arsenic contamination in groundwater from parts of ambagarh chowki block chhattisgarh india source and release mechanism arsenic contamination in tube well water in ambagarh chowki block central india is restricted to local areas confined within the n s trending dongargarh rift zone affected areas are preferentially located in acid volcanics close to shear zones and also in granites dug wells even in severely contaminated areas generally have as concentration 10 g l but in kaurikasa area several tube wells and dug wells are severely polluted weathered rocks and soils are also enriched in as from severely contaminated areas as preferentially occurs in iron enriched soil and similarly altered biotite chlorite in granite as sorbed in hydrated iron oxide hfo that preferably occurs in acid leachable fraction and possibly as coatings on kaolinite illite and goethite in soil or as coatings and along cleavage traces on weathered biotite and chlorite reductive dissolution of hfo released sorbed as to groundwater and enriched it in fe pyrite in volcanic and shear zone rocks although locally as bearing is a minor source of as in groundwater

elasticity and pressure induced structural changes in vitreous mgsio3 enstatite to lower mantle pressures abstract knowledge of the pressure density relations and elastic properties of silicate melts at high pressure and temperature conditions is fundamental for a better understanding of the dynamics and properties of the earth s interior here we report the sound velocities and elastic properties of vitreous mgsio 3 enstatite a simple analog for melts in the earth s mantle determined up to 33 4 1 2 gpa in a diamond anvil cell by brillouin scattering spectroscopy the adiabatic bulk and shear moduli of mgsio 3 glass at ambient conditions are k s0 78 4 6 gpa and 0 41 1 3 gpa corresponding to compressional and shear wave velocities of v p 6 969 30 km s and v s 3 868 20 km s on compression both longitudinal v p and transverse v s modes exhibit anomalous change in slope at 8 gpa and between 15 0 1 and 17 9 2 gpa that are associated with polyamorphic phase transitions in the glass the acoustic data were used to determine the density and compressibility of mgsio 3 glass at high pressure in both compression and decompression experiments in contrast to velocities and elastic moduli the density increases smoothly without singularities upon compression over the investigated pressure range densities of recovered glasses at room pressure are 1 5 to 2 4 higher than uncompressed glasses indicating pressure induced irreversible densification the anomalous changes in velocities and compressibility with pressure are consistent with structural modifications that have been identified as the main densification mechanisms of the glass by in situ spectroscopic studies and molecular dynamic calculations the results suggest that the residual densification of recovered glasses is associated with irreversible structural changes in the intermediate range order i e ring statistics rather than with changes in the coordination number of si upon pressurization if the changes in compressibility of mgsio 3 glasses identified in the present brillouin study also occurs in the analog melts they may have important implications for the present day dynamics of the mantle and early evolution of the earth during a magma ocean phase

impact of sedimentary provenance and weathering on arsenic distribution in aquifers of the datong basin china constraints from elemental geochemistry arsenic as contaminated aquifer sediments from datong basin china have been analyzed to infer the provenance and depositional environment related to as distribution in the aquifer sediments the as content in the sediments ranged from 2 45 to 27 38 mg kg with an average value of 9 54 mg kg which is comparable to the average value in modern unconsolidated sediments however minor variation in as concentration with depth has been observed in the core there was a significant correlation between fe and al and as which was attributed to the adsorption or co precipitation of as onto with fe oxides hydroxides and or fe coated clay minerals post archean australian shale paas normalized rees patterns of sediment samples along the borehole were constant and the sediments had a notably restricted range of la n yb n ratios from 0 7 to 1 0 these results suggested that the provenance of the datong basin remained similar throughout the whole depositional period the analysis of major geochemical compositions confirmed that all core sediments were from the same sedimentary source and experienced significant sedimentary recycling the co variation of as v al ni al and chemical index of alteration cia values in the sediments along the borehole suggested that as distribution in the sediments was primarily controlled by weathering processes the calculatedmore cia values of the sediments along the borehole indicate that a relative strong chemical weathering occurred during the deposition of sediments at depths of similar to 35 to 88 m which was corresponding to the depth at which high as groundwater was observed at the site strong chemical weathering favored the deposition of fe bearing minerals including poorly crystalline and crystalline fe oxide mineral phases and concomitant co precipitation of as with these minerals in the sediments subsequent reductive dissolution of as bearing poorly crystalline and crystalline fe oxides would result in the enrichment of as in groundwater in general the chemical weathering during the deposition of the sediments governed the co accumulation of fe oxides and as in the aquifer sediments and then the reductive dissolution of fe oxides hydroxides is the mechanism of as enrichment in the groundwater in the datong basin less

femg interdiffusion in olivine up to 9 gpa at t 600 900 c experimental data and comparison with defect calculations abstract interdiffusion data at high pressures are needed to provide good estimates of the closure temperatures of geothermometers based on fe mg exchange in olivine in contact with other phases and to understand the pressure dependence of high temperature deformation in olivine we report here measurements of the interdiffusion coefficient of fe mg in san carlos olivine of mean composition mg mg fe 0 90 in the range of temperatures t 600 900 c and pressures p 0 5 9 gpa the measurements were performed by preparing olivine samples covered by a thin layer of fayalite these specimens were annealed in a uniaxial split sphere apparatus ussa 2000 the fe mg interdiffusion profiles were analysed by rutherford back scattering rbs the results yield a pre exponential factor d 0 7 7 10 8 cm 2 s 1 7 7 10 12 m 2 s 1 and an activation energy e 147 58 kjmol 1 or 62 58 2 sd kj mol 1 if a p o 2 1 6 correction is performed corresponding to the expression d d 0 exp e rt exp x fe exp pv rt our data are fitted best with 3 x fe fe fe mg is between zero and one in the present experiments x fe is around 0 1 p is the pressure and v is found to be 0 5 0 6 cm 3 mol 1 or 1 0 9 cm 3 mol 1 if a p o 2 1 6 correction is performed i e about zero in the p and t range investigated comparisons between the present results obtained at relatively low temperature under extrinsic conditions for diffusion with other fe mg interdiffusion data at high temperature 1125 c or more under intrinsic conditions allow us to deduce that the migration activation volume for point defects is v m 0 whereas that for formation is v f 5 5 cm 3 mol 1 this has important implications for the creep sensitivity to pressure numerical simulations involving energy minimizations and performed with the cascade and parapocs codes confirm these conclusions one finds v m 0 and v f 4 8 cm 3 mol 1 the activation energy e deduced from the experiments as well as the pre exponential factor d 0 now permit precise estimation of the closure temperatures of geothermometers based on the fe mg exchange between olivine and spinel

structure and elasticity of serpentine at high pressure abstract serpentines occur in the subduction zone settings both along the slab and within the mantle wedge they are candidates for transporting water in to the deep earth their presence is manifested by serpentine mud volcanoes high electrical conductivities magnetic and seismic anomalies using theoretical methods we predict a pressure induced structural transformations in serpentine the transformations are related to the behavior of the silicate framework and misfit between octahedral and tetrahedral layers as the structure is compressed the octahedral layer and tetrahedral layers are compressed at different rates at 7 gpa the misfit between the layers vanishes this causes non linear pressure dependence of tetrahedral rotational angle this is also manifested by the onset of anomalous pressure dependence of the elastic constants c 11 c 33 c 12 c 13 beyond 7 gpa the misfit between the layers grows again reaching extremum at 22 gpa this is also manifested by discontinuity in average si o bond length volume of tetrahedron and re orientation of hydroxyl vector the symmetry of the crystal structure however remains unaffected evidence of pressure induced hydrogen bonding is absent in serpentine as evident from reduction of o h bond length upon compression results of compression for the low pressure regime p k 0 79 gpa k 0 12 and k 0 2 where k is the bulk modulus prime indicates pressure derivatives and o refers to zero pressure our best estimates of k 0 k 0 and the gruneisen parameter at 300 k and zero pressure based on our results are 61 gpa 17 and 0 77 respectively at low pressures serpentine structure is anisotropic with c 11 2 4 c 33 the pressure derivative of elastic constants c ij p are such that around 22 gpa c 11 c 33 an elastic instability c 66 50 gpa is also noted the elastic constant tensor reveals large acoustic anisotropy 41 in v p and seismic wave velocities that are significantly higher than those inferred from experiments on serpentinites

experimental evidence for a phase transition in magnesium oxide at exoplanet pressures little is known about the structure of possible mantle materials of extra solar super earths with interior pressures of up to 1 000 gpa dynamic x ray diffraction measurements of ramp compressed magnesium oxide an important component of earth s mantle show a solid solid state transition at about 600 gpa with a high pressure structure that is stable up to 900 gpa

hot dry rock geothermal energy in the jemez volcanic field new mexico abstract large young calderas possess immense geothermal potential due to the size of shallow magma bodies that underlie them through the example of the valles and toledo calderas new mexico and older more deeply eroded and exposed calderas it is possible to reconstruct a general view of geothermal environments associated with such magmatic systems although a zone of anomalous heat flow extends well beyond caldera margins high to moderate temperature hydrothermal systems appear to be restricted to zones along intracaldera faults and may account for only about five percent of the thermal energy available from the magmatic system much of the remaining thermal energy resides within caldera fill and basement rocks under and along the flanks of the caldera and can only be extracted by manmade geothermal systems depending upon the age and cooling history considerable thermal energy may still reside in crystallizing magma

new aspects of rhomb structures abstract the acute angles of 48 rhombic trapezoidal and triangular grabens horsts and upthrusts throughout the world were determined the results indicate an angular spread of 7 73 in most structures the two acute angles differ considerably most rhomb structures are grabens which show affinities to seismic faults and only a few are horsts and upthrusts in this connection modes of static crustal fracture propagation are compared to dynamic propagation rhomb structures occur along strike slip faults and in rifts these results question the universality of the pull apart model as a mechanism for rhomb structure development the two mechanisms that can lead to the formation of rhomb structures are 1 interaction of en echelon or non coplanar fractures by shear and extensional modes and 2 fracture bifurcation in an extensional mode the two mechanisms may result in faults of different shapes characterized by curved and straight boundaries respectively the grabens and horsts in extensional regions are the consequence of early fracture and later vertical displacements

tectonic and geologic evolution of the espanola basin rio grande rift structure rate of extension and relation to the state of stress in the western united states abstract the espanola basin of the rio grande rift began as a broad crustal downwarp in latest oligocene time most of the basin is 2 3 km deep but localized faulting allowed accumulation of up to 5 km of sedimentary fill in a central sub basin the localized early faulting ended before filling of the central espanola basin was completed about 10 m y ago movement on faults that define the present western margin of the espanola basin began 10 m y ago jemez mountain volcanism in the western espanola basin also began at about this same time west tilting of up to 30 occurred due to movement along pervasive n trending intrabasin faults about 7 5 m y ago in conjunction with continued movement along the western border faults volcanism continued after this tilting forming many of the large volcanic constructs of the jemez mountains regional uplift of the entire northern rio grande rift began 7 m y ago movement on the pajarito fault zone began about 5 m y ago and continues to the present this fault zone defines the western margin of the velarde graben a narrow central sub basin where recent movement has been concentrated some volcanism also has occurred within the southern velarde graben total extension across the espanola basin since 26 m y ago is estimated to have been 5 5 km roughly 10 or between 3 5 and 8 km assuming high angle planar faulting the 0 2 mm yr averaged long term rate of extension has been separated into three periods of activity 1 1 0 14 mm yr from 26 to 10 m y ago 2 2 0 5 mm yr from 10 to 5 m y ago 3 3 0 14 mm yr from 5 m y ago to present a change in least principal stress direction from wsw ene to wnw ese that occurred throughout the western united states about 10 m y ago coincides with a roughly 3 5 times increase in the rate of extension preferential development and movement of n to ne trending normal faults and a few degrees of clockwise rotation of rocks in the western espanola basin similar to the espanola basin initial basins of the southern rio grande rift were broad downwarps and rifting was greatly accelerated after 10 m y ago accelerated uplift of the northern rio grande rift also occurred at about this time indicating that activity in the entire rio grande rift was modulated by this change in extension direction 10 m y ago that appears related to pacific north american plate interactions this modulation coupled with major faulting 10 m y ago preceding uplift 7 m y ago in the espanola basin suggest a passive rifting process for the rio grande rift whereby stresses due to plate interactions elsewhere cause faulting in the lithosphere which leads to the development of a passive asthenospheric uplift furthermore the roughly 20 m y pre uplift history of sediment accumulation in basins of the central and southern rift and the inherited character trend and geometry of the rio grande rift as a whole are also more consistent with a passive rifting process

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

evidence for a ubiquitous seismic discontinuity at the base of the mantle a sharp discontinuity at the base of earth s mantle has been suggested from seismic waveform studies the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first order discontinuity superimposed on global seismic velocity structure derived from tomography the observations can be modeled by a solid solid phase transition that has a 200 kilometer elevation above the core mantle boundary under adiabatic temperatures and a clapeyron slope of about 6 megapascal per kelvin

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

some mineral physics constraints on the rheology and geothermal structure of earth s lower mantle we explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of earth s lower mantle we show that mgsio3 perovskite is significantly stronger than mgo periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase periclase we calculate viscosities of the lower mantle for two cases 1 where periclase occurs as isolated grains and 2 where periclase occurs as continuous films using mineral physics data and models of two phase rheology we find that the effective viscosity for the former is about 10 1000 times higher than the latter we therefore suggest that the rheology of the lower mantle is structure and hence strain dependent leading to weakening at large strains due to the formation of continuous films of periclase overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient both mgsio3 perovskite and periclase have relatively small activation energies e g r t m with g 10 14 where r is the gas constant and t m is melting temperature and therefore the depth variation of viscosity is rather small even for a nearly adiabatic temperature gradient however the geothermal gradients consistent with the geodynamical inference of nearly depth independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood a superadiabatic gradient of up to 0 6 k km is also consistent with mineral physics and geodynamical observations

ab initio study of the composition dependence of the pressure induced spin crossover in perovskite mg1 x fex sio3 abstract we present ab initio calculations of the zero temperature iron high to low spin crossover in mg 1 x fe x sio 3 perovskite at pressures relevant to earth s lower mantle equations of state are fit for a range of compositions and used to predict the fe spin transition pressure and associated changes in volume and bulk modulus we predict a dramatic decrease in transition pressure as fe concentration increases this trend is contrary to that seen in ferropericlase and suggests the energetics for spin crossover is highly dependent on the structural environment of fe both local density approximation lda and generalized gradient approximation gga exchange correlation methods are used and both methods reproduce the same compositional trends however gga gives a significantly higher transition pressure than lda the spin transition is made easier by the decreasing spin flip energy with pressure but is also driven by the change in volume from high to low spin volume trends show that high spin fe 2 is larger than mg 2 even under pressure but low spin fe 2 is smaller at ambient conditions and approximately the same size as mg 2 under high pressure indicating that low spin fe 2 is less compressible than high spin fe 2 we find large changes between high and low spin in the slope of volume with fe concentration although these changes are small in absolute magnitude for small fe content they are still important when measured per fe and could be relevant for calculating partitioning coefficients in the lower mantle

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

elasticity of mgo to 130 gpa implications for lower mantle mineralogy abstract the aggregate shear wave velocities of mgo periclase have been determined throughout earth s lower mantle pressure regime approaching 130 gpa using brillouin spectroscopy in conjunction with synchrotron x ray diffraction technique in a diamond anvil cell apparatus we found that the extrapolations of the high pressure shear wave velocities and shear moduli to ambient pressure are highly consistent with earlier studies however the measurements over a wide pressure range revealed that the pressure derivative of the shear modulus d g d p g 0 of mgo is 1 92 2 which is distinctly lower than that of previous lower pressure experiments compared with the previous results on mg fe o ferropericlase there is no clear correlation between iron content and g 0 we calculate that the shear wave velocity profile of lower mantle along the adiabatic geotherm applied by the lower g 0 value of periclase can remarkably well reproduce the global seismological 1 d velocity profile model with uniform composition model the best fitting result indicates the possibility of a lower mantle mineralogy with 92 vol silicate perovskite phase implying that the bulk composition of lower mantle is likely not to be pyrolitic but more chondritic the present acoustic measurements performed over the large pressure range have thus led us to a better understanding of compositional model of the earth s lower mantle

dynamics and structure of a stirred partially molten ultralow velocity zone abstract the seismic properties of thin 5 40 km thickness patches exhibiting low seismic velocities termed ultralow velocity zones or ulvz just above the core mantle boundary cmb might be explained by the presence of partially molten rock where a liquid phase occupies interstices within a skeletal network of solid grains however a key problem with this explanation is that in the absence of improbably strong surface tension effects partial melt is expected to drain by percolation over geological time scales to form a dense melt rich layer at the cmb with physical properties that are inconsistent with seismic and other geophysical constraints here we consider whether stirring within ulvz driven by viscous coupling to convective motions in the overlying mantle can inhibit the production of such stratification and maintain a partially molten region with a structure and constitution comparable to what is inferred seismically we use two dimensional numerical simulations of the response of a melt solid mixture to stirring imposed from above and scaling analysis to identify conditions leading to melt separation retention and drainage over a broad range of parameters we find that melt migration at plausible ulvz conditions is governed predominantly by dynamic pressure gradients arising from the viscous deformation related to mantle stirring rather than by the buoyancy effects driving melt percolation in particular dense melt that would otherwise drain downward and accumulate at the cmb is expected to remain in suspension as a result of the stirring driven within ulvz in addition our model predicts that partially molten ulvz patches will be characterized by a positive gradient in seismic shear velocity i e increasing with depth consistent with seismic inferences and may persist in this state over geological time scales

distribution of groundwater arsenic in xinjiang p r china although potential contamination of groundwater as is expected to occur in xinjiang p r china few data are available for the regional distribution of groundwater as in this study the spatial distribution of groundwater as was investigated in the chepaizi cpz n and shihezi shz n areas of northern xinjiang the balikun yiwu basin by e in eastern xinjiang and the tarim trm s and yanqi yq s basins in southern xinjiang arsenic concentrations greater than 10 g l were found in 12 of analyzed groundwaters all groundwater samples collected in cpz n had as concentrations greater than 10 g l 25 185 g l 30 in shz n 10 g l was found in the eastern and southern trm s and yq s distribution of groundwater as showed a tremendous spatial variability which greatly varied over a short distance horizontally arsenic concentration generally increased with increasing sampling depth the spatial distribution of groundwater as would be regulated by as source and hydrogeochemical processes higher ph and or lower orp values were generally observed in high as groundwater 10 g l in comparison with low as groundwater 10 g l arsenic mobility in shz n and cpz n may result from as desorption under relatively high ph conditions and more tentatively from reductive dissolution of fe iii oxides in by e and trm s however detailed mechanisms of as mobilization in these regions need further investigation

fracture interaction in the gregory rift east africa abstract vertical fracture is important and fracture interaction is quite intensive in the central gregory rift crack branching and non coplanar crack interactions in the rift are characterized for major and minor faults these two manifestations follow theoretical and experimental angular relationships of fracture reasonably well mantle diapirism seems to have been responsible for both tensile probably unstable fracture and block tilting ultimately resulting in fault dips deviating from the vertical

tectonic rotations within the rio grande rift evidence from paleomagnetic studies paleomagnetic studies on miocene pliocene volcanic rocks from the espanola basin of the rio grande rift new mexico reveal directions discordant from the expected mean direction for north america the paliza canyon formation tschicoma formation and lobato basalt all sampled in the jemez mountains west of the pajarito fault zone have mean declinations east of the expected mean the cerros del rio volcanics lying east of the pajarito fault zone have a westerly declination combined with published data on the santa fe group sediments east of the fault zone and the valles rhyolite west of the fault zone distinct rotations of the two areas are evident the western block has rotated clockwise 12 while the eastern block shows 16 of counter clockwise motion differential rotations of 25 30 are calculated between the two blocks 4 m y is the minimum differential rotation for the past 5 m y geologic explanations for these rotations include the opening of the rio grande rift in response to clockwise rotation of the colorado plateau and significant left slip along the rio grande rift

effusive eruptions from a large silicic magma chamber the bearhead rhyolite jemez volcanic field nm abstract large continental silicic magma systems commonly produce voluminous ignimbrites and associated caldera collapse events less conspicuous and relatively poorly documented are cases in which silicic magma chambers of similar size to those associated with caldera forming events produce dominantly effusive eruptions of small volume rhyolite domes and flows the bearhead rhyolite and associated peralta tuff member in the jemez volcanic field new mexico represent small volume eruptions from a large silicic magma system in which no caldera forming event occurred and thus may have implications for the genesis and eruption of large volumes of silicic magma and the long term evolution of continental silicic magma systems 40ar 39ar dating reveals that most units mapped as bearhead rhyolite and peralta tuff the main group were erupted during an 540 ka interval between 7 06 and 6 52 ma these rocks define a chemically coherent group of high silica rhyolites that can be related by simple fractional crystallization models preceding the main group minor amounts of unrelated trachydacite and low silica rhyolite were erupted at 11 9 and 8 ma respectively whereas subsequent to the main group minor amounts of unrelated rhyolites were erupted at 6 1 and 1 5 ma the chemical coherency apparent fractional crystallization derived geochemical trends large areal distribution of rhyolite domes 200 km2 and presence of a major hydrothermal system support the hypothesis that main group magmas were derived from a single large shallow magma chamber the 540 ka eruptive interval demands input of heat into the system by replenishment with silicic melts or basaltic underplating to maintain the bearhead rhyolite magma chamber although the volatile content of main group magmas was within the range of rhyolites from major caldera forming eruptions such as the bandelier and bishop tuffs eruptions were smaller volume and dominantly effusive bearhead rhyolite domes occur at the intersection of faults and are cut by faults suggesting that the magma chamber was structurally vented preventing volatiles from accumulating to levels high enough to trigger a caldera forming eruption

hydrogeological survey assessing arsenic and other groundwater contaminants in the lowlands of sumatra indonesia abstract groundwater conditions in the lowlands of sumatra where peat swamps are the dominant landscape were investigated based on topography soil and geological surface properties this large area about 100 000 km 2 is vulnerable to groundwater as enrichment under reducing aquifer conditions the reconnaissance groundwater survey was conducted in the province of south sumatra covering both presumed low and high risk areas of as enrichment five distinct types of groundwater were recognized reflecting a variety of geological sources and chemical conditions which are understood to be typical for the whole east coast of sumatra groundwater collected from tubewells in the youngest holocene swamp deposits had elevated as concentrations 10 g l 1 with a maximum of 65 g l 1 other elements exceeding the who drinking water guideline values include b mn and se in contrast to large deltas of continental south and se asia significantly lower sediment loads are transported by the rivers of sumatra the organic rich holocene sediments are hence relatively thin tubewells tapping the oldest geological formations of the study area middle miocene to pliocene have a broad range of redox conditions reflecting variations in aquifer geochemistry this group is generally characterized by alkaline ph conditions and high contents of na b se and sr oxic groundwaters were found in regions elevated above 20 m a s l and are characterized by low concentrations of dissolved solids and acidic ph values average 5 1 to date groundwater data for the increasingly populated island of sumatra are non existent in the international literature and this study thus provides a basis for future in depth groundwater studies the complete georeferenced database of groundwater analysis is provided as supplementary material

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

ab initio investigations of native and protonic point defects in mg2sio4 polymorphs under high pressure abstract density functional theory simulations were carried out to study the formation and migration energetics and geometric structures of the native point defects and protons in mg 2 sio 4 polymorphs namely forsterite wadsleyite and ringwoodite up to 30 gpa pressure the energetic favorability of the vacancy and interstitial defects was shown to strongly depend on the atomic and electron chemical potentials among the charge balanced defects studied the mg 2 frenkel defects are energetically most favorable in forsterite whereas the mgo pseudo schottky defects are energetically most favorable in wadsleyite and ringwoodite our results for the ion migration enthalpies calculated using the nudged elastic band technique suggest that the mg migration is easiest in forsterite and ringwoodite whereas si migration is easiest in wadsleyite the proton incorporations at the interstitial and vacant cationic sites were investigated in the extrinsic limit the proton incorporation is energetically most favorable at v si site for up to three protons addition of one more proton prefers to go to v mg site in the intrinsic limit however the interstitial and mg vacancy sites remain the most favorable the predicted barrier for the interstitial to interstitial proton migration is smaller than that for the magnesium vacancy to interstitial migration and among three phases ringwoodite has the lowest barrier the effects of proton incorporation on the transition pressure and pressure volume equation of state were shown to be significant

geometry and rate of extension across the pajarito fault zone espanola basin rio grande rift northern new mexico the central velarde graben is the active subbasin of the espanola basin section of the rio grande rift in north central new mexico the velarde graben is bounded on the west in the jemez volcanic field by the pajarito fault zone this fault zone has produced a steep fault scarp about 100 m high where it cuts the l l m y old tshirege member of the bandelier tuff detailed mapping along the north trending pajarito fault zone has revealed a fairly simple geometry in the tshirege member the faults follow numerous vertical joints below this member fault dips are 60 and not listric at shallow depths this simple geometry allows calculation of a mean rate of extension of 0 05 mm yr across the pajarito fault zone for the past 1 1 m y if extension is not perpendicular to the fault zone the extension rate could be as great as 0 07 mm yr lack of transverse tilt of the velarde graben wedge implies that the extension rate across the eastern margin is about the same as for the western margin comparison with a published extension rate for the northern albuquerque belen basin just to the south of the jemez mountains of 0 3 mm yr both sides since rifting began 26 m y ago indicates a slower opening for the velarde graben during the past 1 1 m y if extension is localized along the margins of the velarde graben with little activity along other fault zones in the espanola basin then both the mean rate of extension and the width of the actively extending region have decreased with time for this section of the rio grande rift

first principles computation of mantle materials in crystalline and amorphous phases abstract first principles methods based on density functional theory are used extensively in the investigation of the behavior and properties of mantle materials over broad ranges of pressure temperature and composition that are relevant a review of computational results reported during the last couple of decades shows that essentially all properties including structure phase transition equation of state thermodynamics elasticity alloying conductivity defects interfaces diffusivity viscosity and melting have been calculated from first principles using mgo the second most abundant oxide of earth s mantle as a primary example and considering many other mantle materials in their crystalline and amorphous phases we have found that most properties are strongly pressure dependent sometimes varying non monotonically and anomalously with the effects of temperature being systematically suppressed with compression the overall agreement with the available experimental data is excellent it is remarkable that the early calculated results such as shear wave velocities of two key phases mgo and mgsio 3 perovskite were subsequently reproduced by experimentation covering almost the entire mantle pressure regime as covered in some detail the defect formation and migration enthalpies of key mantle materials increase with pressure the predicted trend is that partial mgo schottky defects are energetically most favorable in mg silicates but their formation enthalpies are high so the diffusion in the mantle is likely to be in the extrinsic regime preliminary results on mgo and forsterite hint that the grain boundaries can accommodate point defects including impurities and enhance diffusion rates at all pressures the structures are highly distorted in the close vicinity of the defects and at the interface with excess space recent simulations of mgo sio 2 binary and other silicate melts have found that the melt self diffusion and viscosity vary by several orders of magnitudes with pressure temperature and composition the predicted high compressibility and complex dynamical behavior can be associated with structural changes involving non bridging oxygen oxygen tri clusters si o pentahedra etc occurring on compression we envision future prospect for massively parallel distributed computing of unprecedented magnitude and scope in the study of relevant materials for earth super earth and other planets a renewed computational theme perhaps should be the first principles simulations of large systems with long runs that are necessary to explore realistic natural compositions polycrystalline phases multi component melts crystal melt interfaces trace element partitioning etc

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

a geological and geophysical appraisal of the baca geothermal field valles caldera new mexico abstract the baca location 1 geothermal field is located in north central new mexico within the western half of the plio pleistocene valles caldera steam and hot water are produced primarily from the northeast trending redondo creek graben where downhole temperatures exceed 260 c at depths of less than 2 km stratigraphically the reservoir region can be described as a five layer sequence that includes tertiary and quaternary volcanic rocks and mesozoic and tertiary sediments overlying precambrian granitic basement production is mainly controlled by fractures and faults that are ultimately related to activity in the rio grande rift system geophysically the caldera is characterized by a gravity minimum and a resistivity low in its western half a 40 mgal gravity minimum over the caldera is due mostly to the relatively low density volcanics and sediments that fill the caldera and probably bears no relation to deep seated magmatic sources two dimensional gravity modeling indicates that the depth to precambrian basement in redondo canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low resistivity zone correlates well with the depth of the primary reservoir inferred from well data telluric and magnetotelluric data have also identified possible fault zones in the eastern and western sections of the production region that may form boundaries to the redondo creek reservoir these data also suggest that the reservoir region is located at the intersection of lineaments that trend north south and northeast southwest magnetotelluric results indicate deep low resistivity at the western edge of the caldera which may be associated with deep hot fluids on the basis of geophysical and well data we make three estimates of reservoir dimensions the estimates of the areal extent of the reservoir range from 10 to 30 km 2 depending on whether the sulphur creek or the valle seco area is considered to contain deep geothermal resources

self diffusion of oxygen and silicon in mgsio3 perovskite abstract we present results of simultaneous measurements of self diffusion of oxygen and silicon in magnesium silicate perovskite oxygen diffusion is 2 orders of magnitude faster than si self diffusion and fe mg interdiffusion in perovskite with d0 9 16 10 4 0 16 9 2 10 6 m2 s and q 501 80 kj mol at 25 gpa despite this high o diffusivity however the electrical conductivity of the lower mantle will be dominated by electronic conduction and the present day core is likely to be out of redox equilibrium with the mantle

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

stable intermediate spin ferrous iron in lower mantle perovskite iron has the ability to adopt different electronic configurations and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics experimental results for two lower mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle

sources and controls of arsenic contamination in groundwater of rajnandgaon and kanker district chattisgarh central india summary a high concentration of arsenic as contamination in ground water has been reported in the village of kaudikasa in rajnandgaon district wherein around 10 of the population is suffering from as borne diseases the region does not share any demographic or geological similarity with the sedimentary aquifers of the bengal delta plain in eastern india but represents an igneous terrain with elevated as concentrations in groundwater there is limited information about the source of as in groundwater and its mobility constraints in this area almost all the wells are located in the granitic terrain with pegmatitic intrusions most of these wells are characterized by as concentration above the world health organization who 1999 and the bis bureau of indian standards standards with the highest being found in a well with more than 250 g l of as here we report petrographic studies of the granitic host rock and x ray diffraction results that indicate that altered realgar as4s4 para realgar ass and or tennantite cu12as4s13 are the main mineral that contain as this element is leached during the weathering and water rock interactions microprobe analysis of the altered realgar grains of in pegmatitic intrusions of the host granite indicate 23 27 wt as remote sensing is useful to delineate the source of this contaminant which appears to lie at the intersection of a mineralized nw se and n s lineaments associated with the kotri rift zone these lineaments are structurally controlled as rifting followed by thrusting and other types of faulting caused left lateral displacement of n s kotri lineament along a nw se fault plane showing sinistral shearing this process caused water drainage in the areas to flow along these highly mineralized weak zones thus the water becomes highly contaminated due to leaching of minerals at the intersection of these lineaments clearly visible at two areas of high contamination that lie very near to this intersection over granitic rock the source of as affecting the rajnandgaon district is located in granites that have pegmatitic intrusions likely generated by hydrothermal activity

ab initio investigation of high pressure phase relation and elasticity in the naalsi2o6 system 1 subducted crusts contain aluminous phases with incompatible elements such as sodium in order to understand the fate of subducted crusts and how they recycle within the earth it is important to investigate high pressure stability and elastic properties of host phases here we have studied naalsi2o6 jadeite a naalsio4 calcium ferrite cf type phase and sio2 stishovite by means of a first principles computation method jadeite was found to dissociate into an assemblage of the cf type phase and stishovite at about 18 gpa associated with remarkable increases of compressional wave 18 7 shear wave 26 4 bulk sound 13 3 velocities and density 15 1 proximity of this transition condition to the 660 km discontinuity in the mantle transition zone suggests that seismically observed splitting of the reflection could be related to this phase transition implying subduction of crustal materials down to the mantle transition zone

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

lateral variations in lowermost mantle shear wave anisotropy beneath the north pacific and alaska s waves recorded by long period world wide standardized seismograph network and broadband stations in north america for deep northwest pacific subduction zone earthquakes provide evidence for anisotropy in the lowermost mantle shear velocity structure beneath the north pacific and alaska systematic delays of up to 4 s are observed between longitudinal components sv and transverse components sh of motion for core reflected scs waves as well as for core grazing and diffracted s waves the absence of significant splitting for s waves that have turning points more than a few hundred kilometers above the core mantle boundary indicates that anisotropy is localized within the d region the lowermost portion of the mantle sv sh differential arrival times for both scs and sdiff along with path length estimates assuming a 250 km thick d region indicate spatial variations in the strength of shear wave anisotropy the strongest anisotropy 1 1 5 is found in the eastern part of the study area with systematic reduction in magnitude toward the west a transverse isotropy model can explain the data with the velocity structure for horizontally polarized waves vsh having a 2 3 discontinuous shear velocity increase at the top of d as proposed in earlier studies of the region and a similar structure for s wave particle motion in the direction normal to the core mantle boundary vsv but with the velocity jump at the top of d and the velocity within d being reduced from that for vsh by 0 5 1 5 km s large uncertainties exist for velocity gradients above and below the velocity jump but the requirement of a reduced vsv relative to vsh in d is clear synthetic waveforms calculated by using separate isotropic structures for sh and sv match the observations well and constrain the basic anisotropic structure because the shear waves all traverse the region with near grazing geometries the study area exhibits strong lateral variations in lower mantle shear velocity structure and variable thickness of the d layer topography of the d layer is not well resolved because of trade off with volumetric heterogeneity

trench parallel anisotropy and large delay times elasticity and anisotropy of antigorite at high pressures 1 using theoretical methods we calculate the full elastic constant tensor and equation of state of antigorite up to 10 gpa a pressure range that encompasses its experimentally observed stability field at ambient conditions the elastic constant tensor reveals significantly large acoustic anisotropy 38 in vp 35 in vs compared to the dominant mantle phase olivine the shear anisotropy is enhanced upon compression upon compression the full elastic constant tensor reveals anomaly at 2 69 gm cm 3 at 2 69 gm cm 3 we find that the pressure volume results for antigorite are well represented by a third order birch murnaghan formulation with k0 52 gpa k0 8 5 and v0 3037 a3 0 2 48 gm cm 3 our results on elasticity and anisotropy at conditions relevant to the mantle wedge indicates that a 10 20 km layer of antigorite might account for the observed shear polarization anisotropy with fast polarization parallel to the trench and associated large delay times of 1 2 sec observed in some subduction zone settings

anthropogenic arsenic menace in delhi yamuna flood plains arsenic one of the most poisonous chemical elements was analyzed in the waters of the host of the 2010 commonwealth games i e new delhi the study revealed shocking outcomes with arsenic concentrations well beyond the safe limits set by who and a maximum concentration up to 180 ppb was found in the groundwater analysis of around 120 water samples collected extensively along the yamuna flood plain showed that more than 55 had arsenic contamination beyond the who limit of 10 ppb the maximum value of arsenic in coal and fly ash from rajghat coal based thermal power plant contained 200 and 3 200 ppb respectively moreover the ore petrography of coal samples shows the presence of arsenopyrite mineral maximum concentration of arsenic contamination is found within a 5 km radius from power plants in the perspective of delhi arsenic contamination is purely anthropogenic due to coal based thermal power plants which had already shown toxic arsenic fluorine and china type coal effects the presence of such power plants in coal field locations e g west bengal and bangladesh could release the arsenic due to combustion in superthermal power plants thus accentuating the arsenic concentration besides the natural arsenic coming from the foreland basins of the himalaya in indian sub continent

block rotations in the rio grande rift new mexico additional paleornagnetic data from the north central rio grande rift support previous suggestions for counterclockwise rotation of a large crustal block thirteen sites from intrusive and extrusive rocks associated with the oligocene espinaso formation in the area around the ortiz mountains central new mexico yield magnetic directions of i 42 1 and d 337 8 alpha 95 10 3 comparison with the expected direction for the oligocene indicates 17 8 11 4 of counterclockwise rotation this agrees with previous studies of miocene to pliocene rocks north of the study area that also show about 15 of counterclockwise rotation and corroborates the timing of this motion as post 5 ma the extent of the rotated block now includes areas in and adjacent to the espanola basin east of the pajarito fault zone from the san luis basin in the north to the albuquerque basin in the south extensive published geologic and structural information indicates that counterclockwise block rotation in the rio grande rift probably results from left slip along the rift the rotated block is diamond shaped and bounded by major fault zones embudo fault to the north pajarito fault zone to the west tijeras canoncito fault zone to the southeast and picuris pecos fault to the east structural consequences of the counterclockwise block rotation are uplift at the acute ends sandia and picuris uplifts and subsidence at the obtuse ends velarde graben and santa fe embayment

first principles viscosity and derived models for mgo sio2 melt system at high temperature 1 the viscosity of silicate liquids at high temperature is crucial to our understanding of chemical and thermal evolution of the earth since its early stages first principles molecular dynamics simulations of seven liquids across the mgo sio2 binary show that the viscosity varies by several orders of magnitudes with temperature and composition our results follow a compensation law on heating the viscosity of all compositions approaches a uniform value at 5000 k above which pure silica becomes the least viscous liquid viscosity depends strongly on composition fourth power implying a strong nonlinear dependence of the configurational entropy on composition using the simulation results we derive and evaluate different types arrhenius and non arrhenius of models for accurate description of the viscosity temperature composition relationship our results span the thermal regime expected in a magma ocean and indicate that melt migration is important for understanding the generation and preservation of melts from frictional heating at very fast slip in impact processes