boron lithium relationships in rhyolites and associated thermal waters of young silicic calderas with comments on incompatible element behaviour abstract this study had three goals 1 1 to study b distribution in a rhyolitic volcanic sequence already extensively investigated for other elements 2 2 to interpret the joint behaviour of b and li during the interaction of such rocks with subsurface waters 3 3 to assess the manner in which water affects the behaviour of incompatible elements such as b and gd new b gd and sm analyses have been made on a suite of yellowstone rhyolites including fresh and partially devitrified glassy obsidian from surface exposures of several flows drill core of increasing degrees of alteration in the biscuit basin flow and two drill cores from other flows within the biscuit basin flow the sm and gd concentrations remain rather constant 9 12 and 8 10 ppm respectively and behave conservatively independent of alteration boron decreases from about 10 to 3 ppm with progressive alteration and li increases from about 40 ppm by a factor of 2 3 in the most altered rocks thermal waters reflect leaching from the fresh rocks but contain much less li than b b li 3 compared with 0 8 in fresh obsidian retention of li was favoured by abundant illitic alteration obsidians from the valles and long valley calderas show greater li loss during alteration all the rhyolitic rocks lose b during aqueous alteration the waters acquire both b and li but proportionately much more b natural waters of all kinds including those from the three calderas show six orders of magnitude range in aqueous b and li with a high degree of linear correlation and an average ratio b li essentially constant at 4 0 the linearity mainly expresses processes of dilution and concentration reactions specific to b or li engender waters with deviating b li the patterns of sm gd b li variation in rocks exemplify two kinds of behaviour in petrological processes with no hydrous phase lunar rocks mantle fresh seafloor basalt the lower continental crust these elements are incompatible and behave similarly when an aqueous phase is present b and li behave independently of sm and gd

direct evidence of active deformation in the eastern indian oceanic plate conventional plate tectonics theory postulates that plates only deform on their boundaries to the contrary there is ample evidence of intraplate deformation in the equatorial indian ocean west of the ninetyeast aseismic ridge prior to this study no direct evidence of deforma tion east of the ninetyeast ridge was available we present the results of a multipurpose geo physical cruise showing that intraplate deformation also occurs in this area long at least 1000 km left lateral north south strike slip faults are active and reactivate fossil fracture zones this style of deformation is strikingly different from the east west folds and reverse faults that affect the region west of the ninetyeast ridge contrasting processes of convergence at the northern plate boundaries can account for the two styles of deformation west of the ninetyeast ridge there is a continent continent collision and east of the ridge oceanic lithosphere subducts along the sumatra trench the ninetyeast aseismic ridge therefore appears to be a mechanical border separating two distinct deformed areas

experimental assessment of the infiltration properties of a coarse soil medium in a dielectric infiltration test an accurate determination of the hydrological characteristics of porous media such as the values of the porosity and effective porosity are essential this is important to understand the transport processes of infiltration and the movement of water and contaminants in the porous media in this study a laboratory soil column experiment to estimate the porosity and effective porosity of toyoura standard sand samples using a dielectric method termed the frequency domain reflectometry with vector network analyzer fdr v was performed the fdr v device uses high frequency microwaves ranging from 0 1 to 3 ghz to measure the complex dielectric constants of the sample from the measured complex dielectric constant the two parameters of the soil samples then were derived using a proposed dielectric mixture model and tracer concentration model the effective porosity of the soil sample is measured at 0 311 with the fdr v dielectric method and 0 345 by the soil tracer column test comparing this with the calculated porosities of the soil sample the ratio of effective porosity is approximately 78 for the dielectric method and approximately 86 for the tracer concentration method these different values can be explained to be within the measurement range with regard to the measurement volume for the soil column these results indicate that measurement by the dielectric method using an fdr v device is an efficient and useful tool for estimating the hydrological parameters of porous media because of the dielectric response of earth materials

distribution of shortening between the indian and australian plates in the central indian ocean we analyze a single channel seismic scs reflection profile that completely crosses the zone of deformed oceanic lithosphere in the central indian ocean at 78 8 e by summing the apparent shortening on all seismically resolvable faults throws 10 m we find that 11 2 2 km of shortening has occurred at this longitude during the past 7 5 m y this estimate together with the 27 f 5 km of shortening previously estimated from a multichannel seismic mcs profile farther east at 81 5 e are consistent with the west to east increase in shortening predicted by euler poles which treat the indian and australian plates as separate tectonic units our result therefore provides direct evidence from the deformation itself that the compression of oceanic lithosphere in the central indian ocean originally regarded as intraplate is better described as constituting part of a broad boundary zone between distinct indian and australian plates we also examine the size statistics of faults revealed in scs and mcs profiles running nearly normal to the deformation trends in the longitude band 78 8 e 81 5 e the n s extent of the deformation does not change appreciably over these longitudes we find that the average fault spacing remains constant at about 7 km whereas the mean throw increases systematically from west to east ff 74 m to n 177 m basically the contribution of small faults those with throws of lo 50 m decreases systematically across the deforming region i e with increasing amount of shortening this suggests that the deformation occurs by reactivation of a select fault population that these faults continue to add displacement with time and that relatively few new faults are initiated we also infer from the fault size statistics that the contribution to the deformation of faults below the resolution of the seismic methods 10 m for scs and 50 m for mcs is likely to be quite limited

from source to surface tracking magmatic boron and chlorine input into the geothermal systems of the taupo volcanic zone new zealand the magmatic contribution into geothermal fluids in the central taupo volcanic zone tvz new zealand has been attributed to either andesitic arc type fluids or rhyolitic rift type fluids to explain the compositional diversity of discharge waters however this model relies on outdated assumptions related to geochemical trends associated with the magma at depth of typical arc to back arc settings current tectonic models have shown that the tvz is situated within a rifting arc and hosts magmatic systems dominated by distinct rhyolite types that are likely to have evolved under different conditions than the subordinate andesites therefore a new appraisal of the existing models is required to further understand the origin of the spatial compositional diversity observed in the geothermal fluids and its relationship to the structural setting here we use volatile concentrations i e h2o cl b from rhyolitic and andesitic mineral hosted melt inclusions to evaluate the magmatic contribution to the tvz geothermal systems the andesite and two different types of rhyolites r1 and r2 are each distinct in cl h2o and b cl which will affect volatile solubility and phase separation vapor vs hydrosaline liquid of the exsolved volatile phase ultimately these key differences in the magmatic volatile constituents will play a significant role in governing the concentration of cl discharged into geothermal systems we estimate bulk fluid compositions b and cl in equilibrium with the different melt types to show the potential contribution of parent fluids to the geothermal systems throughout the tvz the results of this analysis show that the variability in fluid compositions partly reflects degassing from previously unaccounted for distinct magma source compositions we suggest the geothermal systems that appear to have an arc type andesitic fluid contribution are actually derived from a rhyolite melt in equilibrium with a highly crystalline andesite magma this model is in better agreement with the current understanding of magma petrogenesis in the central tvz and its atypical rifted arc tectonic setting and show that the central tvz records an arc not back arc fluid signature

early pre 8 ma fault activity and temporal strain accumulation in the central indian ocean the diffuse deformation zone in the central indian ocean is the classical example of distributed deformation of the oceanic lithosphere where shortening between the indian and capricorn plates is manifest as reverse faulting 5 10 km spaced faults and long wavelength 100 300 km folding the onset of this deformation is commonly regarded as a key far field indicator for the start of major uplift of the himalayas and tibet some 4000 km further to the north due to increased deviatoric stresses within the wider india asia area there has been disagreement concerning the likely timing for the onset of deformation between plate motion inversions and seismic reflection based studies in the present study fault displacement data from seismic reflection profiles within the central indian ocean demonstrate that compressional activity started much earlier than previously thought at around 15 4 13 9 ma from reconstructions of fault activity histories we show that 12 of the total reverse fault population had been activated and 14 of the total strain accumulated prior to a sharp increase in the deformation rate at 8 0 7 5 ma there is no evidence for any regional unconformity before 8 0 7 5 ma early shortening was accommodated by activity on single isolated fault blocks total strain estimates derived are more variable and complex than those predicted from plate inversion and they do not show simple west to east increase

etude geochimique des elements condenses au cours du refroidissement de la phase gazeuse volcanique etna 1976 des sublimes ont ete recoltes a l etna en 1976 le long d un tube en silice la mesure de la temperature du depot et l analyse elementaire par activation neutronique permettent de mieux comprendre des mecanismes magmatologiques metallogeniques et volcanologiques

vanadium sublimates from the fumaroles of izalco volcano el salvador abstract prior to the recent discovery of high temperature vanadium sublimates at the fumaroles of izalco volcano el salvador the only vanadium minerals known were those formed at low temperature surface conditions six new vanadium compounds have already been discovered at izalco volcano and five of these have been elevated to mineral status two of the minerals are among the most vanadium rich compounds known in nature field studies and studies of the crystal chemistry of the sublimate phases have allowed delineation of the conditions of exsolution of vanadium bearing gases from the magma and conditions of sublimation of the vanadium compounds a vanadium halogen or oxyhalogen gas phase was exsolved from a basaltic magma when the magma was 550 m below the summit crater as the gas rose to the fumaroles and mixed with the atmosphere the oxygen fugacity rose from that of the magma to at least 10 3 5 bar at the fumaroles the vanadium compounds sublimated at various temperatures but a minimum temperature of 760 can be determined for one of the phases based on geothermometry determined from phase relations in the system cuo v 2 o 5 the studies have demonstrated that a vanadium bearing gas can segregate from a magma with normal basaltic concentrations of vanadium

the boron isotope systematics of the yellowstone national park wyoming hydrothermal system a reconnaissance abstract boron concentrations and isotope compositions have been measured in fourteen hot spring waters two drill hole waters an unaltered rhyolite flow and hydrothermally altered rhyolite from the geothermal system in yellowstone national park wyoming the samples are representative of the major thermal areas within the park and span the range of fluid types for the fluids the b concentrations range from 0 043 2 69 mm kg and the 11 b values range from 9 3 to 4 4 there is no relationship between the dissolved b concentrations or isotope compositions with the concentration of any major element other than cl or physical property each basin is characterized by a restricted range in b cl ratios and 11 b values hot spring waters from the morris basin upper geyser basin calcite springs and clearwater have 11 b values close to that of unaltered rhyolite 5 2 and are interpreted to have derived their b from this source waters from mammoth hot springs sheepeater and rainbow springs have lower 11 b values close to 8 these lower values may reflect leaching of b from sedimentary rocks outside the yellowstone caldera but they are similar to the 11 b value of hydrothermally altered rhyolite 9 7 hence the light boron isotope compositions recorded in these hot spring waters may reflect leaching of previously deposited hydrothermal minerals cooler springs along the yellowstone river just outside the park boundary have lower b concentrations and higher 11 b values that may reflect mixing with shallow meteoric water

self consistent modeling of crustal thickness at chagos laccadive ridge from bathymetry and gravity data the chagos laccadive ridge clr is an aseismic ridge in the indian ocean that formed by the action of the reunion mantle plume we use modeling of bathymetry and gravity data to constrain the crustal thickness variations at three locations from 0 s to 6 s where the plume was likely interacting directly with the carlsberg spreading center ambiguities in the modeling were reduced by requiring both the density and thickness of the crust to be consistent with a single set of mantle melting conditions in this case using a passive upwelling model in which mantle potential temperature is the controlling factor mean crustal thicknesses beneath the ridge at the three locations predicted from the gravity modeling were 16 6 12 5 and 27 0 km these thicknesses are up to 50 greater than would be obtained had we not required self consistency in the modeling if the thick crust is produced entirely by elevated potential temperatures in the melting region mantle temperatures would have to be 100 250 c higher than normal abrupt decreases in crustal thickness at a large offset fracture zone are consistent with previous models for plume spreading center interactions

combined interpretation of pumping and tracer tests theoretical considerations and illustration with a field test pumping and tracer tests are two well established ground water reservoir tests hydraulic conductivity can be derived from both conductivities are studied in a mainly layered heterogeneous coastal aquifer in belgium with a pumping and tracer test and results of both are compared characteristics and important points in performance and interpretation of the tests are discussed the interpretation method of pumping tests must be chosen very carefully application of interpretation methods based on models underestimating or even neglecting the leakage towards the pumped permeable layer results in an overestimation of the horizontal conductivity of this layer the larger the distance of the used observation well s the larger this overestimation becomes this is illustrated here with the interpretation of the drawdown data obtained during the pumping test using different analytical models and a numerical model with an inverse axi symmetric numerical model incorporating layered heterogeneity results of the pumping test are in good agreement with results from the tracer test many discrepancies between pumping and tracer test data performed in layered heterogeneous media can be explained when realistic pumping test interpretation methods are applied and when leakage is not underestimated

a high resolution model for eurasia north america plate kinematics since 20 ma summary we derive the first chronologically detailed model of eurasia north america plate motion since 20 ma from ship and airplane surveys of the well expressed magnetic lineations along this slowly spreading plate boundary including previously unavailable dense russian magnetic data from the southern reykjanes ridge and northern mid atlantic ridge near the charlie gibbs fracture zone from more than 7000 crossings of 21 magnetic anomalies from anomaly 1n 0 78 ma to anomaly 6n 19 7 ma we estimate best fitting finite rotations and realistic uncertainties linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations with the outward shift ranging from more than 5 km between iceland and the charlie gibbs fracture zone to 2 km elsewhere this outward displacement which is a consequence of the finite zone of seafloor accretion degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis the corrected plate motion rotations reveal surprising previously unrecognized features in the relative motions of these two plates within the uncertainties motion was steady from 20 to 8 ma around a pole that was located 600 km north of the present pole with seafloor spreading rates that changed by no more than 5 per cent 1 mm yr 1 along the reykjanes ridge during this period seafloor spreading rates decreased abruptly by 20 2 per cent at 7 5 6 5 ma coinciding with rapid southward migration of the pole of rotation and a5 10 counter clockwise change in the plate slip direction eurasia north america plate motion since 6 7 ma has remained remarkably steady with an apparently stationary axis of rotation and upper limit of 2 per cent on any variations in the rate of angular rotation during this period based on the good agreement between seismotectonic constraints on present deformation in northeast asia and directions of motion that are predicted by our 6 7 ma to present pole we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published gps estimates for eurasia north america motion we find however that gps estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from europe give implausible estimates of recent motion with the most recently published gps model predicting convergence along the southern gakkel ridge and in the laptev sea where seafloor spreading occurs an alternative gps estimate that is not tied to the international terrestrial reference frame and employs gps station velocities from northeastern asia is marginally consistent with our 6 7 0 ma motion estimate

seismic reflection images of intraplate deformation central indian ocean and their tectonic significance multichannel seismic reflection profiles collected from the intraplate deformation area in the central indian ocean basin are used to describe brittle structures produced under compressive stress reflectors within oceanic basement are divided into four types north dipping and south dipping reverse faults that are interpreted as reactivations of structures formed at the spreading centre as outward and inward dipping faults respectively lower angle north dipping reflectors that probably represent new faults or faults just initiating and sub horizontal reflectors within the uppermost crust that are interpreted as hydrothermal alteration fronts within the sedimentary cover upwards fault propagation shows the faults steepening from c 40 just above basement to near vertical and is preceded by sediment folding a fractal analysis of faulting suggests two fault populations possibly reflecting different criteria for brittle failure measurements of north south crustal shortening indicate a shortening rate of 2 5 0 9 mm a 1 which is at the lower end of predictions from plate motions but significant enough to recognize this area as a diffuse plate boundary the formation of long wavelength basement undulations and the reactivation of fracture zones and ridge parallel fault fabrics are linked in a unified tectonic model driven by the high level of intraplate compressive stress in the area there is little evidence from the seismic profiles for intraplate deformation starting before the widespread unconformity dated as 7 ma

effective equation to assess solute transport in two lithology reservoirs abstract understanding solute transport in heterogeneous porous media is a challenging problem due to the degree of complexities coming from the spatial variations of petrophysical properties the developments of theoretical formulations are powerful tools used to obtain insights regarding the phenomenology involved in the transport process when analyzing large scale systems in this context and within the framework of the volume averaging method in this work we present an effective one equation model and its validity conditions for the solute transport in heterogeneous reservoirs characterized by two lithology arrangements for this purpose the hypothesis of local mass equilibrium was assumed valid and what follows included the determination of physical constraints supporting such a hypothesis in a previous work aguilar madera et al 2019 the closure problems to calculate the effective coefficients of the two equation model were presented and with this base we present here the numerical estimation of the effective velocity vector and the mass dispersion tensor included in the one equation model as one application the numerical solution of the one equation model was carried out for different lithology arrangements and the breakthrough curves for two permeability ratio scenarios were analyzed the results confirm that the permeability ratio dramatically impact not only the tracer dispersion but also the arrival time at observation points which is strongly correlated to the velocity vector field and its spatial deviations we found that the local mass equilibrium is met more easily in lenticular reservoirs provided that the boundary and initial conditions have no long term effects finally the dispersion coefficient was compared against reported reservoir field data finding similarities in the orders of magnitude for certain geologies

motion between the indian capricorn and somalian plates since 20 ma implications for the timing and magnitude of distributed lithospheric deformation in the equatorial indian ocean summary approximately 2200 magnetic anomaly crossings and 800 fracture zone crossings flanking the carlsberg ridge and central indian ridge are used to estimate the rotations of the indian and capricorn plates relative to the somalian plate for 20 distinct points in time since 20 ma the data are further used to place limits on the locations of the northern edge of the rigid capricorn plate and of the southern edge of the rigid indian plate along the central indian ridge data south of and including fracture zone n the fracture zone immediately south of the vema fracture zone which intersects the central indian ridge near 10 s are well fit assuming rigid capricorn and somalian plates while data north of fracture zone n are not in agreement with prior results data north of fracture zone h which intersects the central indian ridge near 3 2 s are well fit assuming rigid indian and somalian plates while data south of and including fracture zone h are not resulting in a smaller rigid indian plate and a wider diffuse oceanic plate boundary than found before the data are consistent with capricorn somalia motion about a fixed pole since 8 ma but require rotation about a pole 15 farther away from the central indian ridge from 20 to 8 ma the post 8 ma pole also indicates capricorn somalia displacement directions that are 7 clockwise of those indicated by the pre 8 ma stage pole in contrast india somalia anomaly and fracture crossings are well fit by a single fixed pole of rotation for the past 20 ma india somalia motion has changed little during the past 20 myr nonetheless astronomically calibrated ages for reversals younger than 12 9 ma allow resolution of the following small but significant changes in spreading rate india somalia spreading slowed from 31 to 28 mm yr 1 near 7 9 ma and later sped up to 31 mm yr 1 near 3 6 ma capricorn somalia spreading slowed from 40 to 36 mm yr 1 near 11 0 ma later sped up to 38 mm yr 1 near 5 1 ma and further sped up to 40 mm yr 1 near 2 6 ma the motion between the indian and capricorn plates is estimated by differencing india somalia and capricorn somalia rotations which differ significantly for all 20 pairs of reconstructions india has rotated relative to the capricorn plate since at least 20 ma if about a pole located near 4 s 75 e the rate of rotation was slow 0 11 0 01 myr 1 95 per cent confidence limits from 20 to 8 ma but increased to 0 28 0 01 myr 1 95 per cent confidence limits at 8 ma the onset of more rapid rotation coincides within uncertainty with the inferred onset at 7 8 ma of widespread thrust faulting in the central indian basin and with the hypothesized attainment of maximum elevation and initiation of collapse of the tibetan plateau at 8 ma the plate kinematic data are consistent with steady india capricorn motion since 8 ma and provide no evidence for previously hypothesized episodic motions during that interval the convergence since 8 ma between the indian and capricorn plates significantly exceeds by 13 to 20 km the convergence estimated from three north south marine seismic profiles in the central indian basin where and how the additional convergence was accommodated is unclear

reconciling plate kinematic and seismic estimates of lithospheric convergence in the central indian ocean the far field signature of the india asia collision and history of uplift in tibet are recorded by sediment input into the indian ocean and the strain accumulation history across the diffuse plate boundary between the indian and capricorn plates we describe the history of india capricorn convergence from updated estimates of india somalia capricorn plate rotations and observations derived from seismic reflection data new india capricorn plate rotations for the past 20 m y are consistent with slow north south convergence from 18 ma about a stationary or nearly stationary pole near the eastern edge of the chagos laccadive ridge simpler than predicted by previous models based on many fewer data the new rotations suggest that convergence began between 18 and 14 ma consistent with marine seismic evidence for an onset of deformation at 15 4 13 9 ma they further show that convergence rates doubled at 8 ma in agreement with a sharp increase in fault activity at 8 7 5 ma seen on seismic reflection profiles a discrepancy between the total strain estimated from kinematic and seismic reflection data can be reconciled if pervasive reverse faulting within the diffuse plate boundary is accompanied by block rotations of 1 3

twin lake tracer tests longitudinal dispersion two natural gradient dispersion tests were conducted at the chalk river nuclear laboratories ontario in 1982 and 1983 in order to quantify field scale dispersion processes over a 20 and 40 m distance of a radiotracer migration the patterns of dispersion that were observed in the field using a dry access tube monitoring technique were compared with patterns predicted by the advection dispersion model with constant parameters analysis of the time concentration profiles of the tracer at observation wells located along the mean direction of the longitudinal spreading showed that the dispersion model adequately describes the dispersion patterns actually observed and averaged over the aquifer depth the values of longitudinal dispersivity determined from continuous time concentration profiles were virtually equal to those obtained from laboratory scale columns the dispersive properties of the aquifer were characterized at the local scale by a constant independent of travel distance dispersivity value of 0 0045 m averaging the test data over the aquifer depth analogous to the information provided by a fully penetrating pumping well yielded a full aquifer dispersivity varying in an irregular fashion from 0 16 to 0 06 m the scale effect observed between local scale and full aquifer dispersivities is the result of inhomogeneity of the aquifer and the concentration averaging produced by the sampling instrumentation the results of two tracer tests also showed that the use of the dry access tube monitoring technique for field experimentation provides detailed representation of spatial and temporal distribution of a radiotracer s activity and consequently provides a practical means to determine the groundwater velocity field and dispersive properties of porous materials

trace element partitioning between vapor brine and halite under extreme phase separation conditions abstract experiments were conducted to investigate the partitioning of li br rb cs and b between vapor brine and halite during subcritical and supercritical phase separation in the nacl h2o system 388 550 c 250 350 bars results indicate that li and br partition preferentially into the low salinity vapor fluids while rb and cs become more enriched in the coexisting brines under more extreme conditions of pressure and temperature in the two phase region especially near the vapor brine halite boundary strong salting out effects imposed on neutral aqueous species enhance significantly partitioning of all trace elements into the low salinity fluid dissolved boron is strongly affected by this and a particularly strong enrichment into vapors is observed a trend that can be effectively correlated with changes in reduced density exclusion of li br rb cs and b from halite when precipitated further increases the solubility of these species in the coexisting cl poor fluid in general the lack of distortion in the partitioning behavior of trace elements between vapor brine and or halite with the transition from subcritical to supercritical conditions in the nacl h2o system precludes the need for special reference to the critical point of seawater when interpreting phase relations in submarine hydrothermal systems the combination of experimentally determined trace element partitioning data with constraints imposed by mineral solubility provides a means to better understand the origin and evolution of hot spring vent fluids for example in brandon hydrothermal system 21 s epr supercritical phase separation and subseafloor mixing appear to be the main heat and mass transport mechanisms fueled by a shallow magmatic intrusion with boron systematics ruling out major contributions from magmatic degassing processes accompanying the near seafloor volcanism

changes in hyporheic exchange flow following experimental wood removal in a small low gradient stream 1 we investigated the response of hyporheic exchange flow hef to wood removal in a small low gradient gravel bed stream in southeast alaska using a series of groundwater models built to simulate hef for the initial conditions immediately after wood removal and 1 month 2 years 4 years and 16 years following wood removal the models were based on topographic surveys of the stream channel and surrounding floodplain and surveyed water surface elevations wses were used to assign stream boundary conditions using the groundwater flow model modflow and the particle tracking model modpath we calculated hyporheic exchange fluxes their residence time distributions and both longitudinal and plan view spatial patterns of downwelling and upwelling zones in the first few years streambed scour and sediment deposition smoothed the streambed and wse profile reducing hef also large contiguous patches of downwelling or upwelling were fragmented nearly doubling the total number of patches present on the streambed as the stream continued to adjust to the loss of wood those trends began to reverse accretion of sediment onto alternating bars resulted in better developed pool riffle morphology enhanced hef and increased residence times and also resulted in downwelling and upwelling zones coalescing into elongated patches along bar margins this study showed that the hyporheic zone is sensitive to changes in wood loading and that initial changes in hef resulting from the direct effects of wood removal were contrary to longer term channel adjustments to changes in wood loading

characterization of hydrogeologic properties for a multi layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey a multi layered aquifer typical of riverbank alluvial deposits in korea was studied to determine the hydrologic properties the geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units silt sand highly weathered and fresh bedrock layers the electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings the laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5 00 10 2 cm s the slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4 32 7 72 10 4 cm s hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2 08 10 3 and 2 44 10 2 cm s with a geometric mean of 6 89 10 3 cm s which is 7 times smaller than that from the laboratory column experiment the trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested the combined hydrogeologic site characterization using hydraulic tests tracer tests and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multi layered alluvial aquifer

fault reactivation in the central indian ocean and the rheology of oceanic lithosphere the intraplate deformation in the central indian ocean basin is a well known example of a deviation from an axiom of plate tectonics that of rigid plates with deformation concentrated at plate boundaries here we present multichannel seismic reflection profiles which show that high angle reverse faults in the sediments of the central indian ocean extend through the crust and possibly into the uppermost mantle the dip of these faults which we believe result from the reactivation of pre existing faults formed at the spreading centre is 40 in the basement which is consistent with the distribution and focal mechanisms of earthquakes on faults now forming at spreading centres this style of deformation coupled with the observation of large earthquakes in the mantle lithosphere indicates that brittle failure of the oceanic lithosphere may nucleate in the vicinity of the brittle ductile transition and propagate through the crust

concentrations of arsenic antimony and boron in steam and steam condensate at the geysers california abstract studies at the geysers geothermal field california indicate that under some circumstances elements that are transported in the vapor phase can become enriched in the liquid phase waters from two condensate traps steam traps on steam lines at the geysers are enriched with arsenic antimony and boron compared to the concentrations of these elements in coexisting steam concentrations of boron in condensate trap waters were as high as 160 mg l arsenic as high as 35 mg l and antimony as high as 200 g l enrichment of arsenic antimony and boron is at least partially controlled by the partitioning of these elements into the liquid phase according to their vapor liquid distribution coefficients after they are transported in steam several of the elements that are most soluble in steam including arsenic and antimony are part of the trace element suite that characterizes precious metal epithermal ore deposits

fault reactivation and selective abandonment in the oceanic lithosphere 1 normal and transform faults originally formed at a spreading centre can be reactivated in diffuse plate boundary zones and in areas of lithospheric flexure such as at peripheral bulges to subduction zones using new seismic reflection profiles and modeling we investigate how the original oceanic fabric is reactivated in the simple case of fault perpendicular compression in the central indian basin well oriented normal paleofaults were reactivated with reverse motion at the very onset of deformation 9 ma but only a small subset remained active past 7 ma suggesting that most of the densely spaced small offset faults were abandoned while deformation localized onto fewer faults with larger spacing we find a similar evolution using a 2d finite element code of lithospheric shortening using a pseudoplastic rheology weak zones 3 km spaced and 30 40 weaker than the surrounding material are introduced to simulate the fabric formed at the ridge axis we show that reactivation and selective abandonment require strain weakening followed by strain rate weakening once a maturation threshold is reached a maturation fault slip of less than 50 m is needed to produce a fault network similar to that in the central indian ocean

constraints on indian plate motion since 20 ma from dense russian magnetic data implications for indian plate dynamics we use more than 230 000 km of russian marine magnetic and bathymetric data from the carlsberg and northern central indian ridges comprising one of the most geographically extensive dense shipboard surveys anywhere in the ocean basins to describe in detail seafloor spreading since 20 ma along the trailing edge of the indian plate india somalia plate rotations for 1 myr intervals over the past 20 myr are derived from inversions of more than 6600 crossings of 20 magnetic reversals and 1400 crossings of fracture zones that offset these two ridges statistical analysis of the numerous data indicates that outward displacement of reversal boundaries due to finite seafloor emplacement widths and correlated noise for anomaly crossings from individual spreading segments constitute two distinct sources of systematic bias in the locations of magnetic anomaly crossings contrary to the often made assumption that random gaussian distributed noise dominates the error budget seafloor spreading rates slowed gradually by 30 from 20 ma to 10 1 ma about a relatively stationary pole of rotation from 11 ma to 9 ma the rotation axis migrated several angular degrees toward the plate boundary modestly increasing the spreading gradient along the plate boundary india somalia kinematic data for times since 9 ma are consistent with remarkably steady motion with no evidence for a change in either the rotation pole or rate of angular opening within the few percent precision of our data the timing and nature of changes in india somalia motion since 20 ma closely resemble those for the capricorn somalia plate pair indicating that india and capricorn plate motions are strongly coupled we speculate that the slowdown in seafloor spreading at the trailing edges of the indo capricorn composite plate from 20 ma to 10 1 ma resulted from the increasing amount of work that was needed to build topography in the himalayan collisional zone the transition to stable india somalia and capricorn somalia seafloor spreading at 10 9 ma corresponds well with the onset at 8 ma of folding and faulting across an equatorial plate boundary separating the indian and capricorn plates suggesting that the latter may have played a fundamental role in restoring equilibrium between the torques that were driving and resisting the northward motions of the indian and capricorn plates

is unique scaling of aquifer macrodispersivity supported by field data spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity which was found to be scale dependent it increases with travel distance stabilizing eventually at a constant value however the question of its asymptotic behavior at very large scale is still a matter of debate it was surmised in the literature that macrodispersivity scales up following a unique scaling law attempts to define such a law were made by fitting a regression line in the log log representation of an ensemble of macrodispersivities from multiple experiments the functional relationships differ among the authors based on the choice of data our study revisits the data basis used for inferring unique scaling through a detailed analysis of literature marcodispersivities in addition values were collected from the most recent tracer tests reported in the literature we specified a system of criteria for reliability and reevaluated the reliability of the reported values the final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship on the contrary our results indicate that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value our investigation concludes that transport and particularly the macrodispersivity is formation specific and that modeling of transport cannot be relegated to a unique scaling law instead transport requires characterization of aquifer properties e g spatial distribution of hydraulic conductivity and the use of adequate models

boron isotope variations in geothermal systems on java indonesia abstract this paper presents 11 b data for hot springs hot acid crater lakes geothermal brines and a steam vent from java indonesia the processes that produce a large range of the 11 b values were investigated including the possible input of seawater as well as the contrast 11 b compositions of acid sulfate and acid chloride crater lakes the 11 b values of hot springs ranged from 2 4 to 28 7 and acid crater lakes ranged from 0 6 to 34 9 the 11 b and cl b values in waters from the parangtritis and krakal geothermal systems confirmed seawater input the 11 b values of acid sulfate crater lakes ranged from 5 5 to 34 9 and were higher than the 11 b of 0 6 of the acid chloride crater lake the heavier 11 b in the acid sulfate crater lakes was caused by a combination of vapor phase addition and further enrichment due to evaporation and b adsorption onto clay minerals in contrast the light 11 b of the acid chloride crater lake was a result of acid water rocks interaction the correlations of 11 b composition with 18 o and 2 h indicated that the b isotope corresponded to their groundwater mixing sources but not for j21 segaran and j48 cikundul that underwent 11 b isotope enrichment by b adsorption into minerals

evidence for long term diffuse deformation of the lithosphere of the equatorial indian ocean the presence of large earthquakes east west striking folds and thrust faults in sediments and east west striking undulations of wavelength 200 km in topography and gravity shows that the equatorial indian ocean is the locus of unusual deformation1 2 3 4 5 6 7 8 this deformation has been interpreted as a diffuse boundary between two tectonic plates9 10 11 12 13 seismic stratigraphy and deep sea drilling at two locations in the bengal fan indicate that the deformation began 7 5 8 0 myr ago3 14 15 here however we show using plate reconructions that motion across this diffuse oceanic plate boundary began more than 10 myr earlier than previously inferred and that the amount of north south convergence across the boundary through the central indian basin has been significantly greater than the convergence estimated from seismic profiles the relative plate velocity accommodated across the central indian basin has varied with time and has been as fast as 6 mm yr 1 about half the separation rate of earth s slowest spreading mid ocean ridge the earliest interval of measurable motion which began more than 18 myr ago may coincide with rapid denudation of the tibetan plateau from 21 myr to 15 17 myr ref 16 the present motion across the central indian basin began no earlier than 11 myr following an earlier interval of slower motion from 18 to 11 myr and may have begun at 8 myr when the tibetan plateau is thought to have attained its maximum elevation16 17

intraplate shortening in the central indian ocean determined from a 2100 km long north south deep seismic reflection profile although intraplate deformation is commonly observed on the continents there are only a few places in the oceans where deformation is distributed over a broad area rather than being localized at a single plate boundary the central indian ocean has long been recognized as a site of active widespread compressive deformation of the oceanic lithosphere reflecting an exceptionally high stress level however the strain pattern derived from indirect and incomplete observations remains poorly known a more complete data set was obtained during the phedre cruise 1991 by means of deep seismic reflection profiling one 2100 km long profile runs along the 81 e meridian from lat 14 s to the coast of sri lanka and provides us with the first long cross section through the region of observed crustal level faults fault analysis offers new estimates of the amount of shortening which was obtained across individual faults by measuring the maximum vertical uplift of sedimentary reflectors at the base of the sedimentary cover and converting it to horizontal throw under various assumptions of the fault geometry the contribution of the seismically resolvable faults amounts to 22 37 km of shortening or 2 5 4 3 this is two to three times greater than previous estimates extrapolated from local measurements on shorter seismic reflection profiles

fluid inclusions and ore precipitation mechanism in the giant xikuangshan mesothermal antimony deposit south china conventional and infrared microthermometric constraints abstract the giant xikuangshan antimony deposit located in the xiangzhong central hunan basin south china is the largest antimony deposit in the world stibnite is the predominant ore mineral and gangue minerals consist of quartz calcite fluorite and barite the ore mineral assemblages include early stage quartz stibnite fluorite quartz stibnite and barite quartz stibnite and late stage calcite stibnite in spite of numerous research works on the xikuangshan deposit during the past several decades the signatures of the ore forming fluids and the ore precipitation mechanisms are poorly constrained in order to characterize the fluids responsible for antimony mineralization and ascertain the genetic processes in the xikuangshan ore district conventional and infrared microthermometric measurements have been performed in this study on fluid inclusions hosted in transparent minerals quartz fluorite and barite and opaque stibnite respectively four types of fluid inclusions were identified for the early stage mineralization based on their phase assemblages including type i pure liquid inclusions type ii two phase liquid rich aqueous inclusions type iii two phase vapor rich aqueous inclusions and type iv pure vapor inclusions stibnite only contains type i and type ii inclusions while all types of fluid inclusions are common in the gangue minerals the homogenization temperatures and salinities of fluid inclusions in stibnite and associated gangue minerals in this ore district display significant differences fluid inclusions in stibnite exhibit relatively low homogenization temperatures 112 323 c and higher salinities 0 2 15 4 wt nacl equiv than inclusions in coexisting gangue minerals 119 366 c 0 2 4 2 wt nacl equiv usually about 50 c less than the intergrown gangue minerals according to the petrography of fluid inclusions and the relationship between their homogenization temperature and salinity it was concluded that stibnite and gangue minerals in the xikuangshan ore district are not co genetic instead they were deposited from two distinctly different hydrothermal solutions fluid mixing was responsible for stibnite precipitation but the precipitation of gangue minerals resulted from fluid boiling due to an abrupt drop in pressure the xikuangshan deposit is a typical example of mesothermal deposits rather than an epithermal deposit as previously considered

etude des mecanismes de condensation des gaz magmatiques exemple de l etna italie des sublimes ont ete recoltes a l etna en 1976 dans les gaz emanant de la voute percee d une coulee de lava active

the motion and boundary between the capricorn and australian plates the motions between the somalian antarctic and australian plates the three plates believed to meet at the rodrigues triple junction in the indian ocean are inconsistent with the assumption that all three plates are rigid the discrepancy is best explained if the australian plate contains two component plates thus the traditionally defined indo australian plate consists of three component plates and multiple diffuse plate boundaries the pattern of present deformation indicates that the boundaries between the three component plates are two unconnected zones accommodating divergence and a larger zone which we interpret as three diffuse convergent plate boundaries and a diffuse triple junction

chemical and isotopic evolution of groundwater through the active andean arc of northern chile abstract the role of rock water reactions leakage of sedimentary brine evaporite dissolution and variations in lithology on the chemical and isotopic evolution of groundwater draining the active arc and preandean basins in the antofagasta region of northern chile has been investigated using li b and sr isotopes the studied basin is that of the upper loa river and its sub basins which is adjacent to the basin occupied by the salar de atacama where li rich brines are commercially exploited due to the arid climate water draining this part of the andes does so primarily through the subsurface water from a thermal source is a common component of water sampled but its geochemical signature evolves through multiple processes including dilution cold rock water reactions influxes of sedimentary brine and evaporite mineral dissolution these processes lead to a range of li and b concentrations in groundwater 0 01 14 mg l and 0 18 20 mg l and isotope compositions 1 to 12 and 6 to 14 the effect of rock dissolution on 7li and 11b within aquifers is apparent from their low values but even in streams these values only undergo small increases relative to other rivers worldwide this may be due to the weathering of ignimbrites producing water with less al and limited clay formation the large reservoir of thermally sourced li and b of which only a small component is removed and because the streams acquire groundwater through their beds the wider range in 11b is a result of variable lithology and dissolution of evaporite minerals which have lesser effects on 7li our multi isotope approach highlights the role of lithology and different processes in defining groundwater chemistry isotopic signatures derived from marine sediments are recognizable in some springs even though this type of rock has nearly no surface exposure due to extensive volcanic rock cover and are acquired directly or via incorporation of these sediments into volcanic systems these high cl rocks can weather to produce water with a chemical composition like that of sedimentary brine but is distinguishable through 11b composition combination of 87sr 86sr 7li and 11b also indicate that mixed salts which contribute to groundwater draining the ignimbrite covered areas of the basin did not form following cold temperature weathering but from water where thermal contributions dominated solute budgets keeping 7li low and li cl and b cl high compared to other fluid reservoirs such as seawater we propose that these saline systems lay within the confines of one of the multiple late miocene pliocene calderas following the active stage of volcanism and while heat gradients remained high

mineral deposits in the rotokawa geothermal pipelines new zealand abstract at the point of flashing at 224 c and 25 bar absolute black silica scales enriched in cu 5 6 ag 4 0 te 3 0 zn 1 5 pb 0 6 and au 0 2 form in the wellhead of production well rk 9 silver pb cu and au are deposited as tellurides cu pb and zn as sulfides and au as a native element these elements decrease rapidly downstream of the wellhead to other parts of the surface geothermal pipeline mercury b as se sb and reduced s are partially transported in the gas phase and largely deposited at a distance from the wellhead total s and b occur primarily in the steam line where b is stabilised by silica deposited from carry over brine and s by sulfide mineralisation arsenic and se are mainly found in scales from the steam and mixing reinjection lines hg in the condensate and mixing reinjection lines and sb in the mixing reinjection line where 80 105 c low salinity condensate mixes with 140 170 c brine a decrease in the solubility of minerals in solution is the primary cause for deposition of opal a and increased concentrations of base and precious metal concentrations in scales scale deposition is thus induced by flashing at the wellhead of the production wells attached to the ormat binary plant phase separation dilution cooling and mixing of cooled brine and condensate the reaction of steel with circulating solutions and gases results in a corrosion mineral assemblage reflecting local oxidation potentials and variations in h2s partial pressures along the pipeline corrosion of steel introduces and augments trace elements such as p cr mn ni and mo in the pipeline solutions selective incorporation or sorption of elements onto opal a and opal ct or corrosion products such as goethite and pyrite may increase concentrations of li b cl and p in opal cr mn ni cu zn and mo in goethite and cu zn as hg sb and se in pyrite wherever water circulates in the pipeline system silica precipitates initially from solution as a gel which later solidifies to opal a and subsequently crystallises to opal ct then quartz aggregates the transformation of opal a to more ordered and stable silica polymorphs in the pipelines is a kinetically induced dissolution reprecipitation crystal growth process that is accelerated at temperatures 200 224 c

antimony in the environment lessons from geochemical mapping abstract the distribution of sb in a variety of sample materials including soils plants and surface water was studied at different scales from continental to local combining published data sets with the aim of delineating the impact and relative importance of geogenic vs anthropogenic sb sources geochemical mapping demonstrates that variation is high at all scales from the detailed scale with sample densities of many sites per km 2 to the continental scale with densities of 1 site per 5000 km 2 different processes govern the sb distribution at different scales a high sample density of several samples per km 2 is needed to reliably detect mineralisation or contamination in soil samples median concentrations are so low for sb in most sample materials below 1 mg kg in rocks and soils below 0 1 mg kg in plants below 0 1 g l in surface water that contamination is easier to detect than for many other elements distribution patterns on the sub continental to continental scale are however still dominated by natural variation given that the geochemical background is characterised by a high variation at all scales it appears impossible to establish a reliable single value for good soil quality or a natural background concentration for sb for any sizeable area e g for europe for such a differentiation geochemical maps at a variety of scales are needed different sample materials can reflect different geochemical sources and processes even when collected from the same survey area weathering soil formation leads to an increased sb concentration in soils compared to rocks organic soils are highly enriched factor 5 10 compared to mineral soils in sb soils and stream sediments return comparable median sb concentrations plants are usually well protected against sb uptake there exist however plant species that can accumulate sb to values of more than 1000 mg kg antimony concentrations in the marine environment are not sufficiently well documented high sb concentrations related to hydrothermal and volcanic processes may have been previously underestimated

evidence for multiphase folding of the central indian ocean lithosphere long wavelength 100 300 km folding in the central indian ocean associated with the diffuse plate boundary separating the indian australian and capricorn plates is earth s most convincing example of organized large scale lithospheric deformation to test the timing and mechanics of this deformation as implied by plate kinematic and deformation models we present a new analysis of the seismic stratigraphy of the bengal fan sediments this analysis shows that the folding of the oceanic lithosphere was multiphase with major events occurring in the miocene 8 0 7 5 ma pliocene 5 0 4 0 ma and pleistocene 0 8 ma the miocene phase was the most intense and involved deformation of an area south of 1 s whereas in the pliocene the activity shifted northward in the final phase pleistocene the activity was focused in the equatorial region no evidence was found for deformation prior to 8 0 7 5 ma the spatial extent of the pleistocene folding event overlaps the pliocene and or miocene folding events and coincides with both the area of most active faulting and the zone of greatest historical seismicity the seismic data show that the timing of reverse faulting and thus more significant shortening of the lithosphere generally coincided with the phases of folding but there are examples of folding of the oceanic lithosphere without associated reverse faulting

toward a minimum change model for recent plate motions calibrating seafloor spreading rates for outward displacement summary we use seafloor spreading distances derived from reconstructions of more than 7000 crossings of young magnetic anomalies along seven plate boundaries to study outward displacement a source of systematic bias in estimates of seafloor spreading rates which is caused by a combination of processes that shift magnetic polarity transition zones away from their idealized locations linear regressions of 81 independent sequences of seafloor opening distances as a function of their magnetic reversal ages for anomalies younger than c3n 1 4 19 ma yield 75 positively valued intercepts for zero seafloor age confirming the ubiquitous outward shift of magnetic reversals reported by previous authors grouping these data into 29 locally consistent clusters yields better constrained zero age intercepts that are uniformly positive and average 2 2 0 3 km globally these values which are 1 3 km at most locations and are significantly larger 3 5 km along the well surveyed reykjanes and carlsberg ridges agree well with published magnetic polarity zone transition widths which are estimated directly from nearbottom seafloor magnetic measurements significant variations in outward displacement along the southeast indian ridge are strongly correlated with changes in axial morphology and axial depth however a similar correlation is not observed along other ridges forward magnetic anomaly modelling suggests that variations in outward displacement can be explained by differences in the magnetic source layers that are assumed to characterize different spreading centres if not corrected for outward displacement the implied systematic upward biases in seafloor spreading rates which are averaged over the width of anomaly 1 the youngest reversal that is used for plate reconstructions range from 6 mm yr 1 along the reykjanes ridge where outward displacement is 4 5 km to 3 mm yr 1 along ridges where outward displacement approximates the global average of 2 km