is the asthenosphere electrically anisotropic abstract two techniques for resolving the conductance of an electrically conductive asthenosphere are presented the first technique combines observatory electromagnetic data in the period range of the daily variation and longer which provides penetration depths of 400 km and deeper with laboratory data of the conductivity of upper mantle materials the conductance can be estimated by this technique but the geometry e g the exact depth is not resolved the second technique extends the classical magnetotelluric mt tensor estimation and decomposition to the period range 1000 30 000 s if an electrical asthenosphere exists then in this period range the electromagnetic field penetrates into it 1000 s but also through it 30 000 s the concept of regional strike directions which has been successfully used to obtain crustal anisotropy directions is again employed at these long periods the surprising result is that in the depth range of the asthenosphere a strong directional dependence of the conductance again occurs although large arrays will be necessary in order to prove that this is really conductivity anisotropy in the asthenosphere first field results from arrays 100 200 km in extent are encouraging the concept of a superposition of crustal and upper mantle anisotropy explains to some extent why earlier magnetotelluric determinations of the asthenosphere had little success only in the fortunate case where a mt experiment was performed not parallel to the direction of the crustal conductor but parallel to the asthenospheric one is the second structure resolved electrical anisotropy in the uppermost mantle supports the concept of intracrystalline water which allows for a contribution of hydrogen diffusity to the conductivity of olivine this diffusity is highly anisotropic with respect to the crystal axis and if the crystals are partly aligned the conductivity measured with mt is also direction dependent

formation of large sulfide mineral deposits along fast spreading ridges example from off axial deposits at 12 43 n on the east pacific rise abstract submersible investigations with nautile near the 13 n hydrothermal field on the epr were made in 1992 we selected diving areas based on deep towed side scan sonar imaging close to a pit crater at the top of a young seamount 2 km east of the axial ridge we discovered one of the largest 70 m high and 200 m in diameter sulfide mounds formed at a fast spreading ridge 12 cm yr despite an overlap in composition between axial and off axial deposits the general trend reflects real differences in compositions off axis deposit differs from axial deposits by the scarcity of zinc sulfides and cobalt and selenium enrichment sulfur isotope variation is minimal for the off axis seamounts and suggests that sulfides precipitated from unmodifed end member hydrothermal solutions axial sulfides have a broader range due to reduction of seawater sulfate at mixing fronts between hydrothermal and seawater solutions along the axial graben fault system lead isotopic compositions of sulfides are in two overlapping but distinct fields indicating different pb sources and separate convective systems for the seamount and the axial deposits our observations suggest that the plumbing system is stable and centred on a shallow localised magma chamber under the seamount this configuration is by far more efficient than unstable axial processes to create during several hydrothermal episodes major sulfide deposits near a fast spreading ridge off axis seamounts are localised areas with high magmatic budget able to drive and focus hydrothermal systems at the same place for a long time other known occurrences of sulfides related to seamounts are at less than 11 km from the ridge axis thus we suggest that off axial volcanoes close to the ridge are first order targets to discover active or inactive large deposits along fast to medium spreading ridges

promotion of graphite formation by tectonic stress a laboratory experiment summary graphitization of less ordered hexagonal carbon was studied under in situ pressure and temperature conditions on anthracite black shale and a synthetic calcite anthracite mixture at upper greenschist facies conditions anthracite exhibited a continuous loss of volatiles in the temperature range from 100 cu p to850 c 9 9 weight per cent at 450 c as detected by differential thermal analysis dta and thermo gravimetry tg energy dispersive x ray diffraction edx revealed a broad amorphous 002 graphite reflection while after p t treatment nearly perfect crystallized graphitic carbon was detected the electrical conductivity was measured at the same time in the frequency range from 0 7 up to 100 khz as a function of time the bulk resistivity was decreased by about three orders in magnitude at constant pressure and temperature conditions 0 7 gpa 450 c while the complex response exhibited a continuous decrease of the imaginary part of the impedance quasi metallic conduction now dominated the charge transport application of pressure strain temperature and time caused an increase in ordering and the degree of interconnection of the formerly randomly oriented carbon sheets the experimental results are an approach towards the explanation of the abundant occurrence of crystalline graphite observed in overthrusts and nappe structures which are distinguished by high conductivity structures

rare earth elements in mussel shells of the mytilidae family as tracers for hidden and fossil high temperature hydrothermal systems abstract bathymodiolus mussels of the mytilidae family live in ecological niches at marine vent sites where hydrothermal fluids discharge at the seafloor and mix with ambient seawater we report the first concentration data for rare earth elements and yttrium rey of bathymodiolus shells and of low temperature diffuse hydrothermal fluids venting in their respective habitat at three hydrothermal vent fields along the mid atlantic ridge mar and for littoral mytilus edulis shells from the western north atlantic dingle bay ireland and from the southern north sea german bight germany similar to high temperature hydrothermal solutions expelled in the respective area the low temperature diffuse fluids from the hydrothermal vent sites display positive eu anomalies these indicate that the fluids carry a component previously involved in high temperature water rock interaction as decoupling of eu from neighbouring rey requires temperatures above about 200 c while the bathymodiolus shells from the hydrothermal vent fields reflect these positive eu anomalies the littoral m edulis shells studied for comparison do not show eu anomalies consistent with the lack of any high temperature hydrothermal activity in their coastal environments shells of mussels of the mytilidae family such as bathymodiolus and m edulis therefore are archives whose rey distribution can be used as a proxy for the eu anomaly of the waters in which the mussels grew although the ca carbonate of a mussel shell is precipitated from the extrapallial fluid of the mussel and not directly from seawater the eu eu ratio of seawater is not significantly modified under the low temperature conditions prevailing during vital processes and biomineralization this allows one to use the positive eu anomalies in the rey distribution patterns of bathymodiolus shells as a tracer for hidden or fossil high temperature hydrothermal systems where other indicators of high temperature hydrothermalism are not available

hydro chemo mechanical modelling of tunnels in sulfated rocks a modelling procedure to address the tunnel anhydritic rock interaction is described in this paper the model incorporates the basic physico chemical phenomena involved in rock swelling often obse

modelling the degradation and swelling of clayey rocks bearing calcium sulphate abstract degradation and swelling of clayey rocks bearing calcium sulphate produces considerable damage to civil engineering works a recent case was the lilla tunnel pertaining to the ave madrid barcelona high speed railway line spain were the floor slab heaved up to 80 cm in the term of a year and a half the present work is based on field and laboratory observations from that case under no confinement degradation of the lilla rock starts immediately upon contact with water degradation develops along a time span of several months and includes development of a crack pattern significant swelling and the extensive growth of gypsum needles within the degraded rock mass a simple numerical model is developed for this process the purpose of the model is to reproduce the swelling process observed in the lilla tunnel from which records of heaves and swelling pressures are available and to check the likeliness of several possible driving mechanisms for the swelling phenomenon the main conclusion of this analysis is that the dissolution of anhydrite and precipitation of gypsum is the most likely mechanism among the three considered the determinant factor behind this conclusion is the physical fact that gypsum has a relatively low solubility which means that the mass of calcium sulphate transported and precipitated as solute is always small

electromagnetic induction studies recent developments in electromagnetic induction studies of the lithosphere and the asthenosphere are reviewed attention is given to geoelectrical studies of active tectonic areas in terms of the major zones of crustal extension the basin and range province along western regions of north america and the rio grande rift studies have also been performed of tectonic activity around iceland the salton trough and cerro prieto and the subduction zones of the cascade mountains volcanic belt where magnetotelluric and geomagnetic variation studies have been done geomagnetic variations experiments have been reported in the central appalachians and submarine electromagnetic studies along the juan de fuca ridge controlled source electromagnetic and dc resistivity investigations have been carried out in nevada hawaii and in the adirondacks mountains laboratory examinations on the conductivity of representative materials over a broad range of temperature pressure and chemistry are described

conductivity and fluids in the oceanic upper mantle abstract three deep electromagnetic soundings in the north pacific ocean were re examined our inversion of existing data showed the presence of conductors below the three sites in very good agreement with previous results we showed that h 2 o rich fluids as well as partial melting account for the conductivities observed this led us to determine temperatures ranging firstly from 1050 to 1150 c when only h 2 o rich fluids were present and secondly from 1300 to 1350 c for partial melting only we suggest that the upper mantle below the two oldest sites 30 and 72 ma is characterized by about 1 of partial melting in the presence of about 1 of h 2 o rich fluids below the third site that nearest to the ridge zone 1 ma the degree of partial melting might reach 10 the presence of 1 of h 2 o rich fluids would reduce the effect of the asthenospheric outflows on the lithospheric magmatism this agrees with the principle of thermodynamic decoupling of the asthenosphere and lithosphere the weakening effect of fluids particularly water on upper mantle rheology is also discussed we suggest that the asthenosphere and lithosphere might be decoupled mechanically which if true would affect small scale convection below the oceanic lithosphere

syngenetic thin graphite rich horizons in lower crustal rocks from the serre san bruno calabria italy and implications for the nature of high conducting deep crustal layers abstract in order to better understand the nature of deep crustal high electrical conductivity we studied the electrical properties of a tilted section of a former lower continental crust exposed in the calabrian arc of the alpine apennine mountain system geoelectric field measurements and impedance measurements on rock samples showed that these high grade metamorphic rocks are generally highly resistive as expected for crystalline electrolytically conducting rocks of low porosity this holds for graphite free metabasites as well as for metapelites which generally contain accessory up to 3 biogenic graphite in the form of isolated grains clearly as an exception a group of thin stratiform black horizons with thicknesses of 1 15 cm within the metapelitic series was detected by means of self potential sp measurements rock samples from these horizons exhibit high quasi metallic bulk conductivities of up to 50 s m 0 02 m in agreeement with up to 20 syngenetic graphite forming a network of interconnected streaks or crack fillings the high amount of carbon most probably originates from organic matter of c org rich black shales relative enrichment of the low mobility graphitic matter compared to the carbon content of the assumed protoliths may have been due to pressure solution and partial melting during prograde metamorphism without major contribution of a fluid phase resulting in isolated graphite flakes although enriched graphite in this form has little effect on electrical conductivity for the calabrian black horizons microscopic analyses make conceivable that in a further decisive step isolated graphite grains were mechanically smeared to continuous pathways during uplift by shearing producing hereby the observed graphitic network which is needed to generate high conductivity as c org rich black shales are common members of sedimentary sequences throughout the earth s history good conductors of this type may be expected in the continental crust at any depth depending on tectonic and metamorphic history with the exception of magmatic protoliths regarding the extremely high conductivity of the meta black shale samples containing syngenetic sheared graphite a total thickness of a few meters of such rocks is sufficient to explain magnetotelluric high conductivity anomalies in the deep crust

back arc rifting in the okinawa trough abstract geological and geophysical data reveal that the okinawa trough shows incipient continental rifting and crustal separation started from about 2 ma the early extensional movements in the trough are probably of miocene age in addition to the miocene phase two main periods of extension are recognized a pleistocene phase between 1 9 and 0 5 ma and the present day phase during the stage short central rifts central grabens were formed the opening however may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr 1 since early pleistocene time producing its present width of several tens of kilometres these activities were well represented by igneous intrusions sedimentary facies and sedimentary structures in and around the okinawa trough the width of the zone affected by back arc extension defined as greater okinawa trough is larger than the present okinawa trough whose width is 200 250 km the present form of the greater okinawa trough started to form at the same time as that of the okinawa trough

extreme expansive phenomena in anhydritic gypsiferous claystone the case of lilla tunnel the paper describes the expansive phenomena affecting lilla tunnel in spain during construction and subsequent operation the geology of the site and the performance of alternative support designs

flow and electrical anisotropy in the upper mantle finite element models constraints on the effects of olivine crystal preferred orientation and microstructure long period magnetotelluric mt data shows that electrical conductivity in the upper mantle is highly anisotropic agreement between high electrical conductivity directions and seismic anisotropy fast directions suggests that anisotropic diffusion of hydrogen along oriented olivine crystals controls the anisotropy of electrical conductivity in the upper mantle since both seismic waves and hydrogen diffusion are faster along the 1 0 0 axis of olivine thus mt electrical anisotropy data like seismic anisotropy may be used to map flow patterns in the upper mantle however observed electrical anisotropies are significantly higher than seismic ones to quantify the influence of strain induced crystal preferred orientations of olivine on upper mantle bulk electrical conductivities we calculate the macroscopic electrical conductivity anisotropy of a series of naturally and experimentally deformed peridotites using an anisotropic finite element model these models which fully take into account the microstructure crystal and shape preferred orientations based on orientation maps obtained by indexation of electron back scattered diffraction ebsd patterns show macroscopic electrical anisotropy factors ranging from 3 to 16 the intensity of electrical anisotropy depends to first order on the intensity of the olivine crystal preferred orientations but the relation saturates for strong crystal preferred orientations in addition the spatial distribution of the various crystal orientations may significantly enhance influence the anisotropy in strongly textured mantle rocks the strongest anisotropy factors 10 occur in mantle rocks in which deformation by dislocation creep has produced not only crystal but also strong shape preferred orientations even if the latter is masked by recrystallization higher anisotropy factors 100 observed in a few mt experiments imply however an additional as yet unknown mechanism controlling electrical conduction at asthenospheric depths in these regions

helium and carbon geochemistry of hydrothermal fluids from the mid okinawa trough back arc basin southwest of japan abstract hydrothermal systems located in the okinawa trough back arc basin are considered to be related to rifting activities in the continental margin hydrothermal fluids sampled from two sites jade and clam are significantly enriched in gas species compared to those from mid oceanic ridges a high temperature fluid 320 c from the jade site shows a co 2 concentration of 200 mmol kg 1 which is more than one order of magnitude higher than that of sediment starved ridge crest hydrothermal systems both helium r r a 6 1 6 5 and carbon 13 c co2 5 0 to 4 7 pdb isotopic compositions are typical of island arc magmatic gases also the abundance ratio of co 2 3 he 3 10 10 is within the range of values found in island arcs chemical and isotopic composition of the jade fluid are considered to indicate that both co 2 and helium are derived from a magmatic source beneath the hydrothermal system without significant contamination contrary to these species ch 4 is attributed to a thermogenic origin based on its isotopic composition 13 c ch 4 41 to 36 pdb and high concentration 7 1 mmol kg 1 which values are similar to those observed in sediment hosted hydrothermal systems the clam fluids show gas geochemistry much more affected by fluid sediment interaction lower 3 he 4 he ratios r r a 3 7 3 8 and higher co 2 3 he ratios 10 11 may reflect involvement of gas species introduced during secondary fluid circulation within the sedimentary pile magmatic activity is the main contributor of gas species to the hydrothermal fluids in both the jade and clam sites although fluid sediment interaction modifies their composition the relatively high abundance of co 2 in the mid okinawa trough hydrothermal systems reflects the geochemical nature of island arc magma

relation between hydrogeological setting and swelling potential of clay sulfate rocks in tunneling abstract in this study an approach to estimate the swelling potential of clay sulfate rocks in tunneling is presented swelling of clay sulfate rocks leads to damage in tunnels that is difficult and costly to repair swelling is caused by the transformation of the sulfate mineral anhydrite into gypsum which involves an increase in rock volume in a system open to water flow knowledge of the hydrogeological situation and the groundwater flow systems at the tunnel is essential to better understand the swelling processes the present study was conducted for the chienberg tunnel in switzerland it investigates the hydrogeological situation of four zones in this tunnel crossing the triassic gipskeuper formation in two of them heavy swelling occurred after tunnel excavation while in the other two no swelling occurred in addition the groundwater flow systems before and after tunnel excavation are investigated based on numerical flow modeling the findings suggest that in certain situations after tunnel excavation depending on geological and changing hydraulic conditions the excavation damaged zone around the tunnel provides a hydraulic short circuit between the weathered gipskeuper and the anhydrite bearing strata of the unweathered gipskeuper as a result water from the weathered gipskeuper gets in contact with anhydrite triggering its transformation into gypsum and thus rock swelling the results of the study may also contribute to improved swelling experiments in the laboratory and a more reliable planning of restoration measures in tunnels that are damaged by rock swelling

rare earth element distribution in 400 c hot hydrothermal fluids from 5 s mar the role of anhydrite in controlling highly variable distribution patterns abstract two submarine hydrothermal vent fields at 5 s mid atlantic ridge mar turtle pits and comfortless cove emanate vapor phase fluids at conditions close to the critical point of seawater 407 c 298 bars in this study the concentration and distribution of rare earth element ree and yttrium y has been investigated independent of the major element composition the fluids display a strong temporal variability of their ree y concentrations and relative distributions at different time scales of minutes to years chondrite normalized distributions range from common fluid patterns with light ree enrichment relative to the heavy ree accompanied by positive eu anomalies type i to strongly ree y enriched patterns with a concave downward distribution with a maximum enrichment of sm and weakly positive or even negative eu anomalies type ii the larger the sum of ree the smaller cecn ybcn and eu eu we also observed a strong variability in fluid flow and changing fluid temperatures correlating with the compositional variability as evident by the positive correlation of total ree ca and sr concentrations in turtle pits and comfortless cove fluids precipitation dissolution of hydrothermal anhydrite controls the variability in ree concentrations and distributions in these fluids and the transformation of one fluid type to the other the variable distribution of ree can be explained by the accumulation of particulate anhydrite with concave downward ree distribution and negative eu anomaly into a fluid with common ree distribution type i followed by the modification of the ree fluid signature due to dissolution of incorporated anhydrite a second model in which the type ii fluids represent a primary ree reaction zone fluid pattern which is variably modified by precipitation of anhydrite can also explain the observed correlations of total ree fractionation of lree hree and size of eu anomaly as well as ca sr the emanation of such a fluid may be favored in a young hydrothermal system in its high activity phase with short migration paths and limited exchange with secondary minerals however this model is not as well constrained as the other and requires further investigations the strongly variable ree fluid signature is restricted to the very hot actively phase separating hydrothermal systems turtle pits and comfortless cove at 5 s and has not been observed at the neighboring red lion vent field which continuously emanates 350 c hot fluid and displays a stable ree distribution type i

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

joint inversion of long period magnetotelluric data and surface wave dispersion curves for anisotropic structure application to data from central germany geophysical datasets sensitive to different physical parameters can be used to improve resolution of earth s internal structure herein we jointly invert long period magnetotelluric mt data and surface wave dispersion curves our approach is based on a joint inversion using a genetic algorithm for a one dimensional 1 d isotropic structure which we extend to 1 d anisotropic media we apply our new anisotropic joint inversion to datasets from central germany demonstrating the capacity of our joint inversion algorithm to establish a 1 d anisotropic model that fits mt and seismic datasets simultaneously and providing new information regarding the deep structure in central germany the lithosphere asthenosphere boundary is found at approx 84 km depth and two main anisotropic layers with coincident most conductive seismic fast axis direction are resolved at lower crustal and asthenospheric depths we also quantify the amount of seismic and electrical anisotropy in the asthenosphere showing an emerging agreement between the two anisotropic coefficients

analysis of undrained soil deformation due to ground loss closed form solutions are presented for obtaining the strain field in an initially isotropic and homogeneous incompressible soil due to near surface ground loss this problem fits into a category of cases in which the imposed boundary conditions are only or mainly in terms of displacements strain controlled problems in these cases there is a possibility of eliminating the stresses and obtaining the strains by using only the incompressibility condition the presence of the top free surface is considered by means of a virtual image technique and some results for the elastic half space the results are simple especially for the movements of the soil surface the application to some typical problems such as soft ground tunnelling and pile driving or extraction shows that the calculated movements agree well with the experimental observations and compare favourably with commonly used numerical methods some hints are given for extending the method to other cases such as to compressible materials des sol

low s velocities under the tornquist teisseyre zone evidence for water injection into the transition zone by subduction a strong low s velocity anomaly at 300 500 km depth coincides with the western boundary of the russian platform the anomaly is too large to be explained by a simple temperature anomaly or by compositional variations nor is it an artifact induced by seismic anisotropy we present a model that explains the anomaly through the injection of water at the time of closure of the tomquist ocean that separated the continents of avalonia and baltica in the early paleozoic dense hydrous magnesium phases are the most likely agents for transporting water to the transition zone but an important role may also be played by nominally anhydrous clinopyroxene when these minerals are brought out of their stability field water is released it may accumulate in spinel or k amphibole and may be released when the mantle warms up after subduction halts the effect of this water is to induce weakening of the shear modulus or even creation of a heavy melt by a conservative estimate a subduction episode lasting 85 m y would inject enough water to saturate a large volume of mantle rock with 0 3 h2o low velocities or low q anomalies have also been observed in the transition zones near currently active slabs

magnetotelluric studies in the central india tectonic zone implications for intraplate stress regimes and generation of shallow earthquakes abstract the central india tectonic zone citz dissects the indian peninsula into the northern and southern crustal blocks the citz has been a seismically active region since the precambrian whereas the relatively deep crustal earthquakes near the narmada faults in the eastern part of the citz have been well investigated the mechanisms for the shallow earthquakes in the western part remain unknown here we present results from a new magnetotelluric study to derive the crustal structure and to understand its implications our data show a thick and highly resistive 500 ohm m crust in the south of tapti river as against a less resistive one in the north these results in conjunction with heat flow values indicate that the crust below the southern part has stable continental cratonic signatures on the northern side of the tapti river we infer the ascent of basaltic magmas from the mantle into the shallow crust and crystallization into layered intrusions these mafic ultramafic bodies could be a potential cause for the shallow earthquakes in the western part of the citz the mafic ultramafic bodies below the crust of citz would locally modify the intraplate stresses which in turn would facilitate the occurrence of earthquakes due to reactivation of pre existing faults thus the large accumulation of strain energy in the deep crust beneath the region can be attributed to the presence of high stress bodies emplaced at depth during the deccan volcanic activity

darcy flux as hydrological indicator for the swelling potential of clay sulfate rocks in tunneling abstract swelling of clay sulfate rocks often poses a severe threat in tunneling it causes serious damage and produces high additional costs during tunnel construction and operation the swelling of clay sulfate rocks requires groundwater inflow into anhydrite bearing layers therefore the darcy flux into anhydrite bearing layers surrounding the tunnel is suggested as a hydrological indicator for the swelling potential a case study from switzerland is presented that uses numerical groundwater models to calculate the darcy flux at the anhydrite level in different tunnel sections after tunnel excavation the approach which assumes that a high darcy flux at the anhydrite level after excavation indicates a high swelling potential is tested at the study site the results suggest that the darcy flux can serve as a hydrological indicator for the swelling potential in tunneling equally important however is the fact that the darcy flux depends on many parameters all of which are uncertain hence a sensitivity study is conducted to analyze the influence of these parameters the sensitivity study shows that the significant parameters in the case study are the hydraulic conductivity of the aquifer above the tunnel the groundwater level in this aquifer as well as the hydraulic properties of the excavation damaged zone of the tunnel lining and of faults based on the results of the sensitivity study implications for site investigation and measures to counteract the swelling problem are discussed the major contributions of this paper are therefore the development of an approach to estimate the swelling potential of clay sulfate rocks based on a hydrological indicator and the derivation of the parameters that have the strongest impact on the swelling potential of such rock

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

heave of a railway bridge induced by gypsum crystal growth field observations the central pillars of a bridge belonging to a recently built high speed railway line experienced an unexpected and continuous heave after the end of construction pillars were founded on 3 3 pile groups capped by a rigid slab the tips of piles supporting the central pillars reached a hard tertiary anhydritic claystone deep extensometers allowed the identification of an active layer 12 15 m thick located below the pile tips observations in recovered cores suggest that the heave is induced by the growth of gypsum crystals in discontinuities of the anhydritic claystone no heave was observed in gypsum rich claystones located above the anhydritic layer gypsum crystal growth is associated with dissolution of anhydrite and subsequent precipitation from a super saturated aqueous solution boreholes and pile construction allowed a hydraulic connection of upper aquifers and the lower anhydritic formation this hypothesis explains the role of the bridge construction in the triggering of a dormant heave phe

evidence from borehole samples for the role of accessory minerals in lower crustal conductivity the high electrical conductivity of the lower continental crust as inferred from geophysical measurements1 has defied a simple explanation both pore saturating brines2 and interconnected carbon films3 5 have been proposed as conducting pathways but their relative importance remains uncertain and may vary from place to place6 so far attempts to address this question in the laboratory have had to rely on samples of metamorphic rock collected from surface exposures7 10 although these rocks almost certainly originated in the lower crust chemical alteration during their transport to and residence at the surface is likely to have affected their conducting properties here we report conductivity data for pristine crustal rocks recovered from depths of up to 4 6 km in the ktb boreholes in southern germany our results show that the electrical conductivity of accessory phases such as fe ti oxides and sulphides can enhance or even surpass the high conductivity produced by saline fluids

magnetotelluric exploration of the north pacific progress report and preliminary soundings near a spreading ridge abstract intensive sea floor magnetotelluric field work has been carried out over the north pacific for the past four years including a total of six experiments each involving the deployment of up to eighteen instruments in clusters or arrays because sea floor magnetotelluric exploration today is still subject to a broad range of often stringent limitations an important objective of this program is to assess the potential contribution of this technique to submarine geophysics by checking the consistency of its predictions with more generally accepted knowledge a progress report is presented on this subject in one of the recent experiments which took place on the cocos plate in the immediate vicinity of the pacific rise crest at 12 n the electrical conductivity is shown to rise rapidly at a depth as shallow as 20 km and to remain relatively high for at least another 150 km this finding is in harmony with earlier electrical conductivity models of the upper mantle proposed for two widely different provinces of the north pacific the experiment reported here includes two stations located 35 and 120 km to the east of the axis of the spreading center and with crustal ages of 0 8 and 2 7 my respectively the conductivity profiles are remarkably similar at both stations with only a slight decrease in the total conductance in the upper 200 km for the eastern station the one most distant from the ridge crest this lateral conductivity evolution is consistent with the progressive cooling of the new lithosphere and with the increased distance from ascending magma another feature common to both soundings is the presence of a significant though small anisotropy of the sea floor impedance that does not seem explainable in terms of the coastal effect a similarity of origin with seismic velocity anisotropy observed on the cocos plate is not excluded the conductivity structure proposed for this pacific rise area appears remarkably similar to that of the atlantic ridge crest beneath northeastern iceland

an application of thin sheet electromagnetic modelling to the tasman sea abstract the method of thin sheet approximation is invoked for the ocean layer to model and interpret magnetotelluric mt data observed on the floor of the tasman sea between australia and new zealand a technique to remove 3d distortion from the observed seafloor mt data is developed from the thin sheet model mt responses the de distorted data then appear isotropic and are reinverted using 1d procedures this approach thus assists interpretation through a combination of 3d forward modelling procedures and 1d inversion a seafloor sediment layer is shown to have a strong effect on observed seafloor mt data also an exercise is carried out to compare the results given by the vertical gradient sounding vgs method with seafloor mt data the electrical conductivity structure beneath the tasman sea is analysed in terms of an upper mantle lithosphere and asthenosphere and a highly conducting lower mantle the observed anisotropy in seafloor mt data is diagnostic of a lithospheric conductivity of less than 10 4 s m 1 conductivity rises by two orders of magnitude below 80 km to greater than 10 2 s m 1 and is probably related to an asthenospheric layer in the upper mantle seismic interpretations similarly place a low velocity zone below a depth of 70 km at a depth of approximately 400 km the conductivity is approximately 1 s m 1 consistent with global estimates for the lower mantle there is little evidence for major change with age in the structure across the tasman sea

experiments and observations bearing on the solubility and diffusivity of carbon in olivine the solubility and diffusivity of c in olivine at 0 1 2 0 and 3 0 gpa have been constrained by annealing single crystals of san carlos olivine in 14c labelled co2 co2 h2o and graphite at 1200 1450 c in nearly all annealed specimens carbonaceous material was observed at the diffusion interface that consisted of either 1 graphite used as a c source 2 elemental c probably graphite formed by reduction of the c o h fluid phase present or 3 carbon rich surface films interpreted as silicate dissolved in the fluid phase at high pressure quenched onto the crystal surface the significant range of 14c beta particles in olivine and photographic emulsion coupled with the presence of carbonaceous material at the diffusion interface gives rise to apparent concentration profiles after removal of the carbonaceous material we retained no unambiguous evidence for c diffusion into olivine the sensitivity and spatial resolution of the beta track method constrain either the solubility to be less than 30 ppmw parts per million by weight c or the diffusivity to be less than 10 12 cm2 s observations and geochemical data on natural rocks bearing on the nature and distribution of c in the earth s upper mantle are discussed in light of these constraints

gypsum a review of its role in the deterioration of building materials the deterioration of buildings and monuments by gypsum is the result of crystallization cycles of this salt although gypsum can dehydrate to a hemihydrate the mineral bassanite and to an anhydrate the mineral anhydrite this reaction occurs in nature on a geological time scale and therefore it is unlikely to occur when gypsum is found on and in building materials the caso4 h2o system appears deceptively simple however there are still discrepancies between the experimental and thermodynamically calculated data the reason for the latter can be attributed to the slow crystallization kinetics of anhydrite apart from this the large numbers of studies carried out on this system have focused on industrially important metastable phases such as the hemihydrate and soluble anhydrite the paper presents a review of the studies dealing with the phase equilibria of the caso4 h2o system as well as the influence of other salts on the solubility of gypsum it tries to glean out the relevant information that will serve to explain the deterioration observed on building materials by the crystallization of gypsum and thus allows developing improved conservation methods

impact of tunneling on regional groundwater flow and implications for swelling of clay sulfate rocks tunnels play a key role in many transportation concepts the swelling of clay sulfate rocks leads to serious damage to many tunnels crossing such rock producing great difficulties and high extra costs in tunnel engineering the swelling is caused by the transformation of the sulfate mineral anhydrite into gypsum entailing a 60 volume increase the transformation involves anhydrite dissolution in water transport of the solution with groundwater flow and gypsum precipitation at a different location therefore the knowledge of groundwater flow systems at the tunnel and adjacent areas is essential to better understand the swelling processes the present study investigates the groundwater flow systems at the chienberg tunnel in switzerland before and after the tunnel excavation based on numerical flow modeling the models include faults and the hydrostratigraphic layering in the subsurface to assess the role of the hydrogeological setting the results of this study indicate effects on groundwater flow caused by the tunneling which may trigger rock swelling by favoring anhydrite dissolution and gypsum precipitation including 1 increase of flow rates around the tunnel 2 broadened shifted and more distributed capture zones leading to a change in origin and age of groundwater 3 access of groundwater from preferential flow paths e g faults due to the drainage effect of the tunnel and 4 change in geochemical equilibrium conditions because of decreased pore water pressures in the tunnel area

fluid deposited graphitic inclusions in quartz comparison between ktb german continental deep drilling core samples and artificially reequilibrated natural inclusions we used raman microsampling spectroscopy rms to determine the degree of crystallinity of minute 2 15 m graphite inclusions in quartz in two sets of samples experimentally reequilibrated fluid inclusions in a natural quartz grain and biotite bearing paragneisses from the ktb deep drillhole in se germany our sequential reequilibration experiments at 725 c on initially pure co2 inclusions in a quartz wafer and the j krautheim 1993experiments at 900 1100 c on organic compounds heated in gold or platinum capsules suggest that at a given temperature 1 fluid deposited graphite will have a lower crystallinity than metamorphosed organic matter and 2 that the crystallinity of fluid deposited graphite is affected by the composition of the fluid from which it was deposited we determined that the precipitation of more crystalline graphite is favored by lower f h2 higher f o2 and that the crystallinity of graphite is established by the conditions including gas fugacities that pertain as the fluid first reaches graphite saturation graphite inclusions within quartz grains in the ktb rocks show a wide range in crystallinity index reflecting three episodes of carbon entrapment under different metamorphic conditions isolated graphite inclusions have the spectral properties of totally ordered completely crystalline graphite such crystallinity suggests that the graphite was incorporated from the surrounding metasedimentary rocks which underwent metamorphism at upper amphibolite facies conditions much of the fluid deposited graphite in fluid inclusions however shows some spectral disorder the properties of that graphite resemble those of experimental precipitates at temperatures in excess of 700 c and at elevated pressures suggesting that the inclusions represent precipitates from c o h fluids trapped under conditions near those of peak metamorphism at the ktb site in contrast graphite that is intimately associated with chlorite and other presumably low temperature silicates in inclusions is highly disordered and spectrally resembles kerogens this graphite probably was deposited during later greenschist facies retrograde metamorphism at about 400 500 c the degree of crystallinity of fluid deposited graphite is shown to be a much more complex function of temperature than is the crystallinity of metamorphic graphite to some extent experiments can provide temperature calibration of the crystallinity index however the difference in time scales between experimental runs and geologic processes makes it difficult to infer specific temperatures for naturally precipitated graphite

gas flow through clay barriers a model for the simulation of gas flow in clayey rocks and clays is described gas migration is associated with the development of preferential paths along existing or pressure dependent discontinu

effects of tunneling on groundwater flow and swelling of clay sulfate rocks 1 swelling of clay sulfate rocks is a major threat in tunneling it is triggered by the transformation of the sulfate mineral anhydrite into gypsum as a result of water inflow in anhydrite containing layers after tunnel excavation the present study investigates the hydraulic effects of tunneling on groundwater flow and analyzes how hydraulic changes caused by excavation lead to water inflow into anhydrite containing layers in the tunnel area numerical groundwater models are used to conduct scenario simulations that allow one to relate hydrogeological conditions to rock swelling the influence of the topographic setting the excavation damaged zone around the tunnel the sealing effect of the tunnel liner and the geological configuration are analyzed separately the analysis is performed for synthetic situations and is complemented by a case study from a tunnel in switzerland the results illustrate the importance of geological and hydraulic information when assessing the risk of swelling at an actual site

chemical compositions of mussels and clams from the tangyin and yonaguni knoll iv hydrothermal fields in the southwestern okinawa trough abstract studies of the chemical characteristics of mussels and clams in seafloor hydrothermal fields are important for understanding mass fluxes and elemental partitioning from hydrothermal vents into the biosphere metal bioaccumulation of seafloor hydrothermal ecosystems and the sources and sinks of biogeochemical and fluid cycles we are the first to measure the mineral major trace and rare earth element and carbon and oxygen isotope compositions of mussels bathymodiolus platifrons and clams conchocele bisecta from the tangyin and yonaguni knoll iv hydrothermal fields in the southwestern okinawa trough mineralogical analysis shows that the carbonate shells of the mussel and clam samples are mainly composed of calcite and aragonite metal elements exhibit linear correlations in the shells e g v and u and tissues e g li and rb of the mussels and clams suggesting that not all positive correlations of elements in tissues are inherited by the shells v as ca sr and fe cr ratios in the mussels and clams are close to those in the seawater indicating that element ratios of seawater might be inherited by the mussels and clams in addition the fe cr ratio of the shells of both mussels and clams can be used to trace the local seawater composition the total lree concentrations of mussel and clam tissue samples are higher than those of the mussel and clam shell samples are similar to the hydrothermal fluids exhibit lree enrichment lacn ndcn ratios 1 86 32 1 and no or only slightly negative eu anomalies indicating that benthic animals are a sink of lrees from hydrothermal fluids and that the eu eu ratios of fluids change when fluids are incorporated into the tissues of the mussels and clams in addition the 13c values of mussel shell samples are heavier than those of the clam shell samples in the hydrothermal field indicating that more than one carbon source may be involved in defining the 13c compositions of the shells the majority of the 18o values of clam shell samples fall in the range of 18o values of the mussel shell samples and are close to the hydrothermal fluid 18oh2o values implying that the 18o values of mussel and clam shell carbonate is influenced by the hydrothermal environment magmatic water and fluid dilution with seawater

a multi isotope study of deep sea mussels at three different hydrothermal vent sites in the northwestern pacific abstract to investigate symbiotic bacterial ecosystems at different deep sea hydrothermal systems in the northwestern pacific compound specific carbon and hydrogen isotope analyses of lipid biomarkers have been performed in addition to bulk c h n s and o isotope analyses on bathymodiolus mussels from the hatoma seamount b platifrons the daiyon yonaguni yonaguni knoll b platifrons and the suiyo seamount b septemdierum the two b platifrons contain large amounts of diploptene while no hopanoid is detected in b septemdierum suggesting that b platifrons and b septemdierum harbors methanotrophic and thiotrophic bacteria respectively in spite of the same symbiont the large bulk 13c difference between the hatoma 44 8 and yonaguni 24 5 mussels reflects isotopically distinct hydrothermal ch4 hatoma 48 yonaguni 26 as a carbon source fatty acids of the hatoma and yonaguni mussels are more enriched in d 144 to 101 than the suiyo mussel 265 to 162 suggesting that d depleted magmatic water or d enriched hydrogen derived from ch4 could be a partial hydrogen source for methanotrophy or thiotrophy respectively apparent positive correlations are observed between 13c and d of the bulk and biomarkers for each mussel due to similar biochemical processes during de novo synthesis the compound specific 13c and d variations have provided much information on not only distinct carbon and hydrogen sources but also the lipid synthesis with respect to different symbiotic bacterial ecosystems

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

the mechanical and electrical properties of earth s asthenosphere abstract an adequate theory of continental drift can be based on heat transfer theory but it does demand the acceptance of a large downward revision of traditional estimates of average upper mantle temperatures and a consistent understanding of lithosphere and asthenosphere in terms of a difference in rheological behaviour under prolonged non hydrostatic stress the recognition that an extremely viscous average state of the upper mantle is self regulating both requires and permits an explanation of magma generation at a strictly limited rate when averaged for the whole planet over a few years in terms of unsteady and local deformational heating the activity of water as a reducer of silicate creep resistance is used to develop the hypothesis that water produced by an amphibole dehydration has been effectively trapped in the earth and is the underlying cause of a low seismic q 50 and an electrical conductivity 10 2 10 1 ohm 1 m 1 at depths of 100 km at the predicted low horizontally avera temperatures the conductivity contrast of rock and aqueous solutions is very large and mantle electrical conductivity studies now look best suited to explore this trapping process and the distinctly recognisable possibility that the uptake of ocean water in the subduction process exceeds the rate of loss that can be explained purely through magmatic activity

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

electric dipole fields over an anisotropic seafloor theory and application to the structure of 40 ma pacific ocean lithosphere summary seismic anisotropy has been detected in the oceanic crust and upper mantle and likewise it is geologically reasonable to expect that a certain amount of lateral anisotropy exists in sea oor electrical properties anisotropy in earth properties can often lead to surprising eiects on geophysical responses that are not anticipated from simple isotropic theories here we investigate the eiects of lateral anisotropy on the frequency domain controlled source electromagnetic csem response of a uniaxially conducting non magnetic sea oor excited by a horizontal electric dipole whose moment is oriented obliquely with respect to the electrical strike direction a paradox of anisotropy is observed in which the sea oor electric eld strength is enhanced in the most conductive direction of the sea oor this enhancement is opposite to what one would expect based on naive isotropic theory we also show that it is possible in certain circumstances to extract the along strike electrical conductivity from marine controlled source electromagnetic data using only isotropic modelling the extraction of across strike conductivity however requires full anisotropic modelling the physical insight into electromagnetic induction in uniaxial media that is presented here should greatly assist the geological interpretation of marine csem experimental data applying our algorithm to the pegasus data set csem data collected over 40 ma paci c ocean lithosphere produces a model with conductivity in the fossil spreading direction that is seven times greater than the conductivity perpendicular to spreading strain aligned mineralogical fabric as predicted by tectonic modelling would explain our result with enhanced conductivities caused by hydrogen conduction along the olivine a axis or connected accumulations of trace conductors such as graphite or magnetite

immobility of reduced carbon along grain boundaries in dunite carbon 14 radiotracer experiments at 10 kbar 1 gpa and 1000 1200 c reveal that due to low diffusivity or low solubility or both carbon is immobile in the grain boundary regions of natural dunite within the resolution of the beta track mapping technique grain boundary diffusion of carbon from a pure graphite source is not detectable in experiments of up to 10 days duration at 1200 c even though measurable volume diffusion profiles are generated at these conditions d 3 4 10 10 cm s in agreement with previous estimates the documented immobility of carbon in dunite grain boundaries precludes development of a continuous carbon film by diffusion from an initially localized source if such a film is the cause of the mantle high conductivity layer it probably originated by a process involving fluid co co2 infiltration and subsequent reduction

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

environmental degradation of claystones the paper presents the results of a comprehensive experimental programme carried out to study the effects of relative humidity cycling on the degradation of argillaceous rocks lilla claystone a low porosity tertiary rock was used for this purpose four aspects were analysed a the influence of the number of relative humidity cycles b the amplitude of relative humidity cycles c the stress level and d the effects of using liquid water or vapour during wetting paths the application of relative humidity cycles induced a progressive degradation of the rock in terms of accumulative irreversible volumetric swelling irreversible reduction in rock stiffness and tensile strength the irreversible expansion increased with the amplitude of the relative humidity change however it reduced with increase of the confining pressure this irreversible behaviour accelerated when liquid water was used during the wetting paths microstructural analysis has shown that the degradation pattern of lilla clayston

an experimental study of oxygen transport in dry rocks and related kinetic phenomena several series of experiments were carried out at 1 gpa and 900 1100 in which grain boundary chemical diffusion of oxygen in dry quartzite and dunite was characterized by use of indicator mineral techniques most experiments involved mixing a small amount of fe2o3 with coarse quartz or olivine powder placing the mixture in an iron container pressurizing in a piston cylinder apparatus and heating rapidly to the desired run temperature in response to the large gradient in oxygen fugacity resulting from the juxtaposition of iron metal i e the container with fe2o3 disseminated through the sample oxygen transport along quartz or olivine grain boundaries took place causing reduction of ferric iron in regions of the sample nearest the container producing wustite in the dunite experiments and fayalite in those on quartz the flux of oxygen and hence the diffusivity could be calculated from the width of the observed reduction zone variations on the method just described included use of cuo rather than fe2o3 as the indicator mineral use of graphite rather than iron as the container and placement of the fe2o3 as a single pellet at the center of the dunite or quartzite sample rather than as a dispersed minor phase for the dispersed fe2o3 experiments on dunite at 1000 and 1100 c the width of the reduced wustite bearing zone was found to be generally proportional to the square root of run duration in accordance with a diffusion controlled transport reduction process at 900 however this relation does not hold and the data suggest vapor phase transport of oxygen prior to closure of sample porosity all experiments on quartzite 900 1100 were plagued by the same problem but in this case sufficiently long experiment durations eventually resulted in no further measurable oxygen transport demonstrating that well annealed quartzite is impermeable to oxygen at the run conditions the net outcome of the experiments is a bulk grain boundary diffusivity for oxygen in dunite given approximately by d 106exp 355 500 rt d in cm2 s r in j deg mol values for quartzite are too low to measure by the techniques attempted the information can be used to argue that heterogeneities in oxygen fugacity on the scale of centimeters to meters can be maintained indefinitely in fluid absent high grade rocks of the continental crust but similar features in a fluid absent mantle would be quickly erased

in defence of a resistive oceanic upper mantle reply to a comment by tarits chave and schultz in a previous paper heinson constable 1992 we discussed the effect of coastlines on sea floor magnetotelluric mt data collected deep within the ocean basins in order to quantify the geomagnetic coast effect we developed a model for oceanic upper mantle electrical conductivity independent of previous sea floor mt interpretations based on sea floor controlled source electromagnetic csem soundings laboratory studies of mantle materials and global geomagnetic sounding estimates for lower mantle conductivity we demonstrated that the coast effect of our model was large was not manifest as severe anisotropy in the mt response if the ocean basins were bounded by coastlines on three or more sides and that a qualitative agreement existed between the mt response of our simple coastline model and published sea floor mt data the implication of the latter is that by including the effect of the coastlines additional mechanisms for enhanced upper mantle conductivity such as volatiles carbon melt hydrogen and other factors may not be required by the mt data tarits chave schultz 1993 question the validity of a large number of aspects of our work their principal conclusions are that a horizontal or vertical leakage paths between the ocean and other oceans or the mantle will substantially reduce the magnitude of the ocean wide coast effect b the principle of extrapolating laboratory electrical conductivity measurements to mantle conditions is unreliable from uncertainties in the understanding of pressure temperature and petrological states of the upper mantle c published sea floor mt data sets examined by us were of such vintage that any conclusions drawn were unreliable or incorrect and d the conductivity profile compiled by chave flosadottir cox 1990 based on 1 d interpretations of sea floor mt and csem data that took no account of the coast effect is consequently a more reliable estimator of mantle conductivity structure than our model while all aspects of tarits et d s comments were addressed to some extent in our original paper we did not investigate all details fully either in the interests of conciseness or because the impact on our conclusions was minimal we will take this opportunity to delve further into some of these issues but before considering the complications it will be useful to reiterate the motivation for our work first oldenburg s 1981 and oldenburg whittal parker s 1984 1 d interpretations of three sea floor mt data sets included a high conductivity zone hcz in the oceanic upper mantle that decreased in magnitude and deepened with increasing age the existence of a hcz has become a paradigm not only amongst the electromagnetic community but also with seismologists petrologists and mineral physicists many entire papers are written on the subject attempting to explain the disparities between laboratory measurements of olivine conductivity at upper mantle temperatures and the hcz correlating the hcz with seismic low velocity zones lvz examining the temporal evolution of the hcz etc the impact of oldenburg s work has been so large that it seemed appropriate to re examine the basis of the hcz and question whether it is indeed required by the data note that

mineralogy and sulfur isotope characteristics of metalliferous sediments from the tangyin hydrothermal field in the southern okinawa trough abstract we present and compare mineralogy and sulfur isotopic composition data of two surface metalliferous sediment samples tvg11 2 and rov11 r2 from the newly discovered tangyin hydrothermal field in the southern okinawa trough s ot and one surface metalliferous sediment sample 2 t4 from the iheya north knoll hydrothermal field in the middle okinawa trough m ot the purpose of this study is to better understand the hydrothermal ore forming environment and material source in the s ot samples tvg11 2 and rov11 r2 were derived from different types of chimneys sample tvg11 2 was derived from a black chimney which experienced formation process from high temperature to low temperature with large gradients and fluctuations rov11 r2 was directly derived from a low temperature white chimney or low temperature diffuse flow the sulfur isotopic compositions of sulfides and native sulfur in the s ot are significantly lower than the sulfur isotopic compositions of pyrite and native sulfur in the m ot indicating there is another source with a lower sulfur isotopic composition the low forming temperature and similar basement rocks of rhyolite in iheya north knoll and dacite in tangyin exclude phase separation and basement rock differences as the main reasons for low sulfur isotopic compositions in tvg11 2 and rov11 r2 the occurrence of different bacterial communities between s ot and m ot may affect the sulfur isotopic compositions but the influencing mechanism is still unclear the addition of magmatic h2s may be the most possible reason for lower sulfur isotopic compositions in the tangyin hydrothermal field

the use of laboratory velocity data for estimating temperature and partial melt fraction in the low velocity zone comparison with heat flow and electrical conductivity studies peridotite is widely considered to be the dominant component of the upper most mantle seismic velocities of a dry peridotite determined in the laboratory at high pressure and hypersolidus temperature show a rapid decrease with increasing temperature the strong temperature dependence of velocities can be used to estimate temperature and melt fraction in the low velocity zone of the earth the laboratory results show that the pressure dependence of both velocity and melt fraction appears to be well accounted for by the pressure dependence of the solidus temperature of the peridotite i e homologous temperature dependence this observation allows us to extrapolate laboratory results to higher pressures greater depths with some confidence requiring only a knowledge of the solidus as a function of pressure using the ratios of lithospheric to asthenospheric velocities temperature and melt fraction in the asthenosphere the low velocity zone can be determined from laboratory velocity data examples of thermal structures of the upper mantle beneath oceanic plates are presented we choose three locations of geophysical interest iceland plateau pacific ocean and philippine sea where reliable seismic velocities have been determined in the upper mantle from surface wave studies a large amount of partial melt 5 vol and a higher temperature than the dry peridotite solidus are inferred in 0 5 m y asthenosphere under the iceland plateau and the active marginal basin of the east philippine sea the partial melt zone appears to extend deeper 100 km and to greater ages 20 m y in the pacific ocean region than under the slowly spreading iceland plateau partial melting is not expected in the asthenosphere older than 5 m y under the iceland plateau even though the volume fraction of partial melt is not so large 3 vol beneath the pacific plate the melting zone may extend to a distance of above 2000 km from the ridge many seamounts observed in the pacific ocean may result from this vast region of melting under the plate we suggest a linear relation between the width of melting zone and the plate velocity the laboratory results are also applied to other low velocity zones it is suggested that a velocity drop up to about 6 in the asthenosphere does not necessarily require the existence of partial melt but can be explained by high subsolidus temperature this implies that partial melt may not exist generally but only in limited areas in the low velocity zone comparison of seismic results with theoretical models may overestimate the temperature and melt fraction if the velocity drop at subsolidus temperature is neglected temperature and melt fraction obtained in this study are discussed together with results from heat flow and electrical studies almost the same temperatures as inferred from seismic velocity and a dry peridotite solidus are calculated from heat flow data indicating that the upper mantle under mid ocean ridges may be fairly dry even a water or co2 undersaturated solidus 0 1 wt does not give a temperature consistent with the lithospheric geotherm and laboratory velocity results it is noted that electrical conductivity studies generally yield lower temperatures and larger melt fractions than this study unknown pressure frequency and impurity effects on laboratory conductivities of partially molten mantle rocks are suggested as possible reasons for this discrepancy

lithospheric structures and precambrian terrane boundaries in northeastern botswana revealed through magnetotelluric profiling as part of the southern african magnetotelluric experiment 1 within the framework of the southern african magnetotelluric experiment a focused study was undertaken to gain improved knowledge of the lithospheric geometries and structures of the westerly extension of the zimbabwe craton zim into botswana with the overarching aim of increasing our understanding of southern african tectonics the area of interest is located in northeastern botswana where kalahari sands cover most of the geological terranes and very little is known about lithospheric structures and thicknesses some of the regional scale terrane boundary locations defined based on potential field data are not sufficiently accurate for local scale studies investigation of the nnw sse orientated 600 km long zim line profile crossing the zimbabwe craton magondi mobile belt and ghanzi chobe belt showed that the zimbabwe craton is characterized by thick 220 km resistive lithosphere consistent with geochemical and geothermal estimates from kimberlite samples of the nearby orapa and letlhakane pipes 175 km west of the profile the lithospheric mantle of the ghanzi chobe belt is resistive but its lithosphere is only about 180 km thick at crustal depths a northward dipping boundary between the ghanzi chobe and the magondi belts is identified and two middle to lower crustal conductors are discovered in the magondi belt the crustal terrane boundary between the magondi and ghanzi chobe belts is found to be located further to the north and the southwestern boundary of the zimbabwe craton might be further to the west than previously inferred from the regional potential field data

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

electrical properties of a graphite rich quartzite from a former lower continental crust exposed in the serre san bruno calabria southern italy abstract in this study electrical properties of a graphite rich quartzite from the former lower crust exposed in the serre san bruno calabria southern italy have been analysed by means of complex electrical conductivity measurements in the frequency range 10 3 to 10 6 hz on plug samples of 25 mm in diameter and 22 mm high the samples were identified as a former oil sandstones containing up to 12 15 flake like graphite which present highly metamorphosed relics of its former hydrocarbon filling though high concentrations of graphite were detected the graphite quartzite is highly resistive the spatial ordering of isolated graphite grains like tiles prevent the generation of interconnected electrical pathways these isolated good conductors are interconnected by electrolyte bridges thus causing the high polarizability indicating redox reactions at the electrolyte graphite interfaces that could be modelled using cpe elements the type of graphite ordering was caused by the early formation of isolated oil droplets in the reservoir sandstone after high grade metamorphism and shearing they appear as flat graphite grains in the foliation plane and were smeared together because of the rigidity of sillimanite and quartz the main rock constituents thus this graphite quartzite is by no means a candidate to enhance the electrical conductivity of the deep continental crust syngenetic graphite in former lower crustal rocks is largely resistant against varying geochemical conditions during prograde and retrograde metamorphism this had also been shown for graphite that is contained in normal metapelites as accessory mineral or enriched in former black shales where it may cause high conductivity jodicke h kruhl j h ballhaus c giese p untiedt j 2004 syngenetic thin graphite rich horizons in lower crustal rocks from the serre san bruno calabria italy and implications for the nature of high conducting deep crustal layers pepi 141 37 58 nover g 2005 electrical properties of crustal and mantle rocks a review of laboratory measurements and their explanations surv geophys 26 5 593 651

vertical electric profile at choutuppal hyderabad in peninsular india abstract natural electromagnetic e m field data form choutuppal hyderabad in the frequency range 2 10 1 1 10 4 hz are processed and resistivities in the principal directions determined a 1 d inversion of the resulting yx curve reveals the existence of three conductive layers 1 depth to the top 16 km thickness 9 km resistivity 35 m 2 depth to the top 90 km thickness 15 km resistivity 15 m and 3 depth to the top 340 km thickness 10 km resistivity 3 m whereas the mid crustal conductor has been visualized as a low velocity layer corresponding to the conrad discontinuity the second conductor has been ascribed to the uplifted asthenosphere as a result of the thinning of the lithosphere and the third has been related to the global conductivity zone arising from olivine to spinel phase transition

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

very long period magnetotellurics at tucson observatory implications for mantle conductivity in a companion paper egbert et al this issue we describe the estimation of very long period 0 16 t 91 days magnetotelluric mt impedances from 11 years of data collected at the tucson geomagnetic observatory here we discuss the implications of these data for mantle conductivity using minimum norm flattest and smoothest inversions we find simple one dimensional models of electrical conductivity in the depth range 0 1500 km we use forward modeling a linearized resolution analysis and constrained one dimensional inverions to delineate the range of models which are consistent with the estimated impedances although the mt data have limited resolution large scale vertical averages of mantle conductivity are well constrained we reach the following conclusions concerning mantle conductivity beneath tucson 1 the upper 200 km has a conductance of order 104 siemens s this anomalously high conductance may be concentrated in an aesthenospheric high conductivity layer but the geometry of the conductive zone is not constrained 2 typical conductivities in the transition zone 400 700 km are 0 1 0 3 s m 1 a step increase to reach this value at or near the 400 km olivine spinel phase transition is consistent with but not required by the data an upper mantle which is resistive throughout 0 05 s m 1 or less is not allowed by the data 3 resolvable large scale averages of conductivity increase from 0 2 s m 1 to 1 0 s m 1 between 600 and 900 km depth a range of models including those with step increases and step decreases at the 670 km seismic discontinuity are consistent with the data 4 between 900 1500 km conductivity increases slowly average conductivities in this region are of the order of 1 s m 1 to within a factor of 2 or 3 while limited zones of highly resistive mantle are consistent with the data a lower mantle which is resistive throughout is not models in which conductivity is always above 5 s m 1 below 1000 km can also be ruled out in conjunction with improved laboratory estimates of electrical conductivities of mantle minerals at high temperatures and pressures these constraints can provide important clues to the composition and physical state of the mantle

the nature and distribution of carbon in submarine basalts and peridotite nodules primary carbonaceous material has been identified in submarine basaltic glasses and mantle derived peridotite nodules from alkali basalts using electron microprobe techniques in the submarine rocks carbon occurs 1 in quench produced microcracks in glasses and phenocrysts 2 in vesicles where it is preferentially concentrated on the sulfide spherules attached to vesicle walls and 3 in microcracks and co2 rich bubbles in inclusions of glass completely enclosed by phenocrysts in peridotite nodules carbon exists in intergrain cracks along grain boundaries and on the walls of fluid inclusions disposed in two dimensional arrays the carbonaceous material is believed to consist of a mixture of graphite other forms of elemental carbon and possibly small amounts of organic matter it is suggested that carbon precipitates by disproportionation of co according to the reaction 2 co c co2 and that this reaction is catalyzed by sulfide oxide surfaces in vesicles once deposition has begun the reaction continues on carbon surfaces as well based on the large amounts of condensed carbon observed in some vapor inclusions and the apparent lack of oxidation features associated with them it is proposed that carbon condensed from a magmatic vapor in which co was a significant constituent this implies that oxygen fugacities of undegassed basaltic melts under confining pressures of the shallow crust are typically lower than those of the qfm buffer at equivalent temperatures this is in agreement with some intrinsic oxygen fugacity measurements on similar undegassed materials regardless of the mechanism of its formation the presence of carbon in co2 rich vesicles and inclusions in basaltic glasses and mantle nodules adds uncertainty to estimates of minimum pressures of entrapment based on measurements of fluid densities condensed carbon also accounts for some of the carbon isotopic characteristics of these rocks

pile groups under deep expansion a case history a viaduct in a high speed railway line experienced severe heave of its central pillars as a result of deep expansion of an anhydrite rock bridge pillars were founded on pile groups that experienced vertical heave displacements as well as lateral displacements and rotations a semi analytical solution for the response of a pile group under loading and arbitrary located soil expansion was developed integrating fundamental solutions for the elastic half space the procedure was first validated and then applied to explain the recorded behaviour of the pile groups the deep expansion was identified from independent surface heave and continuous extensometer readings group rotations were well predicted observed tensile fissures at the cap pile contact were explained by the calculated forces and moments on the piles

free carbon electrical conductivity in the earth s mantle laboratory measurements indicate that solid carbon either amorphous or as graphite enhances the electrical conductivity of rocks carbon in quantities of only a few ppm providing it forms an interconnected phase could give rise to electrical conductivities of the order seen in the high conductivity layers in the earth s mantle this possibility is consistent with carbon petrology in mantle rocks and puts the formation and migration of abiogenic carbon compounds into a broader context

heave of a railway bridge modelling gypsum crystal growth the heave of the central pillars of a railway bridge founded on large diameter bored piles is a consequence of gypsum crystal growth in an anhydritic claystone stratum underlying the tip of the piles the heave mechanism is explained by the presence of circulating water in the fractured anhydritic level the model developed to reproduce the observed phenomena integrates a set of balance equations that includes two soluble species gypsum and anhydrite in addition to the inert minerals kinetic equations for dissolution and precipitation mechanical equilibrium and the effect of precipitated mass on induced volumetric strains model calculations are compared with measured long term field records of heave most of the model parameters are physico chemical constants a positive feature that limits the effort to calibrate material constants the model is capable of accurate mid term heave prediction and it also correctly includes the effect of building a surface embankment with the purpose of reducing th

conductivity structure of oceanic upper mantle beneath the pacific plate summary ocean bottom magnetotelluric responses from three ages on the pacific plate have been inverted to reveal the presence of a conductive zone whose depth is a function of lithospheric age the conductivity achieves its maximum value 0 1 sm 1 at depths near 70 120 and 180 km for lithospheric ages of 1 30 and 72 myr respectively the existence of this conductive structure has firmly been established by constructing a number of different acceptable models and also by obtaining unique averages over depth of the conductivity an explanation in terms of partial melting in the upper mantle has produced lower bounds for the volume fraction of melt which must exist in order to produce the high conductivity beneath jdf t 1 myr the lower bound lies in the range 0 04 0 12 beneath cal t 30 myr it lies in the range 0 02 0 10 and beneath ncp t 72 myr it lies in the range 0 008 0 02 the distributions of partial melt show that the major portion of melt beneath jdf lies between 40 and 90 km and that melting has ceased by depths of about 170 km at all three sites geotherms have been computed and they are qualitatively similar to those predicted from a convective system where the temperature increases rapidly through a boundary layer to achieve a maximum value and then possibly decreases with depth the depth at which the maximum temperature is reached is about 125 km for cal and about 175 km for ncp and the maximum temperatures are estimated to be 1400 1500 c lastly as an independent check upon the partial melt explanation the location and magnitude of the seismic low velocity zone has been correlated positively with the computed distribution of partial melt at all three ocean bottom sites

europium redox equilibria in aqueous solution thermochemical data and recent advances in theoretical aqueous solution chemistry enable prediction of the relative stabilities of aqueous eu2 and eu3 over a wide range of temperatures and pressures at low temperatures near earth surface conditions the aqueous geochemistry of europium should be dominated by the trivalent state except possibly in the most reducing alkaline pore waters of anoxic marine sediments however at temperatures greater than about 250 c and elevated pressures divalent europium should predominate even with significant amounts of complexing trivalent europium is not stable at elevated temperatures and pressures consequently under most hydrothermal and metamorphic conditions europium in aqueous solution should be divalent at intermediate temperatures around 100 c significant activities of both eu2 and eu3 and related complexes can occur in aqueous solutions depending on the oxidation state and the ph of the solutions and the activities of potential ligands such as sulfate carbonate and chloride the predicted stability of divalent europium in aqueous solution at elevated temperatures is consistent with the large positive europium anomalies in rare earth element patterns of high temperature barites of hydrothermal and metamorphic origin reported by guichard et al 5 and with the observed depletion of europium as a result of high temperature sericitization of feldspar bearing assemblages discovered by alderton et al 1 it is suggested that significant fractionation of europium relative to the other rare earth elements may take place during high temperature hydrothermal alteration processes such as in the mid oceanic ridge systems because of the expected stability of divalent europium during these processes

decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield decomposition analysis of the bear magnetotelluric data implications for the upper mantle conductivity in the fennoscandian shield

velocity conductivity relations for cratonic lithosphere and their application example of southern africa 1 seismic velocity is a function of bulk vibrational properties of the media whereas electrical resistivity is most often a function of transport properties of an interconnected minor phase in the absence of a minor conducting phase then the two should be inter relatable primarily due to their sensitivity to temperature variation we develop expressions between shear wave velocity and resistivity for varying temperature composition and water content based on knowledge from two kimberlite fields jagersfontein kaapvaal craton and gibeon rehoboth terrane we test the expressions through comparison between a new high resolution regional seismic model derived from surface wave inversion of earthquake data from africa and the surrounding regions and a new electrical image from magnetotelluric mt data recorded in samtex southern african magnetotelluric experiment the data defined robust linear regression between the two is found to be statistically identical to the laboratory defined expression for 40 wt ppm water in olivine cluster analysis defines five clusters that are all geographically distinct and tectonically relate to i fast cold and variably wet kaapvaal craton ii fast and wet central botswana iii slow warm and wet rehoboth terrane iv moderately fast cold and very dry southernmost angola craton and v slow warm and somewhat dry damara belt from the linear regression expression and the mt image we obtain predicted seismic velocity at 100 km and compare it with that from seismic observations the differences between the two demonstrate that the linear relationship between vs and resistivity is appropriate for over 80 of southern africa finally using the regressions for varying water content we infer water content in olivine across southern africa

mineralogy geochemistry and sr pb and in situ s isotopic compositions of hydrothermal precipitates from the tangyin hydrothermal field southern okinawa trough evaluation of the contribution of magmatic fluids and sediments to hydrothermal systems abstract the okinawa trough ot is a back arc basin where rifting is in its initial stages and where hydrothermal fields htfs have developed above terrigenous sediments and volcaniclastics layers of variable thickness the source of ore forming materials within the hydrothermal systems of the ot is complex and may include seawater magmatic rock magmatic fluid and sediments the contribution of magmatic fluids and sediments to the hydrothermal systems of the ot is still uncertain at least 10 modern seafloor htfs have been reported from the ot including the jade hakurei iheya north knoll clam tangyin yonaguni knoll iv hatoma and irabu here we report results of mineralogical geochemical and whole rock sr pb and in situ s isotopic analyses of hydrothermal precipitates from the tangyin htf in the southern ot this field was discovered during the hobab3 cruise in 2014 and contains four types of hydrothermal precipitates fe zn and zn pb rich massive sulfides silica rich precipitates and native sulfur rich samples sulfates in zn pb fe zn and silica rich samples have 87sr 86sr ratios of 0 71068 0 71750 which are higher than those of modern seawater and magmatic rocks and indicate that the sr is derived mainly from seawater and sediments the zn pb fe zn and silica rich samples have 206pb 204pb 18 5129 18 5307 207pb 204pb 15 6374 15 6489 and 208pb 204pb 38 8759 38 9113 ratios that are intermediate between sediments and magmatic rocks suggesting the pb is a mixture of sediment and magmatic rock derived pb the in situ s isotopic data indicate that the ore forming fluids associated with all sample types had low 34s values with the fe zn mean 34s 1 27 1 38 sd n 12 and zn pb rich mean 34s 0 93 0 32 n 36 massive sulfides and silica rich precipitates mean 34s 2 85 1 14 n 58 having lower 34s values than those of native sulfur rich samples mean 34s 4 23 0 72 n 5 the zn pb and fe zn rich massive sulfides and silica rich precipitates represent the medium high temperature 120 c early middle stages of mineralization formed under reducing conditions at low sulfur fugacity fs2 based on the occurrence of low fs2 mineral assemblages e g high fe sphalerite isocubanite pyrrhotite the low 34s values of these three types of samples and of the hakurei and clam htfs with low fs2 mineral assemblages and low concentrations of cu bi and au most likely reflect the incorporation of biological sulfur previously formed by msr within the sediments the native sulfur rich samples of the tangyin htf formed at low temperatures

swelling potential of clay sulfate rocks in tunneling in complex geological settings and impact of hydraulic measures assessed by 3d groundwater modeling abstract swelling of clay sulfate rocks is a feared problem in tunneling in such rock causing heave of the tunnel invert and leading to swelling pressures that seriously damage the tunnel lining prediction of the swelling potential of rocks in different tunnel sections and tools to evaluate measures that aim at reducing the swelling risk would be a major aid for designers of tunneling projects and rehabilitation works in order to respond adequately to the swelling problem the study presents a hydrogeological approach to assess the swelling potential of clay sulfate rocks in tunneling using the belchen tunnel in switzerland as a case study it shows that this approach can be applied to complex geological settings using structurally consistent 3d numerical models to simulate groundwater flow influenced by tunneling the models are in particular used to evaluate hydraulic measures that aim at preventing or minimizing water inflow into clay sulfate rocks after tunneling analyzed hydraulic measures include pumping shafts connected to the tunnel drainage sealing structures applied to the rock zone around the tunnel damaged by the excavation process excavation damaged zone as well as groundwater level drawdown in aquifers crossing the tunnel a sensitivity study addresses model uncertainties and evaluates the impact of model parameters on the swelling potential promising measures include the installation of pumping shafts in tunnel sections of clay sulfate rocks at the border to aquifers and permeable fault zones the study shows that monitoring of hydraulic heads as well as of groundwater volumes drained by the tunnel would increase the predictive capability of the models presented results are site specific however the approach to assess the swelling potential of clay sulfate rocks in tunneling and to assess hydraulic measures to respond to the swelling problem can be transferred to other tunneling projects

on the crystallisation pressure of gypsum we estimate the crystallisation pressure of gypsum quantitatively with reference to the geological context of the gypsum keuper formation the formation contains sulphatic claystones which have the property of swelling in the presence of water and have caused substantial structural damage to the linings of several tunnels in switzerland and germany the swelling of these rocks is attributed to the transformation of anhydrite into gypsum which occurs via the dissolution of anhydrite in pore water and the precipitation of gypsum from the solution this simultaneous dissolution precipitation process happens because the solubility of gypsum is lower than that of anhydrite under the conditions prevailing after tunnelling and it does not cease until all of the anhydrite has been transformed the elementary mechanism behind the development of the macroscopically observed swelling pressure is the growth of gypsum crystals inside the rock matrix if a crystal is in contact with a supersaturated solution but its growth is prevented by the surrounding matrix it then exerts a so called crystallisation pressure upon the pore walls in the present paper the crystallisation pressure is calculated by means of a thermodynamic model that takes coherent account of all relevant parameters including the chemical composition of the pore water and pore size variations in these parameters lead to a very wide range of crystallisation pressures from zero to several tens of megapascals by using the results of mercury intrusion porosimetry and chemical analyses of samples from three swiss tunnels however we show that the range of predicted values can be reduced significantly with the help of standard project specific investigations

geophysical constraints on partial melt in the upper mantle this paper addresses the conditions under which partial melt can exist in the mantle in order to be observed as a geophysical anomaly typical observed anomalies are high electrical conductivity of the order of 0 1 s m or greater velocity decreases of 7 10 seismic q values less than 100 and a frequency band for seismic effects in the region near 1 hz existing theories of electrical conduction in partial melts and of frequency dependent seismic properties together with recent measurements of melt electrical conductivity viscosity and partial melt texture can be used to establish requirements for melt to be observed by geophysical methods from electrical anomalies mainly sensitive to melt volume and its interconnection one can require a minimum melt fraction of several percent at temperatures close to the solidus 1150 1300 c however seismic models demand only a small volume in very flattened shapes aspect ratio 0 001 melt fraction 0 1 further if melt configuration permits seismic dissipation in bulk that is there exist flattened voids intersecting more or less equant voids then it is possible to infer melt fractions for elastic anomalies that are consistent with the several percent required for electrical anomalies observed equilibrium textures of partly melted peridotite together with inferred melt solid surface energies suggest that melt on a grain size scale in a gravitational field segregates into a strongly anisotropic pattern thus if partial melt causes mantle geophysical anomalies it should exist in a variety of void shapes and probably of sizes while the association of electrical and elastic anomalies with indications of reduced density volcanism and high heat flow makes the hypothesis of partial melting an attractive explanation the minimum physical requirement is for existence of relatively high temperature