given that light si isotopes are preferentially incorporated into secondary clay minerals here we investigate how si depletion in soils and associated clay mineralogy influence the si isotope fractionation associated with clay mineral formation we report 30 si compositions in bulk soils and clay fractions relative to their parent andesite in three soil weathering sequences from guadeloupe that were formed under contrasting climatic conditions strongly desilicated soils containing kaolinite that formed in wet areas high precipitation are compared with less desilicated soils containing smectite formed in drier conditions low precipitation clay fractions are isotopically lighter than the parent andesite 30 si 0 23 and increasingly lighter with si depletion in soils which supports the view that the si isotope composition in secondary clay fractions is controlled by the degree of soil desilication it is shown that the si isotope fractionation factor between the parent silicate material and the secondary clay minerals is smaller for si rich secondary clay minerals such as smectite and larger for si poor secondary clay minerals such as kaolinite this study provides new insights to better define si isotopes as a proxy for environmental conditions for clay neoformation

mantle contributions to crustal thickening during continental collision evidence from cenozoic igneous rocks in southern tibet the tibetan crust is twice as thick as average continental crust crustal compression and shortening as a result of indian asian collision isoftenconsideredtobetheprimarycauseforthecrustalthickening inthispaper weshowthatmagmaticcontributionisalsoimportant we come to this conclusion by documenting the paleogene linzizong volcanic succession lvs its coeval granitoid batholiths and the miocene adakitic rocks along the gangdese magmatic belt in southern tibet it has been widely accepted that the indian asian collision proceeded from a soft phase at 65 70 ma to a hard phase at 45 40 ma followed by continued post collisional convergence to the present in response to the collision and post collision convergence are a series of tectono magmatic events recorded in the gangdese magmaticbelt theseinclude 1 thesyn collisionallvsvolcanism 65 40ma andtheemplacementofsoutherngangdesebatholiths a peakageof 50ma 2 aperiod 40mato25ma thatismagmaticallyquiescent yettectonicallydominatedbyactivecompressionand crustal shortening and 3 the emplacements of post collisional adakitic rocks 25 12 ma potassic ultrapotassic volcanics 25 10 ma and peraluminous muscovite bearing granites between 24 and 18 ma these three major events contribute in different ways to the crustal thickness phase i formation of the lower juvenile crust from 65 ma to 50 ma with crustal thickening largely concentrated at 50 40maviainputofmantle derivedmagmas phaseii crustalthickeningbytectonicshorteningat 40 25ma andphaseiii retaining crustal thickness but thinning of the lithospheric mantle since 25 ma in response to crustal extension and upwelling and lateral flow of asthenosphericmantle weemphasizethatcollision inducedcrustalthickeningtookplacemainlyintheperiodof 50 40maand 25ma i e the period between the late stage of the lvs volcanism and the beginning of the adakitic rock emplacement most of the lvs rocks and the collision related granitoids in southern gangdese have end 0 attesting to the significance of mantle input most likely through remelting of mantle derived basaltic rocks including the subducted neo tethyan ocean crust the petrologic and geochemical characteristics of the miocene potassic adakitic rocks support the idea that the lower portion of the thickened tibetan crust is mafic and is genetically associated with the earlier lvs magmatism we estimate that the mantle material input contributed about 30 of the total thickness of the present day tibetan crust by assuming a pre collision crustal thickness of 35 km then the tectonic contribution would be about 20 km

yttrium the immobility mobility transition during basaltic weathering trace elements have been used as provenance indicators of igneous rocks for many years even though the conditions under which they remain immobile during subaerial weathering have not been thoroughly defined we have used a novel geochemical and quantitative mineralogical data set of variably weathered basaltic rocks from northeast ireland to investigate the immobility of various elements titanium and niobium seem to be the most immobile of all elements relative to these elements zirconium is predominantly depleted but is also locally enriched yttrium displays a marked depletion from the early stages of weathering during the growth of clay minerals yttrium zirconium and their ratios with other elements should thus be used with caution as provenance indicators unless the rocks show no detectable signs of weathering

the silicon isotopic composition of fine grained river sediments and its relation to climate and lithology abstract the 30si stable isotopic composition of silicon in soils and fine grained sediments can provide insights into weathering processes on continents with important implications on the si budget of modern and past oceans to further constrain the factors controlling the distribution of si isotopes in sediments we have analysed a large number n 50 of separate size fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide this includes some of the world s largest rivers e g amazon congo mackenzie mississippi murray darling nile yangtze and rivers from the case study areas of the congo river basin and northern ireland silt size fractions exhibit a mean si isotopic composition 30si 0 21 0 19 2 s d similar to that previously inferred for the upper continental crust in contrast clay size fractions display a much larger range of 30si values from 0 11 to 2 16 which yield a global 30siclay of 0 57 0 60 2 s d representative of the mean composition of the average weathered continental crust overall these new data show that the si isotopic signature transported by river clays is controlled by the degree of chemical weathering as inferred from strong relationships with al si ratios at a global scale the clay bound si isotopic composition of the world s largest river systems demonstrates a link with climate defining a general correlation with mean annual temperature mat in corresponding drainage basins while the distribution of si isotopes in river sediments also appears to be influenced by the tectonic setting lithological effects and sediment recycling from former sedimentary cycles our results pave the way for their use as paleo weathering and paleo climate proxies in the sedimentary record

quantifying representative elementary volume of connectivity for translucent granular materials by light transmission micro tomography aquifers composed of granular materials are major repositories of groundwater resource in which water can flow freely and be stored abundantly undoubtedly exploring connectivity of granular materials is essential to understand the mechanism of water and contaminant migration in subsurface environment while characterizing the connectivity remains a difficult task currently this study proposes a new light transmission micro tomography ltm with high resolution to address this problem the new approach relies on scanning micro structure by light transmission through translucent granular materials in given thickness an experiment of light transmission through a two dimensional 2d sandbox packed by heterogeneous translucent silica is conducted to examine the efficiency of ltm in capturing all the features of connectivity including porosity n density solid phase pores interface area asp and tortuosity considering the importance of representative elementary volume rev in characterizing the representativeness and reliability of connectivity associated rev scales of characteristic variables are also estimated using a criterion of relative gradient error egi results suggest that the frequencies of minimum rev sizes of connectivity are close to gaussian distribution in 0 0 12 0 mm and the rev size of approximately 10 0 mm is available to represent connectivity of translucent silica then the quantification of connectivity and the corresponding rev estimates are significant for accurate simulation of fluid migration and for associated optimal design of contaminant remediation in subsurface environment more important this study provides the possibility of rapid handy and economical on site measurements of connectivity for translucent materials

lithium magnesium and silicon isotope behaviour accompanying weathering in a basaltic soil and pore water profile in iceland this study presents lithium magnesium and silicon isotope ratios from pore waters and soils from a well characterised histic andosol in south west iceland the soil 7li composition ranges between values slightly lighter than basalt to those that are much heavier 1 1 to 26 8 and are possibly influenced by sea salt in contrast precipitation corrected dissolved pore water 7li values 1 8 10 0 appear to reflect preferential adsorption of 6li onto secondary minerals where allophane supersaturation results in high 7li values conversely low 7li together with high li are probably due to destabilisation of allophane at low ph and thus desorption of li when compared to icelandic river values it would appear that soil pore waters reflect an intermediate isotope composition between basalts and river waters precipitation corrected pore water mg isotope ratios 26mg range between 0 46 and 0 12 and correlate with the amount of heavy mg adsorbed onto the soil exchange complex silicon isotopes in the soils are isotopically lighter 30si 0 91 to 0 53 than basalt 0 29 whereas pore waters are heavier 0 13 to 1 03 soil 30si values show a clear evolution between unweathered basalt and a hypothetical isotopically light endmember representing secondary minerals dissolved si isotopes also respond to chemical weathering processes and show that isotopically heavy 30si corresponds to high cation fluxes and high secondary mineral formation however comparison of all these proposed isotopic weathering tracers suggests that they respond differently to the same chemical weathering conditions this indicates a differing behaviour during secondary mineral neoformation or adsorption depending on whether the incorporated element is a major or trace constituent in turn this behaviour can potentially yield important information on secondary mineral behaviour and destabilisation and thus on the chemical weathering processes

constraining models of the tectonic setting of the giant olympic dam iron oxide copper gold deposit south australia using deep seismic reflection data abstract in the gawler craton the completeness of cover concealing the crystalline basement in the region of the giant olympic dam cu au deposit has impeded any sufficient understanding of the crustal architecture and tectonic setting of its iocg mineral system to circumvent this problem deep seismic reflection data were recently acquired from 250 line km of two intersecting traverses centered on the olympic dam deposit the data were recorded to 18 s twt 55 km the crust consists of neoproterozoic cover in places more than 5 km thick over crystalline basement with the moho at depths of 13 14 s twt 40 42 km the olympic dam deposit lies on the boundary between two distinct pieces of crust one interpreted as the archean paleoproterozoic core to the craton the other as a meso neoproterozoic mobile belt the host to the deposit a member of the 1590 ma hiltaba suite of granites is situated above a zone of reduced impedance contrast in the lower crust which we interpret to be source region for its 1000 c magma the crystalline basement is dominated by thrusts this contrasts with widely held models for the tectonic setting of olympic dam which predict extension associated with heat from the mantle producing the high temperatures required to generate the hiltaba suite granites implicated in mineralization we use the seismic data to test four hypotheses for this heat source mantle underplating a mantle plume lithospheric extension and radioactive heating in the lower crust we reject the first three hypotheses the data cannot be used to reject or confirm the fourth hypothesis

in situ stress conditions at iodp site c0002 reflecting the tectonic evolution of the sedimentary system near the seaward edge of the kumano basin offshore from sw japan this paper presents a complete set of in situ stress calculations for depths of 200 1400 mbsf meters below seafloor at iodp site c0002 near the seaward margin of the kumano forearc basin offshore from southwest japan the vertical stress component was obtained by integrating bulk density calculations from moisture and density logging data and the two horizontal components were stochastically optimized by minimizing misfits between a probabilistic model and measured breakout widths for every 30 m vertical segment of the wellbore our stochastic optimization process reveals that the in situ stress regime is decoupled across an unconformity between an accretionary complex and the overlying kumano forearc basin the stress condition above the unconformity is close to the critical condition for normal faulting while below the unconformity the geologic system is stable in a normal to strike slip fault stress regime the critical state of stress demonstrates that the tectonic evolution of the sedimentary system has been achieved mainly by the regionally continuous action of a major out of sequence thrust fault during sedimentation in the forearc basin the stable stress condition in the accretionary prism is interpreted to have resulted from mechanical decoupling by the accommodation of large displacement along the megasplay fault

geological and geochemical constraints on the genesis of the huachanggou gold deposit western qinling region central china the huachanggou gold deposit is located in lueyang county shaanxi province central china it is situated in the mian lue sutural zone in the western qinling orogen and controlled by a wnw striking ductile shear zone the ore deposit is developed in spilite limestone and phyllite in the middle lower devonian sanhekou group and the wall rocks show evidence of deformation pyrite is the main gold bearing mineral and the native gold is either visible or microscopic the huachanggou gold deposit is considered to be an orogenic gold deposit controlled by a ductile shear zone related to the indosinian qinling orogenic event the ores show a strong enrichment in au ag and as but exhibit a simple assemblage of au and ag that are strongly correlated together gold was deposited from a moderate to low salinity salt solution co2 hydrothermal fluid at medium temperature variations in s pb c and o isotopic composition indicate that the sulfur was derived from the reduction of seawater sulfate in the wall rocks the lead was derived mainly from the wall rocks the carbon was derived from the dissolution of marine carbonate the variations in h and o isotopic composition indicate that the ore forming fluids were derived originally from metamorphic fluid with meteoric water mixing in later stages au migrated mainly in the form of au hs 2 to form the deposit boiling of the fluid triggered the precipitation of the metal sulfides that contain the gold

simulation of dnapl migration in heterogeneous translucent porous media based on estimation of representative elementary volume when the dense nonaqueous phase liquid dnapl comes into the subsurface environment its migration behavior is crucially affected by the permeability and entry pressure of subsurface porous media a prerequisite for accurately simulating dnapl migration in aquifers is then the determination of the permeability entry pressure and corresponding representative elementary volumes rev of porous media however the permeability entry pressure and corresponding representative elementary volumes rev are hard to determine clearly this study utilizes the light transmission micro tomography ltm method to determine the permeability and entry pressure of two dimensional 2d translucent porous media and integrates the ltm with a criterion of relative gradient error to quantify the corresponding rev of porous media as a result the dnapl migration in porous media might be accurately simulated by discretizing the model at the rev dimension to validate the quantification methods an experiment of perchloroethylene pce migration is conducted in a two dimensional heterogeneous bench scale aquifer cell based on the quantifications of permeability entry pressure and rev scales of 2d porous media determined by the ltm and relative gradient error different models with different sizes of discretization grid are used to simulate the pce migration it is shown that the model based on rev size agrees well with the experimental results over the entire migration period including calibration verification and validation processes this helps to better understand the microstructures of porous media and achieve accurately simulating dnapl migration in aquifers based on the rev estimation

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

the silicon isotope composition of granites because weathering results in preferential incorporation of the lighter si isotopes into clay minerals the si in magmas derived from meta sedimentary lithologies enriched in such phases should also be isotopically light relative to melts derived from igneous sources with the advent of new high precision techniques it should therefore be possible to resolve such differences hence si isotopes have to potential to distinguish between and characterise different magmatic source regions to explore this here we report the si isotopic compositions of a suite of phanerozoic i s and a type granites and mineral separates as well as samples of associated country rock the whole rock data fall between 30si 0 40 and 0 11 0 04 95 s e this range is more limited than that defined by previous low precision measurements of granites but is significantly broader than that displayed by more recent high precision measurements of high si extrusive igneous rocks as predicted s type granites are on average isotopically lighter than i and a type samples and negative correlations with alumina saturation index asi values and initial 87sr 86sr provide evidence that si isotope variations in granites can be explained by variable incorporation of an enriched sedimentary component however the relatively small isotopic perturbations and apparent degree of overlap between granite affinities suggest that si isotopes are not as sensitive to sedimentary input relative to more established proxies such as for example o isotopes the average si isotope value of all granites analysed in this study is 30si 0 23 0 15 2 s d which is entirely consistent with a recently published estimate for the continental crust based on an andesitic bulk composition and the well defined relationship between si isotopes and magmatic fractionation

silicon isotopes in 3 8 ga west greenland rocks as clues to the eoarchaean supracrustal si cycle we report mc icp ms si isotopic measurements 29si recalculated as 30si on micro subsamples at 500 m scale from several major rock types of the 3 8 ga old isua greenstone belt igb southern west greenland and surrounding eoarchaean terrains with a large overall range of variations 2 80 30si 0 68 they demonstrate strong involvement of surface fluids enriched with dissolved si the resistance of si isotopes to metamorphic resettings and metasomatic overprints is also established metabasaltic pillows and metasediments display similar 30si enriched signatures suggesting that emergent surfaces of the eoarchaean protocrust were composed of slightly weathered hydrothermally altered mafic ultramafic bodies isua magnetite quartz banded iron formation bif is strongly depleted in 30si relative to all coeval rocks this depletion supports rayleigh controlled precipitation from seafloor vented hydrothermal fluids in contrast banded quartz pyroxene rocks from akilia island some 150 km southwest of the igb which some authors have identified as bif related yield quartz with si isotopic composition 30si 0 36 similar to metamorphic derived quartz 30si 0 50 this supports their derivation from tectonic reworking of ultramafic protoliths penetrated by metamorphic silica and is at variance with their proposed role as harboring earliest biogenic tracers

redistribution and mobilization of titanium zirconium and thorium in an intensely weathered lateritic profile in western australia abstract the mobility of titanium zirconium and thorium elements commonly considered insoluble during supergene weathering is still not well understood especially in intensely weathered regolith thus an intensely weathered lateritic profile jg developed on meta granitoids in jarrahdale western australia was investigated the mobility of ti zr and th has been assessed at both mineral assemblage and profile scales and the mode of occurrence has been investigated through the combined use of geochemical data from bulk regolith particle size fractions and sequential extractions with in situ data determined by electron probe micro analyzer and synchrotron x ray powder diffraction neoformed poorly crystalline phases containing trace to minor amounts of zr ce and th unassociated with silicates or phosphates were identified on the walls of al fe rich pores in the ferruginous duricrust this implies that some mobilization and redistribution of zr and th occurs within a sample scale breakdown of primary thorite and rare earth element rich fluorocarbonates is thought to be the source for zr and th in the neoformed phases rather than zircon thus the mineral hosts of zr ti and th in the parent rock and their relative susceptibility to weathering are the fundamental controls on subsequent mobility during initial weathering trace amounts of th in secondary phases such as rhabdophane and florencite show translocation of th at the mineral scale while strong partitioning of th into gravel rather than matrix reflects redistribution of th at the profile scale the absence of primary sphene from the regolith and the presence of partially dissolved ilmenite and rutile grains in the ferruginous mottled zone suggest mobilization and translocation of ti at a mineral assemblage scale furthermore the fluctuation of ti zr in the ferruginous zone is in contrast to the consistency of zr hf throughout the profile in general within the range of parent meta granitoid this suggests that ti and zr fractionate from each other and partition between gravel and matrix during extreme weathering and advanced lateritization this study demonstrates that ti zr and th are mobile at a variety of scales an important consideration that is often overlooked when calculating element mass flux in intensely weathered regolith