changes in co2 diffuse degassing induced by the passing of seismic waves abstract solfatara crater located in the campi flegrei caldera is a volcano with one of the highest degassing rates on earth more than 1500 t of co 2 released by diffusion or through vents here we investigated how this gas release can be disrupted by the passage of seismic waves we performed continuous soil co 2 flux measurements during the propagation of seismic vibrations in the range of 5 hz to 200 hz induced by a vibroseis truck the co 2 flux was continuously recorded using the accumulation chamber method the data show a temporary and drastic up to two fold increase in co 2 flux exclusively during the vibrations before returning to the initial flux values these transient variations are interpreted as fluidization of the surficial granular layer that releases the stored gas similar degassing processes might occur at a larger scale during earthquakes to cause temporary increases in the total gas outflow in volcanic or tectonic areas our findings are useful to better assess and monitor the potential hazard from sudden co 2 flux release during earthquakes as several cases of intoxication or death have already been related to volcanic degassing

estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

estimating the electrical conductivity of the melt phase of a partially molten asthenosphere from seafloor magnetotelluric sounding data seafloor magnetotelluric soundings provide models of electrical conductivity distributions in the earth s oceanic mantle by inverting the sounding results a high conductivity typically 0 01 0 1 s m layer is often obtained in the oceanic upper mantle which is referred to as the electrical asthenosphere the obtained high conductivity is then interpreted in terms of the amount of additional conduction that accounts for the conductivity value based on a physical model of the asthenosphere there are two major candidates that are considered as the cause of the asthenosphere the effect of water and partial melting in this paper we consider the partial melting hypothesis we propose a method to estimate the electrical conductivity of the melt phase that is responsible for high conductivity by assuming the melt fraction distribution in the asthenosphere we applied this method to one dimensional conductivity profiles recently obtained from three regions of different seafloor age and the results indicate that the proposed approach combined with other approaches such as seismology and mineral physics will provide useful information in testing a partial melting hypothesis for the cause of the asthenosphere

reply to comment on high and highly anisotropic electrical conductivity of the asthenosphere due to hydrogen diffusion in olivine by dai and karato earth planet sci lett 408 2014 79 86

sill cube an automated approach for the interpretation of magmatic sill complexes on seismic reflection data abstract the use of conventional interpretation techniques like manual interpretation seismic attribute analysis and opacity rendering or geobody extraction have demonstrated significant success in interpreting magmatic sills from seismic reflection data nonetheless the downsides of seismic imaging and interpretation of magmatic sills are that they are rarely drilled or too thin to be detected we present an automated approach for interpreting magmatic sills from seismic reflection data by using a newly designed meta attribute called as the sill cube sc the sc meta attribute is generated by amalgamating a number of different attributes that are trained over the interpreter s knowledge of the sill networks through a supervised scheme of neural learning the approach has shown its efficiency by delivering enhanced images of magmatic sills from seismic data in three frontier areas i e the kora prospect offshore taranaki basin new zealand the utgard and the tulipan prospects both offshore voring basin norway the sc meta attribute has completely captured the saucer shape geometry of most of the sills additionally the meta attribute has brought out different structural elements such as the limbs bridges junctions and fingers and highlighted the overlying forced folds the interpreted sills cover areas of 6 16 km2 in the kora prospect 105 1140 km2 in the utgard prospect and 15 60 km2 in the tulipan prospect such an interpretational approach does not only honour the interpreter s knowledge of sills networks but also add values in understanding the tectonic architecture

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

electrical conductivity of mantle clinopyroxene as a function of water content and its implication on electrical structure of uppermost mantle abstract the electrical conductivity of san carlos clinopyroxene aggregates with various water contents were measured under ni nio buffer at 1 5 gpa and 600 1200 k in a dia type apparatus the conductivity increases with increasing water content in clinopyroxene hidden conduction mechanism was detected because of the much smaller iron content in clinopyroxene which was usually covered by small polaron conduction in other nominally anhydrous minerals the identified activation enthalpies ranged from 0 70 0 75 ev to 1 23 1 37 ev our result reveals that the dominant charge carrying species in electrical conductivity could change with temperature and water content at high temperatures relevant to asthenospheric condition activation enthalpy for the conductivity agrees well with that for the hydrogen self diffusion the dominant charge carrier therefore might be m site vacancy however contrary to previous view that all hydrogens contribute to increasing conductivity equally our result shows that only a limited amount 20 40 of hydrogen acts as effective charge carrier in clinopyroxene on the other hand the activation enthalpy for the conductivity at low temperatures is significantly lower than that for the hydrogen self diffusion similar to what has been observed in olivine and orthopyroxene this type of conduction is probably caused by fast diffusion of specific hydrogen or fast hydrogen grain boundary diffusion at low temperatures the proton conduction of clinopyroxene is nearly one order and two orders of magnitude lower than those of olivine and orthopyroxene respectively and tends to converge at high temperatures using the present data combined with conductivity of olivine and orthopyroxene a laboratory based conductivity depth profile in the uppermost mantle shows that hydrous clinopyroxene cannot account for the high conductive regions observed beneath the ocean floor near eastern pacific rise the presence of partial melt would be unavoidable

changes in seismic anisotropy shed light on the nature of the gutenberg discontinuity the boundary between the lithosphere and asthenosphere is associated with a platewide high seismic velocity lid overlying lowered velocities consistent with thermal models seismic body waves also intermittently detect a sharp velocity reduction at similar depths the gutenberg g discontinuity which cannot be explained by temperature alone we compared an anisotropic tomography model with detections of the g to evaluate their context and relation to the lithosphere asthenosphere boundary lab we find that the g is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled lab implying that the two are not equivalent interfaces the origin of the g is a result of frozen in lithospheric structures regional compositional variations of the mantle or dynamically perturbed lab

buoyant melting instabilities beneath extending lithosphere 1 numerical models buoyant decompression melting instabilities in regions of partially molten upper mantle have been proposed to be an important process that might account for some characteristics of intraplate volcanism on earth and other terrestrial planets the instability is driven by variations in the melting rate within a partially molten layer whenever a relative decrease in density accompanies decompression melting of ascending mantle here the development of buoyant decompression melting instabilities in a plane layer of passively upwelling and partially melting mantle beneath diffusely extending lithosphere is studied using numerical convection models covering a wide range of physical parameters we find that the occurrence and nature of these instabilities in such a scenario is strongly affected by the rate of extension and melt percolation as well as depth distribution of solid density variations arising from melt depletion in some cases instabilities do not occur during extension but only develop after extension has slowed or stopped completely this behavior creates two pulses of magma generation due to passive upwelling accompanying extension followed by the subsequent instability and is favored by a faster rate of extension higher mantle viscosity higher rate of melt percolation and smaller amount of solid residuum depletion derived buoyancy larger degrees of solid density changes accompanying melt depletion can enhance the instability of partially molten mantle during extension but decrease the cumulative volume of generated melt this kind of behavior modifies the conventional expectation of spatially and temporally correlated volcanism and extension and may lend insight into the observed increase in localized volcanic activity following miocene basin and range extension in the western united states

numerical models on the influence of partial melt on elastic anelastic and electrical properties of rocks part ii electrical conductivity abstract partial melting influences both the elastic and electrical properties of mantle rocks significantly but in a different manner a set of theoretical models of the electrical conductivity of partially molten rocks is developed for different geometries of the melt distribution the models correspond to a similar set on elasticity and anelasticity presented in a preceding paper part i both model sets allow combined interpretations of seismic and geoelectric observations from anomalous hot mantle regions by a systematic variation of the melt geometry the following melt geometries are assumed in the conductivity models melt films tubes isolated ellipsoidal inclusions films and ellipsoidal inclusions with a variable degree of interconnection distributed geometries and superpositions of spheres with films and with tubes unexplored conduction mechanisms near the melting temperature film thicknesses of molecular sizes or effects of volatiles are not considered resistor network theory is utilized to account for a variable degree of interconnection and distributed geometries thereby a new possible interpretation of archie s law is found in terms of varying interconnection furthermore it is found that a reduced degree of interconnection may have an important influence on the conductivity at melt fractions characteristic for a weak to moderate decrease in seismic velocity the model results are compiled together with the elastic models of part i in a set of diagrams which may be applied systematically to observed electrical and seismic data to find constraints on the state of melting

groundwater recharge and discharge dynamics in an arid zone ephemeral lake system australia the coongie lakes are a series of ephemeral freshwater lakes on the lower reaches of cooper creek a large intermittent river of the arid lake eyre basin australia hydrogeological chemical and isotopic observations in conjunction with numerical modeling of groundwater responses to lake inundation events have been used to identify the dominant processes linking shallow unconfined groundwater with the hydrology of the lakes during wet and dry periods the lakes are predominantly zones of net groundwater recharge during inundation events however soil profile data suggests that drying of some of these lakes allows evaporative groundwater discharge to occur through the soil profile of the dry lake beds resulting in salinization of the soil profile of the more ephemeral lakes the occurrence of young high salinity groundwater is best explained by variations in soil profile flushing in response to wet and dry interannual periods of river discharge during interannual drier phases when filling of previously dry lakes is more common recharge is mostly via macropore flow during the rising stage of the inundation increased salinization of the lake bed sediments occurs during longer dry periods due to transport of solutes to the near surface from lake bed evaporation and limited flushing of the soil profile because of the macropore dominated flow during recharge during wet periods recharge is more likely dominated by matrix flow that results in leaching of the soil profile and increased export of solutes into the alluvial aquifer

isotopic tracing of the source water for cedar bog in west central ohio usa abstract cedar bog a boreal fen in west central ohio is home for many endangered plants and animals the whereabouts of the water source that sustains cedar bog has been the subject of several investigations in the past two decades some of these studies indicated that a recharge area lies to the east and northeast of the bog using environmental isotopes of oxygen and hydrogen the present study positively identifies a major recharge area located northeast of the bog and enclosed by two small tributaries of the mad river oxygen isotopic composition and tritium contents of ground water suggest that the bog water is only a few years old

electrical conductivity structure of southeastern north america implications for lithospheric architecture and appalachian topographic rejuvenation abstract we present the first three dimensional view of the lithospheric electrical conductivity structure beneath southeastern north america by inverting earthscope long period magnetotelluric mt data we obtain an electrical conductivity image that provides new insights into both the architecture of the appalachian orogen and the cryptic post rifting geodynamic history of the southeastern united states our inverse solutions reveal several elongate electrically conductive features that we interpret as major terrane sutures within the appalachian orogen most significantly we resolve a highly electrically resistive layer that extends to mantle depths beneath the modern piedmont and coastal plain physiographic provinces as high resistivity values in mantle minerals require cold mantle temperatures the mt data indicate that the sub piedmont thermal lithosphere must extend to greater than 200 km depth this firm bound conflicts with conclusions from seismic results the boundary between the anomalously thick resistive sub piedmont lithosphere and the relatively thin moderately conductive sub appalachian lithosphere corresponds within resolution to the modern appalachian topographic escarpment this newly recognized contrast in lithospheric properties likely has important implications for appalachian topographic rejuvenation

deuterium hydrogen exchange in olivine implications for point defects and electrical conductivity 1 knowledge about hydrogen self diffusion dh is critical for determining mantle hydrogen distribution and understanding point defects also chemical diffusion of hydrogen in olivine such as redox exchange with polarons dredox depends on dh in this study deuterium 2h was exchanged into hydrogen 1h saturated single crystals of san carlos olivine between 750 and 900 c at 2 gpa we measured and fit the resulting 2h profiles to obtain dh 100 10 4 9 1 4 e 140 30kj mol rt m2 s which is 1 log unit lower than dredox 100 with similar activation enthalpy ha by comparing these two diffusion coefficients we estimate the small polaron diffusion coefficient additionally we estimate dh in the 010 and 001 orientations demonstrating that dh is highly anisotropic in olivine these dhvalues were used with the nernst einstein relation to estimate the electrical conductivity by hydrogen in olivine h 101 1 e 130kj mol rt s m for 10 2 wt h2o that is lower in magnitude than previous measurements our results suggest that hydrogen alone cannot account for high electrical conductivity anomalies observed at asthenospheric depths 10 2 to 10 1 s m the maximum anisotropic variation of dh and hin olivine is 2 log units between 750 and 900 c and increases when extrapolated to higher temperature 3 3 at 1400 c anisotropy observed in the mantle may indicate substantial amounts of hydrogen in olivine with lattice preferred orientation

the effect of small amounts of h2o on olivine to ringwoodite transformation growth rates and implications for subduction of metastable olivine abstract it has been suggested that in relatively cold subduction zones the interior of down going lithospheric plates may be cool enough to inhibit the transformation of olivine to its high pressure polymorphs wadsleyite and ringwoodite resulting in the persistence of metastable olivine in the mantle transition zone the rapid transformation of this metastable olivine has been identified as a possible cause of deep focus earthquakes however it is known that olivine can incorporate hydrogen at high pressure and this hydrogen may enhance transformation rates we conducted a series of high pressure experiments to hydrate and then partially transform olivine to ringwoodite we measured transformed rim thickness as a function of run duration and fit a linear function to our results to determine transformation growth rates the addition of h2o to olivine appears to promote olivine to ringwoodite transformation by increasing the growth rate decreasing the activation enthalpy for growth and weakening the ringwoodite and or olivine to allow for dissipation of elastic strain sufficient to maintain constant or near constant growth rates throughout transformation the addition of approximately 300 ppmw 2h2o to olivine increases the growth rate of olivine to ringwoodite transformation at 1100 c and 18 gpa by almost a factor of 40 from 4 0 0 8 10 9 ms 1 to 1 5 0 3 10 7 ms 1 there is a corresponding decrease in the activation enthalpy of growth from 392 kj mol to 237 kj mol assuming activation volume of 0 cm3 mole analyses of hydrogen distributions in partially transformed samples suggest that the hydrogen concentration in the bulk of the olivine crystal may be less important than hydrogen at the olivine and ringwoodite interface

role of a low viscosity zone in stabilizing plate tectonics implications for comparative terrestrial planetology 1 earth s near surface layer its lithosphere is broken into quasi rigid plates that form the upper thermal boundary layer for mantle convection since the discovery of plate tectonics it has been widely conjectured but only recently demonstrated that this peculiar style of convection may be facilitated by an upper mantle low viscosity zone lvz over which the plates glide easily the lvz or asthenosphere concept dates from 19th century investigations of isostatic support of mountain belts and is supported by modern evidence for a seismic low velocity zone and by studies of postglacial rebound and dynamic compensation of the earth s gravity field here we show in both two dimensional 2 d cartesian and 3 d spherical earth models that combining a pronounced lvz and a plastic yield stress to allow localized weakening of the cold thermal boundary layer results in a distinctly plate tectonic style of convection with 30 toroidal surface motion for the 3 d case recycling of water into the upper mantle at subduction zones is a plausible cause of earth s lvz whereas venus is dry and lacks both an lvz and plate tectonics

experimental determination of melt interconnectivity and electrical conductivity in the upper mantle the presence of a small fraction of basaltic melt is a potential explanation for mantle electrical conductivity anomalies detected near the top of the oceanic asthenosphere the interpretation of magnetotelluric profiles in terms of the nature and proportion of melt however relies on mathematical models that have not been experimentally tested at realistically low melt fractions 0 01 in order to address this we have performed in situ electrical conductivity measurements on partially molten olivine aggregates the obtained data suggest that the bulk conductivity follows the conventional archie s law with the melt fraction exponents of 0 75 and 1 37 at melt fractions greater and smaller than 0 5 vol respectively at 1350 c our results imply multiple conducting phases in melt bearing olivine aggregate and a connectedness threshold at 0 5 vol of melt the model predicts that the conductive oceanic upper asthenosphere contains 0 5 to 1 vol of melt which is consistent with the durable presence of melt at depths over millions years while the oceanic plates spread apart at the mid ocean ridge beneath ridges a minimum permeability may allow mid ocean ridge basalts to rise out of the mantle where our model indicates that melt is present in proportions of up to 4 vol

controlled source electromagnetic sounding of the oceanic lithosphere the attenuation of ionospheric signals in the frequency range 0 06 24 hz by sea water effectively precludes using the magnetotel luric method to study the electrical structure of the upper oceanic lithosphere we have carried out a dipole dipole electromagnetic sounding in the north pacific by injecting electromagnetic signals into the ocean and sea bed the crust at the site is 25 myr old and has a thin sediment cover the technique similar to that used in earlier work1 2 involves dragging a horizontal dipole antenna along the sea floor the electric fields that propagated through the resistive basement were detected by seafloor receivers at ranges of 10 65 km as the ambient electric field is very small varying from 10 18 v2 m 2 hz 1 at 0 1 hz to 10 24 v2 m2 hz 1 above 1 hz ref 3 the controlled source signals could be easily monitored our data are consistent with a simple one dimensional earth model consisting of a 3 7 km thick crustal layer of moderate conductivity 0 001 s m 1 underlain by a thicker region of very low conductivity 2 10 5 s m 1 the results suggest an upper mantle water content of at most 0 1 by volume

very long period magnetotellurics at tucson observatory estimation of impedances eleven years 1932 1942 of electric potential and magnetic measurements at the tucson observatory represent a unique very long period magnetotelluric mt data set we report here on a careful reanalysis of this data using modern processing techniques we have developed and used novel methods for separating out the quasi periodic daily variation fields and for cleaning up outliers and filling in missing data in the time domain mt impedance tensors estimated using the cleaned and filled data and using robust frequency domain methods are well determined and smoothly varying for periods between 4 hours and 10 days at longer periods the electric field data are swamped by large amplitude incoherent noise particularly after the third year of the experiment although we find no evidence for contamination of any field components by oceanic motional induction at tidal periods the mt impedance estimates do show evidence of small systematic biases due to finite spatial scale geomagnetic sources at harmonies of the daily variation period these periods are thus removed from the time series and not used in further analysis we show that the resulting impedance tensor is well modeled by a real frequency independent distortion of a scalar impedance which is consistent with non inductive distortion of the electric fields by local surface geology to estimate the undetermined static shift of the mt impedance we compare the long period mt results to equivalent mt impedances determined from 46 years of geomagnetic data combining the geomagnetic and undistorted mt impedances results in scalar impedance estimates for periods 0 17 t 91 days of unprecedented precision however for periods less than one day the phase and amplitude of this impedance while individually consistent are not mutually consistent with any one dimensional conductivity distribution the inconsistency probably results from a combination of subtle multidimensional effects and systematic biases

a comparison of electromagnetic distortion and resolution of upper mantle conductivities beneath continental europe and the mediterranean using islands as windows abstract to investigate the potential of utilising islands as windows through which oceanic mantle conductivities might be imaged simultaneous magnetotelluric mt measurements were carried out continuously over a 3 month duration at two continental stations one in the swabian alps southern germany the other in the bourgogne central france and on the mediterranean islands of montecristo mchr and mallorca mall the mt transfer functions to 1 5 cycles per day cpd and single site z h transfer functions for the first four harmonics of the solar quiet sq daily field variations are presented the transfer functions derived at the island sites are corrected for the distortive and inductive effects arising from the mediterranean bathymetry relative to the transfer functions calculated at the continental stations using three dimensional thin sheet modelling the corrections are formulated in terms of the magnetic perturbation tensor w static shifts in the mt transfer functions are corrected using the z h transfer functions and by comparison with hypothesised resistivity jumps at the transition zones models are derived jointly from the residual mt and z h transfer functions constraints on the resistivities of the upper mantle are investigated despite the widely different tectonic settings no significant differences in the conductivities of the upper mantle below 100 km are detected the disadvantages of utilising widely spaced islands as windows to the mantle are highlighted by departures from one dimensionality in the complex tectonic setting of the mediterranean region

seismic attribute illumination of an igneous reservoir in china when lava flows and pyroclastic deposits exhibit sufficient porosity and permeability extrusive igneous rocks have the potential to host large hydrocarbon accumulations the porosity in these deposits can come from either vesicular porosity or from secondary porosity that resulted from later fracturing and hydrothermal alteration recent studies feng 2008 show that significant hydrocarbon reserves are contained in volcanic rocks in china which are primarily found in the songliao bohai bay and erlian basins these hydrocarbon rich reservoirs range from upper jurassic to tertiary in age

determination of groundwater flow through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns a numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake many different possible flow regimes are identified however in this paper attention is focused on flow through water bodies as these are the flow regimes observed in field validation two shallow lakes on the swan coastal plain of south west western australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow through groundwater flow regime predicted by the modelling confirming the validity of the approach the flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices cl l cl and 1000 l 1000 these ratios are introduced as an additional two of nine non dimensional ratios that are necessary to analyse the problem the ratios represent the chloride and isotopic composition ci l and l respectively in the groundwater release zones of the lakes relative to these parameters in the groundwater capture zone cl and for the lake field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions it is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake aquifer interaction the tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case specific examples of groundwater surface water interaction and will improve the scientific basis of decision making concerning lake and wetland management and groundwater interaction by water resource and environmental managers

point defect populations of forsterite revealed by two stage metastable hydroxylation experiments hydroxylation is a method that allows decoration of the pre existing point defect structure of nominally anhydrous minerals such as olivine we tested this method on synthetic forsterite fo text mg 2 text sio 4 crystals to control starting point defect structures fo crystals were pre annealed at different temperatures 1100 1500 circ text c silica activity conditions forsterite enstatite fo en and forsterite periclase fo per and oxygen fugacity 0 21 and 10 6 bars then low temperature hydroxylation 900 c 1 5 gpa of the crystals successfully allowed the decoration with protons of pre existing point defect structures as subsequently revealed by infrared spectroscopy protons are arranged in three different point defect stoichiometries in fo related to mg and si vacancies mg and si respectively as well as to a trivalent cation associated substitution mechanism triv over the timescale and equilibrium conditions studied hydroxylation does not reset the point defect structure inherited from pre anneal the data further show that the concentrations of mg si and triv hydrated defects are function of pre anneal silica activity and temperature laser ablation inductively coupled plasma mass spectrometry la icp ms analysis of the crystals revealed diffusion of al and fe into the crystals during the pre annealing a phenomenon clearly promoted at high text a text sio 2 the data confirm a very fast mechanism of al diffusion in fo during pre annealing and suggest a strong coupling between text h and text al 3 during hydroxylation overall they show the strong importance of text a text sio 2 and temperature in the incorporation of trace cations in forsterite and the subsequent effects of incorporation of trace cations on mg and si related point defects in fo the dry point defect population of fo is determined by interactions between the trace trivalent cations and dry si and mg vacancies without trace elements t only has a limited effect on mg and si related point defect populations finally approaching or potentially slightly exceeding the fo en solidus leads to strong changes in the trace element concentration and point defect population in fo which may be related to either partial melting or pre melting effects

conductivity discontinuities in the upper mantle beneath a stable craton we present evidence for approximate collocation of seismic and electrical transitions in the upper mantle more than two years of very long period magnetotelluric mt data were recorded at a lakebottom observatory in the central canadian shield after processing to contend with non stationary source effects and removal of galvanic distortion the underlying structure is 1d for periods of one hour to four days the response was extended to periods of 100 days by appending geomagnetic depth sounding data to the mt curves minimum structure linearised inversion nonlinear extremal inversion and a new genetic algorithm for nonlinear hypothesis testing reveal discrete jumps in conductivity at depths near the major upper mantle seismic discontinuities the jumps occur over limited depth ranges

impact of shallow volcanics on seismic data quality in chicontepec basin mexico chicontepec basin is one of the most productive in mexico unlike the world famous cantarell and poza rica carbonate fields characterized by high producing wells tapping large continuous reservoirs the chicontepec play is characterized by thin sometimes multistoried turbidite and fan reservoirs encased in shales and cut by mud slumps and mass transport complexes the sand reservoirs are relatively small and have very low permeability most new wells need to be hydraulically fractured with anomalously higher production being hypothesized as due to fractures draining nearby otherwise disconnected sand bodies

water in the mantle results from electrical conductivity beneath the french alps 1 a deep magnetotelluric sounding in the french alps provided a vertical electrical conductivity profile between 200 1000 km two prominent features are observed first the conductivity in the depth range 400 800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm second the data do not require the conductivity to change throughout the transition zone 410 660 km in this part of the mantle a temperature of 350 450 c less than normal explains the magnetotelluric conductivity profile at 200 400 km our model favors a cold mantle with 1000 1500 ppm of water dissolved in olivine if correct this model suggests that the subducted slab is dehydrated before reaching the transition zone

chemical evolution of groundwater near a sinkhole lake northern florida 1 flow patterns age of groundwater and influence of lake water leakage leakage from sinkhole lakes significantly influences recharge to the upper floridan aquifer in poorly confined sediments in northern florida environmental isotopes oxygen 18 deuterium and tritium chlorofluorocarbons cfcs cfc 11 ccl3f cfc 12 ccl2f2 and cfc 113 c2cl3f3 and solute tracers were used to investigate groundwater flow patterns near lake barco a seepage lake in a mantled karst setting in northern florida stable isotope data indicated that the groundwater downgradient from the lake contained 11 67 lake water leakage with a limit of detection of lake water in groundwater of 4 3 the mixing fractions of lake water leakage which passed through organic rich sediments in the lake bottom were directly proportional to the observed methane concentrations and increased with depth in the groundwater flow system in aerobic groundwater upgradient from lake barco cfc modeled recharge dates ranged from 1987 near the water table to the mid 1970s for water collected at a depth of 30 m below the water table cfc modeled recharge dates based on cfc 12 for anaerobic groundwater downgradient from the lake ranged from the late 1950s to the mid 1970s and were consistent with tritium data cfc modeled recharge dates based on cfc 11 indicated preferential microbial degradation in anoxic waters vertical hydraulic conductivities calculated using cfc 12 modeled recharge dates and darcy s law were 0 17 0 033 and 0 019 m d for the surficial aquifer intermediate confining unit and lake sediments respectively these conductivities agreed closely with those used in the calibration of a three dimensional groundwater flow model for transient and steady state flow conditions

transient electrical response of san quintin dunite as a function of oxygen fugacity changes information about charge carriers the electrical conductivity of san quintin dunite sqd measured between 950 and 1150 c at controlled oxygen fugacity fo2 within the olivine stability field shows transients in response to changes in fo2 such behavior has not been reported previously for measurements made under similar conditions on either olivine single crystals or polycrystalline samples dunites and lherzolites in which olivine is the major phase in general for olivine an increase in fo2 results in an increase in the transient is manifested as a change in from a stable equilibrium value at a specific fo2 to a quickly established subsequent value the direction of which is opposite that of the final value that will be attained for the fo2 change this transient may be caused by a changing population of electrons produced by oxygen vacancies the grain boundaries or a short lived defect we postulate that the transient is observed in this particular dunite because of its large surface area to volume ratio the transient is more pronounced at relatively high fo23 and temperatures between 950 and 1100 c at relatively low fo2s and temperatures higher than 1100 c the effect is diminished the seebeck coefficient s at 1200 c is slightly smaller than that reported for single crystal olivine and at 1100 c is similar to that reported for single crystal olivine

electrical conductivity of molten basalt and andesite to 25 kilobars pressure geophysical significance and implications for charge transport and melt structure electrical conductivities of molten hawaiian tholeiite and crater lake andesite were measured between 1200 c and 1400 c at atmospheric pressure and at pressures up to 17and 25 kbar respectively isobaric plots of log versus 1 t is electrical conductivity are linear with the exception of the zero pressure tholeiite melt data conductivities decrease with increasing pressure in both melts with the andesitic melt exhibiting a greater pressure dependence between 5 and 10 kbar abrupt decreases in the slopes of isothermal log versus p plots i e decreases in activation volume are observed for both rock melts this discontinuity probably reflects changes in melt structure as opposed to changes in conduction mechanism in each pressure range the data for each rock melt can be described reasonably well by an equation of the form 0 exp ea p v kt where 0 is a preexponential constant ea is the activation energy and v is the activation volume a qualitative model involving depolymerization of the melt with increased pressure leading to increased efficiency of packing can explain the observed discontinuity in activation volume as well as the observed pressure dependences of other melt physical properties such as viscosity and density conductivity versus melt fraction curves for partially molten peridotite are reevaluated using high pressure tholeiitic melt conductivities and crystalline conductivity values recently determined by other workers minimum melt fraction estimates of 5 10 are required to explain upper mantle regions of anomalously high electrical conductivity in terms of a partial melting hypothesis

magnetic resonance sounding evidence shows that shallow groundwater discharge maintains the lake landscape in the hunshandake sandy land north china the hunshandake sandy land hsl is a well known water rich sandy region in china that is home to many lakes most of these lakes are sustained by groundwater inflow however due to the limited hydrogeological survey data the mechanism by which the lakes interact with groundwater is not well understood magnetic resonance sounding mrs is a geophysical method that has emerged in recent years that can directly detect the distribution of groundwater and determine the lithology of the aquifer medium compared with drilling this method is convenient rapid and inexpensive in this study to determine how the lakes are recharged by groundwater a field experiment using mrs was conducted on haoletuyin lake which is located in the central hsl the results showed that compared with borehole data the mrs derived aquifer depth has an uncertainty of 6 88 additionally the lithology of the media derived from the mrs is consistent with that derived from the borehole data this finding suggests that the mrs derived results are highly accurate based on the mrs derived results two hydrogeological profiles were plotted and they show that the lake in the experimental area is recharged primarily by shallow groundwater and not by deep groundwater this study is significant because it not only reveals the mechanism by which haoletuyin lake is maintained but also proves that mrs is an excellent tool for studying lake groundwater relations in desert sandy land regions with limited hydrogeological survey data

hydrogeochemistry and isotope techniques to determine water interactions in groundwater dependent shallow lakes wet pampa plain argentina this paper gives an account of the implementation of hydrochemical and isotopic techniques to identify and explain the processes that govern solute exchange in two groundwater dependent shallow lakes in the southeastern pampa plain of argentina water samples lakes streams spring water and groundwater for hydrochemical and stable isotopic determination were collected and the main physical chemical parameters were measured the combination of stable isotope data with hydrogeochemical techniques was used for the identification of sources and preferential recharge areas to these aquatic ecosystems which allowed the explanation of the lake water origin the hydrochemical processes which explain los padres lake water chemistry are evaporation from groundwater co2 input calcite dissolution na release by ca2 and mg2 exchange and sulfate reduction the model that best aligns with la brava lake hydrochemical constraints includes mixing co2 and calcite dissolution cationic exchange with na release and mg2 adsorption and to a lesser extent ca na exchange this model suggests that the fractured aquifer contribution to this water body is greater than 50 an isotopic specific fingerprint for each lake was identified finding a higher evaporation rate for la brava lake compared to los padres lake isotopic data demonstrate the importance of these shallow lakes as recharge areas to the regional aquifer becoming areas of high groundwater vulnerability the tandilia range system considered in many hydrogeological studies as the impermeable bedrock of the pampean aquifer acts as a fissured aquifer in this area contributing to low salinity waters and with a fingerprint similar to groundwater isotopic composition

evidence of electrical anisotropic structures in the lower crust and the upper mantle beneath the rhenish shield abstract we present the results of a long period electromagnetic investigation of the crust and upper mantle beneath the rhenish shield in western germany the magnetotelluric phase data reveal a frequency dependent regional strike that varies only smoothly across the array at short periods t 1000 s there is a consistent striking in we direction which provides strong evidence of an anisotropic structure in the upper mantle too geomagnetic data were also used whereas we reference the magnetic field components of all sites to an arbitrarily chosen field site that provides a direct view of the anomalous current flow we show that in case of a non one dimensional electrical substructure of the reference site all magnetic transfer functions of the other sites can be affected by lateral conductivity contrasts beneath the reference site a simple method to remove such effects is introduced applying this method the magnetic data show a distinct anomaly in the northwestern part of the area finally we present a 3d model of the conductivity structure beneath the rhenish shield which contains a superposition of two anisotropic structures in the lower crust 2000 s and the upper mantle 20 000 s respectively and a local anomaly in the upper crust 4000 s

electrical conductivity of enstatite as a function of water content implications for the electrical structure in the upper mantle abstract the electrical conductivity of ca free aluminous enstatite with various water contents has been determined at a pressure of 3 gpa in a kawai type multi anvil apparatus impedance spectroscopy was performed for both hydrogen doped and undoped samples in a frequency range from 0 1 hz to 1 mhz to examine the effect of water on conductivity two conduction mechanisms were identified for hydrogen undoped samples at temperature of 1000 1723 k and for hydrogen doped samples at relatively lower temperature range of 500 900 k to minimize dehydration of samples for the hydrogen undoped samples the activation enthalpy is around 1 9 ev at the higher temperatures range 1300 k suggesting that the dominant charge transfer mechanism is fe 2 fe 3 hopping small polaron conduction for the hydrogen doped samples measured below 900 k the activation enthalpy decreases from 1 11 to 0 70 ev and the conductivity values systematically increase with increasing water content suggesting that proton conduction is the dominant conduction mechanism taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account all electrical conductivity data were fitted to the formula 0 h exp h h kt 0 p c w exp h p 0 c w 1 3 kt where 0 is pre exponential factor c w is the water content in weight percent h is the activation enthalpy h p 0 is the activation enthalpy for proton conduction at very low water concentration is the geometrical factor k is the boltzmann constant t is absolution temperature and subscripts h and p represent hopping and proton conductions respectively using the present results a laboratory based conductivity depth profile in the earth s upper mantle has been constructed as a function of water content comparison of our model with the currently available geophysical observations beneath the eastern pacific rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine

high and highly anisotropic electrical conductivity of the asthenosphere due to hydrogen diffusion in olivine experimental studies on electrical conductivity in hydrated olivine had been made only at relatively low temperatures the extrapolation of these data to asthenosphere temperatures shows that explaining high and highly anisotropic conductivity by hydrogen is difficult we present new experimental results on the electrical conductivity in hydrated olivine single crystals measured under a broader temperature range than before t temperature 573 1373 k at p pressure 4 gpa the new results agree well with the previous results at low temperatures t 1000 kt 1000 k substantial deviations from the previous results are observed i anisotropy in conductivity increases with temperature and ii activation energies at high temperature regime are substantially higher than those at lower t the high temperature behavior is consistent with a model invoking diffusion of two protons at m site vacancy whereas the low temperature behavior suggests conduction by more mobile species such as free proton the present results i explain the discrepancy between different previous studies conducted under different temperature regimes and ii show that most of geophysical observations on the electrical conductivity in the asthenosphere including the high and highly anisotropic conductivity can be explained by high water content in the asthenosphere that is consistent with the geochemical model combining with a previous model of low seismic wave velocity of the asthenosphere a subsolidus model invoking the role of hydrogen provides a unified explanation for the geophysical anomalies of the asthenosphere

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

surface water groundwater interaction near shallow circular lakes flow geometry in three dimensions steady flow regimes for three dimensional lake aquifer systems are studied via idealized mathematical models that are extensions of earlier simplified vertical section models of interaction between shallow lakes and underlying aquifers the present models apply to a shallow circular lake at the surface of a rectangular aquifer of finite depth yielding a truly three dimensional representation of the resulting flow system flux boundary conditions are applied at the ends of the aquifer with net vertical recharge or evapotranspiration at the water table the lake is defined by a region with constant head by determining and visualizing solutions to the discretized saturated flow equations a range of possible flow regimes is identified and their topological properties are studied tools for analyzing flow regimes are described including a method for locating and mapping three dimensional dividing surfaces within steady flow fields results show strong similarities between two and three dimensional systems including a large number of flow through recharge and discharge regimes and reverse flow cells flow lines calculated on a vertical plane through the middle of a lake resemble but are not identical to two dimensional streamlines for a range of aquifer flow and recharge conditions estimates of the widths and depths of capture and release zones for various lake aquifer geometries are asymptotic to earlier results for two dimensional systems numerical predictions are compared with analytical results for certain limiting flow regimes

comment to high and highly anisotropic electrical conductivity of the asthenosphere due to hydrogen diffusion in olivine by dai and karato earth planet sci lett 408 2014 79 86 dai and karato 2014a reported new electrical conductivity measurements on oriented single crystals of hydrous olivine showing a higher increase in conductivity and conductivity anisotropy at high temperature than previously reported after recalling that the highest conductivities of the upper mantle e g 0 1 s m cannot reasonably be explained by previous hydrous olivine conductivity data they concluded from their new measurements that olivine hydration can actually account for the electrical anomalies of the upper mantle however we analyze the data of dai and karato 2014a and demonstrate that they are not higher but lower than most previous measurements and models including those of the same authors even when extrapolated at upper mantle temperatures this new study therefore does not extend but restricts the magnitude of olivine conductivity enhancement by water we show that the high temperature conduction regime reported by dai and karato 2014a cannot result from the diffusion of vacancy hydrogen complexes as proposed by the authors but is compatible with the diffusion of interstitial protons we show that the high conductivity anisotropy observed in their olivine samples with high water concentration 1000 wt ppm must be drastically reduced at mantle relevant water concentrations view the mathml source 100 wt ppm since dry olivine is weakly anisotropic we conclude from all of the existing models that olivine with mantle relevant water concentrations is unlikely to produce significant conductivity anisotropy in deformed mantle and is unable to produce the highest conductivities of the upper mantle which therefore likely result from partial melting

long period 30 days 1 year electromagnetic sounding and the electrical conductivity of the lower mantle beneath europe the c response connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations and forms the basis for deriving the conductivity depth profile of the earth time series of daily mean values at 42 observatories typically with 50 years of data are used to estimate c responses for periods between 1 month and 1 yr the z y method is applied which means that the vertical component is taken locally whereas the horizontal components are used globally by expansion in a series of spherical harmonics in combination with results from previous analyses the method yields consistent results for european observatories in the entire period range from a few hours to 1 yr corresponding to penetration depths between 300 and 1800 km 1 d conductivity models derived from these results show an increase in conductivity with depth z to about 2 s m 1 at z 800 km and almost constant conductivity between z 800 and z 2000 km with values of 3 10 s m 1 in good agreement with laboratory measurements of mantle material below 2000 km the conductivity is poorly resolved however the best fitting models indicate a further increase in conductivity to values between 50 and 150 s m 1

anisotropy of the asthenosphere the higher mode data of the pacific revisited surface wave data previously used by the authors to constrain upper mantle anisotropy in the pacific ocean are re examined after an error was found in the calculations of the love wave phase velocities sub lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed using different parameterizations of the upper mantle we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the pacific beneath north america no revision of our data is required and anisotropy could extend to around 400 km depth our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present day plate motion we suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low velocity layer

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

influence of regional setting on the interaction between shallow lakes and aquifers 1 interaction between surface water and groundwater depends on the position of a lake within the regional flow system the approach in this paper is to nest a local scale two dimensional 2 d lake aquifer model within a 1 d regional aquifer model to examine the effect of the regional setting on surface water groundwater interaction this extends previous steady state flow modeling which is presented in earlier publications the results indicate that the type of regional setting and position of the lake within that setting impose constraints on the near field flow geometry only nine of 39 previously identified flow regimes are possible in the regional flow system considered flow through lakes are dominant and can occur anywhere within the regional flow recharge and discharge lakes are more likely to occur near the groundwater divide where regional hydraulic gradients are flattest and can be counteracted by local forcing in and near the lake

three dimensional electrical resistivity of the north central usa from earthscope long period magnetotelluric data abstract we present initial results from three dimensional inversion of long period earthscope magnetotelluric mt transportable array data from 232 sites covering the north central us the study area covers the 1 1 ga mid continent rift mcr system which cuts across a series of archean and paleoproterozoic lithospheric blocks the western arm of the mcr is clearly evident in shallow depth sections with a narrow resistive core flanked by elongate conductive basins other prominent upper crustal features mapped include the moderately conductive michigan and illinois basins and extremely high conductivities in foreland basin rocks at the southern margin of the superior craton the most prominent conductive anomalies in an otherwise relatively resistive mid lower crust are two elongate east west oriented structures which are closely aligned with previously inferred continental sutures the first underlies the southern margin of the superior craton just north of the niagara fault nf and can be associated with the 1 85 ga penokean orogeny a second further south beneath iowa and western wisconsin lies just south of the spirit lake tectonic zone sltz and can be identified with yavapai accretion at 1 75 ga both of these conductive sutures are cleanly cut by the mcr which is otherwise not clearly evident in the deeper parts of the resistivity model the break in the anomalies is narrow comparable to the surface expression of the mcr indicating that rifting impacts on the entire crustal section were highly localized both suture related anomalies are imaged as extending into and perhaps through the lithosphere as dipping diffuse zones of reduced mantle resistivity sense of dip of these structures southward for the nf anomaly northward for sltz agrees with previously inferred models for subduction and accretion suggesting that a conductive phase most likely carbon has been thrust deep into the lower crust and uppermost mantle providing a marker of the three dimensional boundary between lithospheric blocks resistivities drop below 100 m below 200 km depth in rough agreement with the seismically determined lithosphere asthenosphere boundary lab there are modest lateral variations in this deep low resistivity layer but the reliability and significance of these are not yet clear

reconciling different equations for proton conduction using the meyer neldel compensation rule 1 proton conduction in nominally anhydrous minerals is the likely explanation for moderate values of electrical resistivity observed in the lithospheric and sublithospheric mantle however results from the various laboratories making the controlled measurements on mantle minerals predominantly olivine are not in agreement with one another importantly the groups use different formalisms to fit their experimental data in this paper we show that neither of the two formalisms employed by the various laboratories is consistent with the meyer neldel rule mnr or compensation law by which the preexponent term of the arrhenian equation is linearly related to the activation energy term we also demonstrate why the formalism of karato and colleagues can be used at low water contents 100 wt ppm and below whereas at higher water contents above 300 wt ppm the formalism of yoshino s and poe s labs needs to be employed a new mnr self consistent formalism is presented that is applicable over all water contents mnr consistency appears to operate for most processes that can be described by an arrhenius equation so its adoption through an mnr consistent formalism is highly recommended when fitting experimental observations

experimental study on the electrical conductivity of pyroxene andesite at high temperature and high pressure the electrical conductivity of pyroxene andesite was in situ measured under conditions of 1 0 2 0 gpa and 673 1073 k using a yj 3000t multi anvil press and solartron 1260 impedance gain phase analyzer experimental results indicate that the electrical conductivities of pyroxene andesite increase with increasing temperature and the electrical conductivities decrease with the rise of pressure and the relationship between electrical conductivity and temperature t conforms to an arrhenius relation within a given pressure and temperature range when temperature rises up to 873 923 k the electrical conductivities of pyroxene andesite abruptly increase and the activation enthalpy increases at this range which demonstrates that pyroxene andesite starts to dehydrate by the virtue of the activation enthalpy 0 35 0 42 ev and the activation volume 6 75 1 67 cm3 mole which characterizes the electrical properties of sample after dehydration we consider that the conduction mechanism is the small polaron conduction before and after dehydration and that the rise of carrier concentration is the most important reason of increased electrical conductivity

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

supercritical fluid in the mantle transition zone deduced from h d interdiffusion of wadsleyite abstract knowledge of the distribution of water in the earth s mantle is key to understanding the mantle convection and geochemical evolution of the earth as wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge where descending slab stagnates at the transition zone however there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite here we report the hydrogen self diffusion coefficient obtained from h d interdiffusion experiments in wadsleyite single crystal couples our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone in contrast the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales this phenomenon provides an alternative explanation for both the high conductivity and seismic velocity anomalies observed in the mantle wedge at the transition zone depth

mantle dynamics beneath the east pacific rise at 17 s insights from the mantle electromagnetic and tomography melt experiment 1 the electromagnetic data from the mantle electromagnetic and tomography melt experiment are inverted for a two dimensional transversely anisotropic conductivity structure that incorporates a correction for three dimensional topographic effects on the magnetotelluric responses the model space allows for different conductivity values in the along strike cross strike and vertical directions along with imposed constraints of model smoothness and closeness among the three directions anisotropic models provide a slightly better fit to the data for a given level of model smoothness and are more consistent with other geophysical and laboratory data the preferred anisotropic model displays a resistive uppermost 60 km thick mantle independent of plate age except in the vicinity of the ridge crest in most inversions a vertically aligned sheet like conductor at the ridge crest is especially prominent in the vertical conductivity its presence suggests that the melt is more highly concentrated and connected in the vertical direction immediately beneath the rise axis the melt zone is at least 100 km wide and is asymmetric having a greater extent to the west off axis and to the east of the ridge the mantle is more conductive in the direction of plate spreading at depths greater than 60 km the flat resistive conductive boundary at 60 km agrees well with the inferred depth of the dry solidus of peridotite and the deeper conductive region is consistent with the preferred orientation of olivine inferred from seismic observations this suggests that the uppermost 60 km represents the region of mantle that has undergone melting at the ridge and has been depleted of water dissolved hydrogen by contrast the underlying mantle has retained a significant amount of water

electrical conductors in archean mantle result of plume interaction 1 from long period magnetotelluric data across the gawler craton we obtain a three dimensional resistivity image of the lithosphere and provide constraints on tectonothermal events dating back to the proterozoic contrary to common observations of archean cratons displaying high electrical resistivity in the mantle lithosphere the magnetotelluric data show low resistivity of around 10 m at 80km depth underneath the 1595ma gawler range volcanics a silicic large igneous province the resistivity distribution appears to be a signature of plume modified orogenesis with low degree partial melting at the base of the lithosphere in a back arc setting the enhanced conductivity is explained through higher hydrogen and iron content in the crystal lattice and also along the grain boundaries of the mantle constituting minerals older arc related magmatism to the southwest across 1620 1610ma st peter suite does not display enhanced conductivity and suggests a depleted mantle lithosphere the data show that yellowstone type mantle plume analogues are preserved through time and still display an elevated electrical signature in the lithosphere today

seo3 a new model of olivine electrical conductivity summary standard electrical olivine 3 seo3 is a new model of electrical conductivity for olivine as a function of temperature and oxygen fugacity and is based on a previous study of point defect behaviour in a dunite that study produced quantitative estimates of mobility and concentration for small polarons and magnesium vacancies as a function of temperature and oxygen fucacity unlike earlier so1 and so2 models of olivine conductivity the dunite sample was buffered by pyroxene and avoided alteration at high temperature the low temperature extrapolation produced by seo3 is in good agreement with so2 while the high temperature extrapolation is significantly more conductive which is in general agreement with many field studies that show the earth s upper mantle to be more conductive than predicted by so2 for reasonable temperatures plausible variations in mantle oxygen fugacity correspond to about half an order of magnitude variation in electrical conductivity equivalent to about 100 degrees in temperature

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

magnetotelluric images of paleoproterozoic accretion and mesoproterozoic to neoproterozoic reworking processes in the northern sao francisco craton central eastern brazil abstract broadband and long period magnetotelluric mt data were collected along an east west oriented 580 km long profile across the northern sao francisco craton where extensive proterozoic and phanerozoic sedimentary cover and lack of deep probing geophysical surveys have prevented to establish unequivocally the cratonic character of the archean paleoproterozoic lithosphere following dimensionality analyses the mt dataset was interpreted using both 2 d and 3 d inversion procedures the near surface structure is better resolved in the 2 d model due to its finer resolution a huge upper crustal conductor is found all along the shallow early neoproterozoic irece basin in the central domain of the craton extending laterally for approximately 150 km and restricting signal propagation below the basin its high conductance is explained by a combination of high porosity and high fluid salinity in the sedimentary package another upper crustal conductor is observed on the west side of the profile interpreted as fractured metasedimentary rocks of the rio preto belt thrusted on top of the craton basement during neoproterozoic marginal collision the 3 d model explains significantly better the measured data related to deep structure contrary to what is expected for a stable cratonic block the geoelectric model shows pronounced electrical complexity and heterogeneity an indication that the cratonic lithosphere was multiply reworked in the past by tectonothermal events different lithospheric resistive blocks bounded by major conductive zones are identified constrained by geochemical and isotopic data these vertical conductive interfaces are interpreted as cryptic suture zones due to large scale amalgamation of continents and microcontinents leading to the assembly of the sao francisco craton in the paleoproterozoic the conductivity enhancement is more likely explained by emplacement of sulfides along previous suture zones during mafic magmatism at upper mantle depths high conductivity observed below most of the profile indicates that metasomatism or refertilization processes with incompatible elements caused by the paleoproterozoic subducting slabs and mesoproterozoic to neoproterozoic upwelling of deep fluids and melts reworked this portion of the craton mantle

transient hydrogeological controls on the chemistry of a seepage lake a solute mass balance method was used to estimate groundwater inflow and outflow rates for nevins lake michigan a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes a 4 year study 1989 1992 of the hydrology and geochemistry of nevins lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals a pronounced acidification of nevins lake from 1986 to 1988 was likely caused by drought induced diminished groundwater inflow rates in this study dissolved calcium the major cation in water of nevins lake groundwater and precipitation was used for estimating mass flow rates during the 1989 1992 period nevins lake showed a reproducible annual cycle in calcium mass immediately following spring snowmelt and the resulting hydraulic gradient reversal the mass of dissolved calcium in the lake increases rapidly and then it decreases steadily throughout the summer and early fall at which time the lake becomes hydraulically mounded and receives no groundwater inflow groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore but spatial and temporal variability in pore water chemistry must be considered stable isotope analyses 18o and 2h of lake water groundwater and pore water samples show that water discharging to nevins lake in the spring is entirely recycled lake water and no groundwater derived from terrestrial recharge reaches the lake the conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

does partial melting explain geophysical anomalies abstract the existence of partial melt is frequently invoked to explain geophysical anomalies such as low seismic wave velocity and high electrical conductivity i review various experimental and theoretical studies to evaluate the plausibility of this explanation in order for a partial melt model to work not only the presence of melt but also the presence of appropriate amount of melt needs to be explained using the mineral physics observations on the influence of melt on physical properties and the physics and chemistry of melt generation and transport i conclude that partial melt model for the asthenosphere with homogeneous melt distribution does not work one needs to invoke inhomogeneous distribution of melt if one wishes to explain observed geophysical anomalies by partial melting however most of models with inhomogeneous melt distribution are either inconsistent with some geophysical observations or the assumed structures are geodynamically unstable and or implausible therefore partial melt models for the geophysical anomalies of the asthenosphere are unlikely to be valid and some solid state mechanisms must be invoked the situation is different in the deep upper mantle where melt could completely wet grain boundaries and continuous production of melt is likely by dehydration melting at around 410 km in the ultralow velocity zone in the d layer where continuous production of melt is unlikely easy separation of melt from solid precludes the partial melt model for low velocities and high electrical conductivity unless the melt density is extremely close to the density of co existing solid minerals or if there is a strong convective current to support the topography of the ulvz region compositional variation such as fe enrichment is an alternative cause for the anomalies in the d layer

electrical conductivity of basaltic and carbonatite melt bearing peridotites at high pressures implications for melt distribution and melt fraction in the upper mantle abstract electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a kawai type multi anvil apparatus in order to investigate melt fraction conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure the silicate samples were composed of san carlos olivine with various amounts of mid ocean ridge basalt morb and the carbonate samples were a mixture of san carlos olivine with various amounts of carbonatite high pressure experiments on the silicate and carbonate systems were performed up to 1600 k at 1 5 gpa and up to at least 1650 k at 3 gpa respectively the sample conductivity increased with increasing melt fraction carbonatite bearing samples show approximately one order of magnitude higher conductivity than basalt bearing ones at the similar melt fraction a linear relationship between log conductivity bulk and log melt fraction can be expressed well by the archie s law archie 1942 bulk melt c n with parameters c 0 68 and 0 97 n 0 87 and 1 13 for silicate and carbonate systems respectively comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry the gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction the melt fraction of the partial molten region in the upper mantle can be estimated to be 1 3 and 0 3 for basaltic melt and carbonatite melt respectively

upper mantle conductivity structure of the back arc region beneath northeastern china the upper mantle electrical conductivity structure of the pacific back arc beneath northeastern china was investigated through long period magnetotelluric mt and geomagnetic depth sounding gds experiments mt and gds responses were obtained up to periods of 105 106 seconds and were inverted to one dimensional 1 d models with minimum and smooth structure constraints respectively the resulting conductivity model was compared with past models and the mantle transition zone beneath northeastern china is more conductive than those of other tectonic settings by almost one order of magnitude in the depth range of 400 600 km this feature may correspond to the presence of a stagnant slab beneath this region in the mantle at a depth of less than 400 km the conductivity profile has a similar feature to that in the thermal and extensional tectonic region in the southwestern united states

seismic and electrical signatures of the lithosphere asthenosphere system of the normal oceanic mantle although plate tectonics started as a theory of the ocean basins nearly 50 years ago the mechanical details of how it works are still poorly known our understanding of these details has been hampered partly by our inability to characterize the physical nature of the lithosphere asthenosphere system las beneath the ocean we review the existing observational constraints on the seismic and electrical properties of the las particularly for normal oceanic regions away from mid oceanic ridges hot spots and subduction zones where plate tectonics is expected to present its simplest form whereas a growing volume of seismic data on land has provided remarkable advances in large scale pictures seafloor observations have been shedding new light on essential details by combing through these observational constraints researchers are unveiling the nature of the enigmatic las future directions for large scale seafloor observations are also discussed

northeastern pacific mantle conductivity profile from long period magnetotelluric sounding using hawaii to california submarine cable data we present results of a long period magnetotelluric mt investigation of the electrical structure beneath the eastern north pacific the electric field data consist of 2 years of continuously recorded voltages across an unpowered 4000 km long submarine telephone cable haw 1 extending from point arena california to oahu hawaii the electric field measurements are coherent to some degree with magnetic field measurements from honolulu observatory at periods of 0 1 to 45 days this coherence is enhanced at long periods over that observed with point electric field sensors due to horizontal averaging of the motional electric fields of spatial scale smaller than the cable length significantly diminishing their effect robust controlled leverage mt response estimates and their jacknife confidence limits are computed for the haw 1 to honolulu data an equivalent scalar mt response obtained from honolulu magnetic variations data is used to correct the haw 1 mt response for static shift and to extend the mt response estimate to periods of 100 days the composite response function satisfies necessary and sufficient conditions for consistency with a one dimensional conductivity structure and is most sensitive to structure between 150 and 1000 km inversion of the mt response reveals a conductive zone 0 05 0 1 s m between 150 and 400 km depth and a positive gradient below 500 km these observations are consistent with previous mt studies in the north pacific this upper mantle conductivity is too high to be explained by solid state conduction in dry olivine using reasonable mantle geotherms calculations based on measurements of hydrogen solubility and diffusivity in olivine indicate that h dissolved in olivine possibly combined with a lattice preferred orientation consistent with measured seismic anisotropy provide sufficient conductivity enhancement to explain the inversion results the high conductivity may also be explained by the presence of gravitationally stable partial melt comparison of the haw 1 results with long period mt studies conducted on land reveals differences in upper mantle conductivity between different tectonic regimes in particular the upper mantle beneath the pacific ocean is considerably more conductive than that beneath the canadian shield and similar in conductivity to that beneath the basin and range

electrical conductivity of hydrous silicate melts implications for the bottom up hydration of earth s upper mantle abstract the upwelling of the hydrous mantle transition zone triggers dehydration induced partial melting atop the 410 km discontinuity here we investigate the electrical conductivity of hydrous silicate melts in the 200 400 km depth range and explore whether melting at the 410 km depths is responsible for the hydration of the upper mantle our experimental electrical conductivity data demonstrate that the mantle at 180 350 km depths is mostly melt free confirming the h2o under saturated conditions however the residual mantle from partial melting atop the 410 km discontinuity may contain various possible amounts of water according to the initial mantle transition zone and melt concentrations this residual h2o could contribute to the hydration of the upper mantle either through diffusion or material replacement by upwelling our calculations suggest that the diffusion may not be responsible for the hydration of the upper mantle to present h2o concentration of 50 200 ppm wt melting of the upwelling mantle transition zone with less than 1500 ppm wt h2o produces residual peridotites with 200 ppm h2o at the 410 km discontinuity continuous upwelling of such hydrous residues would gradually replace the dry upper mantle with depleted residual hydrous peridotites in less than 260 ma in this study we propose a bottom up hydration mechanism for the earth s upper mantle driven by dehydration melting at the 410 km discontinuity the hydrous partial melting at the top of the asthenosphere appears to be a consequence of h2o saturation in the upwelling residual peridotites

an upper bound on the electrical conductivity of hydrated oceanic mantle at the onset of dehydration melting abstract electrical conductivity soundings provide important constraints on the thermal and hydration state of the mantle recent seafloor magnetotelluric surveys have imaged the electrical conductivity structure of the oceanic upper mantle over a variety of plate ages all regions show high conductivity 0 02 to 0 2 s m at 50 to 150 km depths that cannot be explained with a sub solidus dry mantle regime without unrealistic temperature gradients instead the conductivity observations require either a small amount of water stored in nominally anhydrous minerals or the presence of interconnected partial melts this ambiguity leads to dramatically different interpretations on the origin of the asthenosphere here i apply the damp peridotite solidus together with plate cooling models to determine the amount of h2o needed to induce dehydration melting as a function of depth and plate age then i use the temperature and water content estimates to calculate the electrical conductivity of the oceanic mantle with a two phase mixture of olivine and pyroxene from several competing empirical conductivity models this represents the maximum potential conductivity of sub solidus oceanic mantle at the limit of hydration the results show that partial melt is required to explain the subset of the high conductivity observations beneath young seafloor irrespective of which empirical model is applied in contrast the end member empirical models predict either nearly dry

spreading rate dependence of three dimensional structure in oceanic spreading centres segmentation by transform faults and other types of along axis discontinuity1 is a well described but poorly explained characteristic of oceanic spreading centres here we use numerical experiments to explore the dynamics of mantle flow and melting beneath a mid ocean ridge buoyant upwelling driven by compositional density variations resulting from the extraction of the melt that forms the ocean crust exhibits a spreading rate dependent transition between two dimensional and three dimensional upwelling structures for low spreading rates and mantle viscosities an initial two dimensional structure transforms into a three dimensional one at high spreading rates an initially two dimensional structure remains two dimensional these results suggest that the origin of spreading centre segmentation may be different at fast and slow spreading rates

structure of the lithosphere beneath the barotse basin western zambia from magnetotelluric data author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in tectonics 38 2 2019 666 686 doi 10 1029 2018tc005246

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

electrical conductivity anisotropy of dry and hydrous olivine at 8 gpa the effects of dissolved h2o on the electrical conductivity and its anisotropy in olivine fo90 at 8 gpa were investigated by complex impedance spectroscopy at nominally anhydrous conditions conduction along 1 0 0 and 0 0 1 is slightly higher than along 0 1 0 in contrast to observations made at lower pressures in earlier studies increasing h2o content increases conductivities but activation energies are lower and h2o concentration dependent the use of polarized ftir spectroscopy to determine h2o concentrations reveals a weaker than expected effect that water has on olivine conductivity and distinguishes our results from earlier studies based on analyses using non polarized infrared spectroscopy we show that at h2o concentrations of a few hundred wt ppm or less that the dominant conduction mechanism at mantle temperatures continues via small polarons such as that observed for anhydrous olivine our results also suggest that at depths greater than 200 km the presence of h2o may not be necessary to explain regions in the upper mantle where both electrical and seismic anisotropy are observed this can be explained by differences in the pressure dependence of the activation energy for conduction along each of the three crystallographic axes however while electrical anisotropy of anhydrous olivine remains weak at 8 gpa it is nevertheless enhanced by elevated concentrations several hundred wt ppm of dissolved h2o at these conditions dominated by proton hopping conductivity along 0 1 0 is highest approximately an order of magnitude greater than along 1 0 0 additionally at 1000 wt ppm and 1500 c an isotropic conductivity derived from the data is about 1 order of magnitude higher than that for nominally anhydrous olivine thus in regions of the mantle characterized by anomalously high conductivities and both electrical and seismic anisotropy significant amounts of dissolved hydrogen can be expected

hydrogen self diffusivity in single crystal ringwoodite implications for water content and distribution in the mantle transition zone hydrogen lattice diffusion in fe bearing ringwoodite was investigated through hydrogen and deuterium interdiffusing in a pair of synthesized single crystals at various temperatures 1000 1300 k at 21 gpa diffusion profiles were investigated by secondary ion mass spectrometer to determine the hydrogen self diffusivity in ringwoodite temperature dependences of hydrogen diffusion in ringwoodite were determined to be dh 10 7 29 0 46 exp 101 10 kj mol 1 rt m2 s in ringwoodite at 21 gpa the proton conductivities of ringwoodite estimated from the present diffusion coefficients are similar to those of yoshino et al 2008 at the transition zone condition at low water content 1000 ppmw if the proton vacancy mechanism is assumed to be a main controlling mechanism contribution of water to the electrical conductivity of ringwoodite is insignificant due to large contribution of hopping conduction at the transition zone condition and global average water concentration in the lower part of transition zone is less than 1000 ppmw

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date