crustal anisotropy from tectonic tremor under washington state in the cascadia we present new observations of crustal shear wave anisotropy extracted from nonvolcanic tremor in cascadia under washington state measurements of crustal anisotropy are extremely sparse and limited in this area mainly due to low level of seismicity abundance of tremor activity during slow earthquakes offers a unique opportunity to measure anisotropy parameters of the continental crust using tremor signal to accomplish this polarization and splitting analyses of nonvolcanic tremor are performed using three component broadband seismic stations splitting times measurements range between 0 08 and 0 17 s and similar to the splitting magnitude typically observed in the continental crust fast direction of shear wave anisotropy generally trends ese wnw fast polarization directions are in general perpendicular to the prevailing maximum compressive stress field but tend to be parallel to several mapped ew and ese wnw trending faults in this area the observed spatial pattern of anisotropy is likely controlled by faulting that accommodates ns compression resulting from the tectonic movement of the oregon block toward north existence of several ew trending crustal faults and source parameters of crustal earthquakes at depth consistent with the regional stress regime indicate that these faults may be the dominant factor causing the observed pattern of shear wave anisotropy

top bottom soil ratios and enrichment factors what do they really show abstract high top bottom soil ratios or high values of enrichment factors efs are used as a proof for major anthropogenic impact on the geochemistry of the earth surface the idea behind calculating such ratios is that soils taken at depth or average crust can provide the geochemical background for the soils collected at the earth surface however a soil profile is not a closed system element exchange between the different layers depending on and varying with the chemical properties of the different elements and their turnover in the biosphere is the essence of soil formation high top bottom soil ratios or efs may thus highlight the geochemical de coupling of the lithosphere from the biosphere rather than contamination this is demonstrated by using regional data from 258 soil o and b horizon samples collected from the czech republic 76 800 km2 results show no relationship between the ratios and the magnitude of anthropogenic emissions the visible relationship between element concentrations and sources in a map of the spatial distribution of the elements is lost when maps for the top bottom soil ratio or efs are constructed the value of the data lies in the spatial elemental distribution and not in ratios calculated based on misconceptions

crustal anisotropy in southern california from local earthquake data 1 shear wave splitting measurements were made for local earthquakes in southern california at incidence angles larger than the critical incidence angle for the region of san bernardino mountains the fast polarization directions vary strongly but are consistently fast for directions roughly perpendicular to the ray paths this observation is most readily explained by transverse isotropy with a vertical symmetry axis and is probably associated with horizontally foliated gneisses or schists in the upper crust other measurements show a predominance of north south fast directions while some data have fast directions that are parallel to the san andreas fault these observations are related to azimuthal anisotropy as found in other local shear wave splitting and sks splitting studies the data show that apart from the free surface effect shear wave splitting measurements for shear waves at shallow incidence angles can have an imprint of transverse isotropy as well as azimuthal anisotropy

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

anisotropy of schists contribution of crustal anisotropy to active source seismic experiments and shear wave splitting observations we have made sets of five independent compressional and shear wave velocity measurements which with density allow us to completely characterize the transverse isotropy of samples from five metamorphic belts the haast schist terrane south island new zealand poultney slate chugach phyllite coldfoot schist and pelona schist united states these velocity measurements include compressional wave velocities for propagation parallel perpendicular and at 45 to the symmetry axis shear wave velocity for propagation and particle motion perpendicular to the symmetry axis and shear wave velocity for propagation parallel to the symmetry axis velocity measurements were made up to pressures of 1 gpa 35 km depth where microcracks are closed and anisotropy is due to preferred mineral orientation our samples exhibit compressional wave anisotropy of 9 20 as well as significant shear wave splitting metamorphic terranes that are anisotropic to ultrasonic waves may also be anisotropic at the scale of active and passive seismic experiments our data suggest that a significant thickness 10 20 km of appropriately oriented steeply dipping foliation schist in the crust could contribute as much as 45 of observed shear wave splitting our data set can also be used to model the effects of crustal anisotropy for active source seismic experiments in order to determine if the anisotropy of the terrane is significant and needs to be taken into account during processing and modeling of the data

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

neoproterozoic granitoid in northwest sulu and its bearing on the north china south china blocks boundary in east china 1 middle neoproterozoic granitoid rocks are found in the wulian region that is located in the northwestern part of the sulu orogen and is approximately bounded by the wulian yantai fault in southeast zircon u pb dating yields concordant ages of 738 10 to 758 5 ma for three granites and one gabbro hornblende ar ar dating on the gabbro gives consistent plateau and isochron ages of 719 1 3 7 and 717 9 7 2 ma respectively this suggests that the wulian granitoids correspond to bimodal magmatism during the mid neoproterozoic in the northern margin of the south china block in response to the breakup of rodinia supercontinent they were tectonic slices scraped off from the upper part of the south china block during the triassic continental subduction this demonstrates that the suture location between the north china block and the south china block lies north of the wulian and penglai groups rather than along the wulian yantai fault that marks the northern margin of ultrahigh pressure metamorphic belt

distribution of rb ga and cs in agricultural land soils at european continental scale gemas implications for weathering conditions and provenance abstract agricultural soil ap horizon 0 20 cm samples were collected from a large part of europe 33 countries 5 6 million km2 as part of the gemas geochemical mapping of agricultural and grazing land soil soil mapping project the soil data have been used to provide a general view of element mobility and source rocks at the continental scale either by reference to average crustal abundances or to normalised patterns of element mobility during weathering processes the survey area includes a diverse group of soil parent materials with varying geological history a wide range of climate zones and landscapes total concentrations of rb ga and cs in european soil were determined by xrf x ray fluorescence spectrometry in addition hot aqua regia available element concentrations were analysed by inductively coupled plasma mass spectrometry icp ms their spatial distribution patterns are shown in geochemical maps the spatial distribution of rb ga and cs in ap soil is quite comparable for the aqua regia and xrf results the cs spatial pattern reflects best the large difference between trace element concentrations in northern europe with predominantly low concentrations and southern europe with approximately two times higher values the maximum extent of the last glaciation is visible as a clear concentration break on the map lithology of the underlying bedrock is inferred as the major source of geochemical anomalies in search for characterising the soil parent material and degree of weathering the soil data were examined for ga and cs using two methods first the estimated degree of extractability dei of an element in a sample was calculated by dividing aqua regia available concentrations by the total concentrations obtained by xrf analysis for al na ca k rb ga and cs the different dei were investigated for 10 geological parent material subgroups alkaline rocks granite calcareous rocks basalt mafic rocks unclassified lithologies precambrian granitic gneiss bedrocks loess organic soils schist and soil developed on coarse grained sandy deposits the role of clay as main carrier of ga and cs phases was inferred for soils developed on several types of bedrock such as granite gneiss and alkaline rocks additionally an affinity of cs for loess and carbonate rocks has been observed

crustal anisotropy in a subduction zone forearc northern cascadia s wave splitting analyses using low frequency earthquake templates at three component stations across southern vancouver island and northern washington indicate the presence of a heterogeneous distribution of crustal anisotropy in the north american plate for southern vancouver island we investigate contributions to anisotropy from the leech river complex a terrane composed of strongly foliated phyllites and schists with steeply dipping foliations striking east west fast directions across mainland southern vancouver island are subparallel to the dominant leech river complex foliation direction east to west increases in delay times and small scale azimuthal variations in fast directions indicate heterogeneous anisotropy we test azimuthally anisotropic leech river complex models constrained by previous geological and seismic reflection studies through forward modeling using 3 d spectral element method simulations the preferred model of a north northeast shallowly dipping wedge of leech river complex material with varying orientation of anisotropy terminating at midcrustal levels explains the splitting observations at a majority of southern vancouver island stations for stations where anisotropic leech river complex models do not recreate observations fast directions are subparallel to local estimates of maximum compressive horizontal stress suggesting that fluid filled cracks could be a source of anisotropy we assert that the leech river complex is the primary source of crustal anisotropy beneath southern vancouver island not cracks as suggested by prior studies fast directions at stations on northern washington exhibit variations with azimuth and incidence angle suggesting complex anisotropy interpreted as due to a combination of cracks and preferred mineral orientation of metamorphosed slates of the olympic core rocks these slates may also underlay stations on southern vancouver island and represent another source of anisotropy

mapping crustal stress and strain in southwest british columbia 1 this paper investigates the orientation and sources of stress in the forearc of the cascadia subduction zone in southwest british columbia using bayesian inversion results from focal mechanism data and comparing results with gps derived short term strain rates the subduction margin in this region includes a change in orientation from n s in washington state to nw se in british columbia over 1000 focal mechanisms from north american crustal earthquakes have been calculated to identify the dominant style of faulting and 600 were inverted to estimate the principal stress orientations and the stress ratio our results indicate the maximum horizontal compressive stress orientation changes with distance to the trench from approximately margin normal along the coast to approximately margin parallel 100 150 km inland from the coast comparing stress orientations with gps data we relate the margin normal stress direction to subduction related strain rates due to the locked interface between the north american and juan de fuca plates just west of vancouver island further from the margin the plates are coupled less strongly and the margin parallel maximum horizontal compressive stress in the north american plate relates to the northward push of the oregon block which is also observed in the horizontal shortening direction of the residual strain rates after the subduction component is removed

investigating high zircon concentrations in the fine fraction of stream sediments draining the pan african dahomeyan terrane in nigeria sixteen hundred stream sediments 150 m fraction collected during regional geochemical surveys in central and sw nigeria have high median and maximum concentrations of zr that exceed corresponding zr concentrations found in stream sediments collected from elsewhere in the world with similar bedrock geology x ray diffraction studies on a sub set of the analysed stream sediments showed that zr is predominantly found in detrital zircon grains however the main proximal source rocks pan african older granites of nigeria and their proterozoic migmatitic gneiss country rocks are not enriched in zircon or zr nevertheless u pb la icp ms dating with cathodoluminescence imaging on detrital zircons both from stream sediment samples and underlying pan african older granites confirms a local bedrock source for the stream sediment zircons a combination of tropical chemical weathering and continuous physical weathering both by wet season flash flooding and dry season unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases thereby increasing the zr contents in stream sediments the strong correlation between winnowing index th al and zr concentration across the study area support this interpretation therefore anomalous high values of zr as well as other elements concentrated in resistant heavy minerals in nigeria s streams may not reflect proximal bedrock concentrations of these elements this conclusion has important implications for using stream sediment chemistry as an exploration tool in nigeria for primary metal deposits associated with heavy minerals

tectonic sediment thickening fluid expulsion and the thermal regime of subduction zone accretionary prisms the cascadia margin off vancouver island tectonic sediment thickening fluid expulsion and the resulting thermal regime of the northern cascadia subduction zone accretionary prism have been described by numerical models both the sediment thickening and the fluid expulsion are found to have important thermal effects constraints on the models are provided by 1 detailed heat flow profiles across the continental slope accretion zone from variations in the thermally controlled depth to a gas hydrate bottom simulating reflector bsr and 2 porosity changes across the accretion zone inferred from the landward variation in the p wave velocity depth profiles the heat flow in the region of rapid prism thickening centered 15 km landward of the deformation front is 20 below that predicted by a larger scale thermal model that ignores the thermal effects of the sediment accretion processes the porosity also is substantially higher in this region compared to at the same depths in the adjacent deep sea cascadia basin the model results are in agreement with both the thermal and velocity data if the incoming sediment section is initially simply tectonically shortened horizontally and thickened vertically generating a high porosity underconsolidated section reconsolidation and fluid expulsion in response to the tectonic thickening is slow occurring mainly 20 30 km landward of the deformation front the maximum predicted fluid expulsion rate is about 4 10 11 m s 1 1 3 mm a 1 the pore pressure distribution across the deformation front region has been estimated from the velocity data using the simplifying assumption that velocity is only a function of effective pressure pore pressures are high reaching 80 of lithostatic 15 to 20 km landward of the deformation front an estimate of the bulk permeability in the seaward tens of kilometers of the prism ranging from 10 16 m2 near the top to about 10 18 m2 near the base has been obtained through matching the pore pressure distribution in the numerical model to that obtained from the velocity data the prism sediments are inferred to be substantially underconsolidated and pore pressures to be high for at least the seaward 30 km of the accretionary prism

shear wave splitting of the 2009 l aquila seismic sequence fluid saturated microcracks and crustal fractures in the abruzzi region central apennines italy

lead and lead isotopes in agricultural soils of europe the continental perspective abstract lead isotopes are widely used for age dating for tracking sources of melts sediments pb products food and animals and for studying atmospheric pb contamination for the first time a map of a pb isotope landscape at the continental scale is presented agricultural soil samples ap horizon 0 20 cm collected at an average density of 1 site 2500 km2 were analysed for pb concentration and pb isotopes 206pb 207pb 208pb lead concentrations vary from 1 6 to 1309 mg kg with a median of 16 mg kg isotopic ratios of 206pb 207pb range from 1 116 to 1 727 with a median of 1 202 the new data define the soil geochemical pb background for european agricultural soil providing crucial information for geological environmental and forensic sciences public health environmental policy and mineral exploration the european continental scale patterns of pb concentrations and pb isotopes show a high variability dominated by geology and influenced by climate lead concentration anomalies mark most of the known mineralised areas throughout europe some local pb anomalies have a distinct anthropogenic origin

trace elements in soils developed in sedimentary materials from northern france abstract a pedo geochemical survey was carried out in the nord pas de calais region france on soils developed in sedimentary materials to estimate their baseline geochemistry and the effect of selected factors on it total concentrations of al fe and 18 trace elements as well as common soil characteristics were determined in samples from 271 surface and 487 deep horizons developed in 22 sedimentary rocks and superficial deposits compared with the upper continental crust the parent materials are enriched with most of the trace elements particularly with as cd sb and se and are impoverished in cu calcareous rocks from the carboniferous cretaceous and jurassic eras are often enriched in cd correlation analysis shows that the least mobile i e ionic potential z r ranges from 3 to 7 geogenic elements bi co cr cu in ni pb sn tl v zn are associated with the

comparing results from two continental geochemical surveys to world soil composition and deriving predicted empirical global soil pegs2 reference values analytical data for 10 major oxides al2o3 cao fe2o3 k2o mgo mno na2o p2o5 sio2 and tio2 16 total trace elements as ba ce co cr ga nb ni pb rb sr th v y zn and zr 14 aqua regia extracted elements ag as bi cd ce co cs cu fe la li mn mo and pb loss on ignition loi and ph from 3526 soil samples from two continets australia and europe are presented and compared to 1 the composition of the upper continetal crust 2 published word soil awerage values and 3 data from other continetal scale soil surveys it cab be demonstrated that average upper continetal crust values do not provide reliable estimates for natural concentrations of elements in soil for many elements there exist substantial differences between published world aoil averages and the median concentrations observed on two continets direct comparison with other continetal datasets is hampered by the fact that often mean instead of the statistically more robust median is reported using a database of the worldwide disstribution of lithological units it can be demonstrated that lithology is a poor predictor of soil chemistry climate related processes such as glaciation and weathering are strong modifiers of the geochemical signature inherited from bedrock during pedogenesis to overcome existing shortcomings of predicted global or world soil geochemical reference values we propose preliminary empirical global soil reference values based on analytical results of a representative number of soil samples from two continets pegs2

effects of the free surface on shear wavetrains summary the behaviour of shear waves is of great importance in identifying and investigating seismic anisotropy in the earth however shear wavetrains recorded at the earth s surface do not always reflect the motion at depth introducing practical problems of interpretation shear wavetrains incident on the surface of an isotropic half space at angles less than critical about 35 are broadly preserved but at greater angles substantial distortions can occur for stations situated close to the source as in local earthquake studies the local sp phase a radially polarized precursor to s may occur the behaviour at the surface of an anisotropic half space is further complicated by the divergence of phase and energy propagation vectors all of these complications suggest that detailed seismogram modelling is essential to any study of shear wave propagation in the earth and in particular to investigations of anisotropy induced shear wave splitting

the influence of parent material on topsoil geochemistry in eastern england the topsoil of around 10 000 km2 in eastern england has recently been sampled intensely at 4609 sites to characterize its geochemistry the parent materials which include both solid geology and quaternary sediments range in age from permian to holocene the distributions of the concentrations of major and trace elements have been characterized geostatistically and the role of parent material on their spatial structure anisotropy and their spatial relationships coregionalization have been investigated analysis of variance with the sites grouped by major parent material type showed that this classi cation accounted for 14 to 48 per cent of the variance for the various elements global variograms of 13 elements al as ca cr cu fe mg mo ni p pb ti and u have been computed and modelled eleven of the variograms seem to comprise two structures both of which we modelled with spherical functions one of short range 3 5 to 9 km and the other with a range of 15 to 23 km the models included a nugget variance which varied from 27 per cent for as fe and mg to 63 per cent for p of the total the long range structures are related to the separations of the major parent materials the variograms of several elements showed appreciable anisotropy most notably that of mg anisotropy is evident at short ranges of less than 5 km this accords with the geological structure of the beds which dip from west to east so that their outcrops are elongated from north to south a linear model of coregionalization tted to the data emphasized several important geochemical associations which we interpret elements commonly associated with clay minerals mg al and the clay size fraction ti are dominated by the long range structure of the coregionalization whilst several trace elements as cr ni and u are spatially correlated with fe over short distances through adsorption of the former on the surfaces of fe oxyhydroxides the topsoil around large urban areas is enriched in lead but it is not clear whether anthropogenic sources are responsible for this metal s anomalous spatial relationships with other elements crown copyright 2003 reproduced with the permission of her majesty s stationery of ce published by john wiley sons ltd

magnitudes and moment duration scaling of low frequency earthquakes beneath southern vancouver island we employ 130 low frequency earthquake lfe templates representing tremor sources on the plate boundary below southern vancouver island to examine lfe magnitudes each template is assembled from hundreds to thousands of individual lfes representing over 269 000 independent detections from major episodic tremor and slip ets events between 2003 and 2013 template displacement waveforms for direct p and s waves at near epicentral distances are remarkably simple at many stations approaching the zero phase single pulse expected for a point dislocation source in a homogeneous medium high spatiotemporal precision of template match filtered detections facilitates precise alignment of individual lfe detections and analysis of waveforms upon correction for 1 d geometrical spreading attenuation free surface magnification and radiation pattern we solve a large sparse linear system for 3 d path corrections and lfe magnitudes for all detections corresponding to a single ets template the spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12 24 h of lfe activity during an ets episode when tidal sensitivity is low the remainder is released in bursts over several days particularly as spatially extensive rapid tremor reversals rtrs during which tidal sensitivity is high rtrs are characterized by large magnitude lfes and are most strongly expressed in the updip portions of the ets transition zone and less organized at downdip levels lfe magnitude frequency relations are better described by power law than exponential distributions although they exhibit very high b values 5 we examine lfe moment duration scaling by generating templates using detections for limiting magnitude ranges mw 1 5 mw 2 0 lfe duration displays a weaker dependence upon moment than expected for self similarity suggesting that lfe asperities are limited in fault dimension and that moment variation is dominated by slip this behavior implies that lfes exhibit a scaling distinct from both large scale slow earthquakes and regular seismicity

elemental weathering fluxes and saprolite production rate in a central african lateritic terrain nsimi south cameroon abstract the comparison between contemporary and long term weathering has been carried out in the small experimental watershed sew of nsimi south cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover we focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer this study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements the mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates i strong depletion profiles for alkalis na k rb and alkaline earths mg ca sr ba ii moderate depletion profiles for si p cd cu zn ni and co iii depletion enrichment profiles for al ga ge sn pb lree hree y u fe v cr mn it is noteworthy that i mn and ce are not significantly redistributed according to oxidative processes as it is the case for fe v and cr and ii ge is fractionated compared to silica with enrichment in fe rich horizons the calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements among which are those specifically accumulated as the redox sensitive elements fe v cr and iron oxide related elements like th the overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy ninety four percent of the whole na flux generated from the hillside corrected from atmospheric deposits 77 mol ha yr represents the current weathering rates of plagioclase oligoclase in the system the other remaining 6 may be attributed to the dissolution of hornblende the silica hillside flux is 300 mol ha yr and can be mostly attributed to the plagioclase and kaolinite dissolution al and ga are exported from the lateritic regolith and maybe due to the dissolution of kaolinite crystals compared to the other immobile elements zr hf nb and th ti is significantly exported among redox sensitive elements fe v cr mn ce only ce and mn are exported out of the hillside system the other elements fe v cr are likely able to be mobilized but over a short distance only rb sr ba ni cu zn are affected by export processes lree and y are exported but in very low amounts in the range from mol ha yr to mmol ha yr while hree and u are exported in negligible quantities a first attempt is carried out to compare the mature ridge top profile from nsimi sew with the immature ridge top weathering profile from the mule hole sew south india developed on similar granodioritic basement in order to get deeper insight into i the contemporary saprolite production rates and ii the combined effect of precipitation in terms of mean annual rainfall mar and evapotranspiration on the aggressiveness of the draining solutions considering i the contemporary na flux as representative of the dissolution of plagioclase crystals and conservative during saprolitization processes and ii steady state of the inter annual recharge r over a 10 years period the current saprolite production rates r are of 22 mm kyr for mule hole sew and 2 mm kyr for nsimi sew respectively even with a very low r mar ratio 0 04 compared to nsimi the chemical weathering at mule hole is active and related to the groundwater exports at mule hole plagioclase crystals are still present in the saprolite and the soil cover leading to a diffuse weathering front the high nsimi r mar ratio 0 2 allows the solution to be still aggressive with respect to the plagioclase and other weatherable minerals at the bedrock interface resulting in their complete breakdown in a few centimetres sharp weathering front leading to a mature saprolite for the nsimi sew if we consider i the low contemporary saprolite production rate 2 mm kyr ii the miocene age average 15 myr of the south cameron plateau landscape and ii the limited movement of africa continent since eocene the long term saprolite production rate should have remained in its lower range from 2 to 10 m myr this suggests that for thick weathering profiles the migration of the weathering front into the bedrock occurs at a relatively uniform rate regardless of present day climatic conditions climate variation leading to the alternation of setup of savanna or humid forest will have an effect on physical erosion rather than chemical erosion for such deep weathering profiles

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

continental crust anisotropy measurements from tectonic tremor in cascadia we present new observations of crustal anisotropy in the southern cascadia forearc from tectonic tremor the abundance of tremor activity in oregon and northern california during slow slip events offers an enormous amount of information with which to measure and analyze anisotropy in the upper brittle continental crust to accomplish this we performed analyses of wave polarization and shear wave splitting of tectonic tremor signals using three component broadband seismic stations the splitting times range between 0 11 and 0 32 s and are consistent with typical values observed in the continental crust fast polarization azimuths are in general margin parallel and trend n s which parallels the azimuths of the maximum compressive stresses observed in this region this pattern is likely to be controlled by the stress field comparatively the anisotropic structure of fast directions observed in the northern section of the cascadia margin is oblique with respect to the southern section of cascadia which in general trends e w and is mainly controlled by active faulting and geological structures source distribution analysis using a bivariate normal distribution that expresses the distribution of tremors in a preferred direction shows that in northern california and oregon the population of tremors tends to distribute parallel to fast polarization azimuths and maximum compressive stresses suggesting that both tremor propagation and anisotropy are influenced by the stress field results show that the anisotropy reflects an active tectonic process that involves the northward movement of the oregon block which is rotating as a rigid body in northern cascadia previous results of anisotropy show that the crust is undergoing a shortening process due to velocity differences between the oregon block and the north america plate which is moving more slowly with respect to the oregon block making it clash against vancouver island

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

indication of high pore fluid pressures in a seismically active fault zone summary polarisations of seismic shear wave splitting observed above small earthquakes in iceland are typically approximately ne to sw parallel to the direction of maximum horizontal stress in contrast the polarisations of shear waves at three new stations sited over the husav ik flatey fault a major seismically active transform fault in northern iceland are approximately nw to se orthogonal to the stress aligned polarisations elsewhere modelling suggests that these 90 flips in polarisations are caused by propagation through cracks containing fluids at high pore fluid pressures within one or two mpa of the critical stress these observations suggest that high pore fluid pressures which play a key role in earthquake source mechanisms can be monitored by analysing shear wave splitting above seismically active fault planes

intraslab stresses in the cascadia subduction zone from inversion of earthquake focal mechanisms at the cascadia subduction zone intraslab earthquakes occur mostly in the northern part of the margin and its southern end the mendocino triple junction mtj we determine intraslab stress orientations by inverting earthquake focal me chanisms and develop working hypotheses to explain the inferred intraslab stresses and observed seismicity our inversion results show that the subducting juan de fuca jdf slab in northern cascadia is primarily under compression normal to the slab surface and tension in the downdip direction most likely controlled by the net slab pull an exception is a northernmost shallow region near the nootka fault zone where the state of stress is dominated by nearly east west tension we hypothesize that the shear force on the nootka fault zone and margin parallel mantle resistance to slab motion induce the east west tension in this region near the mtj stresses in the jdf plate are dominated by north south compression down to about 20 km depth consistent with a strong push by the pacific plate from south of the mendocino trans form fault but the deeper part of the slab shows downdip tension similar to northern cascadia deviatoric stresses in the jdf slab appear to be very low resulting in very low intraslab seismicity in comparison with northern cascadia the stresses in most of southern cascadia are even lower resulting in nearly no intraslab seismicity

a global geochemical mass budget applied to the congo basin rivers erosion rates and continental crust composition rivers carry the products of continental denudation either in a dissolved form chemical erosion or in a solid form physical erosion we focus in this paper on the relationship between physical erosion and chemical erosion we establish the mass budget of the congo basin rivers using chemical complementarities between river suspended sediments sandy bedload and dissolved load of the congo basin rivers reported in a previous paper dupre et al 1995 a series of equations are presented assuming that the physical and chemical erosion processes are in a steady state during one year the total mass of river borne material dissolved and particulate transported in the river over a given period of time should balance the mass of upper continental crust eroded during this time we show that the local continental crust on each drainage basin can be estimated and solve our steady state weathering model using an inversion procedure the very good agreement between modelled and measured values of the river suspended sediment concentrations validates the steady state hypothesis in this wet tropical area consequently in this area the sediment yield provide a good estimate of the rates of mechanical denudation this result also validates the calculation of the chemical and isotopic composition of the local continental upper crust using the bulk river load erosion rates for the silicate upper crust and thus independent of the lithological variability silicates evaporites and carbonates of the drainage basins are calculated mechanical erosion rates and chemical erosion rates for the congo basin at brazzaville are 8 t km2 y and 5 t km2 y the corresponding consumption of atmospheric co2 by weathering process is estimated to 51 103 mol km2 an these weathering and consumption rates are low in spite of the severity of the weathering conditions of the high soil temperature and of the intensity of precipitations these conclusions indicate the limiting influence the dynamic equilibrium of soils for silicate weathering finally by estimating the local continental crust chemical composition before the onset of erosion processes especially for the most soluble elements we can test the model of taylor and mclennan

gemas source distribution patterns and geochemical behaviour of ge in agricultural and grazing land soils at european continental scale abstract agricultural soil ap horizon 0 20 cm and grazing land soil gr horizon 0 10 cm samples were collected from a large part of europe 33 countries 5 6 million km 2 as part of the gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element mobility and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area includes a diverse group of soil parent materials with varying geological history a wide range of climate zones and landscapes the concentrations of ge in european soil were determined by icp ms after an aqua extraction and their spatial distribution patterns generated by means of a gis software the median values of ge and its spatial distribution in ap and gr soils are almost the same 0 037 vs 0 034 mg kg respectively the majority of ge anomalies is related to the type of soil parent material namely lithology of the bedrock and minor influence of soil parameters such as ph toc and clay content metallogenic belts with sulphide mineralisation provide the primary source of ge in soil in several regions in europe e g in scandinavia germany france spain and balkan countries comparison with total ge concentrations obtained from the baltic soil survey shows that aqua regia is a very selective method with rather low efficiency and cannot provide a complete explanation for ge geochemical behaviour in soil additionally large differences in ge distribution are to be expected when different soil depth horizons are analysed

major and trace elements of stream sediments from the lowermost amazon river geochemical results from river bottom sediments taken from the lowermost amazon river are presented bedload sediments were analyzed for 10 major and 38 minor elements mud bulk sediments exhibit a tendency to a slight enrichment in cr mn rb sr zr cs ba and hf pointing to the importance of these elements in the silt fraction generally cu zn rb cs ba and sn are clearly associated with clay minerals while y zr hf th and u are associated with heavy minerals the location of this area in an intensive chemical weathering environment results in the strong modification of sediment composition chemical weathering processes strongly modify original sediment composition and can be recognized apart from provenance processes on the basis of their geochemical signature discriminant analysis makes the detection of less marked differences in sediment characteristics possible thus improving the accuracy of distinctions between groups the amazon mouth and xingu mouth xm are discriminated principally by the textural maturity of their sediments the jari mouth jm shows highest co and fe2o3 contents despite similarities between the amazon north branch anb and amazon south branch asb the anb can be differentiated on the basis of its higher sr p2o5 and na2o contents the asb on the basis of its higher zn mno and cao contents and the estreitos de breves est based on its higher abundance of ni and cu higher contents in p2o5 fe and mn are related to laterite covers

ree in the great whale river estuary northwest quebec we report rare earth element ree concentrations of a longitudinal profile within the estuary of the great whale river in northwest quebec and in hudson bay all of the measured ree have concentrations less than those predicted by conservative mixing of seawater and river water demonstrating removal of the ree from solution ree removal is rapid occurring primarily at salinities less than 2 removal of the ree is greatest for the light ree and ranges from about 7 for the light ree to no more than 40 for the heavy ree fe removal is essentially complete at low salinity the shape of the fe and ree vs salinity profiles is not consistent with a simple model of destabilization and coagulation of iron and ree bearing colloidal material a linear relationship between the activity of free ion ree3 and ph is consistent with a simple ion exchange model for ree removal surface and subsurface samples of hudson bay seawater are characterized by high ree concentrations and high la yb relative to average seawater the subsurface sample has a nd concentration of 100 pmol kg and an end of 29 3 0 3 these characteristics are consistent with the high ree concentration high la yb and low end of river inputs into hudson bay these results indicate that rivers draining the canadian shield are a major source of non radiogenic nd and ree to the atlantic ocean we estimate that outflow of water from hudson bay to the labrador sea could supply 30 of the non radiogenic nd in north atlantic deep water

simplified analysis of horizontal stresses in a buttressed forearc sliver at an oblique subduction zone forearc slivers are commonly present at obliquely convergent margins such slivers are often buttressed at their leading edges but no quantitative model of the buttress effect exists i consider the horizontal stresses in a buttressed sliver using a simple plan view two dimensional elastic model the driving force created by the subducting plate is approximated by a body force in the direction of plate convergence an airy stress function solution relates the stress field to the boundary and body forces that allows the relative importance of different forces driving and resisting the sliver to be evaluated oblique subduction can easily cause arc parallel compression in the buttressed sliver especially near the leading edge because the arc parallel component of the driving force by the subducting plate is integrated over a much larger distance than its arc normal component for the southwest kuril arc the stress field predicted by the simple model agrees with that inferred from geological structures it is possible that the model can also explain the stress field of the cascadia forearc as constrained by earthquake focal mechanisms and in situ stress measurements

trench parallel crustal anisotropy along the trench in the fore arc region of japan in northeastern japan the pacific plate is descending beneath the north american plate it is generally understood that trench normal principal stress is dominant in the crust along the japanese island arc because the stress field is controlled by the force of the subducting slab observations of shear wave splitting using crustal earthquakes reveal a marked lateral variation in fast polarization direction with distance from the trench trench normal and trench parallel fast polarization directions are observed on the back arc and fore arc sides respectively in this study two dimensional finite element modeling with subducting slab was conducted to investigate the interseismic stress field during earthquake cycles taking into account linear viscoelasticity in the model trench normal compression is found to dominate in the island arc region however an extensional field appears in the shallow upper crust of the fore arc region during earthquake cycles the trench parallel crustal anisotropy can be explained by this extensional field

agricultural geochemistry in viticulture an example of cu accumulation and geochemical fractionation in mediterranean calcareous soils nemea region greece abstract the nemea region has been devoted to viticulture from historic times and currently is one of the most important wine producing areas in greece in this study we report the extent of cu and other element as cd co cr mn ni pb and zn enrichment their geochemical partitioning into the soil components evaluated by a seven step sequential extraction procedure and the plant availability of cu defined as the diethylene triamine pentaacetic acid dtpa extracted cu major soil properties were also determined total cu contents in the nemea topsoil were in the range 33 1 291 mg kg 1 enrichment factors ef calculated against uncultivated soils from the neighboring argos region showed that the nemea topsoil was significantly enriched with cu median ef 5 9 and in a limited number of samples moderately enriched median efs 2 5 with p as cd and mn on average 20 of total cu was readily available for plant uptake application of principal component analysis pca showed that natural cu present in nemea soil was principally associated with the residual and oxidizable fractions on the other hand anthropogenic related cu was linked to acid soluble and reducible geochemical phases exhibiting a strong affinity with the plant available cu nickel and cr were principally found in the residual fraction supporting their origin from ophiolitic rocks manganese and co were mostly associated with mn oxides cd was found in labile fractions whereas as pb and zn were bound more or less to reducible and oxidizable substrates copper and p were the only elements that were found to decline at the 50 cm soil depth despite the decline with depth cu contents did not reach background levels we did not find differences in cu availability and partitioning between the surface and deep soil samples inferring that cu migrated to the soil profile by tillage practices finally the comparison of the geochemical composition of vineyard soils with the nearby argos citrus soils revealed the pronounced enrichment of the citrus soils with p zn and cd due to intensive fertilizer applications in contrast the vineyard soils are more susceptible to cu and as accumulation

moderate chemical weathering of subtropical taiwan constraints from solid phase geochemistry of sediments and sedimentary rocks abstract the well known earthquake and storm triggered extremely high physical weathering rate in taiwan is consistent with present geochemical studies of sediments from different subenvironments offshore coastal river and lake and sedimentary rocks of different geological ages indicating a moderate chemical weathering condition major and trace element concentrations normalized to the average upper crust of yangtze craton show that the sediments and the average composition of sedimentary rocks of taiwan are depleted in ca mg na and sr enriched in rb and zr and unchanged with respect to k indicating their moderately altered nature the mean chemical index of alteration cia 71 75 and plagioclase index of alteration pia 81 86 values of coastal and offshore sediments reveal the sediments derivation from sedimentary rocks by moderate silicate chemical weathering processes the mean cia value 62 of sedimentary rocks of taiwan is similar to that for chinese sediment 61 further confirming

stress forecasting not predicting earthquakes a paradigm shift after 120 years of unsuccessful endeavor a paradigm shift is required before earthquakes can be predicted the most sensitive diagnostic of low level changes of stress in in situ rock variations in microcrack geometry can be monitored by analyzing shear wave splitting the suggested paradigm shift is that instead of investigating the source zone we monitor stress accumulation before earthquakes at possibly substantial distances from the source characteristic temporal variations of shear wave time delays have been observed in retrospect before 14 earthquakes worldwide on one occasion when changes were recognized early enough the time magnitude and fault break of an m 5 earthquake in southwest iceland were successfully stress forecast in a narrow time magnitude window such stress accumulation can be theoretically modeled and is believed to be at least partially understood when sufficient shear wave source earthquakes are available increasing time delays also show an abrupt decrease shortly before the impending earthquake occurs this is not fully understood but is thought to be caused by stress relaxation as microcracks coalesce onto the eventual fault break the new result confirming these ideas and justifying the paradigm shift is that logarithms of the durations of both increases and decreases in time delays are found to be proportional self similar to the magnitudes of impending earthquakes

evidence from shear wave splitting for the restriction of seismic anisotropy to the upper crust the existence of anistropy in the propagation speed of seismic waves through the earth s crust has been attributed to the non random alignment of microcracks in the crust1 for sparsely distributed parallel vertical cracks perturbation theory predicts the splitting of a shear wave into two orthogonally polarized waves2 4 here we present extremely clear evidence for shear wave splitting in three component seismograms from crustal and sub crustal microearthquakes recorded in the shikoku district of japan quantitative analysis of travel time differences between split shear waves leads to the conclusion that the observed anisotropy is limited to the upper crust shallower than 10 15 km this model is consistent with recent results from reflection seismology5 and implies that microcrack density or orientation changes from the upper to the lower crust

two unique weathering regimes in the changjiang and huanghe drainage basins geochemical evidence from river sediments the present research reconstructs the histories of chemical weathering in the drainage basins of the changjiang and huanghe based on the chemical compositions of the river sediments the silicate weathering of the changjiang basin is strong and naand ca silicate minerals are considerably dissolved while other silicate minerals are less attacked in comparison the huanghe basin is characterized by very weak silicate weathering and the weathering degree corresponds well with that of the loess which is the predominant source of the huanghe sediment overall the changjiang and huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage the similarity of chemical compositions between upper continental crust and the huanghe sediments as well as the low degree of chemical weathering in the huanghe basin imply that the river sediments can be considered to be the representative of ucc and are suitable for studying the evolution of continental crust our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins while controls by source rocks and relief are subordinate highly erosive river basins such as the huanghe produce poorly weathered materials which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering differences in silicate weathering processes between the changjiang and huanghe basins may provide more constraints in estimating atmospheric co2 budget in china d 2003 elsevier b v all rights reserved

new constraints on subduction zone structure in northern cascadia summary a detailed passive seismic experiment was carried out across southwestern british columbia and northwestern washington to investigate the structure of the subducting juan de fuca plate and mantle wedge in cascadia and its relation to intraslab seismicity as part of the polaris project 31 three component broad band stations were deployed in an approximately linear array spanning southern vancouver island the gulf and san juan islands watcom county and the british columbia lower mainland p wave coda from 41 teleseismic events have been employed in formal inversions for fine scale shear velocity structure our results indicate a structure very similar to that identified across a comparable profile in central oregon the continental moho is evident at the eastern end of the profile near 35 km depth but disappears towards georgia strait puget sound a prominent low s velocity zone is clearly evident below southern vancouver island dipping eastwards through georgia strait puget sound and coincides with the e reflection zone originally identified in lithoprobe studies structure below the e layer is much less prominent and varies intermittently along the array based on the observations and interpretations of similar structures beneath oregon alaska and south america and its projection to mantle depths we suggest that the low velocity e layer represents the dehydrating oceanic crust of the subducting juan de fuca plate this interpretation is consistent with recent seismicity studies that place shallow wadati benioff events within the oceanic mantle and implies that the oceanic crust is 6 8 km shallower beneath vancouver island than previously assumed as in oregon we interpret the diminished signature of oceanic crust below a depth of 45 km to signal the presence of eclogitization which in turn supplies water to serpentinize the overlying forearc mantle

crustal seismic anisotropy beneath shillong plateau assam valley in north east india shear wave splitting analysis using local earthquakes abstract we present crustal anisotropy estimates constrained by shear wave splitting sws analysis using local earthquakes in the shillong plateau and assam valley area north east india ne india region splitting parameters are determined using an automated cross correlation cc method we located 330 earthquakes recorded by 17 broadband seismic stations during 2001 2014 in the study area out of these 330 events seismograms of 163 events are selected for the sws analysis relatively small average delay times 0 039 0 084 s indicate existence of moderate crack density in the crust below the study area it is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions the spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the indian plate towards ne presence of several e w and n s trending active faults in the area also play an important role on the observed pattern of crustal anisotropy

origin of silica paleoenvironment and organic matter enrichment in the lower paleozoic niutitang and longmaxi formations of the northwestern upper yangtze plate significance for hydrocarbon exploration abstract lower paleozoic shale is an important source rock and reservoir for gas in the northwestern upper yangtze plate the paleoenvironment and its impact on organic matter enrichment of the shale plays a vital role in the exploration and development of the resource based on the analysis of the results of total organic carbon toc maceral examination bitumen reflectance rb major elements trace elements rare earth elements rees and x ray diffraction xrd of shale samples from the niutitang and longmaxi formations the origin of silica the paleoenvironment and the mode of organic matter enrichment of the shale were examined the shales of the niutitang and longmaxi formations have high toc abundance with type i organic matter and high maturity quartz and clay minerals dominate the mineral constituents leading to characterization as siliceous shale the average sio2 content of the shale in the niutitang and longmaxi formations is above 70 wt al2o3 and tfe2o3 total iron are the next most abundant major elements with average values of 12 80 wt and 1 95 wt in the niutitang formation and average values of 11 44 wt and 4 09 wt in the longmaxi formation compared with the upper continental crust ucc v mo and u are the most enriched elements the average lree hree of the shale samples is very low and the chondrite normalized ree distribution pattern shows sloping lree trends and flat hree trends towards the right the total rare earth elements of the shale vary within the range of 147 85 219 60 ppm and 159 90 222 02 ppm in both the niutitang and longmaxi formations suggesting that the shale has not been subject to obvious hydrothermal fluid activities the correlation diagrams of sio2 al2o3 sio2 toc and siexcess toc the diagrams of hydrothermal origins and the elemental parameters indicate that the silica of the shales from the niutitang and longmaxi formations are mainly of biogenic origins with a lesser contribution from terrigenous detrital sources the ratios of mno2 tio2 and al2o3 al2o3 tfe2o3 of the shale samples all show limited variability illustrating that the shales are mainly deposited on the continental margin the average chemical alteration index cia values of the niutitang and longmaxi formations are 71 25 and 72 77 with little variation and the average sr cu ratios are 4 38 and 2 22 reflecting a warm and humid paleoclimate for both formations the average ni co th u and u readings of the shale samples of the formations are 10 91 0 97 and 1 51 and 12 69 0 43 and 1 75 indicating that the redox conditions during the sedimentation of the formations were anoxic the positive correlations between toc and paleoenvironmental proxies reveal a warm and humid climate and that anoxia had a positive effect on organic matter enrichment these conditions have laid a geological foundation for the enrichment of shale gas and that the upper yangtze plate is favorable for future shale gas exploration

sks splitting beneath mount st helens constraints on subslab mantle entrainment the broadband seismic component of the imush project was supported by national science foundation grants ear 1144568 ear 1144351 ear 1460291 and ear 1444275 cme acknowledges support from the australian research council de190100062 we thank the 2017 iris undergraduate summer intern program for providing support to a w to work with e a w at the university of washington the facilities of iris data services and specifically the iris data management center were used for access to waveforms related metadata and or derived products used in this study iris data services are funded through the seismological facilities for the advancement of geoscience and earthscope sage proposal of the national science foundation under cooperative agreement ear 1261681

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others

extensive seismic anisotropy in the lower crust of archean metamorphic terrain south india inferred from ambient noise tomography abstract we use rayleigh and love wave empirical green s function egf recovered from the cross correlation of seismic ambient noise to study the spatial distribution of radial anisotropy in the southern india crust the corresponding dispersion curves in the period 2 to 32 s are measured from ambient noise data recorded at 57 sites and the strength of anisotropy computed from the discrepancy between shear velocities obtained from rayleigh v sv and love v sh at various depths down to 40 km in upper crust up to a depth of 20 km the region is characterized by anisotropy coefficients of 2 to 2 that could be explained due to a combination of fluid filled open cracks and foliated metamorphic rocks at deeper levels beyond 20 km except for the archean metamorphic terrain most part of south india has anisotropies of up to 5 this may be due to rocks with varying degree of metamorphism beneath the archean metamorphic terrain the anisotropy is recorded up to 9 in the depth range of 20 40 km this high anisotropy is unlikely to be the manifestation of any recent geodynamic process considering that the region has low surface heat flow 30 mw m 2 we propose that the observed strong anisotropy in the metamorphic belt of southern india crust could best be explained as due to the presence of micaceous minerals or amphiboles in the deep crust that are formed possibly during the evolution of granulite terrain at 2 5 ga

deep high amplitude reflections from a major shear zone above the subducting juan de fuca plate seismic reflection data show that a regionally extensive band of landward dipping reflections exists above the subducting juan de fuca plate at the western canadian continental margin the reflections truncate at depth a major terrane boundary mapped near the surface and must have a structural origin many reflections are very strong having reflection coefficients locally as high as 10 20 these amplitudes are consistent with theoretical calculations of reflections from sharp poirosity contrasts if the pores are very thin however seismic data from the accreted sedimentary melange farther seaward from which much of the deep reflective zone is derived suggest that significant porosity contrasts do not occur alone because higher reflection amplitudes are found in regions of inferred high strain both geometric and amplitude constraints imply that the deep reflective layering represents intensely sheared rocks possibly originating close to the subduction decollement

high pore fluid pressures at bhuj inferred from 90 flips in shear wave polarizations summary shear wave splitting above local earthquakes in the aftershock zone of the 2001 m w7 6 bhuj earthquake display a spatial variation of anisotropy related to crack orientation at most seismic stations the fast polarization directions are approximately nne ssw parallel to the inferred directions of maximum horizontal stress suggesting the dilatancy induced anisotropy resulting from approximately stress aligned parallel vertical microcracks in contrast the fast polarization directions at station samkhyali skl very close to the epicentre of the main shock are fault parallel approximately ew and almost orthogonal to the stress aligned polarizations elsewhere ape modelling and observations elsewhere suggest that these are 90 flips in shearwave polarizations caused by propagation through microcracks containing fluids at critically high pore fluid pressures surrounding the seismically active fault plane the presence of high pore fluid pressures on all seismogenic faults also explains the high scatter in shear wave time delays the average path normalized delay time varies from 2 to 4 ms km 1 except at station skl where higher delays of up to 13 ms km 1 are found the large scatter in measured time delays is caused by cracks saturated with high pressure pore fluids these observations can be explained by the presence of both normal stress aligned and 90 flipped shear wave polarizations at bhuj this suggests that the kutch mainland fault is a major tectonic feature

geochemistry of fine grained clastic sedimentary rocks of the neoproterozoic ikorongo group ne tanzania implications for provenance and source rock weathering abstract the neoproterozoic ikorongo group which lies unconformably on the late archaean nyanzian supergroup of the tanzania craton is comprised of conglomerates quartzites shales siltstones red sandstones with rare flagstones and gritstones and is regionally subdivided into four litho stratigraphic units namely the makobo kinenge sumuji and masati formations we report geochemical data for the mudrocks i e shales and siltstones from the ikorongo basin in an attempt to constrain their provenance and source rock weathering these mudrocks are compositionally similar to paas and ps indicating derivation from mixed mafic felsic sources however the siltstones show depletion in the transition elements cr ni cu sc and v and attest to a more felsic protolith than those for paas and ps the chemical index of alteration cia 52 82 reveal a moderately weathered protolith for the mudrocks the consistent ree patterns with lree enriched and hree depleted patterns la yb cn 7 3 38 3 coupled with negative eu anomalies eu eu 0 71 on average which characteristics are similar to the average paas and ps illustrate cratonic sources that formed by intra crustal differentiation geochemical considerations and palaeocurrent indications suggest that the provenance of the ikorongo group include high mg basaltic andesites dacites rhyolites and granitoids from the neoarchaean musoma mara greenstone belt to the north of the ikorongo basin mass balance calculations suggest relative contributions of 47 42 and 11 from granitoids high magnesium basaltic andesites and dacites respectively to the detritus that formed the shales corresponding contributions to the siltstones detritus are 53 43 and 4

predominant floodplain over mountain weathering of himalayan sediments ganga basin we present an extensive river sediment dataset covering the ganga basin from the himalayan front downstream to the ganga mainstream in bangladesh these sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column mineral sorting is the first order control on the chemical composition of river sediments taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain by comparing sediments sampled at the himalayan front with sediments from the ganga mainstream in bangladesh it is possible to budget weathering in the floodplain assuming a steady state weathering regime in the floodplain the weathering of himalayan sediments in the gangetic floodplain releases ca 189 92 10 9 and 69 22 10 9 mol yr of carbonate bound ca and mg to the dissolved load respectively silicate weathering releases 53 18 10 9 and 42 13 10 9 mol yr of na and k while the release of silicate mg and ca is substantially lower between ca 0 and 20 10 9 mol yr additionally we show that sediment hydration h2o is a sensitive tracer of silicate weathering that can be used in continental detrital environments such as the ganga basin both h2o content and the d h isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions by comparing the chemical composition of river sediments across the floodplain with the composition of the eroded himalayan source rocks we suggest that the floodplain is the dominant location of silicate weathering for na k and h2o overall this work emphasizes the role of the gangetic floodplain in weathering himalayan sediments it also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account 2012 elsevier ltd all rights reserved

crustal anisotropy in the forearc of the northern cascadia subduction zone british columbia summary this paper aims to identify sources and variations of crustal anisotropy from shear wave splitting measurements in the forearc of the northern cascadia subduction zone of southwest british columbia over 20 permanent stations and 15 temporary stations were available for shear wave splitting analysis on 4500 event station pairs for local crustal earthquakes results from 1100 useable shear wave splitting measurements show spatial variations in fast directions with margin parallel fast directions at most stations and margin perpendicular fast directions at stations in the northeast of the region crustal anisotropy is often attributed to stress and has been interpreted as the fast direction being related to the orientation of the maximum horizontal compressive stress however studies have also shown anisotropy can be complicated by crustal structure southwest british columbia is a complex region of crustal deformation and some of the stations are located near large ancient faults to use seismic anisotropy as a stress indicator requires identifying which stations are influenced by stress and which by structure we determine the source of anisotropy at each station by comparing fast directions from shear wave splitting results to the maximum horizontal compressive stress orientation determined from earthquake focal mechanism inversion most stations show agreement between the fast direction and the maximum horizontal compressive stress this suggests that anisotropy is related to stress aligned fluid filled microcracks based on extensive dilatancy anisotropy these stations are further analysed for temporal variations to lay groundwork for monitoring temporal changes in the stress over extended time periods determining the sources of variability in anisotropy can lead to a better understanding of the crustal structure and stress and in the future may be used as a monitoring and mapping tool

characterization of a weathering sequence of soils derived from volcanic ash in cameroon taxonomic mineralogical and agronomic implications the characteristics of eight pedons developed in quaternary basaltic pyroclasts in western cameroon under humid tropical conditions are reported the soil weathering sequence consists of an andept tropept udalf udult association andic properties physico chemical characteristics and weathering stage clearly distinguish the taxonomic units the total reserve in bases trb and the clay content measured after adequate h2o dispersion with na resins both appear to be suitable weathering indices clay mineralogy of non andic soils shows direct relationships between interstratified halloysite smectite content cec of the clay fraction and weathering stage the weathering stage of the investigated soils is reflected not only in their components and classification but also in their nutrient status and banana crop performance

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

a new calibration of seismic velocities anisotropy fabrics and elastic moduli of amphibole rich rocks 1 a large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase we have measured p and s wave velocities vp and vs and anisotropy of 17 amphibole rich rock samples containing 34 80 vol amphibole at hydrostatic pressures p up to 650 mpa combined petrophysical and geochemical analyses provide a new calibration for mean density average major element contents mean vp p and vs p coefficients intrinsic vp and vs anisotropy poisson s ratios the logarithmic ratio rs p and elastic moduli of amphibole rich rocks the vp values decrease with increasing sio2 and na2o k2o contents but increase with increasing mgo and cao contents the maximum 0 38 0 40 km s and minimum s wave birefringence values occur generally in the propagation direction parallel to y and normal to foliation respectively amphibole plays a critical role in the formation of seismic anisotropy whereas the presence of plagioclase quartz pyroxene and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations cpos the cpo variations cause different anisotropy patterns illustrated in the flinn diagram of vp x vp y vp y vp z plots the results make it possible to distinguish in terms of seismic properties the amphibolites from other categories of lithology such as granite granodiorite diorite gabbro diabase felsic gneiss mafic gneiss eclogite and peridotite within the earth s crust hence amphibole aligned by dislocation creep anisotropic growth or rigid body rotation is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs which contains rather little phyllosilicates such as mica or chlorite

shear wave splitting above the subducting juan de fuca plate shear wave splitting observed in three component broadband recordings of local earthquakes near southern vancouver island british columbia provide the first constraints on shear wave anisotropy in the continental crust above the subducting juan de fuca plate waveforms of 22 shallow earthquakes 15 30 km depth and 16 deep earthquakes 40 60 km depth were examined for shear wave splitting the fast polarization direction is well defined at 312 19 for the deep earthquakes and 293 27 for the shallow earthquakes these fast polarization directions are approximately parallel to the continental margin and coincide with the orientation of the pressure axes of small crustal earthquakes in this region interpreting this polarization pattern in terms of the extensive dilatancy anisotropy model indicates a margin parallel compressive stress regime comparing the average time delays between the fast and slow shear waves for the deep earthquakes 0 32 s and the shallow earthquakes 0 20 s suggests that the source of the seismic anisotropy is stronger in the upper 20 km of the continental crust here the average differential shear wave anisotropy is estimated at 2 3 these observations support the theory of weak coupling between the downgoing juan de fuca plate and the overlying north america plate as the principal stress is perpendicular to the direction of subduction and the s wave splitting above the subducting plate is nearly perpendicular to the sks splitting direction in the upper mantle beneath the subducting plate

importance of geomorphology and sedimentation processes for metal dispersion in sediments and soils of the ganga plain identification of geochemical domains abstract the ganga plain one of the largest alluvial plains of the earth is under severe environmental stress due to rapid industrial and urban development and exploding population growth disposal of industrial and urban wastes and the ignorance of their management have resulted severe environmental problems especially metal pollution in the present study an attempt is made to understand the transport and dispersion processes of metal contaminants in sediments and soils in kanpur unnao industrial region of the ganga plain the significance of geomorphology and monsoon rain is assessed in determining the distribution of contaminated sediments in this area three regional geomorphic surfaces t0 t1 and t2 are identified each with its characteristic river channel patterns and sediment distribution system which influence the dispersion and accumulation of the metal contaminants the sediment and water distribution regime depends on the nature of geomorphic features and character of the river channels geomorphic features sedimentation processes the nature of the river channels and distribution of excess rain water of the monsoon season have given the bases to delineate five geochemical domains in the study area each geochemical domain is an independently operating system with its own geomorphic and geochemical characters chemical parameters e g ph metal concentrations and dispersion of metal contaminated sediments and soils vary from domain to domain in comparison to reference values each domain exhibits its own enrichment of elements namely the loni river domain has high contents of c org cd cr zn the ganda nala domain of c org cu cr the ganga river domain of c org cr cu pb sn zn the sewage network domain of c org cd cr cu pb ni sn zn and the pandu river domain of c org cd cu ni zn patterns of changes in metal concentrations from one monsoon year to the other and in different seasons of a monsoon flood cycle are also domain specific each geochemical domain exhibits its own degree of metal enrichment in sediments and soils by anthropogenic activities and physico chemical processes identification of geochemical domains with their specific physico chemical processes in the fluvial system of the ganga plain will certainly help in assessing the environmental problems and land contamination of this region

processing modelling and predicting time lapse effects of overpressured fluid injection in a fractured reservoir summary time lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs we analyse two 4 d 3c onshore surveys from vacuum field new mexico usa where the reservoir of interest is a fractured dolomite in phase vi a time lapse survey was acquired before and after a pilot tertiary recovery programme of overpressured co2 injection which altered the fluid composition and the pore fluid pressure phase vii was a similar time lapse survey in the same location but with a different lowerpressure injection regime applying a processing sequence to the phase vi data preserving normal incidence shearwave anisotropy time delays and polarization and maximizing repeatability interval time analysis of the reservoir interval shows a significant 10 per cent change in shear wave velocity anisotropy and 3 per cent decrease in the p wave interval velocities a 1 d model incorporating both saturation and pressure changes is matched to the data the saturation changes have little effect on the seismic velocities there are two main causes of the time lapse changes any change in pore fluid pressures modifies crack aspect ratios additionally when there are overpressures as there are in phase vi there is a 90 change in maximum impedance directions and the leading faster split shear wave instead of being parallel to the crack face as it is for low pore fluid pressures becomes orthogonal to the crack face the anisotropic poro elasticity ape model of the evolution of microcracked rock calculates the evolution of cracked rock to changing conditions ape modelling shows that at high overburden pressures only nearly vertical cracks to which normal incidence p waves are less sensitive than s waves remain open as the pore fluid pressure increases ape modelling matches the observed time lapse effects almost exactly demonstrating that shear wave anisotropy is a highly sensitive diagnostic of pore fluid pressure changes in fractured reservoirs in this comparatively limited analysis ape modelling of fluid injection at known pressure correctly predicted the changes in seismic response particularly the shear wave splitting induced by the high pressure co2 injection in the phase vii survey ape modelling also successfully predicted the response to the lower pressure injection using the same phase vi model of the cracked reservoir the underlying reason for this remarkable predictability of fluid saturated reservoir rocks is the critical nature and high crack density of the fluid saturated cracks and microcracks in the reservoir rock which makes cracked reservoirs critical systems

chemical denudation rates of the western canadian orogenic belt the stikine terrane we report in this paper major element and sr isotopic ratio analyses for 19 rivers draining the stikine province in the western canadian cordillera dissolved solutes suspended sediments and river sands were analyzed the aim of the paper is to calculate chemical denudation rates for this uplifted accretionary prism mainly dominated by volcanics and volcanic derived sedimentary rocks the major chemical features of the stikine rivers are their dilute character and the excess of ca mg and sr in the dissolved load with regards to na molar ca na ratios from 2 to 14 mean value of 5 4 are observed although the region is dominated by silicate rocks suspended sediments show ca na ratios close to 0 4 isotopically most of the rivers investigated display lower sr isotopic ratios in the dissolved load compared to the suspended load which is very unusual to account for the excess of cations three different hypotheses are tested by an inversion method allowing us to determine the origin of each major solute the first scenario assumes that the excess of ca and mg is due to the dissolution of unradiogenic carbonates the second scenario supposes that the excess of base cations is derived from the preferential dissolution of ca and mg rich minerals such as amphiboles in the third scenario all solutes are assumed to derived from silicate weathering the cationic weathering rates of silicates although imprecise are in the order of 2 5 tons km2 year for the two first hypotheses if all solutes are taken into account denudation rates are between 9 and 15 tons km2 year on a global scale these numbers are among the lowest found for rivers draining basaltic rocks they are however found to be consistent with the global law for chemical weathering rates established for basaltic rocks showing that chemical denudation rate are linearly correlated to runoff and depend on temperature according to an arrhenius law the rivers draining the complex assemblage of volcanic and volcanic derived rocks in the subduction collision geological context of the stikine province thus respond similarly to the other volcanic provinces of the world this does not seem to be true for associated co2 consumption rates the abundance of sulfate ions in the dissolved load possibly derived from oxidative weathering of sulfides may indeed provide a non negligible part of the protons necessary for chemical weathering within canada the stikine geologic province is one whose silicates weather at a high rate the order of chemical weatherabilty of canadian geological province from the lowest to the highest is established as follows granites shales of the rockies volcanics of the western cordillera shales of the interior platform carbonates

contrasting upper mantle shear wave anisotropy across the transpressive queen charlotte margin abstract in order to investigate upper mantle and crustal anisotropy along the transpressive queen charlotte margin between the pacific pa and north america na plates we conducted shear wave splitting analyses using 17 seismic stations in and around the island of haida gwaii canada despite the limited station coverage at present our reconnaissance study does reveal a systematic pattern of mantle anisotropy in this region fast directions derived from teleseismic sks phase splitting are mostly margin parallel nnw sse near the plate boundary but transition to predominantly e w trending farther away we propose that the former is associated with the absolute motion of pa and the latter reflects a transition from this direction to that of the absolute motion of na the broad width of the zone of transition from the pa to na direction is probably caused by the very obliquely subducting pa slab that travels primarily in the margin parallel direction anisotropy of haida gwaii based on local earthquakes features a fast direction that cannot be explained with regional stresses and is probably associated with local structural fabric within the overriding crust our preliminary shear wave splitting measurements and working hypotheses based on them will serve to guide more refined future studies to unravel details of the geometry and kinematics of the subducted pa slab as well as the viscous coupling between the slab and upper mantle in other transpressive margins

split from slip and schist crustal anisotropy beneath northern cascadia from non volcanic tremor 1 polarization and splitting analyses of minute long windows of non volcanic tremor at 3 component stations in the vicinity of southern vancouver island provide new evidence for the presence of anisotropy within the crustal portion of the north american plate beneath cascadia as reported previously tremor particle motions are predominantly horizontal and inferred to manifest an upgoing wavefield composed primarily of s waves under this assumption estimates of incidence angle and back azimuth can be deduced from orientation of the smallest principle direction of motion when subjected to standard s wave splitting analysis most stations yield systematic and reproducible fast polarization directions estimates of original polarization direction are more scattered and splitting times often exhibit multimodal distributions numerical simulations wherein band limited synthetic seismograms comprising contributions from multiple sources are analyzed for splitting neatly reproduce these characteristics and thereby provide a framework for interpretation a number of stations in our study sit astride the san juan fault which based on reflection studies dips approximately 60 to 70 to the north underlying these stations is the leech river complex consisting of strongly foliated greenschist facies phyllites with steeply dipping foliations striking parallel to fast polarization directions of split s waves detailed laboratory velocity measurements at elevated pressures show that as little as 2 to 3 km of vertically dipping leech river phyllite are required to produce the observed splitting these phyllites have some of the highest s wave anisotropies measured to date and are part of a once continuous belt of anisotropic crust extending over 2000 km along the western north american coast from southern vancouver island to southwest alaska

geochemistry of mesoproterozoic sedimentary rocks of upper vindhyan group southeastern rajasthan and implications for weathering history composition and tectonic setting of continental crust in the northern part of indian shield abstract the upper vindhyan succession of southeastern rajasthan is divisible into kaimur rewa and bhander groups the major and trace element including rare earth elements data of the upper vindhyan shales and sandstones are investigated to determine the weathering history composition and tectonic setting of mesoproterozoic continental crust cia chemical index of alteration values a cn k plot a al2o3 cn cao na2o k k2o and depletion in u na2o cao sr and ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions provenance modeling indicates that the kaimur sandstones are best modeled with a mixture having 40 granitic gneiss 20 tonalite trondhjemite granodiorite ttg 20 mafic enclaves and 20 berach granite of the banded gneissic complex bgc a mixture of 60 granitic gneiss 20 mafic enclaves and 20 berach granite of the bgc can model the rewa and bhander groups it is suggested that the upper vindhyan sedimentation commenced at the time of delhi sausar orogeny at about 1100 1000 ma the orogenic movements uplifted the parts of old continental crust in the bgc terrain creating positive areas which exposed older crustal blocks containing ttg as important component the debris of kaimur sandstone probably derived from these uplifted blocks as indicated by palaeocurrent data the rewa and bhander formations were derived from bundelkhand granitic gneiss complex bggc occurring to the north of the basin and or the chotanagpur granitic gneiss complex cggc of eastern indian shield the derivation of lower and upper groups of vindhyan succession from different source terrains of identical composition suggests that at the time of vindhyan sedimentation the bgc of rajasthan the bggc of central india and the cggc of eastern india had similar lithological composition this implies that well before the origin of the vindhyan basin these discrete terrains evolved as a single unit that existed as a mesoarchaean nucleus in the northern part of the indian shield

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

geochemical fingerprinting and source discrimination of agricultural soils at continental scale 2108 agricultural soil samples ap horizon 0 20 cm were collected in europe 33 countries area 5 6 million km2 as part of the recently completed gemas geochemical mapping of agricultural and grazing land soil soil mapping project gemas soil data have been used to provide a general view of element origin and mobility with a main focus on source parent material and source rocks at the continental scale either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes the survey area covers a large territory with diverse types of soil parent materials with distinct geological history and a wide range of climate zones and landscapes to normalize the chemical composition of european agricultural soil mean values and standard deviation of the selected elements have been compared to model compositions of the upper continental crust ucc and mean european river suspended sediment some elements are enriched relative to the ucc al p pb zr whereas others such as mg na and sr are depleted the concept of the ucc extended normalization pattern has been applied to selected elements the mean values of rb k y ti al si zr ce and fe are very similar to the values from the ucc model even when standard deviations indicate slight enrichment or depletion zirconium has the best fit to the ucc model using both mean value and standard deviation lead and cr are enriched in european soil when compared to the ucc model but their standard deviation values span a large particularly towards very low values which can be interpreted as a lithological effect gemas soil data have been normalized to al and na taking into account the main lithologies of the ucc in order to discriminate provenance sources additionally sodium normalization highlights variations related to the soluble and insoluble behavior of some elements e g k rb versus ti al si v y zr ba and la respectively their reactivity e g fe mn zn and association with carbonates e g ca and sr maps of europe showing the spatial distribution of normalized compositions and element ratios reveal difficulties with the use of classical element ratios because of the large lithological differences in compositions of soil parent material the ratio maps and color composite images extracted from the gemas data can help to discriminate the main lithologies in europe at the regional scale but need to be used with caution due to the complexity of superimposed processes responsible for the soil chemical composition

geometry and structure of a fault bounded extensional basin by integrating geophysical surveys and seismic anisotropy across the 30 october 2016 mw 6 5 earthquake fault central italy the pian grande di castelluccio basin

the composition of suspended matter from ganges brahmaputra sediment dispersal system during low sediment transport season abstract suspended matter supplied from the ganges brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load november december 1997 the absolute amount of suspended matter ranges between 500 mg l near the river mouth and chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source compositional changes are based on grain size partitioning quartz and heavy minerals are precipitating sooner leaving the suspended matter from the outer shelf depleted in quartz ree zr hf nb ta w u th y and ca the other part of the compositional changes is based on the reaction of suspended matter with seawater manganese hydroxide is producing coatings on suspended matter grains and adsorbing elements out of the seawater as a consequence enrichment of mn zn ni cr co li cs as sb pb tl and cd can be observed in the suspended matter from the outer shelf arsenic is accumulating on the inner shelf by a factor of 2 chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals more than 90 of the total arsenic is bound to nearly insoluble phases of the suspended matter e g crystalline iron oxides residual minerals for comparison with suspended matter adjacent surface sediments were sampled and analysed in this sediment the dominating phase is the one which settled down during the times of high suspended load with more quartz and heavy minerals and consequent chemical composition the enrichment of manganese oxide and adsorbed transition metals gets lost because of anaerobic conditions in the bottom near seawater they dissolve from the sediment and get recycled in seawater arsenic is found in nearly insoluble parts of the sediment as it is the case in the suspended matter