possible magma intrusion revealed by temporal gravity ground deformation and ground temperature observations at mount komagatake hokkaido during the 1996 1998 crisis summary mount komagatake 1131 m above sea level is a subduction related active volcano in hokkaido japan where two phreatic eruptions occurred in 1996 march and 1998 october after 54 years of dormancy we analyse four sessions of geodetic microgravity and ground temperature observations made over a two year period from november 1996 to may 1997 neither significant gravity nor significant elevation changes gps or levelling were observed from may 1997 to november 1997 we observed a slight subsidence 1 2 cm and contraction within 1 cm of the edifice a gravity increase 15 30 gal at the benchmarks inside the 2 km wide summit crater and a local temperature increase of 15 20 c at the summit crater from november 1997 to may 1998 we observed an edifice wide gravity increase of about 15 gal with no significant elevation change for benchmarks outside the summit crater besides this edifice scale variation we recorded a subsidence of about 5 6 cm and apparently no change of gravity inside the summit crater we inverted our data using models of increasing complexity elastic models are able to explain our deformation observations but they cannot explain either the gravity data or the temperature observations satisfactorily we introduced both an isothermal and a non isothermal porous medium filled with fluids to model deformation and gravity variations and we used a fissure model to invert the temperature anomaly our observations are consistent with a model of underground shallow water evaporation occurring as a result of heat rising from a hot and dense body density contrast of 200 kg m 3 of about 1011 kg at 4 5 km depth this interpretation suggests a possible intrusion of a magmatic body within the edifice

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

tectonics of the east pacific rise near 12 50 n a submersible study abstract using the diving saucer cyana a portion of the east pacific rise between 12 38 and 12 54 n has been studied and mapped four main zones are defined 1 an active volcanic zone located in the central graben the graben displays a variable relief along strike from less than 10 m up to 55 m and has an en echelon pattern in plan view 2 an active tectonic zone comprising the central graben and extending up to about 2 km from either side of the rise axis 3 an inactive tectonic zone starting 2 km away from the axis and formed by discontinuous horst and graben type of structures and 4 off axis volcanoes seamounts located less than 20 km on either side of the rise axis at 12 50 n the active tectonic zone is extremely narrow and the mode of deformation is through fissuring in strong contrast with that observed in slow or intermediate rate ridges the presence or absence of a magma reservoir at shallow depth explains the difference in the width of the active tectonic zone the state of isostatic equilibrium or lack of equilibrium explains the different modes of deformation

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

groundwater recharge and evolution in the dunhuang basin northwestern china groundwater recharge and evolution in the quaternary aquifer beneath the dunhuang basin was investigated using chemical indicators stable isotopes and radiocarbon data to provide guidance for regional water management the quality of groundwater and surface water is generally good with low salinity and it is unpolluted the dissolution of halite and sylvite from fine grained sediments controls concentrations of na and k in the groundwater but na cl molar ratios 1 in all samples are also indicative of weathering of feldspar contributing to excess na the dissolution of carbonate minerals yields ca2 to the groundwater thereby exerting a strong influence on groundwater salinity the delta o 18 and delta h 2 values in unconfined groundwater are enriched along the groundwater flow path from sw to ne in contrast confined groundwater was depleted in heavy isotopes with mean values of 10 4 parts per thousand delta o 18 and 74 4 parts per thousand delta h 2 compared with the precipitation values all of the groundwater samples were strongly depleted in heavy isotopes indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited the unconfined water is generally young with radiocarbon values of 64 9 79 6 pmc in the northern basin radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of similar to 15 ka indicates that this groundwater was recharged during a humid climatic phases of the late pleistocence or early holocene the results have important implications for inter basin water allocation programmes and groundwater management in the dunhuang basin c 2012 elsevier ltd all rights reserved

hydrogeochemical processes in the groundwater environment of heihe river basin northwest china the heihe river basin is a typical arid inland river basin for examining stress on groundwater resources in northwest china the basin is composed of large volumes of unconsolidated quaternary sediments of widely differing grain size and during the past half century rapid socio economic development has created an increased demand for groundwater resources understanding the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management of groundwater resources in the heihe river basin to this end a total of 30 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions and its quality for irrigation chemical analysis shows that water presents a large spatial variability of chemical facies so42 hco3 so42 cl and cl so42 as groundwater flow from recharge area to discharge area the ionic ratio indicates positive correlation between the flowing pairs of parameters cl and na r 0 95 so42 and na r 0 84 hco3 and mg2 r 0 86 and so42 and ca2 r 0 91 dissolution of minerals such as halite gypsum dolomite silicate and mirabilite na2so4 10h2o in the sediments results in the cl so42 hco3 na ca2 and mg2 content in the groundwater other reactions such as evaporation ion exchange and deposition also influence the water composition the suitability of the groundwater for irrigation was assessed based on the us salinity laboratory salinity classification and the wilcox diagram the results show that most of the groundwater samples are suitable for irrigation uses barring a few locations in the dessert region in the northern sub basin

off axis hydrothermal circulation parametric tests of a refined model of processes at deep sea drilling project ocean drilling program site 504 we have developed a refined model of coupled heat and fluid flow to numerically simulate off axis hydrothermal circulation through the upper oceanic crust the new representation includes mesh elements with curved sides and noncentered nodes these curvilinear elements allow improved simulation of topography at the seafloor and within underlying sediment and basaltic layers curvilinear simulations of circulation at deep sea drilling project ocean drilling program site 504 confirm the broad conclusions derived from the rectilinear simulations of fisher et al 1990 but also suggest that permeability within the upper few hundred meters of crust around hole 504b must be concentrated within several narrow zones this interpretation is consistent with core observations and wireline logs from hole 504b within these highly permeable zones absolute permeability may be several orders of magnitude higher than the bulk permeability measured for the upper crust as a whole a series of detailed parametric simulations was conducted to determine the quantitative importance of basal heat flow seafloor bathymetry basement relief and differential sediment thickness in modifying the geometry and intensity of off axis hydrothermal circulation these studies reveal that basement relief and differential sediment thickness are more important than seafloor bathymetry in enhancing off axis convection within the seafloor observed natural correlations between seafloor bathymetry and heat flow may exist because bathymetry is a proxy for the other two important parameters basement relief and differential sediment thickness off axis convection at geochemically significant velocities is possible even with heat input appropriate for some of the oldest oceanic crust a thick sediment layer over older crust may cause enough conductive refraction at the seafloor to mask the variations in seafloor heat flow often associated with off axis hydrothermal convection

numerical heat and fluid flow modeling of the panorama volcanic hosted massive sulfide district western australia exceptional exposure of the archean pilbara block in western australia reveals a cross section through an archean massive sulfide hosting volcanic succession with underlying subvolcanic intrusion in the panorama district a numerical model based on available detailed geologic information has been constructed to simulate heat and fluid flow in the panorama district the modeling provides insight into the evolution of the hydrothermal system and evaluates key geologic parameters and their influence on fluid flow hydrothermal circulation and the genesis of massive sulfide orebodies the model simulates important aspects of the panorama massive sulfide district such as temperature distribution relative alteration zonation and the size and distribution of orebodies predicted temperatures ranging from 150oc at the top of the volcanic pile to 400oc at the andesite diorite interface are comparable to temperature estimates based on previously published oxygen isotope mapping modeled fluid discharge temperatures are highest for the sulphur springs deposit 300o 400oc and lower for the kangaroo caves and other deposits 250o 350oc the most favorable conditions to reproduce the orebodies and their related alteration zonation occur at anisotropic rock permeabilities comparable to the upper oceanic crust 10 15 10 14 m2 and higher fault permeabilities 10 14 10 13 m2 with a specific fault arrangement similar to that mapped in the field the 4 6 million metric tons mt sulphur springs orebody is predicted to form in less than 5 000 yr assuming a hydrothermal fluid with seawater salinity 10 ppm base metal concentration and a low deposition efficiency 10 other deposits form above the faults under similar conditions a large range of base metal concentrations in the fluids can account for the known orebodies but high temperatures 250oc and high flow velocities 10 7 m s are necessary to produce the observed alteration patterns and distribution of ore deposits results indicate that the establishment of a significant hydrothermal system capable of forming economic massive sulfide deposits is favored in fresh volcanic rock packages that have not been affected by earlier compaction or alteration under these conditions economic massive sulfide orebodies 5 mt of 10 zn cu may form in a few thousand years although the overall lifespan of the hydrothermal system may be between 30 000 and 200 000 yr depending on the variations in rock and fault permeability with time

fracture induced hydrothermal convection in the oceanic crust and the interpretation of heat flow data small scale seafloor heat flow variations with a characteristic wavelength of about 1200 m have been observed on a profile over a sediment sealed ridge flank two theories have been advanced to explain them low aspect ratio hydrothermal convection in a highly permeable basement layer 600 m thick or high aspect ratio convection in an anisotropic permeable layer 200 m thick induced by 20 m topographic variations with a 1000 m half wavelength neither theory is totally satisfactory the first requires a very thick highly permeable zone while the absence of any resolvable basement relief on a complementary seismic survey limits the credibility of the second we hypothesize that sub critical hydrothermal convection in normal upper oceanic crust driven by discrete fractures can cause the observed heat flow anomalies we test the hypothesis by using a finite element code to solve the coupled time dependent heat transport and fluid flow differential equations discrete fractures are incorporated explicitly we show that the inclusion of fractures in layers 2a and 2b promotes convection fluid flow through fractures causes horizontal thermal gradients and initiates and maintains sub critical convection within the upper basalts the predicted heat flow variations are comparable with the observed data

hydrochemical water evolution in the aral sea basin part i unconfined groundwater of the amu darya delta interactions with surface waters summary the aral sea which has been affected by lake level lowering of approximately 25 m and a salinity increase from 10 to 100 g l since 1963 represents along with the amu dary delta a dynamic hydrological system under an arid climate regime the system receives river water inflow at high seasonal and inter annual variability from remote alpine source areas in the amu darya delta there is a distinct salinity contrast between the low salinity river water 1 g l and the salinity of the unconfined gw gw unconf 10 95 g l the gw unconf levels are predominantly controlled by the seepage of the river water inflow and gw discharge into the shrinking aral sea in june 2009 and august 2009 we sampled water from various sources including surface waters gw unconf lake water and soil leachates for chemical analyses evaporative enrichment precipitation dissolution of gypsum and precipitation of calcite drive the gw unconf to an nacl so 4 water type presenting a positive correlation between na and so 4 we model the hydrochemical evolution of the gw unconf in a box model which considers the capillary rise of near surface gw the precipitation of minerals in the unsaturated horizon and the seasonal re flushing of adhesive residual brines and soluble salts the model documents a rapid increase in salinity over a few annual cycles furthermore the model simulations demonstrate the importance of the aeolian redistribution of soluble salts on the hydrochemical gw evolution in a lab experiment halite hexahydrite and starkeyite are precipitated during the late stages of evaporative enrichment from a representative local brine processes specific to different water compartments plausibly explain the variations of selected element ratios for example the precipitation of low sr calcite in irrigation canals and natural river branches of the delta lowers ca sr the dissolution of gypsum in soils ca sr mole ratio 150 and the possible precipitation of srso 4 associated with sr depletion in adhesive residual brines increases ca sr in seepage and re increases ca sr in the unconfined gw aral sea water which receives high ca sr surface and groundwater inflow developed due to continued precipitation of high ca sr calcite the almost lowest ca sr ratio 25 over time we observed spatial variations in the gw unconf composition i ammonium levels increase strongly due to interaction with lake sediments rich in organic matter and ii distinct increases in levels of nitrate u mo and se locally reflect oxygenation when gw levels decrease the amu darya delta acts as a sink for boron uptake via terrestrial vegetation and a source for bromide release by degradation of organically bound br our results concerning the hydrochemical evolution of the gw unconf and additional data from the aral sea constrain the parameter gw discharge in water budget models of the lake and improve the basis for palaeoclimatic interpretations of sediment records from the aral sea

multiple scale hydrothermal circulation in 135 ma oceanic crust of the japan trench outer rise numerical models constrained with heat flow observations anomalous high heat flow is observed within 150 km seaward of the trench axis at the japan trench offshore of sanriku where the old pacific plate 135 ma is subducting individual heat flow values range between 42 and 114 mw m 2 with an average of 70 mw m 2 these values are higher than those expected from the seafloor age based on thermal models of the oceanic plate i e 50 mw m 2 the heat flow exhibits spatial variations at multiple scales regional high average heat flow 100 km and smaller scale heat flow peaks 1 km we found that hydrothermal mining of heat from depth due to gradual thickening of an aquifer in the oceanic crust toward the trench axis can yield elevated heat flow of the spatial scale of 100 km topographic effects combined with hydrothermal circulation may account for the observed smaller scale heat flow variations hydrothermal circulation in high permeability faults may result in heat flow peaks of a subkilometer spatial scale volcanic intrusions are unlikely to be a major source of heat flow variations at any scale because of limited occurrence of young volcanoes in the study area hydrothermal heat transport may work at various scales on outer rises of other subduction zones as well since fractures and faults have been well developed due to bending of the incoming plate

predicted groundwater circulation in fractured and unfractured anisotropic porous media driven by nuclear fuel waste heat generation the concept of nuclear fuel waste disposal underground is drawing increasing attention due to its many advantages against the current storage methods at surface in this paper we employ the galerkin finite element technique to solve the coupled time dependent heat transfer and fluid flow differential equations and to predict the evolving behaviour of groundwater flow and subsurface temperature distribution associated with a proposed disposal system at the whiteshell research area in southeastern manitoba a two dimensional 2 d numerical model is conceptualized from geological constraints in this particular area to investigate the free convection of groundwater flow driven by nuclear fuel waste heat generation we assume the 2 d model has a flat upper boundary so as to eliminate the effect of topography head buoyancy force due to fluid density variations is therefore the sole driving mechanism for fluid migration case studies for both unfractured and fractured porous media confirm that thermal decay of the buried fuel waste can initiate fluid circulation in the presence of discrete fractures the deep and hot fluid nearby the disposed contaminant can discharge to the biosphere thus potentially threatening human health and the natural environment

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

basin scale numerical modeling to test the role of buoyancy driven fluid flow and heat transfer in the formation of stratiform zn pb ag deposits in the northern mount isa basin numerical fluid flow and heat transport modeling was undertaken on a well constrained geologic section through the northern mount isa basin in order to test the possibility of forming stratiform zn pb ag deposits by buoyancy driven free convection of marine fluids the major two dimensional geologic section used for the modeling was based on recent geologic mapping and sequence stratigraphic interpretation combined with geophysical interpretation from regional seismic aeromagnetic and gravity data sets the basin fill termed the leichhardt calvert and isa superbasins forms a south dipping wedge of sedimentary and minor volcanic rocks up to 25 km thick a number of major subvertical synsedimentary normal faults cut through this fill and are rooted in the basement two potential aquifer sequences have been identified sandstones and volcanic rocks of the big supersequence at the base of the calvert superbasin and sandstones and conglomerates comprising the mount guide quartzite at the base of the older leichhardt superbasin there are three stratiform zn pb ag deposits in the younger isa superbasin close to the section line selected for modeling century is a world class and high grade stratiform zinc deposit which contains over 14 mt of zn metal hosted by 1595 ma black shales and siltstones pb pb isotope studies suggest the deposit formed about 1575 ma walford creek and blue bush are large but low grade pyrite rich and zinc poor stratiform deposits hosted in 1640 ma carbonaceous shales and siltstones numerical modeling of fluid flow at about 1575 ma shows that buoyancy driven convection is controlled by the relationship between the faults and aquifers the synsedimentary faults given high permeabilities in the model because they were active during the mineralizing event act as either recharge or discharge zones for fluid flow marine fluids commonly recharge the basin via the minor faults and flow through the sandstone and volcaniclastic aquifer sequences at depths of 5 to 10 km these fluids have the potential to leach zinc and lead from the clastic material comprising aquifer and adjacent volcanic rock layers the heated metalliferous fluids discharge to the surface where the aquifers intersect the major faults hydrothermal discharge temperatures from the termite range fault were computed to be in the range 100 to 180 c with fluid velocities of 1 to 8 m per year these conditions are suitable for the formation of a century sized zn deposit at the discharge point adjacent to the termite range fault over a period of 0 65 m y provided a suitable chemical trap environment is present several numerical simulations were run with different aquifer and fault properties designed to understand the hydrological constraints for the formation of major zn deposits aquifer permeability fault permeability and fault penetration depth were shown to be the major factors controlling the fluid flow and temperature regime significantly higher discharge fluid temperatures and velocities were obtained when the depth of penetration of the termite range fault was increased from 15 to 30 km the results of the numerical modeling are significant in understanding geologic and hydrological controls on the formation and location of major stratiform zn deposits the permeability and thickness of potential aquifers their depth in the basin the presence of stacked aquifer sequences and the relationship between aquifers and synsedimentary faults all have important exploration implications in particular the termite range fish river and elizabeth creek faults are interpreted to be major deep faults that have controlled basin wide convective fluid flow and therefore the location of major base metal deposits

upwelling variability off southern indonesia over the past two millennia modern variability in upwelling off southern indonesia is strongly controlled by the australian indonesian monsoon and the el nino southern oscillation but multidecadal to centennial scale variations are less clear we present high resolution records of upper water column temperature thermal gradient and relative abundances of mixed layer and thermocline dwelling planktonic foraminiferal species off southern indonesia for the past two millennia that we use as proxies for upwelling variability we find that upwelling was generally strong during the little ice age lia and weak during the medieval warm period mwp and the roman warm period rwp upwelling is significantly anticorrelated to east asian summer monsoonal rainfall and the zonal equatorial pacific temperature gradient we suggest that changes in the background state of the tropical pacific may have substantially contributed to the centennial scale upwelling trends observed in our records our results implicate the prevalence of an el nino like mean state during the lia and a la nina like mean state during the mwp and the rwp

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

hydrothermal models for the generation of massive sulfide ore deposits the discovery of massive sulfide ore deposits at certain sites at active seafloor spreading centers provides a basis for considering the energetics of processes that have concentrated similar large ore deposits that have been preserved in volcanic rocks on land in this paper we construct transport models based on hydrothermal convection systems in the oceanic crust we investigate models in which the circulation is driven by heat extracted from the permeable crustal rocks themselves as well as by heat conducted through the roof of a replenished vigorously convecting crustal magma chamber if the hydrothermal fluids carry 100 ppm dissolved iron as found in black smokers on the east pacific rise and exit at 350 c or greater calculations show that the heat content of the oceanic crust is insufficient to account for ore deposits of 3 mt or greater heat extraction through the roof of a magma chamber in conjunction with the formation of a thin 1 km layer of plated gabbro may account for ore bodies of the order of 3 mt provided the permeability of the oceanic crust in the magma hydrothermal fluid contact zone is 10 15 m2 or less if the conducting boundary layer were only 1 m thick locally for 103years the permeability could be as high as 10 13 m2 the permeability in the discharge zone could conceivably be two orders of magnitude greater than the permeability at depth more work is needed on the details of the effects of magma chamber replenishment and off axis dike injection and on the role of magmatic fluids very large ore deposits i e 100 mt are probably formed in multiple hydrothermal cycles

hydrothermal fluid migration and brine pool formation in the red sea the atlantis ii deep numerical heat and fluid flow simulations of the atlantis ii deep in the red sea were conducted to investigate the development migration and discharge of hydrothermal fluids into a submarine depression and determine the conditions necessary to form a brine pool high salinity fluids are predicted to form by leaching miocene evaporates migrate and convect within young oceanic crust and discharge onto the seafloor predicted fluid discharge temperatures t max 301 c discharge fluid velocities v max 0 09 m s and salinities s max 21 wt increase over time and reach values comparable to modern seafloor observations established convection patterns and discharge behavior are robust and are not greatly affected by geometry of rock property changes modeling results were used to calculate the minimum conditions for hydrothermal fluids from a developing hydrothermal system to mix with seawater reverse buoyancy and begin to form a brine pool in a submarine depression under conditions encountered on the seafloor t 25 300 c s 5 25 wt fluid mixtures predicted to pond on the seafloor range from late in the mixing process 99 at low temperatures t 26 c to much earlier 36 mixing at higher temperatures t 94 c a model of brine pool evolution is proposed that describes the processes and conditions necessary to initiate brine pool formation and compares formation conditions with accumulated ore material in the atlantis ii deep and other locations

contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings we present alkenone derived sea surface temperature sst records from three marine cores collected within the southern benguela upwelling system bus spanning the last 3 ka the sst evolution over the last 3 millennia is marked by aperiodic millennial scale oscillations that broadly correspond to climatic anomalies identified over the north atlantic region the bus sst data further suggest cooling and warming trends opposite to the temperature evolution in the moroccan upwelling region and in antarctica in contrast the last decades are marked by a cooling of unprecedented magnitude in both the benguela and moroccan upwelling systems which is not observed in the antarctic record these contrasted responses in atlantic upwelling systems triggered by natural and anthropogenic forcings shed light on how different climatic mechanisms are mediated by ocean atmosphere interactions and transmitted to the geological records of past and present climate changes citation leduc g c t herbert t blanz p martinez and r schneider 2010 contrasting evolution of sea surface temperature in the benguela upwelling system under natural and anthropogenic climate forcings geophys res lett 37 l20705 doi 10 1029 2010gl044353

influence of normal faults and basement topography on ridge flank hydrothermal fluid circulation mid ocean ridge flank hydrothermal fluid circulation is drawing increasing attention since about 70 per cent of the advective heat flux through oceanic crust occurs on ridge flanks previous numerical studies have largely considered the effect of basement relief but ignored the role of normal faults although it is well known that normal faults are pervasive in the ridge flank environment this paper investigates the importance of normal faults and basement topography in controlling ridge flank hydrothermal convection numerical experiments are conducted using a sophisticated finite element software package jhu2d a 2 d conceptual model is constructed based on a variety of in situ geophysical data recently collected around the dsdp odp site 504b four scenarios are examined in which basement topography and active and inactive normal faults are included numerical simulation results indicate the active normal faults that penetrate through the sediment layer to the seafloor are a key factor governing the sea water circulation and the thermal regime within the oceanic crust the presence of these faults challenges the previously discovered correlation among the seafloor heatflow bathymetry and basement relief it is the spacing between adjacent faults that determines the wavelength of the heatflow variations basement relief becomes important only when there are no active faults present fluid circulation is thus then confined mainly within the pillow lavas layer and the seafloor heatflow anomalies therefore have the same wavelength as that of the basement topography

numerical investigation of salinity in controlling ore forming fluid transport in sedimentary basins example of the hyc deposit northern australia this paper presents the first hydrogeological model that fully couples transient fluid flow heat and solute transport associated with the formation of the hyc sedex deposit in the mcarthur basin northern australia numerical results reveal that salinity plays an important role in controlling hydrothermal fluid migration in particular it appears that it is the distribution of evaporitic units within a given basin rather than their absolute abundance that controls the development of free convection relatively saline conditions at the seafloor strengthen the thermally induced buoyancy force and hence promote free convection of basinal solutions whereas high salinities at the bottom counteract the thermal function of natural geothermal gradient and suppress the development of convective hydrothermal fluid circulation in the latter case higher thermal gradients are required to initiate substantial free convective fluid flow numerical experiments also suggest the position of an ore body with respect to its vent system may be controlled by the spatial and temporal salinity distributions in the basin vent distal ore formation a result of exhalation of brines that are denser than seawater and hence can flow away from the vent region is promoted by moderate salinity at the seafloor and higher salinity in the aquifer vent proximal ore accumulation a result of pluming upon exhalation of brines less dense than seawater is favored by the highest salinity conditions occurring near the level of the seafloor

groundwater chemistry and mass transfers in the independence aquifer central mexico by using multivariate statistics and mass balance models in the light of progressive depletion of groundwater reservoir and water quality deterioration of the independence aquifer an investigation on chemical data of dissolved major and minor constituents in 246 recent groundwater samples was performed the main objective was the detection of processes responsible for the geochemical evolution and mineralization throughout the area multivariate techniques revealed different sources of solutes a dissolution of calcium and magnesium carbonate minerals b weathering of acid volcanic minerals c alteration of manganese containing alkaline silicates d leaching of halite deposits of meteoric origin e contamination from agricultural and urban wastewaters and f evaporative effects due to intensive irrigation although nitrate contamination is associated with pollution from intensive cultivated areas natural contamination plays an important role in the study area the investigation reveals that weathering of acid volcanic rocks rhyolite and oxidation of arsenic bearing sulfide minerals are the responsible processes for high fluorine up to 16 mg l and arsenic up to 0 12 mg l contents respectively exceeding the mexican maximum admissible concentration for drinking water except for kaolinite all recharge processes are dissolution oriented co2 calcite dolomite k feldspar plagioclase silicate precipitation amorphous silica and chalcedony is of growing importance in discharge zones cation exchange is not an important issue in the whole study area

sea salt corrections and interpretation of constituent ratios in marine precipitation differentiation of sea salt and non sea salt or excess components is essential for many studies of marine aerosol and precipitation chemistry uncertainties in such calculations arise from 1 uncertainties in the composition of seawater 2 analytical uncertainties 3 the amount of dry deposited sea salt in samples 4 the validity of assuming a purely marine source for the sea salt reference species and 5 the validity of assuming no fractionation during or after production of sea salt aerosols we assessed these uncertainties and using the reduced major axis regression technique evaluated these assumptions by analyzing the composition of precipitation at amsterdam island 38 s 78 e and at bermuda 32 n 65 w precipitation on amsterdam island contained significant excess concentrations of na 2 and cl 5 relative to mg2 indirect evidence indicates that these departures from seawater ratios are probably not due to the influence of terrestrial material the excess cl was sufficient to account for approximately 20 of free acidity suggesting that scavenging of vapor phase hcl may affect the acid base chemistry of precipitation at the site volume weighted excess so42 based on na and mg2 differed by 11 a nonnegligible source of bias in estimating the wet deposition of non sea salt sulfur precipitation on bermuda contained significant concentrations of locally derived alkali and alkaline earth metals the influence of continental and non sea salt marine sources on concentrations of excess so42 was also evident these observations suggest that assumptions involved in sea salt corrections are not always satisfied and that it is therefore necessary to evaluate individual data sets using objective criteria to select the appropriate reference species

three dimensional numerical simulation of the hydrothermal system within tag like sulfide mounds a 3 d finite element algorithm with incorporated explicit pipe like elements is developed to solve the coupled time dependent heat transport and fluid flow differential equations and yield the internal temperature and fluid velocity fields for tag like mounds a range of models with permeable and impermeable upper boundaries and different thermal conductivities are investigated the solutions have three common features a central high temperature zone which coincides with a non magnetic zone inferred from magnetic data fluid upflow along the vertical high permeability column surrounding a central pipe and a maximum fluid velocity of the order of the observed maximum value at the central black smokers thermal conductivity variations strongly influence the temperature distribution but not the fluid velocity pattern

hydrochemical characteristics and environmental significance in different ablation period in hulugou river basin in qilian mountain in order to research hydro geochemistry characteristic and environmental significance of river and spring water 68 samples were collected in different ablation periods initial ablation period ablation period end ablation period in hulugou river basin the results showed that the chemical type of the river and spring in different ablation period was so4 2 ca2 mg2 type in hulugou river basin compared with water samples in different ablation the order of the total ionic concentration was the initial ablation period the end ablation period ablation period with the mean was 238 29 237 19 and 178 19 mg l respectively from the analysis of ionic sources which indicated the chemical composition of river and spring water was controlled by crustal materials during the different ablation period in the hulugou river basin and the dominant processes were water rock intersection especially the weathering and dissolution of dolomite meanwhile the results of enrichment factor also confirmed that most of the ions influenced by local soil source in study area but the ratios of no3 so4 2 and cl to na also confirmed that anthropogenic also influenced the water chemistry in study area the results are also helpful for further understanding the hydro geochemistry characteristic in different ablation period in the alpine regions of western china and providing scientific basis for further study on hydro geochemistry

geochemical characteristics of water and sediment of the indus river trans himalaya india constraints on weathering and erosion abstract the indus river carries a huge amount of chemical and sediment load while traversing the himalayas the present study deals with the chemistry of major ions ca mg hco3 na k cl so4 sio2 and trace metal contents ba sr zn ni cu co mn of the river indus one of its major tributaries the river beas many adjoining hot and cold water springs and the high altitude lake 5700 m kyung tso although anthropogenic activities like farming grazing and tourism have started in large parts of this terrain our study indicates that chemistry of indus water is influenced mostly by the lithology of the basin and most of its ionic concentration appears to have been derived from weathering of carbonates and silicates in the catchment area for the first time bed and suspended sediments of the river indus have also been studied and compared with average post archean shale pas and greywacke the sediments of the indus river in its headwater region closely reflect the exposed portion of the crust in its catchment area the headwater part of the indus basin in ladakh and karakorum is characterised by rapid uplift and therefore subject more to intense physical weathering than chemical weathering as is evidenced by the suspended and dissolved load carried by the river physical weathering and erosion is expected to have major controls on the grain size and therefore the chemical nature of the sediments

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

the relationship between flow and permeability field in seafloor hydrothermal systems the permeability of oceanic crust is spatially variable and probably anisotropic as well using realistic permeability fields for young oceanic crust we have performed numerical simulations of finite amplitude steady and unsteady convective fluid flow in layered and or anisotropic porous media heated from below to investigate particular patterns of fluid flow and temperature in mid ocean ridge hydrothermal systems on the flanks of mid ocean ridges permeability measurements in deep sea boreholes suggest that only the top few hundred meters of oceanic crust is permeable given this permeability structure and assuming some minimum permeability and layer thickness our models predict that convection occurs in the form of numerous cells with aspect ratios of order unity within this permeable layer such convection results in fluid flux and diagenetic reactions within the permeable layer with a negligible effect on heat flow at the seafloor in agreement with field observations estimates of oceanic crust permeability based on hydrothermal veins in ophiolites and measurements in deep sea boreholes suggest that pillow basalts lava flows are much more permeable than underlying sheeted dikes this is particularly true at the ridge crest where voids have not yet collapsed and filled given this permeability structure our study suggest that a small percentage of the fluid entering the ridge crest circulates through the sheeted dikes before exiting the system at high temperatures in very focused discharge zones in our models these discharge zones narrow considerably at the interface between the sheeted dikes and the pillow basalts lava flows much of the fluid entering the system however never circulates below the pillow basalts lava flows and exits the seafloor at low temperatures in general discharge zones are more focused than recharge zones these results are consistent with observations of narrow and focused discharge zones in ophiolites and localized high temperature venting amid widespread low temperature flow on the ridge crest the spacing of upflow zones at the surface is strongly controlled by convective flow in the bottom permeable layer in our models near field effects dominate over far field effects in systems with lateral variations in permeability and no large scale flow develops between widely spaced areas of contrasting permeability the time to steady state and evolution of convective flow in porous media vary considerably with initial conditions our simulations suggest that the time to steady state is relatively long and that it is possible that hydrothermal convection at the ridge axis never reaches a steady state flow pattern in the sense that the variations in the system boundary conditions such as basal heat flux may occur on a time scale less than the response time of the hydrothermal system it is possible however that these systems may be quasi steady for significant periods of time

numerical computation of hydrothermal fluid circulation in fractured earth structures summary hydrothermal fluid circulation through porous earth materials is an important physical phenomenon occurring in both submarine and continental environments irregularly interconnected discrete fractures are pervasive in nearly all earth materials providing preferential paths for fluid flow and controlling the circulating fluid patterns most mathematical algorithms addressing hydrothermal convection problems treat rocks as ecewise continuous media the representation of local large changes in permeability requires a high level of discretization for accurate results and a corresponding large number of unknowns the alternative is to incorporate fractures discretely through special adaptation of the numerical code we adopt this approach to solve the coupled time dependent heat and fluid transport differential equations using the finite element method the final algorithm is validated against both an analytical solution and merical solutions from a complementary but less general finite difference scheme case studies of some simplified fractured models indicate that fractures can induce and maintain hydrothermal fluid circulation in media which would otherwise be passive fracture location can control both convection pattern and vigour in a closed system discrete fractures can also significantly change an established convection pattern multiply fractured porous media are comparable with the homogeneously aniso tropic media in the numerical solutions if the effective average horizontal and vertical permeabilities are kept the same

groundwater ages recharge conditions and hydrochemical evolution of a barrier island freshwater lens spiekeroog northern germany freshwater lenses below barrier islands are dynamic systems affected by changes in morphodynamic patterns groundwater recharge and discharge they are also vulnerable to pollution and overabstraction of groundwater basic knowledge on hydrogeological and hydrochemical processes of freshwater lenses is important to ensure a sustainable water management especially when taking into account possible effects of climate change this is the first study which gives a compact overview on the age distribution recharge conditions and hydrochemical evolution of a barrier island freshwater lens in the southern north sea spiekeroog island eastfrisian wadden sea two ground and surface water sampling campaigns were carried out in may and july 2011 supplemented by monthly precipitation sampling from july to october 3h 3he ages stable oxygen and hydrogen isotopes and major ion concentrations show that the freshwater lens reaches a depth of 44 mbsl where an aquitard constrains further expansion in vertical direction groundwater ages are increasing from 4 4 years in 12 mbsl up to 70 years at the freshwater saltwater interface stable isotope signatures reflect average local precipitation signatures an annual recharge rate of 300 400 mm was calculated with 3h 3he data freshwater is primarily of na ca mg hco3 and ca na hco3 cl type while lowly mineralized precipitation and saltwater are of na cl types a trend towards heavier stable isotope signatures and higher electric conductivities in the shallower younger groundwater within the freshwater lens may indicate increasing atmospheric temperatures in the last 30 years

geochemistry of the maroni river french guiana during the low water stage implications for water rock interaction and groundwater characteristics abstract the maroni river draining a basin of 60 000 km 2 and flowing down to the atlantic ocean between french guiana and surinam was studied during a low flow period using the chemical and isotopic composition of its dissolved load the dissolved concentrations of major ions cl so 4 no 3 hco 3 ca na mg k trace elements rb and sr stable isotopes o and d and strontium isotopes 87 sr 86 sr were determined on samples from the main stream of the river and its tributaries and from groundwaters collected in wells and two boreholes the total dissolved solid tds and the sum of cations agree with those summarised for the major guyanan rivers the orinoco and amazon on a tds vs na na ca diagram all the data from the maroni catchment plot in the precipitation dominance field close to the plots of the tefe and negro rivers the groundwaters collected from wells largely mimic the surface waters and may represent alluvial groundwater along the maroni terraces whereas the groundwaters collected from the boreholes show clearly higher values and reflect an increase in water rock interaction the river and groundwaters of the maroni catchment have been isotopically enriched 18 o vs 2 h through evaporation and the 18 o and 2 h can be used as mixing tracers of river waters within the catchment after corrections for rainwater addition were computed for selected elements and for 87 sr 86 sr ratios using chloride as an atmospheric input reference the water rock interaction along the maroni catchment was investigated for cations and sr isotopes

passive off axis convection through the southern flank of the costa rica rift pore fluids are passively convecting through young oceanic sediments and crust around deep sea drilling project dsdp site 504 on the southern flank of the costa rica rift as inferred from a variety of geological geochemical and geothermal observations the presence of a fluid circulation system is supported by new data collected on ocean drilling program odp leg 111 and a predrilling survey cruise over the heavily sedimented 5 9 ma site during the latter elongated heat flow anomalies were mapped subparallel to structural strike with individual measurements of twice the regional mean value and strong lateral and vertical geochemical gradients were detected in pore waters squeezed from sediment cores also there is a strong correlation between heat flow bathymetry sediment thickness and inferred fluid velocities up through the sediments on an earlier dsdp leg an 8 bar underpressure was measured in the upper 200 m of basement beneath thick sediment cover although the forces which drive passive circulation are not well understood it has generally been thought that the length scale of heat flow variations provides a good indication of the depth of hydrothermal circulation within the oceanic crust this assumption was based on analytical and numerical analyses of relatively simple porous media models deep crustal convection had been inferred near site 504 based on the geometry of surface heat flow anomalies with a wavelength of 4 7 km but appears to be precluded by low crustal permeability as measured in dsdp hole 504b the widely varied geothermal and hydrogeological observations near site 504 are readily explained by a model which combines 1 basement relief 2 irregular sediment drape 3 largely conductive heat transfer through the sediments overlying the crust and 4 thermal and geochemical homogenization of pore fluids at the sediment basement interface which results from 5 topographically induced passive hydrothermal circulation with large aspect ratio convection cells this convection involves mainly the permeable upper 200 300 m of crust the deeper crust is not involved this convection is induced through a combination of buoyancy fluxes due to heating from below and topographic variations on the seafloor and at the basement sediment interface this model was designed to incorporate data from both near the sediment surface and deep within boreholes it is successful in duplicating numerous field observations

geochemical and hydrological processes controlling groundwater salinity of a large inland wetland of northwest australia abstract understanding mechanisms of hydrochemical evolution of groundwater under saline and brine wetlands in arid and semiarid regions is necessary to assess how groundwater extraction or injection in large scale basins may affect the natural interface between saline fresh aquifers in those systems we investigated the evolution of groundwater of the fortescue marsh a large inland wetland of northwest australia that is mainly supplied by floodwater from the upper fortescue river catchment the marsh is located in the pilbara region one of the world s major iron ore provinces where mining activities often occur below water tables here we quantified the stable isotope and chemical composition of groundwater surface water and rainfall in and around the marsh to better understand how saline marshes and playa lakes function geochemically hydrologically and ecologically the deep groundwater 50 m depth of the fortescue marsh is highly saline 100 g l 1 whilst shallow groundwater 0 20 m depth and surface water are mainly fresh or brackish currently the marsh is mainly recharged by occasional floodwater consequently salt in the marsh is concentrated by evaporation of rainfall we expected that the hydrochemical composition of surface and groundwater would therefore reflect the chemical composition of rainwater we analysed 206 water samples for stable isotope composition 2 h 18 o and water chemistry including ph dissolved oxygen electrical conductivity ec and total dissolved solids tds as well as na ca mg k si fe hco 3 so 4 cl sr and br we then developed geochemical models and a salt inventory to estimate the geological time of salt accumulation and to decouple geochemical characteristics of salt from modern groundwater we found that groundwater associated with the marsh can be divided into two distinct groups that are characterised by their stable isotope compositions i fresh and brackish groundwater tds 1 18 o 8 0 0 9 and ii saline and brine groundwater tds 10 g l 1 18 o varies from 2 5 to 7 2 fresh groundwater was evaporated by

finite element modeling of transient saline hydrothermal fluids in multifaulted sedimentary basins implications for ore forming processes a finite element algorithm is presented to simulate fully coupled transient fluid flow heat and solute transport in discretely fractured porous media and yield the regional scale free thermohaline convection patterns for the mcarthur basin in northern australia numerical results indicate that salinity variation throughout the basin has an important influence on fluid migration and the thermal regime the spatial and temporal distribution of saline fluids can either promote or impede free convection relatively saline conditions 10 wt at the basin floor favour free convection whereas high salinities at depth suppress the development of convective hydrothermal systems when salinity increases with depth a higher geothermal gradient is required to induce and maintain significant fluid circulation the implication is that sedimentary exhalative ore deposits are more easily formed when evaporation first produces surface brines and then these brines sink and displace pore waters in the basin