dissolved constituents and sr isotopes in river waters from a mountainous island the danshuei drainage system in northern taiwan abstract taiwan is a typical active orogenic belt situated at the collision boundary between the eurasian continental plate and the philippine sea plate dissolved major and trace constituents as well as sr and sr isotopes in river waters collected from the danshuei river basin in northern taiwan have been studied to evaluate chemical weathering processes the results of principal component analysis show that the ion sources in these river waters can be categorized into 3 major components chemical weathering seasalt contribution and local anthropogenic input the chemical weathering is the most dominant factor that contributes about 85 of total variances significantly increased na cl and ca cl as well 87 sr 86 sr were observed in most upper stream samples the na cl and ca cl ratios in the dahan stream however are much higher than the shindien stream even though average rainfall is stronger in the shindien drainage basin chemical evidence from river waters supports less intense weathering in the region selective dissolution of secondary calcites explains the observed high ca cl sr cl and ca na in the dahan stream these results highlight the potential importance of tectonic factors such as uplift and physical erosion in studying chemical weathering in an active orogenic belt the variations of 87 sr 86 sr in the danshuei river are quite large reflecting some strata that released sr most of the upstream waters exhibit more radiogenic 87 sr 86 sr 0 713243 0 714338 due to weathering of ambient low grade metamorphic rocks 0 71678 0 72216 the distributions of cl sr and 87 sr 86 sr in the main stream were affected by somewhat conservative mixing with sources varing between ambient rocks and seasalt in the upper dahan stream heavy 87 sr 86 sr ratios were coincident with large deviations of na cl from the average seawater value as high as 40 the degree of chemical weathering in ambient rocks plays a dominant role in affecting the distribution of sr and 87 sr 86 sr in the danshuei river this isotopic characteristic makes 87 sr 86 sr an invaluable tracer for studying source mixing migration pathways and chemical weathering in an active orogenic belt

the serchio river catchment northern tuscany geochemistry of stream waters and sediments and isotopic composition of dissolved sulfate abstract the serchio river and its tributaries in northern tuscany were investigated for the chemical and isotopic compositions of waters and bed sediments bedrocks are mostly limestone dolomite and siliciclastics thermal spring systems are present in the catchment and the main industrial activity is represented by paper mills main results obtained are 1 major ions in solution appear to be basically controlled by precipitation and lithology as well as subordinately by direct inputs of thermal springs 2 human influence on metals in the waters along the main serchio and lima rivers is indicated at a number of sites by increases in concentration compared to the chemical composition of upstream tributaries 3 s and o isotope compositions delineate two main sources for aqueous so 4 2 that is dissolution of triassic evaporite directly or via thermal springs and oxidation of sulfide dispersed in siliciclastic rocks anthropogenic contributions are probable but they cannot be quantitatively assessed only so 4 2 in the notoriously polluted ozzeri tributary is suspected to be largely anthropogenic and 4 the chemical composition of bed sediments is mainly influenced by lithology apart from a number of technogenic elements in the upper part of the serchio river and in some tributaries contamination possibly occurs at other sites but geochemical indications are weak

behavior of gold in the lateritic equatorial environment weathering and surface dispersion of residual gold particles at dondo mobi gabon abstract a supergene gold dispersion halo has developed at dondo mobi southern gabon from the weathering of an auriferous lisvenite under equatorial humid rain forest conditions morphological and chemical studies were performed on gold particles extracted from both fresh and weathered rocks from different parts of the dispersion halo the results demonstrate that the gold particles are residual and are subjected to increasing weathering upward through the profile from the protore to the surface in the central part of the halo and at the surface both laterally upslope and downslope weathering continues downward into the formerly barren saprolites which were derived from proterozoic schist and archean gneiss rim of the halo thus the au content progressively decreases as does the ag content of gold particles with distance from the center of the ore body gold particles subjected to increased weathering are smaller with more rounded shapes and surfaces pitted by dissolution the dispersion pattern is controlled by au dissolution and translocation of residual gold particles these processes involve an autochthonous evolution in the central part of the halo and a para autochthonous evolution at the rim of the halo at dondo mobi chloride and humic substances are the only ligands present in significant concentrations that are capable of complexing au thermodynamic calculations demonstrate that under such acidic conditions ph ranges from 4 to 6 gold stability increases with increasing silver content the dominant au complexes formed have been calculated to be an aurous hydroxichloride complex and an organometallic complex both of which are stable at surficial conditions thus both chemical and translocation processes control the mobility of au and gold particles in equatorial lateritic weathering profiles

hydrocarbon generation and expulsion characteristics of the source rocks in the third member of the upper triassic xujiahe formation and its effect on conventional and unconventional hydrocarbon resource potential in the sichuan basin abstract the third member of the upper triassic xujiahe formation t3x3 is a typical source reservoir cap unit for natural gas exploration in the sichuan basin however most previous studies mainly focused on the t3x3 as a source rock ignoring its role as a reservoir as a result the evaluation of hydrocarbon resource potential was not accurate this study established a hydrocarbon generation and expulsion model through analyzing the geological and geochemical characteristics of the t3x3 source rocks and calculated the resource potential of conventional gas tight gas and shale gas systematically with combining the lower boundary of buoyancy dominated accumulation lbba the results indicated that the thickness of the source rocks dominated by mudstone was distributed widely with an average value of more than 45 m the sedimentary environment was salty lacustrine deposits they have a high content of total organic carbon toc with an average value of 4 80 wt the kerogen is mainly type iii with minor type ii and the thermal evolution has entered the high to over mature stage the hydrocarbon generation threshold was determined to be 0 5 ro while the hydrocarbon expulsion threshold and the lbba were determined to be 0 83 ro and 1 12 ro respectively the efficiency of hydrocarbon expulsion was relatively high with an average of about 56 also the maximum hydrocarbon generation and expulsion intensity reached to 110 108 m3 km2 and 53 108 m3 km2 the amounts of hydrocarbon generation expulsion and residual associated with the t3x3 source rocks were 125 68 1012m3 70 38 1012m3 and 55 30 1012m3 respectively under the criterion condition of the lbba the conventional gas resource was 7 21 1010m3 the tight gas resource was 294 34 1010m3 and the shale gas resource was 2488 50 1010m3 it indicated good prospects for exploration

deep upper mantle melting beneath the tasman and coral seas detected with multiple scs reverberations abstract multiple scs reverberations are used to search for mantle reflectors beneath the tasman and coral seas with a hierarchical waveform inversion migration method in addition to the major transition zone discontinuities a low velocity layer above the 410 km discontinuity is detected the top of the low velocity layer lies at an average depth of 352 km indicating that the layer could be more than 70 km thick if it persists to the 410 km discontinuity which occurs at an average depth of 420 km along paths containing the low velocity layer we attribute the low velocities to partial melt resulting from volatile induced melting the considerable thickness of the partial melt layer may require thin films of a hydrous melt with a zero degree dihedral angle surrounding grains or the combined effect on melting of the addition of both water and carbon to the deep upper mantle via subduction although the depths of the transition zone discontinuities do not indicate that the transition zone itself is rich in water the impedance contrasts do contain a subtle signature that could be related to transition zone water namely a decrease in the impedance contrast across the 410 km discontinuity and a relatively strong 520 km discontinuity

a complex 660 km discontinuity beneath northeast china abstract we present a detailed seismic study of the 660 km discontinuity beneath northeast china using the receiver function technique we use seismic data collected from 24 broadband stations in northeast china analysis of these data shows that the 660 km discontinuity is locally depressed in the region from longitude 128 0 e to 130 5 e and latitude 40 0 n to 44 0 n and then it splits into multiple discontinuities in the surrounding regions the complexity of the 660 km discontinuity beneath the subduction zones is probably attributable to the interaction between the upper mantle and subducted slab we speculate that the flattening of the subducted lithosphere near the bottom of the upper mantle causes the multiple discontinuity structure and that the slab penetrating the 660 km discontinuity into the lower mantle causes the narrow 660 km depression area

variations of chemical features in a monsoon glacier watershed southeastern tibet plateau the ph ec electric conductivity 18o and major ions in melt water precipitation runoff and groundwater samples which were collected in baishui basin were analyzed based on chemical analysis the characteristic variations are analyzed in this paper the melt water precipitation runoff and groundwater were ca2 mg2 hco3 type with similar ion compositions but showed different ion concentrations normally the content is high in groundwater and runoff water but low in melt water and precipitation from the upper basin glacier downward there was a general increasing trend for the total ion concentrations in basin hco3 and ca2 accounted for more than 80 of total ions in samples indicating that ions mainly came from limestone and water typical of carbonate solution water water rock interaction is the significant contributor to water geochemistry the concentration of inorganic ion in melt water had an obvious diurnal variation with temperature change the 18o values increases with the altitude decrease the similarity of 18o in runoff and groundwater samples was due to their frequent transformation in karst regions

hydrogeochemistry of three watersheds the erlqis zhungarer and yili in northern xinjiang nw china abstract in the arid region of northern xinjiang one of the least studied areas in china three watersheds namely those of the yili zhungarer and erlqis have become the focus of attention due to rapidly increasing human population and water demands the hydrogeochemistry of natural water from the three watersheds was investigated the ionic chemistry of natural waters from these watersheds changes considerably on a regional scale the waters are neutral to alkaline in nature and most of them are soft fresh waters the total dissolved solid tds varies over two orders of magnitude with a mean value of 580 mg l about 1 2 times and 4 6 times those of the huanghe yellow river and the world spatial median respectively but only 40 and 0 8 of those of the tarim and the western alashan watersheds respectively much of the solutes and physicochemical parameters in these waters are under the highest desirable limits of the world health organization who for drinking purpose and a plot of sodium adsorption ratio versus ec shows that most waters are of good water quality for irrigation water rock interaction and saturation index si for selected minerals are evaluated the si of these natural waters is out of equilibrium undersaturated with respect to major carbonates calcite and dolomite and evaporites gypsum and halite the high concentrations of alkali earth metals alkalinity and the high ca mg na k and na cl ratios indicate that the release of major solutes in these waters is controlled largely by dissolution processes of carbonate and partly by silicate weathering while cation exchange reactions soil salt leaching and evaporation processes also play an important role the effects of local pollution are minimal in the montane and piedmont areas of these watersheds but are significant in the oases and central areas of the drainage basins

mechanisms controlling the silicon isotopic compositions of river waters it has been proposed that silicon si isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions in this study the first seasonal variations of stable isotope compositions of dissolved riverine si are reported and compared with concomitant changes in water chemistry four different rivers in switzerland were sampled between march 2004 and july 2005 the unique high resolution multi collector icp ms nu1700 has been used to provide simultaneous interference free measurements of 28si 29si and 30si abundances with an average limiting precision of 0 04 on 30si this precision facilitates the clarification of small temporal variations in isotope composition the average of all the data for the 40 samples is 30si 0 84 0 19 1 sd despite significant differences in catchment lithologies biomass climate total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved si in each river is strikingly similar with means of 0 70 0 12 for the birs 0 95 0 22 for the saane 0 93 0 12 for the ticino and 0 79 0 19 for the verzasca however the 30si undergoes seasonal variations of up to 0 6 comparisons between 30si and physico chemical parameters such as the concentration of dissolved si and other cations the discharge of the rivers and the resulting weathering fluxes permits an understanding of the processes that control the si budget and the fate of dissolved si within these rivers the main mechanism controlling the si isotope composition of the mountainous verzasca river appears to be a two component mixing between the seepage of soil ground waters with heavier si produced by clay formation and superficial runoff associated with lighter si during high discharge events a biologically mediated fractionation can be excluded in this particular river system the other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment in these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of si contributed by biological processes as opposed to abiotic weathering the presence of seasonal variations in si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved si delivered to the oceans the oceanic si isotope composition is very sensitive to even small changes in the riverine si isotope composition and this parameter appears to be more critical than plausible changes in the si flux therefore concurrent changes in weathering style may need to be considered when using the si isotopic compositions of diatoms sponges and radiolaria as paleoproductivity proxies

a low velocity zone atop the transition zone in northwestern canada 1 seismic studies over the past decade have identified an s wave low velocity zone lvz above the transition zone at various locations around the globe this layer is hypothesized to be a lens of dense hydrous silicate melt ponding atop the 410 km discontinuity beneath the silicate melt density crossover predicted to exist within the upper mantle we have assembled a p and s receiver function data set to quantify the physical properties and geographical extent of the layer in northwestern canada geographic profiles formed from 1 d migration of receiver functions computed for the canadian northwest experiment canoe and portable observatories for lithospheric analysis and research investigating seismicity polaris slave arrays reveal an lvz beneath many stations at a nominal depth of 340 km to constrain layer thickness and poisson s ratio we performed a grid search over a suite of 1 d velocity profiles to model the relative delay times of direct conversions and reverberations from the top of the lvz and 410 km discontinuity as recorded at the yellowknife array in addition we performed linearized inversion of transmission coefficient amplitudes to estimate s velocity contrasts at the bounding interfaces the lvz is characterized by a thickness of 36 km with an s velocity contrast of 7 8 and poisson s ratio of 0 42 taken at face value the two latter results require an increase in p velocity into the lvz the poisson s ratio lies well above the iasp91 average of 0 29 0 3 for this depth range and favors the presence of high melt or fluid fractions

sulfur isotope and chemical compositions of the wet precipitation in two major urban areas seoul and busan korea abstract the seasonal variations of 34s together with major ions in snow and rainwater samples were measured in urban areas precipitation samples were collected from metropolitan city seoul and large port city busan korea for about one year from june 2002 to june 2003 the 34s values of sulfate in precipitation ranged from 4 3 to 6 6 mean 3 72 and 1 0 to 18 6 mean 5 55 in seoul and busan respectively even though both of the study areas have large populations and transportation infrastructure 34s values of sulfate in seoul precipitation originate more from anthropogenic sources relative to that of busan the elevated anthropogenic sources in seoul might be influenced by human activities from surrounding industrial cities while the scatter of 34s values in busan may be influenced by marine air during the study 34s values are high in the fall season and low in the spring season it may be inferred from this data that spring time 34s values are affected more by biogenic sources compared to the fall season as such seoul and busan showed significant differences in chemical compositions such as 34s and nss so 4 2 especially 34s values in the seoul show very good relationship with anthropogenic emissions e g emission from coal combustion and 34s values in the busan may be influenced by sea spray from the oceanic surface micro layer this correlation and the 34s values indicate that the major source in this region is likely to be anthropogenic source in seoul and sea spray in busan rather than traditionally suggested sources such as soil resuspension stratospheric air intrusion volcanic emissions and biogenic emissions

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

spatial and temporal analysis of water chemistry records 1958 2000 in the huanghe yellow river basin 1 the chemistry of major dissolved ions ca2 mg2 na k hco3 so42 cl and dissolved silica sio2 in the river water of the huanghe yellow river china was studied from historical records at 100 stations in the drainage basin for the period 1958 2000 not all the parameters were continuously monitored during the entire period this river system 750 000 km2 presents an exceptional temporal and spatial water chemistry variability compared to other major rivers the total dissolved solid tds concentration of the huanghe varied over 2 to 3 orders of magnitude throughout the basin with a median tds concentration of 452 mg l which is about 4 times the world spatial median value wsm in particular the concentrations of na k so42 and cl were 10 20 times higher than in other major world rivers similar to the changjiang yangtze river and many other himalayan rivers the tds at a given station is seasonally variable and inversely related to river runoff with a variation factor less than 2 0 despite a water dilution of fourfold to fivefold in the summer flood season in addition to chemical weathering of sedimentary rocks evaporation and fractional crystallization were found to be the major natural process controlling the major element chemistry of the huanghe owing to the abundance of loess and clastic rocks under arid and semiarid climates a persistent increasing trend from year to year has been observed in the concentrations of tds and all the salts except for hco3 at all main channel stations except for the uppermost lanzhou the rate of increase in the tds concentration was the highest in the middle reaches 10 52 mg l yr 1 at toudaoguai and remained to be unusually high in the lower reaches 5 5 mg l yr 1 at stations luokou and lijin the increasing trend coincided with a significant decrease in water discharge at most of the main channel stations in the past 40 years and is attributed to increasing regulations of reservoirs and intensive water withdrawal for irrigation and diversions as well as many other anthropogenic processes despite the increasing trend in tds concentrations the seaward tds flux to the sea by the huanghe has decreased dramatically from more than 20 109 kg yr in the 1960s to less than 10 109 kg yr at present due to the sharp decrease in water discharge sometimes completely dried up in the lower reaches of the river the significant decreases in sea ward fluxes of water and dissolved salts are expected to have profound physical ecological and socio economic impacts on the lower reaches of the river the coastal areas and the bohai sea

mantle discontinuity structure beneath the colorado rocky mountains and high plains analysis of mantle discontinuity structure using converted p to s pas phases beneath colorado from the program for array seismic studies of the continental lithosphere passcal rocky mountain front rmf experiment reveals significant topography at the 410 and 660 km depth discontinuities and corresponding transition zone thickness variations a stack of all radial receiver functions resolves the 410 and 660 km discontinuities at average depths of 419 and 677 km respectively imaging of lateral variations in mantle discontinuity structure is accomplished by geographically binning the pds conversion points and then stacking the receiver functions in each bin to form spatial images analogous to common depth point stacking corrections for lateral velocity heterogeneity are calculated using the local s wave tomographic model of lee and grand 1996 and a constant lnvs lnvp scaling of 1 3 this scaling value is determined from the relative scaling between teleseismic p and s wave travel time residuals measured from the rocky mountain front deployment mantle discontinuity images using 150 km square bins show 20 km of 410 km discontinuity topography 30 km of 660 km discontinuity topography and up to 40 km of transition zone thickness variation features of the discontinuity structure include a 20 km depression of the 660 km discontinuity beneath western colorado and a gradual 10 km dip of the 410 km discontinuity beneath the high plains the thickening of the transition zone beneath southwest colorado is consistent with the presence of the subducted farallon slab in this region as imaged by van der lee and nolet 1997 in general our results show that the transition zone discontinuity structure is more complex than that predicted by the simple model of olivine phase boundaries modulated by vertically coherent thermal anomalies

brittle shear tectonics in a narrow continental rift asymmetric nonvolcanic barmer basin rajasthan india abstractour field studies emphasizing brittle shear p and y planes along the margins of the barmer basin rajasthan india support its two phase nw se followed by ne sw extension during early cretaceous and late cretaceous paleocene periods we also document nearly ne trending megascale transfer zones along the northern margin of the barmer basin preexisting brittle planes in the malani basement rocks guided the relay structures here structures at the western basin shoulder margin indicate ne sw extension and the crosscut relation connotes the relative timing of the two extension phases the crosscutting conjugate fault sets are non andersonian the nw trending faults produced by the second phase extension and the inherited nnw trending brittle features are dominantly dip slip prior fractures of the malani rocks at 45 to the ne sw principal extension direction extended the barmer basin obliquely during the late cretaceous paleocene period the asymmetric nature of the rift too connotes its ob

receiver function images of the mantle transition zone beneath ne china new constraints on intraplate volcanism deep subduction and their potential link abstract in order to better understand the deep subduction geometry of the pacific plate and genesis of intraplate volcanism in northeast china ne china we computed a total of 45 505 receiver functions from 788 teleseismic events recorded by 255 stations necessarray temporal and permanent stations in ne china we used a common conversion point stacking ccp method to generate a 3d reflectivity volume beneath the study area to position the p to s conversions to the correct depths we employed 3d crustal and mantle models as references to make time to depth conversion the 3d reflectivity volume was generated in an area between 115 135 e and 40 49 n in the depth range of 300 to 800 km we found significant topographic relief on the 660 km discontinuity across the study area in particular in a westward pacific plate subduction section between 40 n and 45 5 n the 660 km discontinuity is depressed by as much as 30 40 km along the western extension of the deep seismicity the depression is elongated along the strike of the deep seismicity and is confined to a 200 300 km region in the e w direction of subduction to the west of this depression the 660 km discontinuity is uplifted by 5 10 km in a rectangular area of 100 km by 200 km centered at about 125 e and 43 n in the north the 660 km discontinuity is moderately depressed 20 km in a broad area that extends further west the high and low regions in the 660 km topographic map correlate respectively with low and high velocity anomalies in the p and s wave tomographic velocity images at the same depth our results suggest that slab stagnation might not be occurring in the southern part of the ne china where the changbaishan volcanic complex is located thus the magmatism is unlikely caused by dehydration of the flat lying pacific slab in the transition zone the low velocity mantle upwelling arising from a gap of stagnant slabs is a likely source that feeds the volcanic complex in ne china

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

solute geochemistry and its sources of the groundwaters in the qinghai lake catchment nw china major ion compositions were analyzed in 65 groundwater samples to decipher water quality solute geochemistry and sources of groundwater within the qinghai lake catchment ne tibetan plateau groundwaters were slightly alkaline with ph varying from 7 2 to 8 7 the total dissolved solids tds varied over two orders of magnitude from fresh 88 to brackish 12 with a mean value of 672 mg l higher than river waters within the qinghai lake catchment and river waters draining the himalayas and the southeastern tibetan plateau most of the samples approximately 80 were the ca 2 mg 2 hco 3 type and suitable for drinking and irrigation some of the lakeside the buha and the qinghai lake water were cl type and not suitable for drinking and irrigation water quality of hargai and shaliu samples was better than the others rock weathering ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the qinghai lake catchment anthropogenic input to the groundwater is minor the forward models on the input of groundwaters from various sources showed that the contributions were 40 1 for carbonate weathering 29 0 for evaporite dissolution 16 8 for atmospheric input and 14 1 for silicate weathering of the total dissolved cations for the whole catchment evaporite dissolution was dominating in the lakeside the buha and the daotang samples contributing 15 3 45 9 20 4 61 1 and 21 3 63 9 of the total dissolved cations respectively carbonate weathering was dominated in the shaliu and the hargai samples contributing 23 9 71 7 and 31 8 95 4 of the total dissolved cations respectively the result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering

correlation of a 410 km discontinuity low velocity layer with velocity tomograms beneath the colorado plateau using the ristra array the transition zone water filter model nature 425 6953 39 44 2003 predicts that a hydrous partial melt layer is only actively produced in a region of upwelling mantle we test the transition zone water filter model via stacking of p to s converted receiver functions by using the iris passcal ristra colorado plateau rio grande rift seismic transect experiment array assuming the high velocity regions found at the northwest and southeast ends of the array at 350 440 km by teleseismic velocity tomograms e g schmandt and humphreys earth and planetary science letters 297 3 4 435 445 2010 are cold and sinking vertically the 410 km low velocity layer should be absent in these regions the receiver function stacking profiles find the mean depths of the two primary discontinuities at 417 7 1 km for the 410 km discontinuity and 667 8 2 km for the 660 km discontinuity the average arrival amplitudes with respect to z component are 3 0 for the 410 km discontinuity 2 8 for the 660 km discontinuity and 1 8 for the 410 km low velocity layer the stacked pds image show the 410 km low cabsent at 350 to 390 km in the high velocity regions but present in low velocity region a correlation plot of sum of the 410 km low velocity arrival amplitudes and p wave perturbation finds a positive linear relationship therefore our findings provide seismic evidence for the transition zone water filter model at a small scale

sources of environmental sulfur in the groundwater system southern new zealand abstract sulfide minerals commonly occur in sediments and basement rocks in southern new zealand as authigenic precipitates from groundwater below the oxygenated surface zone there are two principal potential sources for sulfur in the groundwater system weathering of sulfide minerals in the metamorphic basement and rainwater derived marine aerosols we present data for these two key sulfur sources metamorphic sulfide and associated hydrothermal au bearing veins within the otago schist average 34s 1 8 2 4 and an inland saline lake s derived entirely from rainwater 34s 21 4 0 8 we use these two end member 34s values to estimate the contributions of these sources of sulfur in authigenic groundwater sulfide minerals and in waters derived from oxidation of these sulfide minerals across a range of environments we show that authigenic groundwater pyrite along joints in the otago schist is derived primarily from metamorphic basement sulfur in contrast authigenic groundwater pyrite cementing miocene recent aquifers shows a substantial marine aerosol component and represents a distinct hydrogeological system we suggest that marine aerosols represent a significant flux to the terrestrial sulfur cycle that has been present through the groundwater system in otago over the past 20 million years

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

emissions of alkaline elements calcium magnesium potassium and sodium from open sources in the contiguous united states models of dust emissions by wind erosion including winds associated with regional activity as well as dust devils and vehicular disturbances of unpaved roads were developed calibrated and used to estimate alkaline dust emissions from elemental soil and road composition data emissions from tillage of soils were estimated from the work of previous researchers the area of maximum dust production by all of those sources is the area of the old dust bowl of the 1930s the panhandles of texas and oklahoma eastern new mexico and colorado and western kansas the areas of maximum alkaline dust production are the arid southwest the dust bowl and the midwestern mideastern states from iowa to pennsylvania our calculations show that calcium is the dominant alkaline element produced by open sources sources too great in extent to be controlled by enclosure or ducting although the largest dust mass source is wind erosion by winds associated with regional activity and convective activity the largest producer of the alkaline component is road dust because the abundance of alkaline materials in road coverings which include crushed limestone is significantly higher than for soils comparing the above estimated sources of alkaline material with inventories of so2 and nox emissions by previous investigators gives the rough approximation that alkaline emission rates are of the order of the so2 nox emissions in the western united states and that they are much smaller than so2 nox in the eastern united states this approximation is substantiated by data on ca so4 no3 for wet deposition for national atmospheric deposition program sites

sensitivity of glacial isostatic adjustment to a partially molten layer at 410 km depth we present a sensitivity analysis aimed at testing whether observables related to glacial isostatic adjustment can support or refute the occurrence of a low viscosity melt rich layer mrl above the mantle transition zone as required by the transition zone water filter model bercovici karato 2003 in total 1600 model runs were performed sampling a range of mrl thicknesses 1 10 and 20 km and viscosities 10 15 10 19 pa s plausible viscosity values in the upper and lower mantle regions and four distinct ice histories to determine decay time constraints we consider relative sea level rsl data from two sites angerman river ar sweden and richmond gulf rg canada and use a new method of observational sea level data correction comparing model output of postglacial decay times and j 2 to observational constraints we find numerous possible solutions largely as a result of parameter trade off the investigated observables are sensitive to the existence of an mrl and reasonable variations in its thickness and viscosity the magnitude and nature of this sensitivity varies between the two data types as well as the adopted background viscosity structure decay time results from either considered location do not strictly support or exclude mrl existence however both locations offer mrl viscosity requirements for given thicknesses with ar being more restrictive rg constraints allow mrl viscosities as low as 10 16 pa s 10 km and 10 17 pa s 20 km ar results narrow these permitted viscosity ranges to 10 18 pa s or greater for both 10 and 20 km mrl thicknesses in the case of a 1 km thick mrl ar constraints permit the viscosity to be as low as 10 17 pa s whereas those of rg permit any mrl viscosity the decay time observations are satisfied by only a small subset of background mantle viscosities regardless of the mrl properties none of which support a spherically symmetric solution of earth viscosity finally comparing model output to the observed j 2 value did not provide any constraints on mrl properties however our results show that this observable has a strong preference for viscosity values in the lower mantle that are equal to or greater than 10 22 pa s

seismic evidence for water transport out of the mantle transition zone beneath the european alps abstract the mantle transition zone has been considered a major water reservoir in the deep earth mass transfer across the transition zone boundaries may transport water rich minerals from the transition zone into the water poor upper or lower mantle water release in the mantle surrounding the transition zone could cause dehydration melting and produce seismic low velocity anomalies if some conditions are met therefore seismic observations of low velocity layers surrounding the transition zone could provide clues of water circulation at mid mantle depths below the alpine orogen a depressed 660 km discontinuity has been imaged clearly using seismic tomography and receiver functions suggesting downwellings of materials from the transition zone multitaper correlation receiver functions show prominent 0 5 1 5 velocity reductions at 750 800 km depths possibly caused by partial melting in the upper part of lower mantle the gap between the depressed 660 km discontinuity and the low velocity layers is consistent with metallic iron as a minor phase in the topmost lower mantle reported by laboratory studies velocity drops atop the 410 km discontinuity are observed surrounding the alpine orogeny suggesting upwelling of water rich rock from the transition zone in response to the downwelled materials below the orogeny our results provide evidence that convective penetration of the mantle transition zone pushes hydrated minerals both upward and downward to add hydrogen to the surrounding mantle

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

geochemical compositions of soluble salts in aeolian sands from the taklamakan and badanjilin deserts in northern china and their influencing factors and environmental implications two large sandy seas in northern china the taklamakan and badanjilin deserts were investigated for geochemical variations of soluble salts in aeolian sands the aim was to explore factors influencing the composition and distribution of soluble salts in aeolian sands and their environmental implications the total concentrations of soluble salt in the aeolian sands range between 0 14 and 1 32 with ph ranging between 8 4 and 9 6 indicating a primary degree of salt accumulation and alkaline soil conditions in these regions sodium chloride and bicarbonate are the major salts high inter regional homogenization and small local differences in the chemical compositions and distributional patterns of salt occur in the two deserts the spatial variations in salt content correlate with regional climatic parameters such as precipitation and temperature this suggests that the regional air temperature and moisture conditions of climate have a significant influence on the soluble salts in aeolian sands the domination of sedimentation of soluble salts in aeolian sands deposited via atmospheric processes which is heavily associated with dry deposition is discussed case studies from the two deserts suggest that variations in salt content in sedimentary sequences interlaid by aeolian and lacustrine sediments should be interpreted with care if the aim is to reveal palaeo environmental changes to a certain extent the two deserts as inferred from the carbon bearing salts and the alkalinity of the sandy soils appear to have potential to provide a significant contribution to the global carbon cycle

multiple oxygen 16o 17o and 18o and sulfur 32s 33s 34s and 36s isotope signatures of the dissolved sulfate from deception island antarctic peninsula implications on sulfate formation transportation and deposition in the antarctic region abstract oxygen 16 o 17 o and 18 o and sulfur 32 s 33 s 34 s and 36 s isotope ratios of and major ion na ca 2 cl no 3 and so 4 2 concentrations in lakes ponds and creeks from deception island antarctic peninsula were analyzed to study the sources of sulfate its oxidation and the surficial processes of the dissolved sulfate the positive relationship between the 34 s sulfate 8 1 to 17 3 and the cl so 4 2 molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals the average sea salt fraction 28 and 34 s nss values from 5 6 to 15 9 indicate that a combination of sea salt and marine biogenic sulfide provide the high 34 s end member of the dissolved sulfates the relatively low 18 o sulfate from 4 6 to 0 7 of deception island water suggests a role of local water in the formation of sulfate slightly negative but mass dependent 17 o sulfate values imply that atmospheric oxidation by o 3 and h 2 o 2 are negligible while these values might suggest a significant role of oxidation by molecular oxygen and oh the distinctly low 34 s sulfate value of two samples dcw 2 and dcw 3 suggests the input of sulfate from sulfide oxidation slight elevation of 34 s sulfate values up to 17 3 compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of deception island water and sediments both 33 s sulfate and 36 s sulfate values are homogeneous and near zero implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to deception island water

intraplate volcanism originating from upwelling hydrous mantle transition zone most magmatism occurring on earth is conventionally attributed to passive mantle upwelling at mid ocean ridges to slab devolatilization at subduction zones or to mantle plumes however the widespread cenozoic intraplate volcanism in northeast china1 3 and the young petit spot volcanoes4 7 offshore of the japan trench cannot readily be associated with any of these mechanisms in addition the mantle beneath these types of volcanism is characterized by zones of anomalously low seismic velocity above and below the transition zone8 12 a mantle level located at depths between 410 and 660 kilometres a comprehensive interpretation of these phenomena is lacking here we show that most or possibly all of the intraplate and petit spot volcanism and low velocity zones around the japanese subduction zone can be explained by the cenozoic interaction of the subducting pacific slab with a hydrous mantle transition zone numerical modelling indicates that 0 2 to 0 3 weight per cent of water dissolved in mantle minerals that are driven out from the transition zone in response to subduction and retreat of a tectonic plate is sufficient to reproduce the observations this suggests that a critical amount of water may have accumulated in the transition zone around this subduction zone as well as in others of the tethyan tectonic belt13 that are characterized by intraplate or petit spot volcanism and low velocity zones in the underlying mantle the widespread intraplate volcanism in northeast china and the unusual petit spot volcanoes offshore japan could have resulted from the interaction of the subducting pacific slab with a hydrous mantle transition zone

the melt content of the low velocity layer in the eastern south china implications for the subduction process of the western pacific plate abstract the low velocity layer lvl atop the mantle transition zone involves diapiric segregating melt upwelling mantle mixing magmatic eruption and the remnants the lateral variations of the lvl could record the process of the subducting plates the lvl beneath the eastern south china intensively affected by the subduction of western pacific plate since mesozoic is imaged with observed p wave triplications recorded by the dense chinese digital seismic network the thicknesses of the lvl are 57 km for sub region a 40 km for sub region b and 20 km for sub region c the melt fractions related to the different velocity structures of the lvl beneath three north to south adjacent sub regions a b and c of the eastern south china are estimated with the bulk solid compositions reference potential temperatures compositions and dihedral angles the spatial characteristics of the melt fractions and the lvl thicknesses are in accord with the recession directions of the subduction fronts of the western pacific plate this consistency provides a powerful information for understanding the plate subduction process

low velocity zone atop the 410 km seismic discontinuity in the northwestern united states the seismic discontinuity at 410 km depth in the earth s mantle is generally attributed to the phase transition of mg fe 2sio 4 from the olivine to wadsleyite structure variation in the depth of this discontinuity is often taken as a proxy for mantle temperature owing to its response to thermal perturbations for example a cold anomaly would elevate the 410 km discontinuity because of its positive clapeyron slope whereas a warm anomaly would depress the discontinuity but trade offs between seismic wave speed heterogeneity and discontinuity topography often inhibit detailed analysis of these discontinuities and structure often appears very complicated here we simultaneously model seismic refracted waves and scattered waves from the 410 km discontinuity in the western united states to constrain structure in the region we find a low velocity zone with a shear wave velocity drop of 5 on top of the 410 km discontinuity beneath the northwestern united states extending from southwestern oregon to the northern basin and range province this low velocity zone has a thickness that varies from 20 to 90 km with rapid lateral variations its spatial extent coincides with both an anomalous composition of overlying volcanism and seismic receiver function observations observed above the region we interpret the low velocity zone as a compositional anomaly possibly due to a dense partial melt layer which may be linked to prior subduction of the farallon plate and back arc extension the existence of such a layer could be indicative of high water content in the earth s transition zone

evaluation of eocene source rock for potential shale oil and gas generation in north cambay basin india abstract source rock potential of 108 representative samples from 3 m intervals over a 324 m thick shale section of middle eocene age from the north cambay basin india have been studied variation in total organic carbon toc and its relationship with loss on ignition loi have been used for initial screening screened samples were subjected to rock eval pyrolysis and organic petrography a toc log indicated wide variation with streaks of elevated toc a 30 m thick organic rich interval starting at 1954 m depth displayed properties consistent with a possible shale oil or gas reservoir toc wt values of the selected samples were found to vary from 0 68 to 3 62 with an average value of 2 2 the modified van krevelen diagram as well as hi vs t max plot indicate prevalence of type ii to type iii kerogen t max measurements ranged from 425 c to 439 c indicating immature to early mature stage which was confirmed by the mean vitrinite reflectance values r o of 0 63 0 65 and 0 67 at 1988 m 1954 m and 1963 m respectively quantification of hydrocarbon generation migration and retention characteristics of the 30 m source rock interval suggests 85 expulsion of hydrocarbon oil in place oip resource of the 30 m source rock was estimated to be 3 23 mmbbls per 640 acres the oil saturation index osi crossover log showed from a geochemical perspective moderate risk for producing the estimated reserve along with well location for tapping the identified resource

seismic evidence for a global low velocity layer within the earth s upper mantle above the 410 km discontinuity in the upper mantle an intermittent layer characterized by low seismic wave velocities is thought to represent partial melting in areas of subduction or mantle plume activity seismic data now show that the low velocity layer extends globally with no affinity to a particular tectonic environment

the effective source rocks in the north cambay basin india abstract source rock screening reveals five laterally extending potential sources ps in the paleogene the pss are sr5 and sr6 in dominantly marine early eocene to late paleocene cambay shale formation and sr7 sr8 9 and sr11 12 in dominantly freshwater early paleocene olpad formation only 3 pss sr11 12 sr8 9 and sr7 have attained vitrinite reflectance of 0 75 at 45 7 and 2 mybp respectively chromatographic and isotope data of oils and ps samples suggest that mainly the olpad source rocks sr7 and sr8 9 contributed to the discovered oils the cambay shale source rocks sr5 and sr6 contrary to the prevalent view possibly have no significant contribution towards the accumulated oils

climatic and geological factors contributing to the natural water chemistry in an arid environment from watersheds in northern xinjiang china a natural water hydrochemical investigation was carried out on three watersheds in northern xinjiang china to evaluate the climatic geological and anthropogenic influence on aqueous major element chemistry in an arid environment wide spatial variations are observed in the dissolved solids tds and water chemistry the hydrochemistry is typically carbonate and alkaline in nature with ca2 hco3 and so42 dominating the major ion composition four major water types ca hco3 ca nda non dominant anion ca so4 and ndc non dominant cation nda or na nda type are identified in terms of the piper model the water chemistry agrees well with the rock dominance mechanism with a tds value of 80 600 mg l and a na na ca2 ratio of 0 1 0 6 correlation analysis suggests that most of the ions derive from multiple sources stoichiometric analyses indicate that carbonate weathering is the primary source of dissolved ions followed by silicate weathering and evaporite dissolution the effects of local pollution have somewhat greater contribution on the oases and central areas of the zhungarer watershed most parts of the rivers show an increasing trend in the dissolved load toward the lower reaches which is primarily attributed to an evaporation process control along the water course variations in water chemistry show clear correlation with the regional lithological distribution topography and atmospheric precipitation using rainwater as a baseline contributions from atmospheric precipitation and rock weathering to the tributary chemistry are roughly evaluated to be in the range of 2 39 average 13 and 59 98 average 86 respectively implying a high effective control of regional geology on stream chemistry compared with that of atmospheric input c 2012 elsevier b v all rights reserved

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

elasticity of superhydrous phase b at the mantle temperatures and pressures implications for 800 km discontinuity and water flow into the lower mantle the thermodynamic properties and elasticity of superhydrous phase b shyb at high pressure and temperature are calculated using first principles calculations based on density functional theory the velocities and densities of shyb are significantly lower than those of bridgmanite and periclase the major minerals in the lower mantle the anisotropy of shyb is unremarkable at relevant mantle conditions the decomposition of shyb into bridgmanite periclase and water which can occur at a depth around 800 km at a cold slab will cause an increase of 7 5 15 0 and 12 on shear velocity compressional velocity and density respectively thus the decomposition of a small amount of shyb can produce a local discontinuity at the depth of 800 km the water released from the decomposition of shyb may rise upward and promote the partial melt which can further explain the low velocity zones just above 800 km discontinuity in western pacific subduction zones

a sporadic low velocity layer atop the 410 km discontinuity beneath the pacific ocean waveforms of ss precursors recorded by global stations are analyzed to investigate lateral heterogeneities of upper mantle discontinuities on a global scale a sporadic low velocity layer immediately above the 410 km discontinuity lvl 410 is observed worldwide including east asia western north america eastern south america the pacific ocean and possibly the indian ocean our best data coverage is for the pacific ocean where the lvl 410 covers 33 50 of the resolved region lateral variations of our lvl 410 observations show no geographical correlation with 410 km discontinuity topography or tomographic models of seismic velocity suggesting that the lvl 410 is not caused by regional thermal anomalies we interpret the lvl 410 as partial melting due to dehydration of ascending mantle across the 410 km discontinuity which is predicted by the transition zone water filter hypothesis given the low vertical resolution of ss precursors it is possible that the regions without a clear lvl 410 detection also have a thin layer therefore the strong lateral heterogeneity of the lvl 410 in our observations suggests partial melting with varying intensities across the pacific and further provides indirect evidence of a hydrous mantle transition zone with laterally varying water content

elasticity of single crystal superhydrous phase b at simultaneous high pressure temperature conditions we investigated the combined effect of pressure and temperature on the elasticity of single crystal superhydrous phase b shy b using brillouin scattering and x ray diffraction up to 12 gpa and 700 k using the obtained elasticity we modeled the anisotropy of shy b along slab geotherms showing that shy b has a low anisotropy and cannot be the major cause of the observed anisotropy in the region modeled velocities of shy b show that shy b will be shown as positive velocity anomalies at the bottom transition zone once shy b is transported to the topmost lower mantle it will exhibit a seismic signature of lower velocities than topmost lower mantle we speculate that an accumulation of hydrous phases such as shy b at the topmost lower mantle with a weight percentage of 17 26 in the peridotite layer as subduction progresses could help explain the observed 2 3 low shear velocity anomalies in the region

a mathematical representation of rock eval hydrogen index vs tmax profiles abstract different types of kerogens have different maturation paths on rock eval hydrogen index hi vs t max plots an equation hi 1 a exp b t max 435 c where a b and c are constants can be used to define hi t max profiles of particular source rock units the constants a b and c characterise the particular kerogen and also allow expression of its transformation ratio tr as a function of the t max by an equation tr hi 0 a exp b t max 435 hi 0 a exp b t max 435 1 where hi 0 1 c the hi t max equation constants were determined by nonlinear curve fitting for three standard type i ii and iii kerogens and for two geological sections second white speckled 2ws formation alberta basin and a source rock unit of cambay basin india high correlation coefficients for the fitted equations for four hi t max data sets of four groups of the 2ws samples segregated using oxygen index oi vs t max cross plot and for one data set of the cambay basin source rock unit show the validity of the proposed hi t max equation comparison of the calculated tr and measured production index pi values for the 2ws samples allow identification of samples that have expelled generated hydrocarbons and samples that contain unexpelled generated hydrocarbons for the cambay basin example where rock eval data of silty and sandy samples were screened out a reasonable match exists between the calculated trs and measured production index values up to a t max value of 445 c indicating onset of oil expulsion the proposed hi t max equation can thus characterise organic matter in a source rock unit with respect to its original generation potential and hydrocarbon generation threshold and rate it may also help to identify the effective source sections that have expelled generated hydrocarbons from several potential source rocks if present in a basin

reply to comment by kawakatsu and abe on nature of the seismic lithosphere asthenosphere boundary within normal oceanic mantle from high resolution receiver functions kawakatsu and abe 2016 have highlighted the potential complicating effect of sediment reverberations on the analysis and interpretation of crust and mantle phases inferred from receiver functions analyzed from ocean bottom seismograms in their comment they identify resonant peaks in the power spectrum at one of the stations t06 in the analysis of olugboji et al 2016 and demonstrate with synthetic modeling how sediment induced resonances can cause instability in the recovered receiver function rf traces they also request a detailed explanation of how lqt rotation is conducted and why its use leads to stable receiver functions in the analysis of olugboji et al 2016 we welcome this query as an opportunity to highlight certain technical aspects of the data analysis procedures used in olugboji et al 2016 our methods derive partly from methods recommended by previous studies of receiver functions estimated from seismic seafloor data bostock and trehu 2012 janiszewski and abers 2015 audet 2016 particularly the use of the modal wavefield decomposition e g reading et al 2003 which we approximated by the lqt rotation to suppress reverberation signals in the overlying water column bostock and trehu 2012 this article is protected by copyright all rights reserved

geochemistry of the amazon 1 precipitation chemistry and the marine contribution to the dissolved load at the time of peak discharge analyses of precipitation and surface water are used to estimate the fluxes of marine cyclic salts through that part of the amazon river system draining past obidos 80 of the basin at the time of peak discharge in june amazon precipitation chemistry can be devided into two principal components marine and terrestrial the marine component determined from analyses of marine rain consists of na k mg ca and cl in approximately sea salt proportions with s doubly enriched the excess sulfur is probably derived from gas phase inputs the terrestrial component makes an important contribution of k ca s and n much of which can be related to biological emissions the emission of reduced sulfur in the marine and terrestrial environment and nitrogen in the terrestrial environment is responsible for a natural acid rain in the amazon region with a ph from 4 7 to 5 7 this is about one tenth the acidity of polluted urban rain the chloride content of lowland rivers which drain regions lacking significant geologic sources of chloride shows a systematic decrease in chloride with increasing distance from the ocean this trend is used to define the cyclic salt background for amazonian surface waters cyclic salts in general make only a minor contribution relative to terrestrial inputs to the chemistry of amazon basin rivers even those draining intensely weathered terrains an estimated 17 6 cl 6 9 na 1 3 mg 3 6 s 0 4 k and 0 1 ca of the dissolved load at obidos during peak discharge is cyclic

seismological detection of low velocity anomalies surrounding the mantle transition zone in japan subduction zone in the japan subduction zone a locally depressed 660 discontinuity has been observed beneath northeast asia suggesting downwelling of materials from the mantle transition zone mtz vertical transport of water rich mtz materials across the major mineral phase changes could lead to water release and to partial melting in surrounding mantle regions causing seismic low velocity anomalies melt layers implied by low velocity zones lvzs above the 410 discontinuity have been detected in many regions but seismic evidence for partial melting below the 660 discontinuity has been limited high frequency migrated ps receiver functions indicate lvzs below the depressed 660 discontinuity and above the 410 discontinuity in the deep japan subduction zone suggesting dehydration melting induced by water transport out of the mtz our results provide insights into water circulation associated with dynamic interactions between the subducted slab and surrounding mantle

changbaishan volcanism in northeast china linked to subduction induced mantle upwelling the changbaishan volcanic complex in china cannot be easily explained as the consequence of a mantle plume seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting pacific plate but is now escaping upwards through a gap in the plate and producing the intraplate volcanism

mapping the subducting pacific slab beneath southwest japan with hi net receiver functions abstract we have used 4th root receiver function stacks and pre stack receiver function depth migrations to study the transition zone discontinuity structure beneath southwestern japan receiver functions were calculated from the quiet short period seismograms recorded by a recently deployed borehole network hi net we found that a relatively broad frequency band can be retrieved from a short period seismogram by a deconvolution of the instrument response the quality of the receiver functions formed from large earthquake recordings is comparable to those from broadband instruments we applied common conversion point gathering to the receiver function data to image the p to s conversion events beneath the network by stacking with a 4th root technique to improve lateral coherence we found that the topographic anomalies of the 410 and 660 km discontinuities beneath southwest japan have very different length scales the former is characterized by a narrow 150 200 km wide topographic high while the latter exhibits a broad 400 km wide moderate topographic low together with a small scale larger amplitude depression a 2 5d pre stack depth migration of the receiver functions shows the transition zone features clearly as well as images of a change of slope in the subducting slab at the 410 discontinuity and flattening of the slab onto the 660 km these observations show that the subducted pacific slab is deflected when it encounters the upper and lower boundaries of the transition zone and is flat lying either above or across the 660 km discontinuity the flat lying slab is however restricted to the bottom of the transition zone and probably experiences much less thickening than is suggested by some global tomographic images in which subhorizontal high velocity anomalies are seen throughout the transition zone between the two discontinuities

chemical versus mechanical denudation in meta clastic and carbonate bedrock catchments on crete greece and mechanisms for steep and high carbonate topography on crete as is common elsewhere in the mediterranean carbonate massifs form high mountain ranges whereas topography is lower in areas with meta clastic rocks this observation suggests that differences in denudational processes between carbonate rich rocks and quartzofeldspathic units impart a fundamental control on landscape evolution here we present new cosmogenic basin average denudation rate measurements from both 10be and 36cl in meta clastic and carbonate bedrock catchments respectively to assess relationships between denudation rates processes and topographic form we compare total denudation rates to dissolution rates calculated from 49 new and previously published water samples basin average denudation rates of meta clastic and carbonate catchments are similar with mean values of 0 10 mm a and 0 13 mm a respectively the contribution of dissolution to total denudation rate was 10 in the one measured meta clastic catchment and 40 for carbonate catchments 0 05 mm a suggesting the dominance of physical over chemical weathering at the catchment scale in both rock types water mass balance calculations for three carbonate catchments suggests 40 90 of surface runoff is lost to groundwater to explore the impact of dissolution and infiltration to groundwater on relief we develop a numerical model for carbonate denudation we find that dissolution modifies the river profile channel steepness and infiltration changes the fluvial response time to external forcing furthermore we show that infiltration of surface runoff to groundwater in karst regions is an efficient way to steepen topography and generate the dramatic relief in carbonates observed throughout crete and the mediterranean

the dynamics of big mantle wedge magma factory and metamorphic metasomatic factory in subduction zones abstract the east asian continental margin is underlain by stagnant slabs resulting from subduction of the pacific plate from the east and the philippine sea plate from the south we classify the upper mantle in this region into three major domains a metasomatic metamorphic factory mmf subduction zone magma factory szmf and the big mantle wedge bmw whereas the convection pattern is anticlockwise in the mmf domain it is predominantly clockwise in the szmf and bmw along a cross section from the south here we define the mmf as a small wedge corner which is driven by the subducting pacific plate and dominated by h 2 o rich fluids derived by dehydration reactions and enriched in large ion lithophile elements lile which cause the metasomatism the szmf is a zone intermediate between mmf and bmw domains and constitutes the main region of continental crust production by partial melting through wedge counter corner flow large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of szmf more fertile and high temperature peridotites are supplied from the entrance to this domain the domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab the bmw occupies the major portion of upper mantle in the western pacific and convects largely with a clockwise sense removing the eastern trench oceanward sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading we envisage that the heat source in bmw could be the accumulated ttg tonalite trondhjemite granodiorite crust on the bottom of the mantle transition zone the ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra oceanic arcs on the subducting philippine sea plate from the south in addition to the sediment trapped subduction by the pacific plate and philippine sea plate the dynamics of mmf szmf and bmw domains are controlled by the angle of subduction a wide zone of mmf in sw japan is caused by shallow angle subduction of the philippine sea plate and the markedly small mmf domain in the mariana trench is due to the high angle subduction of pacific plate the domains in ne japan and kyushu region are intermediate between these two during the tertiary a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of tethyan asia which may be related to the collision of india with asia and the indentation the volume of upper mantle under asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of asia leading to the formation of a series of marginal basins the western pacific domain in general is characterized by double sided subduction from the east by the oldest pacific plate and from the south by the oldest indo australian plate the old plates are hence hydrated extensively even in their central domains and therefore of low temperature the cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle thus a fluid dominated upper mantle in the western pacific drives a number of microplates and promote the plate boundary processes

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

pyrolysis gas chromatography of asphaltenes kerogens from source rocks of the gandhar field cambay basin india abstract pyrolysis gas chromatography of rocks from three exploratory wells in the gandhar area of the cambay basin india reveals that the organic matter is dominated by input from higher land plants the pyrograms of asphaltenes and kerogens demonstrate that the hazad and cambay shale were deposited in different environments with the former being an overall regressive deltaic environment and the latter a marine transgressive sequence studies of toc values range from 1 to 2 6 rock eval hi values range from 70 to 183 pyrolysis gas chromatography vitrinite reflectance r o range from 0 4 to 0 8 bitumen extracts and isotopic ratios demonstrate that both hazad and upper cambay shale can act as effective source rocks wherever they are thermally mature

thermal equation of state of natural ti bearing clinohumite the natural occurrence of clinohumite in metabasalts and hydrothermally altered peridotites provides a source of water rich minerals in subducted slabs making knowledge of their phase relations and crystal chemistry under high p t conditions important for understating volatile recycling and geodynamic process in the earth s mantle here we present a synchrotron based single crystal x ray diffraction study on two natural ti bearing clinohumites up to 28 gpa and 750 k in order to simulate conditions within subducted slabs no phase transition occurs in clinohumite over this p t range pressure volume relationships of both compositions at room temperature were fitted to a third order birch murnaghan equation of state eos with v0 650 4 3 a3 kt0 141 4 gpa and kt0 4 0 6 for ti poor clinohumite 0 07 ti per formula unit pfu and v0 650 8 3 a3 kt0 144 4 gpa and kt0 3 6 7 for ti rich clinohumite 0 21 ti pfu both clinohumites exhibit anisotropic compression with b c a we also refined p v t equation of state parameters using the high temperature birch murnaghan htbm eos yielding kt0 t p 0 040 10 gpa k and t 5 1 6 10 5 k 1 for ti poor clinohumite kt0 t p 0 045 11 gpa k and t 5 7 6 10 5 k 1 for ti rich clinohumite ti poor and ti rich clinohumites display similar equations of state but are 20 more incompressible than mg pure clinohumite and display 5 higher bulk sound velocity than olivine at upper mantle conditions our results provide constraints for modeling geodynamic process related to the subduction and transport of potentially water rich slabs in the mantle

receiver functions in northeast china implications for slab penetration into the lower mantle in northwest pacific subduction zone abstract seismic studies of the subducting lithosphere and the upper mantle discontinuities in the northwest pacific subduction zone beneath japan and northeast china have suggested contrary subduction scenarios there was little consensus on the issue whether the subducting slab penetrates the upper mantle discontinuities into the lower mantle or it is deflected atop of the 660 km discontinuity over several hundred kilometers we calculate receiver functions from a recent seismic broadband station network located in northeast china and find topographic variations of the upper mantle discontinuities a deeper than normal 660 km discontinuity is observed over an area of 400 km and it coincides with the stagnant slab imaged by seismic tomography the 660 km discontinuity is locally depressed by more than 35 km and the transition zone is thickened by more than 20 km in the east of the region where it encounters the slab these observations provide evidence of the slab accumulating in the mantle transition zone and locally penetrating into the lower mantle

mapping seismic anisotropy using harmonic decomposition of receiver functions an application to northern apennines italy 1 isotropic and anisotropic seismic structures across the northern apennines italy subduction zone are imaged using a new method for the analysis of teleseismic receiver functions rfs more than 13 000 p wave coda of teleseismic records from the 2003 2007 retreating trench extension and accretion tectonics retreat experiment are used to provide new insights into a peculiar subduction zone between two continental plates that is considered a focal point of mediterranean evolution a new methodology for the analysis of receiver functions is developed which combines both migration and harmonic decomposition of the receiver function data set the migration technique follows a classical common conversion point scheme and helps to focus on a crucial depth range 20 70 km where the mantle wedge develops harmonic decomposition of a receiver function data set is a novel and less explored approach to the analysis of p to s converted phases the separation of the back azimuth harmonics is achieved through a numerical regression of the stacked radial and transverse receiver functions from which we obtain independent constraints on both isotropic and anisotropic seismic structures the application of our method to the retreat data set succeeds both in confirming previous knowledge about seismic structure in the area and in highlighting new structures beneath the northern apennines chain where previous studies failed to clearly retrieve the geometry of the subducted interfaces we present our results in closely spaced profiles across and along the northern apennines chain to highlight the convergence of the tyrrhenian and the adriatic microplates which differ in their crustal structure where the adriatic microplate subducts beneath tuscany and the tyrrhenian sea a signature of the dipping adriatic moho is clearly observed beneath the tyrrhenian moho in a large portion of the forearc region in the area where the two mohos overlap our new analysis reveals the presence of an anisotropic body above the subducted moho there is a strong ps converted phase with anisotropic characteristics from the top of the adriatic plate to a depth of at least 80 km because the ps conversion occurs much deeper than similar ps phases in cascadia and japan dehydration of oceanic crust seems unlikely as a causative factor rather the existence of this body trapped between the two interfaces supports the hypothesis of lower crustal delamination in a postsubduction tectonic setting

pervasive seismic low velocity zones within stagnant plates in the mantle transition zone thermal or compositional origin abstract we exploit conversions between p and s waves for large scale high resolution imaging of the mantle transition zone beneath northwest pacific and the margin of eastern asia we find pervasive reflectivity concentrated in two bands with apparent wave speed reduction of 2 to 4 about 50 km thick at the top of the transition zone and 100 km thick at the bottom this negative reflectivity associated with the scattered waves at depth is interpreted jointly with larger scale mantle tomographic images and is shown to delineate the stagnant portions of the subducted pacific plate in the transition zone with largely positive shear wave velocity contrasts the upper reflectivity zone connects to broad low velocity regions below major intra plate volcanoes whereas the lower zone coincides locally with the occurrence of deep focus earthquakes along the east asia margin similar reflectivity is found in pacific northwest of the usa we demonstrate that the thermal signature of plates alone is not sufficient to explain such features alternative explanations for these reflective zones include kinetic effects on olivine phase transitions meta stability compositional heterogeneities within and above stagnant plates complex wave propagation effects in the heterogeneous slab structure or a combination of such factors we speculate that part of the negative reflectivity is the signature of compositional heterogeneities as revealed by numerous other studies of seismic scattering throughout the mantle and that such features could be widespread across the globe

intensive hydration of the mantle transition zone beneath china caused by ancient slab stagnation the mantle transition zone beneath china is anomalously hydrated geochemical analyses of basalts erupted above the mantle transition zone in northeast china indicate that water may have been added to this zone during the dehydration of subducted slabs on two separate occasions over the past one billion years

large cold anomalies in the deep mantle and mantle instability in the cretaceous two large cold masses in the deep mantle have been delineated by using long wavelength seismic tomographic models in conjunction with mineralogical experimental data at high pressure these cold anomalies are found under the western pacific and the americas with temperatures more than 1000 degrees below the ambient mantle temperature these strong cold anomalies existing in the lower mantle today would suggest that there might have existed not too long ago a substantial temperature jump across a thermal boundary layer between the upper and lower mantle numerical simulations in an axisymmetric spherical shell model incorporating the two major phase transitions have shown that very large pools of cold material with temperatures of around 1500 k can be flushed down to the core mantle boundary during this tumultuous gravitational instability a correlation is found between the current locations of these very cold masses and regions of past subduction since the cretaceous correlation analysis shows that the slab mass flux into the lower mantle does not behave in a steady state fashion these findings may support the idea of a strong gravitational instability with origins in the transition zone as suggested by numerical models of mantle convection

topography of the 660 km discontinuity beneath northeast china implications for a retrograde motion of the subducting pacific slab 1 clear s to p converted waves at the 660 km discontinuity s660p are observed at stacked seismograms of deep earthquakes occurring in northeast china and japan sea recorded by broadband seismic arrays in north america and europe differential travel times between the s660p and p waves are used to constrain depth variations of the 660 beneath northeast china a rapid change in the depth of the 660 is observed within a narrow longitudinal range of 130 8 e 131 4 e where the lower boundary of the subducting slab encounters the 660 towards the west the 660 deepens steadily as it approaches the coldest core of the slab the maximum depression occurs at the west end of the studied region with an amplitude of 20 km to the east the 660 appears to be flat showing no obvious effect of the subducting slab these observations are consistent with a scenario for a retrograde moving pacific slab lying over the upper and lower mantle boundary progressively from west to east