feldspar dissolution rates in the topopah spring tuff yucca mountain nevada abstract two different field based methods are used here to calculate feldspar dissolution rates in the topopah spring tuff the host rock for the proposed nuclear waste repository at yucca mountain nevada the center of the tuff is a high silica rhyolite consisting largely of alkali feldspar 60 wt and quartz polymorphs 35 wt that formed by devitrification of rhyolitic glass as the tuff cooled first the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff and an ambient dissolution rate is calculated by using the estimated thermal history second the feldspar dissolution rate is calculated by using measured sr isotope compositions for the pore water and rock pore waters display systematic changes in sr isotopic composition with depth that are caused by feldspar dissolution the range in dissolution rates determined from secondary mineral abundances varies from 10 16 to 10 17 mol s 1 kg tuff 1 with the largest uncertainty being the effect of the early thermal history of the tuff dissolution rates based on pore water sr isotopic data were calculated by treating percolation flux parametrically and vary from 10 15 to 10 16 mol s 1 kg tuff 1 for percolation fluxes of 15 mm a 1 and 1 mm a 1 respectively reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a 1 or less the calculated feldspar dissolution rates are low relative to other measured field based feldspar dissolution rates possibly due to the age 12 8 ma of the unsaturated system at yucca mountain because oxidizing and organic poor conditions limit biological activity and or because elevated silica concentrations in the pore waters 50 mg l 1 may inhibit feldspar dissolution

the microstructures of perthitic alkali feldspars revealed by hydrofluoric acid etching etching of alkali feldspar cleavage fragments with hydrofluoric acid vapor followed by study of the surfaces by scanning electron microscopy sem is a simple and rapid technique for characterizing the microtextures of crypto and microperthites this technique has a number of advantages over conventional transmission electron microscopy tem including ease of sample preparation and the large areas of crystals which can be imaged alkali feldspars studied by the method can yield important information on the cooling history of igneous and metamorphic rocks fluid feldspar interactions and the morphology and microstructures of albite exsolution lamellae some of these applications are illustrated by examples of etched crypto and micro perthites from the klokken layered syenite south greenland and the shap granite north west england

resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

loki io a periodic volcano loki is the most powerful volcano in the solar system it has been observed to be in continuous though variable activity since 1979 synthesis of more than a decade of groundbased data suggests that loki eruptions are cyclic with a 540 day period application of a simple lava cooling model to temperatures in loki patera and eruption start and end times implies that brightenings are due to a resurfacing wave propagating across the patera the data are most consistent with lava lake overturn but resurfacing by lava flows cannot be ruled out a porosity gradient in the lake crust could cause lava lake overturn to occur periodically on the timescale observed

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

magnetic remote sensing of europa s ocean tides abstract recent analyses of galileo magnetometer and gravity data justifies approximations that allow estimates of the magnetic fields generated by europa s ocean tides to be made even though some of the ocean parameters that would generally be required are unavailable we show solutions for the magnetic fields generated by published estimates of ocean tides on europa and provide simple scaling formulas that can be used to estimate the magnetic field amplitudes for other choices for the ocean tidal state because of the distinguished spatial temporal form of these fields it is expected that europa s ocean tides can be inferred from remote magnetic sensing by an orbiter of sufficient duration

observation of primitive clay precursors during microcline weathering high resolution transmission electron microscopy of clay formation on microcline has revealed a poorly ordered hydrated silicate phase with an ultrathin 200 250 a circular form which occurs on the feldspar surface and appears to represent the first phase before the development of normal crystalline clays probe analysis at ca 100 a intervals reveals that during the formation of this material the feldspar loses silicon potassium and aluminium while the intermediate incorporates iron this primitive structure may result from rearrangement of the feldspar framework following the potassium hydrogen ion exchange process involved in weathering

nanotunnels and pull aparts defects of exsolution lamellae in alkali feldspars we have studied defects associated with flat lens shaped perthitic albite lamellae in alkali feldspars using sem and tem in orthoclase phenocrysts from the shap granite cumbria nw england bulk composition or 70 20 ab 29 05 an 0 85 no dislocations were found even in optically fresh parts of grains instead dissolution inferred to be localized on edge dislocation loops has created tiny nanotunnels typically t effect of the 1 an in the feldspars is taken into account for commencement of coherent exsolution the orientation of the pericline twins was fixed shortly after coherent exsolution began previous work has indicated that edge dislocations would start to form during cooling at 400 c so that nanotunnels form at still lower t dry heating experiments were carried out to establish the stability of the defects and the homogenization behavior of the exsolution lamellae na k exchange is rapid on heating above the coherent solvus and chemical homogenization of lamellae is complete after 24 h at 700 c in contrast nanotunnels persist for 148 h at 1000 c and 5748 h at 700 c below the coherent solvus exsolution lamellae thin on heating leaving nanotunnels stranded in the orthoclase matrix microtextures related to si al ordering patterns in the framework such as albite twins are not eliminated forming ghost like lamellar strain patterns in chemically homogeneous feldspar the presence of nanotunnels in optically fresh alkali feldspars shows that not only granites but also granulite facies rocks have been pervasively affected by fluids at low t both nanotunnels and pull aparts have important implications for feldspar reactivity in the upper crust for 18 o exchange and for transport of 40 ar both in nature and in laboratory step heating

ocean driven heating of europa s icy shell at low latitudes on jupiter s icy moon europa enigmatic chaos terrain where the icy crust is cut by a jumble of ridges and cracks occurs most commonly at lower latitudes simulations of convection in the ocean underlying europa s icy crust suggest that ocean dynamics can control an enhanced flow of heat to europa s equatorial surface and hence geological activity

tem and sfm of exsolution and twinning in an alkali feldspar transmission electron microscopy tem reveals exsolution lamellae in a cryptoperthite their spacing results in a greenish yellow iridescent color high resolution tem images show that the boundaries between ab rich and or rich lamellae are semi coherent along the b axis scanning force microscopy sfm of a 001 cleavage surface reveals exsolution lamellae wave like 001 surfaces of the ab rich lamellae and surface steps with heights of 6 6 and 3 a the wave like 001 surfaces of albite twin lamellae may result from surface relaxation surface height differences between ab and or rich lamellae in some areas indicate a semi coherent boundary along the c axis

thermal equilibrium states of europa s ice shell implications for internal ocean thickness and surface heat flow abstract ice shell thickness and ocean depth are calculated for steady state models of tidal dissipation in europa s ice shell using the present day values of the orbital elements the tidal dissipation rate is obtained using a viscoelastic maxwell rheology for the ice the viscosity of which has been varied over a wide range and is found to strongly increase if an inviscid internal ocean is present to determine steady state values the tidal dissipation rate is equated to the heat transfer rate through the ice shell calculated from a parameterized model of convective heat transfer or from a thermal conduction model if the ice layer is found to be stable against convection although high dissipation rates and heat fluxes of up to 300 mwm 2 are in principle possible for europa these values are unrealistic because the states for which they are obtained are thermodynamically unstable equilibrium models have surface heat flows around 20 mwm 2 and ice layer thicknesses around 30 km which is significantly less than the total thickness of the h2o layer these results support models of europa with ice shells a few tens of kilometers thick and around 100 km thick subsurface oceans

origins of the surface roughness of unweathered alkali feldspar grains abstract the origins of surface roughness of powdered feldspar grains the ratio of the total surface area quantified by gas adsorption to the surface area estimated by assuming an average grain geometry has been investigated by a detailed study of alkali feldspars from a range of igneous rocks and from pegmatites the of 125 63 m powders of ten different feldspar samples ranges from 5 16 22 00 and correlates well with mineral microtexture powders of feldspars which are homogeneous or have straight lamellar exsolution microtextures yield mean values of 5 59 whereas powders of vein macroperthites give a mean of 6 64 and powders of braid macroperthites yield mean values of 12 15 microtexture influences by partly controlling the manner in which feldspar grains break during grinding and this affects the frequency of steps on grain surfaces feldspars which are homogeneous or have straight lamellar exsolution microtextures break to produce a relatively high proportion of grains with smooth step poor external surfaces whereas vein macroperthites and braid microperthites break to produce grains with much rougher step rich surfaces microtexture is able to influence style of breakage because the presence size and crystallographic orientation of exsolution lamellae has a significant influence on the trajectories of fractures propagating through grains as they fragment during grinding we found little correlation between internal surface area due to micropores expressed as either microporosity or mean perimeter area of micropores and indicating that microporosity is a significantly less important contributor to than external surface area due to steps this conclusion is supported by an analysis of the of a number of different size fractions of two of the feldspar powders the origin of is only one part of the more important question of how closely measured surface areas are related to the proportion of grain surfaces which are reactive during experimental dissolution and natural weathering

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

deleterious reactions of aggregate with alkalis in concrete concrete in the built environment the word concrete is derived from the latin concretus compact condensed representing a conjunction of con together and the past participle of cresco to grow compare crescendo thus concrete could be liberally translated as grown solid together alluding to the consolidation of a particulate aggregate material with a cement binder of some sort concrete containing aggregate has been used in construction by the ancient greek and romans possibly as a further development of clay initially used by the assyrians and babylonians as a binder later superseded by burnt lime and gypsum by the egyptians as a construction material concrete allows architects and engineers to design a structure with only minimal constraints to its form a complicated shape requiring great effort to chisel out from a piece of stone can simply be poured in a mold and reproduced as often as desired also ex situ both the invention of ordinary portland cement opc first patented by british bricklayer joseph aspdin in 1824 and of reinforced concrete first patented by parisian gardener joseph monier in 1867 for making durable flower pots contributed to the development of mechanically stronger concrete allowing yet slimmer and taller structures to be built today concrete is the most popular building and construction material with an annual production volume exceeding 7 5 km3 or about 20 billion tonne concrete is the prime ingredient in the world s largest and most prominent structures and landmark edifices including hydropower dams e g three gorges dam yichang cn also see charlwood and solymar 1995 coastal defense works e g delta works nl telecommunication e g cn tower toronto ca office skyscrapers e g burj khalifa dubai uae theatres e g opera house sydney au hotels and casinos e g marina bay area singapore sg nuclear power plants oil and gas drilling and productions rigs e g sakhalin ru sea ports and harbors e g

tidal heating in icy satellite oceans abstract tidal heating plays a significant role in the evolution of many satellites in the outer solar system however it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source tyler tyler r h 2008 nature 456 770 772 tyler r h 2009 geophys res lett 36 doi 10 1029 2009gl038300 suggested that obliquity tides could drive large scale flow in the oceans of europa and enceladus leading to significant heating a critical unknown in this previous work is what the tidal quality factor q of such an ocean should be the corresponding tidal dissipation spans orders of magnitude depending on the value of q assumed to address this issue we adopt an approach employed in terrestrial ocean modeling where a significant portion of tidal dissipation arises due to bottom drag with the drag coefficient o 0 001 being relatively well established from numerical solutions to the shallow water equations including nonlinear bottom drag we obtain scalings for the equivalent value of q as a function of this drag coefficient in addition we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal orbital evolution models our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness using these novel scalings we calculate the ocean contribution to the overall thermal energy budgets for many of the outer solar system satellites although uncertainties such as ocean thickness and satellite obliquity remain we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid body tidal heating of known satellites triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long term thermal evolution

formation of iddingsite veins in the martian crust by centripetal replacement of olivine evidence from the nakhlite meteorite lafayette abstract the lafayette meteorite is an olivine clinopyroxenite that crystallized on mars 1300 million years ago within a lava flow or shallow sill liquid water entered this igneous rock 700 million years later to produce a suite of secondary minerals collectively called iddingsite that occur as veins within grains of augite and olivine the deuterium hydrogen ratio of water within these secondary minerals shows that the aqueous solutions were sourced from one or more near surface reservoirs several petrographically distinct types of veins can be recognised by differences in their width shape and crystallographic orientation augite and olivine both contain veins of a very fine grained hydrous fe and mg rich silicate that are 1 2 m in width and lack any preferred crystallographic orientation these narrow veins formed by cementation of pore spaces that had been opened by fracturing and probably in response to shock the subset of olivine hosted veins whose axes lie parallel to 0 0 1 have serrated walls and formed by widening of the narrow veins by interface coupled dissolution precipitation widening started by replacement of the walls of the narrow precursor veins by fe mg silicate and a crystallographic control on the trajectory of the dissolution precipitation front created micrometre scale 1 1 1 serrations the walls of many of the finely serrated veins were subsequently replaced by siderite and the solutions responsible for carbonation of olivine also partially recrystallized the fe mg silicate smectite was the last mineral to form and grew by replacement of siderite this mineralization sequence shows that lafayette was exposed to two discrete pulses of aqueous solutions the first of which formed the fe mg silicate and the second mediated replacement of vein walls by siderite and smectite the similarity in size shape and crystallographic orientation of iddingsite veins in the lafayette meteorite and in terrestrial basalts demonstrates a common microstructural control on water mineral interaction between mars and earth and indicates that prior shock deformation was not a prerequisite for aqueous alteration of the martian crust

opal a in the nakhla meteorite a tracer of ephemeral liquid water in the amazonian crust of mars the nakhlite meteorites are clinopyroxenites that are derived from a 1300 million year old sill or lava flow on mars most members of the group contain veins of iddingsite whose main component is a fine grained and hydrous fe and mg rich silicate siderite is present in the majority of veins where it straddles or cross cuts the fe mg silicate this carbonate also contains patches of ferric oxy hydroxide despite 40 years of investigation the mineralogy and origins of the fe mg silicate is poorly understood as is the paragenesis of the iddingsite veins nanometer scale analysis of fe mg silicate in the nakhla meteorite by electron and x ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal a this hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine each opal a nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine siderite crystallized subsequently and from solutions that were alkaline and reducing and replaced both the nanoparticles and olivine the fluids that formed both the opal a ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the martian atmosphere the last event recorded by the veins was alteration of the carbonate to a ferric oxy hydroxide that probably took place on mars although a terrestrial origin remains possible these results support findings from orbiter and rover based spectroscopy that opaline silica was a common product of aqueous alteration of the martian crust

denticles on chain silicate grain surfaces and their utility as indicators of weathering conditions on earth and mars abstract denticulated margins also known in older literature as sawtooth cockscomb or hacksaw terminations are a common feature of pyroxenes and amphiboles visible in optical and electron microscopes denticles are remnants of undissolved material that formerly constituted the walls between elongate etch pits the characteristic aqueous dissolution form of chain silicate minerals denticles occur widely in terrestrial near surface materials that have experienced low temperature aqueous alteration including chemically weathered regoliths soils in a variety of climatic and geomorphic settings sediments and sedimentary rocks ranges of dissolution forms and dimensions commonly tens of microns in length are identical on both pyroxenes and amphiboles in these materials denticles on terrestrial chain silicates are formed by low temperature aqueous alteration denticles on a soil mineral grain of unknown composition at the phoenix mars lander site and on terrestrial pyroxenes naturally weathered in terrestrial low temperature aqueous environments are broadly similar in size shape and orientation relationships between denticles however quantitative morphometric parameters vary among different terrestrially weathered pyroxenes and even between different images of compositionally identical pyroxenes from the same naturally weathered sample such variations are too large to allow simple identification of minerals of unknown composition from morphology alone nevertheless the overall morphological similarities are consistent with a low temperature aqueous corrosion origin of denticles at the phoenix mars lander site

oceans in the icy galilean satellites of jupiter abstract equilibrium models of heat transfer by heat conduction and thermal convection show that the three satellites of jupiter europa ganymede and callisto may have internal oceans underneath ice shells tens of kilometers to more than a hundred kilometers thick a wide range of rheology and heat transfer parameter values and present day heat production rates have been considered the rheology was cast in terms of a reference viscosity 0 calculated at the melting temperature and the rate of change a of viscosity with inverse homologous temperature the temperature dependence of the thermal conductivity k of ice i has been taken into account by calculating the average conductivity along the temperature profile heating rates are based on a chondritic radiogenic heating rate of 4 5 pw kg 1 but have been varied around this value over a wide range the phase diagrams of h2o ice i and h2o 5 wt nh3 ice have been considered the ice i models are worst case scenarios for the existence of a subsurface liquid water ocean because ice i has the highest possible melting temperature and the highest thermal conductivity of candidate ices and the assumption of equilibrium ignores the contribution to ice shell heating from deep interior cooling in the context of ice i models we find that europa is the satellite most likely to have a subsurface liquid ocean even with radiogenic heating alone the ocean is tens of kilometers thick in the nominal model if tidal heating is invoked the ocean will be much thicker and the ice shell will be a few tens of kilometers thick ganymede and callisto have frozen their oceans in the nominal ice i models but since these models represent the worst case scenario it is conceivable that these satellites also have oceans at the present time the most important factor working against the existence of subsurface oceans is contamination of the outer ice shell by rock rock increases the density and the pressure gradient and shifts the triple point of ice i to shallower depths where the temperature is likely to be lower then the triple point temperature according to present knowledge of ice phase diagrams ammonia produces one of the largest reductions of the melting temperature if we assume a bulk concentration of 5 wt ammonia we find that all the satellites have substantial oceans for a model of europa heated only by radiogenic decay the ice shell will be a few tens of kilometers thinner than in the ice i case the underlying rock mantle will limit the depth of the ocean to 80 100 km for ganymede and callisto the ice i shell on top of the h2o nh3 ocean will be around 60 to 80 km thick and the oceans may be 200 to 350 km deep previous models have suggested that efficient convection in the ice will freeze any existing ocean the present conclusions are different mainly because they are based on a parameterization of convective heat transport in fluids with strongly temperature dependent viscosity rather than a parameterization derived from constant viscosity convection models the present parameterization introduces a conductive stagnant lid at the expense of the thickness of the convecting sublayer if the latter exists at all the stagnant lid causes the temperature in the sublayer to be warmer than in a comparable constant viscosity convecting layer we have further modified the parameterization to account for the strong increase in homologous temperature and therefore decrease in viscosity with depth along an adiabat this modification causes even thicker stagnant lids and further elevated temperatures in the well mixed sublayer it is the stagnant lid and the comparatively large temperature in the sublayer that frustrates ocean freezing

tem edx study of weathered layers on the surface of volcanic glass bytownite and hypersthene in volcanic ash from sakurajima volcano japan transmission electron microscopy tem and energy dispersive x ray edx analysis were used to characterize naturally weathered layers on the surface of volcanic glass bytownite hypersthene and secondary precipitates in volcanic ash erupted from the sakurajima volcano japan tem analysis of the volcanic ash revealed sharply bounded leached layers on the surface of the volcanic glass and bytownite that were thin structureless coatings mostly 0 1 m thick edx analysis showed that the leached layer on the volcanic glass surface is preferentially depleted in si and enriched in al relative to its parent matrix whereas the leached layer on the bytownite surface is extremely depleted in al and enriched in si relative to the original bytownite matrix these chemical characteristics of the weathered layers indicate that incipient dissolution of volcanic glass and bytownite proceeded by preferential leaching of si and al respectively on the surface of hypersthene a noncrystalline weathered layer generally 0 01 m in thickness which has nearly the same composition as that of the parent matrix was observed this weathered layer was produced by precipitation of noncrystalline hydrous ferric oxide with partly developed to poorly crystallized fe si mg rich phyllosilicate the volcanic ash sample contains small amounts of noncrystalline secondary precipitates exhibiting three distinct morphologies 1 aggregates of very fine fibers 2 aggregates of fine fibers with crinkled fringes and 3 spherical forms composed of roughly curled fringes these noncrystalline precipitates are enriched in al and si and contain variable amounts of fe depending on their morphology the fe content of these materials decreases drastically in the sequence morphology 1 morphology 2 morphology 3 which is consistent with the transformation from al si and fe rich fine fibers to spherical halloysite by elimination of fe from the fibers these alterations of the volcanic ash took place in the crater of the sakurajima volcano by interaction with near neutral to weakly acidic solutions under relatively low temperature conditions

characterization of alteration textures in cretaceous oceanic crust pillow lava from the n atlantic dsdp hole 418a by spatially resolved spectroscopy abstract the habit mineralogy crystallography and fe speciation of tubular and granular alteration textures in basaltic glass recovered from dsdp hole 418a which have previously been associated with biologically mediated alteration were investigated using an integrated suite of microscopic and spectroscopic approaches in order to shine light on their formation and mineralization history two different analytical approaches were used 1 micro scale investigations with conventional petrographic optical microcopy and microscale x ray fluorescence mapping and x ray absorption spectroscopy and 2 nano scale analyses with fib focused ion beam milling to prepare cross sections for tem transmission electron microscopy eels electron energy loss spectroscopy and stxm scanning transmission electron microscopy analyses the integrated data show that tubular and granular textures are similar in chemical mineralogical and structural habit both granular and tubular alteration textures show a marked transition from ferrous iron in the glass matrix to ferric iron in the textures granular and tubular textures are filled with sheet silicates of similar chemistry and both exhibit thin amorphous alteration rims 10 20 nm wide the alteration rims are typically depleted in ca and fe ca is enriched at the contact between the secondary mineralization and the alteration rims whereas fe is enriched throughout the alteration features and is mainly present as fe iii in contrast to fe ii in the host glass carbon is enriched only in a few areas and could possibly be of organic origin but is not bound in carbonate the mineralization of the features follows the sequence dissolution of the glass formation of a leached amorphous rim mineralizing the cavities by smectide type clays and subsequently congruent growing of the texture diameter by diffusing of the elements through the alteration layer none of the features could be linked solely to a biogenic origin and hence the biogenicity of the textures can neither be refuted nor supported by this micro and nano scale data set

microtextural controls of diagenetic alteration of detrital alkali feldspars a case study of the shap conglomerate lower carboniferous northwest england abstract the diagenetic alteration of detrital alkali feldspar grains in the lower carboniferous shap conglomerate which were derived from the nearby lower devonian shap granite was strongly influenced by their pre diagenetic microtextures alkali feldspars collected from a working quarry in the shap granite are perthites composed of two types of microtextures primary igneous and deuterically altered primary igneous microtextures which formed during early cooling of the pluton are composed of albite exsolution lamellae in tweed orthoclase small lamellae platelets form cryptoperthites whereas larger lamellae films form microperthites albite platelets have coherent interfaces with orthoclase i e the crystal structure is strained but continuous across the interface of the exsolution lamellae whereas larger films are semicoherent i e dislocations have formed to relieve strain at the exsolution interface deuteric alteration leads to the development of micropore rich veins composed of discrete subgrains of albite and microcline referred to as patch perthites which cut the cryptoperthites and microperthites these veins formed during fluid feldspar interaction within the granite in the later stages of igneous cooling subgrains within these veins are semicoherent or are incoherent i e there is no continuity in crystal structure across the subgrain boundary during diagenesis of shap granite derived alkali feldspars in the shap conglomerate the semicoherent and incoherent albite in microperthites and patch perthites was selectively dissolved or replaced by microcline whereas coherent albite platelets in cryptoperthites remained largely unaltered this diagenetic history reflects an interplay between two main determinants of alteration i the nature of the pore fluids which resulted in albite rich feldspar being more heavily altered than orthoclase rich feldspar and ii the coherency of interfaces which determined the specific albite rich feldspar microtextures that were affected fluid feldspar interaction was favored at semicoherent and incoherent interfaces owing to their high surface and strain energies release of energy stored at such interfaces is also the major intragranular driving force of deuteric alteration of alkali feldspars in cooling igneous rocks in general as a result petrographically and geochemically similar microtextures may result from both deuteric and diagenetic alteration and care must be taken to discriminate between them results of this study underscore the importance of understanding the nature of alkali feldspars in igneous and metamorphic rocks for an accurate interpretation of their subsequent diagenetic history

the durability of rocks developing a test of rock resistance to chemical weathering dissolution rates of 39 rock forming minerals were determined at 20 c and 100 c and different ph values using experimental set ups which achieve near zero cation concentrations weathering rates in nature for rock above surface were estimated from data in this study and data in the literature extraction in a soxhlet extractor with boiling 2 5 m acetic acid causes an acceleration of such estimated natural weathering rates by a factor of 0 25 103 to 7 104 for nearly all important rock forming minerals including the carbonates the applicability of such a comparative test for rock resistance to chemical weathering was corroborated by testing 32 different rocks and building stones run times of only one to four days were needed for a reliable result

characterization of mineral surfaces using fib and tem a case study of naturally weathered alkali feldspars using a focused ion beam fib instrument electron transparent samples termed foils have been cut from the naturally weathered surfaces of perthitic alkali feldspars recovered from soils overlying the shap granite northwest england characterization of these foils by transmission electron microscopy tem has enabled determination of the crystallinity and chemical composition of near surface regions of the feldspar and an assessment of the influence of intragranular microtextures on the microtopography of grain surfaces and development of etch pits damage accompanying implantation of the 30 kv ga ions used for imaging and deposition of protective platinum prior to ion milling creates amorphous layers beneath outer grain surfaces but can be overcome by coating grains with 85 nm of gold before fib work the sidewalls of the foil and feldspar surrounding original voids are also partially amorphized during later stages of ion milling no evidence was found for the presence of amorphous or crystalline weathering products or amorphous leached layers immediately beneath outer grain surfaces the absence of a leached layer indicates that chemical weathering of feldspar in the shap soils is stoichiometric or if non stoichiometric either the layer is too thin to resolve by the tem techniques used i e similar to 2 5 nm or an insufficient proportion of ions have been leached from near surface regions so that feldspar crystallinity is maintained no evidence was found for any difference in the mechanisms of weathering where a microbial filament rests on the feldspar surface sub micrometer sized steps on the grain surface have formed where subgrains and exsolution lamellae have influenced the propagation of fractures during physical weathering whereas finer scale corrugations form due to compositional or strain related differences in dissolution rates of albite platelets and enclosing tweed orthoclase with progressive weathering etch pits that initiated at the grain surface extend into grain interiors as etch tubes by exploiting preexisting networks of nanopores that formed during the igneous history of the grain the combination of fib and tem techniques is an especially powerful way of exploring mechanisms of weathering within the internal zone beneath outer grain surfaces but results must be interpreted with caution owing to the ease with which artifacts can be created by the high energy ion and electron beams used in the preparation and characterization of the foils

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

tidal dynamical considerations constrain the state of an ocean on enceladus abstract in previous work solutions to the non dissipative laplace tidal equations lte were used to provide bounds on the heat generated by the response of a subsurface ocean on enceladus to an obliquity component of tidal forces here we improve these bounds using solutions from the lte with a generic dissipation term explicitly added we find solutions for a wider range of ocean tidal responses that include both unstratified barotropic and stratified baroclinic flow responses to obliquity as well as eccentricity components of the tidal forces we consolidate the results in three ocean tidal scenarios on enceladus that can explain the high heat fluxes 7 mw m 2 globally averaged inferred from measurements by the cassini spacecraft 1 a deep 1 50 km barotropic ocean responding to obliquity tidal forces where obliquity is at least 0 1 2 a shallow 360 m barotropic ocean responding to eccentricity tidal forces 3 a stratified baroclinic ocean responding to eccentricity tidal forces where the density weighted equivalent depth typically much smaller than the ocean s physical depth is near 360 m the ocean is assumed to be global but extensions for a semi global case are also described a more general result which is independent of the specific scenarios proposed is that an ocean attempting to freeze with an associated decrease in its liquid depth which affects the ocean s dynamical response to the tidal forcing must first pass through resonant configurations with a greatly increased generation of ocean tidal heat exceeding 1 w m 2 to 1 kw m 2 that would act to halt further freezing and stagnate the ocean state in this configuration so long as there is still orbital energy to provide the tidal forces with an additional assumption that the ocean has evolved from a more energetic state where the depth of the liquid ocean was greater we obtain the three scenarios proposed

biogenic iron oxyhydroxide formation at mid ocean ridge hydrothermal vents juan de fuca ridge here we examine fe speciation within fe encrusted biofilms formed during 2 month seafloor incubations of sulfide mineral assemblages at the main endeavor segment of the juan de fuca ridge the biofilms were distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic fe oxidizing microorganisms our objectives were to determine the form of biofilm associated fe and identify the sulfide minerals associated with microbial growth we used micro focused synchrotron radiation x ray fluorescence mapping mu xrf x ray absorption spectroscopy mu exafs and x ray diffraction mu xrd in conjunction with focused ion beam fib sectioning and highresolution transmission electron microscopy hrtem the chemical and mineralogical composition of an fe encrusted biofilm was queried at different spatial scales and the spatial relationship between primary sulfide and secondary oxyhydroxide minerals was resolved the fe encrusted biofilms formed preferentially at pyrrhotite rich fe1 xs 0 x 0 2 regions of the incubated chimney sulfide at the nanometer spatial scale particles within the biofilm exhibiting lattice fringing and diffraction patterns consistent with 2 line ferrihydrite were identified infrequently at the micron spatial scale fe mu exafs spectroscopy and mu xrd measurements indicate that the dominant form of biofilm fe is a short range ordered fe oxyhydroxide characterized by pervasive edge sharing fe o6 octahedral linkages double corner sharing fe o6 linkages which are common to fe oxyhydroxide mineral structures of 2 line ferrihydrite 6 line ferrihydrite and goethite were not detected in the biogenic iron oxyhydroxide bio the suspended development of the bio mineral structure is consistent with fe iii hydrolysis and polymerization in the presence of high concentrations of fe complexing ligands we hypothesize that microbiologically produced fe complexing ligands may play critical roles in both the delivery of fe ii to oxidases and the limited fe iii oxyhydroxide crystallinity observed within the biofilm our research provides insight into the structure and formation of naturally occurring microbiologically produced fe oxyhydroxide minerals in the deep sea we describe the initiation of microbial seafloor weathering and the morphological and mineralogical signals that result from that process our observations provide a starting point from which progressively older and more extensively weathered seafloor sulfide minerals may be examined with the ultimate goal of improved interpretation of ancient microbial processes and associated biological signatures

evidence of a global magma ocean in io s interior extensive volcanism and high temperature lavas hint at a global magma reservoir in io but no direct evidence has been available we exploited jupiter s rotating magnetic field as a sounding signal and show that the magnetometer data collected by the galileo spacecraft near io provide evidence of electromagnetic induction from a global conducting layer we demonstrate that a completely solid mantle provides insufficient response to explain the magnetometer observations but a global subsurface magma layer with a thickness of over 50 kilometers and a rock melt fraction of 20 or more is fully consistent with the observations we also place a stronger upper limit of about 110 nanoteslas surface equatorial field on the dynamo dipolar field generated inside io

crustal control of dissipative ocean tides in enceladus and other icy moons abstract could tidal dissipation within enceladus subsurface ocean account for the observed heat flow earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust i propose here the first model of dissipative tides in a subsurface ocean by combining the laplace tidal equations with the membrane approach for the first time it is possible to compute tidal dissipation rates within the crust ocean and mantle in one go i show that oceanic dissipation is strongly reduced by the crustal constraint and thus contributes little to enceladus present heat budget tidal resonances could have played a role in a forming or freezing ocean less than 100 m deep the model is general it applies to all icy satellites with a thin crust and a shallow ocean scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean if the ocean has low viscosity the westward obliquity tide does not move the crust therefore crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

nonlinear tidal dissipation in the subsurface oceans of enceladus and other icy satellites abstract subsurface ocean tides act as a mechanism to dissipate tidal energy in icy satellite interiors we numerically model the effect of an ice shell on ocean tides using non linear bottom drag for the first time we demonstrate that subsurface oceans experience tidal pressurization due to the confining nature of the ice shell and find that enceladus eccentricity forcing can generate up to 2 2 kpa of pressure excess at the ocean surface existing free surface oceanic energy dissipation scaling laws are extended to subsurface oceans and are benchmarked against our numerical results to within 10 we show that for the large bodies ganymede europa and titan an ice shell increases eccentricity tidal heating due to self gravity whereas the shell s suppressive mechanical forcing reduces eccentricity tide dissipation on enceladus and dione by several orders of magnitude due to their high effective rigidities in contrast the ice shell enhances obliquity forced dissipation in all satellites investigated except triton because the largely divergence free ocean response is unaffected by the shell s rigidity but is still enhanced by self gravity we conclude that the fundamental difference in ocean response to obliquity and eccentricity forcing combined with self gravity results in increased obliquity heating and suppressed eccentricity heating in small satellites for large satellites with low effective rigidities the type of ocean response is less important because the shell s mechanical forcing has little impact on the flow whereas self gravity will enhance the response and consequently dissipation regardless of the forcing overall obliquity tides are likely to dominate the tidal heating budget of icy satellite oceans remaining the most prominent source of fluid dissipation in subsurface barotropic ocean tides

tidal resonance in icy satellites with subsurface oceans tidal dissipation is a major heat source for the icy satellites of the giant planets several icy satellites likely possess a subsurface ocean underneath an ice shell previous studies of tidal dissipation on icy satellites however have either assumed a static ocean or ignored the effect of the ice lid on subsurface ocean dynamics in this study we examine inertial effects on tidal deformation of satellites with a dynamic ocean overlain by an ice lid based on viscoelasto gravitational theory although ocean dynamics is treated in a simplified fashion we find a resonant configuration when the phase velocity of ocean gravity waves is similar to that of the tidal bulge this condition is achieved when a subsurface ocean is thin 1 km the enhanced deformation increased h2 and k2 love numbers near the resonant configuration would lead to enhanced tidal heating in the solid lid a static ocean formulation gives an accurate result only if the ocean thickness is much larger than the resonant thickness the resonant configuration strongly depends on the properties of the shell demonstrating the importance of the presence of a shell on tidal dissipation

microtextural controls of weathering of perthitic alkali feldspars the relationship between the microtexture and dissolution behaviour of fresh hf acid etched and naturally weathered alkali feldspar phenocrysts from the lower devonian shap granite has been investigated by sem and tem a novel resin impregnation technique has revealed the three dimensional shape and interconnectivity of etch pits beneath the weathered crystal surface further electron microscope work suggests that shap phenocrysts are representative of the alkali feldspar in the protolith of many soils fresh and unweathered shap feldspars have a complex microtexture comprising areas of pristine cryptoperthite and lamellar microperthite cross cut by volumes of microporous altered feldspar or patch perthites cryptoperthites are made up of 75 nm wide albite films the platelets are coherent but albite films have numerous edge dislocations along their interface with orthoclase 001 and 010 cleavage surfaces intersect 2 3 edge dislocations m2 in three dimensions these edge dislocations form an orthogonal net in the murchison plane of easy fracture close to 601 patch perthites are irregular semicoherent to incoherent intergrowths of albite and irregular microcline subgrains with 0 65 0 70 sub m to m sized pores m2 microporous patch perthites form by dissolution reprecipitation reactions with magmatic or hydrothermal fluids and pores are present before the alkali feldspars enter the weathering regime dissolution of shap feldspars during natural weathering and laboratory acid etching is controlled by their microtexture especially by dislocations and exsolution lamellae the core and strain energy associated with dislocation outcrops on 001 and 010 cleavage surfaces promotes rapid dissolution at those sites and formation of nn sized etch pits after 30 s of laboratory etching with hf acid vapour with progressive hf etching crystallographically controlled differences in the reactivity of etch pit walls cause them to expand more rapidly into orthoclase than albite naturally weathered feldspars were collected from the glacial erratic boulders fine gravels surrounding exposed granite surfaces and from peat soil overlying the granite during natural weathering etch pits on microperthites enlarge almost exclusively by dissolution of albite and resin casts demonstrate that they can penetrate 15 m below the cleavage surface forming an interconnecting ladder like grid of submicrometer wide channels in the murchison plane coherent albite platelets and volumes of albite between dislocations in films dissolve uniformly but faster than orthoclase this is probably because the albite lamellae have significant elastic coherency strain but this is much less per unit volume of albite than the core and strain energy associated with edge dislocations patch perthites etch in hf vapour and weather rapidly in nature to produce a honeycomb like texture of interconnecting nanometer to micrometer sized pits which nucleate at preexisting micropores or incoherent subgrain boundaries the size and density of etch pits on microperthite surfaces which is determined by rates of growth and coalescence may be a useful progress variable for natural and experimental dissolution all alkali feldspars are highly heterogeneous materials whose chemical composition and microtexture can vary on a submicrometer scale these microtextures are critical variables with regard to the origin of surface roughness of fresh and weathered grains the controls on absolute dissolution rates and why they commonly change over time the nonlinear variation of dissolution rate with grain size the ratio of alkali ions released into solution and disparities between laboratory dissolution rates and those observed in the field

dissolution of olivine during natural weathering abstract naturally weathered olivine occurring as phenocrysts in hawai ian volcanic rocks from several volcanic centers and regolith outcrop settings and as tectonized olivines from several metadunite bodies in the southern appalachian blue ridge are all similarly corroded by natural weathering conical funnel shaped etch pits occur as individual pits base to base pairs of cone shaped pits or en echelon arrays etch pit shapes and orientations in the smallest etch pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering etch pits occur in samples with chemical and or mineralogical evidence of weathering and or are associated with or proximal or directly connected to fractures or exposed outcrop surface and therefore are formed by weathering and not inherited from pre weathering aqueous alteration e g serpentinization iddingsitization of these parent rocks many etch pits are devoid of weathering products natural weathering of olivine is surface reaction limited similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization recrystallization history eruption weathering exposure ages of the olivine s host rock and the local regolith history

thin elastic shells with variable thickness for lithospheric flexure of one plate planets summary planetary topography can either be modelled as a load supported by the lithosphere or as a dynamic effect due to lithospheric flexure caused by mantle convection in both cases the response of the lithosphere to external forces can be calculated with the theory of thin elastic plates or shells on one plate planets the spherical geometry of the lithospheric shell plays an important role in the flexure mechanism so far the equations governing the deformations and stresses of a spherical shell have only been derived under the assumption of a shell of constant thickness however local studies of gravity and topography data suggest large variations in the thickness of the lithosphere in this paper we obtain the scalar flexure equations governing the deformations of a thin spherical shell with variable thickness or variable young s modulus the resulting equations can be solved in succession except for a system of two simultaneous equations the solutions of which are the transverse deflection and an associated stress function in order to include bottom loading generated by mantle convection we extend the method of stress functions to include loads with a toroidal tangential component we further show that toroidal tangential displacement always occurs if the shell thickness varies even in the absence of toroidal loads we finally prove that the degree one harmonic components of the transverse deflection and of the toroidal tangential displacement are independent of the elastic properties of the shell and are associated with translational and rotational freedom while being constrained by the static assumption degree one loads can deform the shell and generate stresses the flexure equations for a shell of variable thickness are useful not only for the prediction of the gravity signal in local admittance studies but also for the construction of stress maps in tectonic analysis

focussed ion beam transmission electron microscopy applications in ore mineralogy bridging micro and nanoscale observations abstract focussed ion beam scanning electron microscopy fib sem is a relatively new analytical tool that has been little applied to problems of ore genesis the technique enables high resolution cross section imaging and can be used to prepare thinned foils for study by transmission electron microscopy tem fib sem methods applied to sulphides and related compounds represent an in situ approach for sample characterisation and thus provides for crystal chemical data that can be placed into the geological context of a given ore deposit we present four study cases these deal with minor element incorporation and release in zns intergrowths and replacement among cu fe sulphides fabrics in au bearing as free pyrite and symplectites of bi sulphosalts within galena the data is discussed in the context of polytypism and planar defects for minor element incorporation and release superstructure ordering and formation of fine particles 100 2500 nm or nanoparticles

the role of intragranular microtextures and microstructures in chemical and mechanical weathering direct comparisons of experimentally and naturally weathered alkali feldspars abstract electron microscopic observations of alkali feldspars from soils show that intragranular microtextures such as exsolution lamellae and microstructures primarily dislocations are both highly significant determinants of the weathering behaviour of these minerals in particular strained structure around intersecting edge dislocations in the plane of exsolution lamellae 6 01 dissolves at a rate which is orders of magnitude greater than unstrained feldspar producing a mesh of intersecting etch tubes extending 5 10 3 cm into the crystal as a result dissolution at dislocations is the major source of solutes during initial stages of chemical weathering in the field with progressive chemical weathering the most highly reactive feldspar is consumed by growth and coalescence of etch tubes but outer parts of the grain are physically weakened leading to mechanical flaking that increases available surface area and exposes further reactive sites in contrast previous dissolution experiments and microscopy of reacted surfaces have shown little or no correlation between dissolution rate and dislocation density and few visible signs of dissolution at particularly reactive sites to resolve the apparent discrepancy between field and laboratory behaviour we have carried out flow through dissolution experiments using ph 2 hcl at 25 c on three alkali feldspars with carefully characterized intragranular microtextures and microstructures these alkali feldspars were 1 eifel sanidine an alkali feldspar that has no microtextures at the tem scale and a low dislocation density 2 3 108 cm 2 and 3 naturally weathered alkali feldspars also from the shap granite which have the same microtextures as unweathered shap granite alkali feldspars but because they have been weathered have a lower density of dissolution reactive dislocations exposed on grain surfaces

influence of amorphous silica layer formation on the dissolution rate of olivine at 90 c and elevated pco2 for mitigating against rising levels of atmospheric co2 carbonation of m2 bearing silicates has been proposed as a possible option for sequestering co2 over long time spans due to its rapid far from equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks olivine has been suggested as a potentially good candidate for achieving this goal although the efficacy of the carbonation reaction still needs to be assessed with this as a goal the present study aims at measuring the carbonation rate of san carlos olivine in batch experiments at 90 c and pco2 of 20 and 25 mpa when the reaction was initiated in pure water the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica this yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude in long term 45 days carbonation experiments with a high surface area to solution volume ratio sa v 24 600 m 1 the final composition of the solution was close to equilibrium with respect to sio2 am independent of the initial concentration of dissolved salts nacl and naclo4 ranging between 0 and 1 m and with an aqueous mg si ratio close to that of olivine no secondary phase other than a ubiquitous thin 40 nm si rich amorphous layer was observed these results are at odds with classic kinetic modeling of the process due to experimental uncertainties it was not possible to determine precisely the dissolution rate of olivine after 45 days but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted taken together these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine an effect which has yet to be quantified and incorporated into standard reactive transport codes

do tidally generated inertial waves heat the subsurface oceans of europa and enceladus some of the moons of the outer solar system harbour subsurface liquid oceans tidal dissipation plays an important role in preventing these oceans from freezing in the past most studies considered only tidal dissipation in the solid layers of these bodies rock and ice recently new studies considering tidal dissipation in the oceans of these moons have appeared all of them make use of the shallow water approximation however the use of this approximation might not be adequate here we consider the linear non hydrostatic three dimensional response of these oceans to tidal forcing with the full coriolis force to do so we consider an ocean of homogeneous density contained within a perfectly spherical shell and neglect the effect of the ice shell we force the ocean with a time changing tidal potential and observe patterns of periodic inertial waves that take energy from the global tidal forcing and focus it along thin shear layers that propagate in the fluid we focus on europa and enceladus showing that inertial waves result in fluid flows of significant amplitude a few cm s nevertheless we find that under the previously mentioned assumptions tidal dissipation due to inertial waves is several orders of magnitude smaller than europa s radiogenic heating and enceladus observed heat flux finally we propose additional dissipation mechanisms that might play a relevant role in europa and enceladus and could be further investigated

subsurface oceans on europa and callisto constraints from galileo magnetometer observations magnetic field perturbations measured during galileo flybys of europa and callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field these fields are close to those expected for perfectly conducting moons we investigate the implications of these observations for the electrical structure of the moon s interiors using a simple shell model it is found that europa and callisto must possess regions where the conductivity exceeds 0 06 and 0 02 s m at a depth of less than 200 and 300 km below the surface respectively this conductivity is unattainable in ice or silicates unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice an ionosphere or a cloud of pick up ions are probably also insufficiently conductive global earth like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick c 2000 academic press

can libration maintain enceladus s ocean abstract the process by which the subsurface ocean on enceladus is heated remains a puzzle tidal interaction with saturn and dione is the leading candidate but whether the dominant heating occurs in the solid core ice crust or in the ocean itself is an outstanding question here we consider the driving effect of the longitudinal libration of the ice crust on the subsurface ocean and argue that the flow response should be turbulent even in the most benign situation of a smooth spherical ice shell when the motion of the boundary is only transmitted viscously a rigorous upper bound on the turbulent viscous dissipation rate is then derived and used to argue that libration should be potent enough to explain the observed heat flux emanating out of enceladus when the effects of tidal distortion and roughness of the ice crust are included

ocean tidal heating in icy satellites with solid shells abstract as a long term energy source tidal heating in subsurface oceans of icy satellites can influence their thermal rotational and orbital evolution and the sustainability of oceans we present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness the stabilizing effect of an overlying shell damps ocean tides reducing tidal heating this effect is more pronounced on enceladus than on europa because the effective rigidity on a small body like enceladus is larger for the range of likely shell and ocean thicknesses of enceladus and europa the thin shell approximation of beuthe 2016 is generally accurate to less than about 4 explaining enceladus endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints the time averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell with higher dissipation near the equator and poles for eccentricity and obliquity forcing respectively this can lead to unique horizontal shell thickness variations if the shell is conductive the surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response for europa and enceladus eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values despite the small obliquity values obliquity forcing generally produces larger phase lags due to the generation of rossby haurwitz waves if europa s shell and ocean are respectively 10 and 100 km thick the tide amplitude and phase lag are 26 5 m and

the deleterious effect of secondary phases on olivine carbonation yield insight from time resolved aqueous fluid sampling and fib tem characterization geological storage of co2 in mafic and ultramafic rocks relies on the dissolution of their silicate components followed by the precipitation of carbonates the overall process being commonly referred to as carbonation to gain a better understanding of the rate and yield controlling factors of mineral carbonation three batch experiments were conducted in co2 saturated water at a 90 c b 120 c and c 170 c respectively with citrate ligands added to the 90 c experiment in a ti reactor at pco2 280 bar using san carlos olivine fo88 as a model mineral of ultra mafic environments those physicochemical conditions were purposely chosen so as to promote the dissolution rate of olivine a at 90 c 40 wt of olivine were dissolved within 3 weeks a result which suggests that the passivation barrier evidenced in previous studies carried out in citrate free media had been overcome however while saturation with respect to magnesite was overstepped in this experiment the carbonation yield remained below 1 wt which we attributed to the slow kinetics of magnesite precipitation b at 120 c the concentration of mg and si monitored by aqueous fluid sampling reached an apparent plateau for over 4 weeks at conditions close to saturation with respect to amorphous silica and with fe concentration being below the detection limit a resumption of the dissolution process was subsequently observed while the concentration of fe suddenly increased in solution the concentration plateau was attributed either to the formation of a protective si fe iii layer or to the occurrence of fe iii phases clogging the porosity of a secondary silica layer the resumption of olivine dissolution was ascribed to the increasingly reducing conditions that led to the breakdown of the protective phases this late resumption led to a carbonation yield slightly above 2 wt c at 170 c fe was incorporated into a presumably permeable fe rich phyllosilicate layer so that the dissolution process was likely less affected by such an interfacial layer nevertheless carbonate minerals still formed in low quantity 6 wt while other amorphous phases represented the main sink for mg cations overall this study emphasizes that achieving carbonation reactions in reducing environments and circum neutral aqueous solutions may represent a necessary requirement for making olivine carbonation a viable process in these temperature ranges it also insists on the importance of transitory phases which form both at the fluid silicate interface and from the bulk solution while they may not appear in overall carbonation equations or in thermodynamic databases arguably they can drive the global kinetics of olivine dissolution and its transformation towards magnesite

uplift soil pipe interaction in granular soil soil pipeline interaction for uplift in granular soil is evaluated by means of a two dimensional finite element fe continuum model with a mohr coulomb mc yield surface for peak strength a strain softening relationship tied to critical void conditions and an equivalent modulus that is consistent with soil deformation at maximum uplift resistance the model accounts for soil migration beneath the pipe through fe mesh adjustment coordinated with upward pipe displacement a systematic comparison of model results with multiple full scale test measurements of pipe in dry sand show excellent agreement both with respect to maximum force and force displacement relationships including post peak performance the relationship between peak upward force and pipe depth is developed for various sand densities all of which show maximum force at a depth to diameter ratio of 30 hyperbolic and bilinear models for vertical upward force versus displacement are presented the analytical approach described in this pape

time dependent feldspar dissolution rates resulting from surface passivation experimental evidence and geochemical implications abstract to which extent does the apparent negative correlation reported between silicate weathering rates and time result from the spontaneous physicochemical evolution of the fluid mineral interface to address this question labradorite powders inserted in nylon bags and buried into two different topsoil horizons for four years were subjected to nanoscale characterization of their near surface regions using transmission electron microscopy these characterizations revealed the occurrence of a 30 to 70 nm thick discontinuous amorphous silica rich surface layer assl with a sharp crystalline amorphous interfacial boundary between labradorite and the layer dissolution experiments conducted in mixed flow reactors at ambient temperature and acidic ph demonstrated that the reactivity of fresh and naturally weathered labradorite powders decreased with time with the dissolution rate of fresh powders remaining systematically greater than that of naturally weathered powders all over the duration of the experiments 3 weeks in addition the dissolution rate of all labradorite batches was noticeably lower in solutions containing elevated concentrations of sio2 aq which we attributed to the passivating effect of the assls this suggestion was confirmed with a simple passivation model which enabled to capture i the greater reactivity of fresh powders ii the dependence of the dissolution rate on sio2 aq iii the gradual decline of powder dissolution rate with time and iv the discontinuous occurrence of assls the model further supports that surface passivation could be one of the non exclusive mechanisms that could account for the so called kinetic field lab discrepancy the geochemical implications of the recognition of the passivation mechanism are broad ranging from the need to revisit the kinetic rate laws implemented in geochemical codes to the questioning of the formalism used for determining weathering rates from the study of u series nuclides in soils and weathering profiles

aragonite in the murray cm2 carbonaceous chondrite implications for parent body compaction and aqueous alteration the matrix of the cm2 carbonaceous chondrite murray contains rare micrometer sized prismatic crystals of aragonite that formed during late stage parent body aqueous alteration the aragonite was identified by x ray microanalysis coupled with electron backscatter diffraction ebsd tem selected area electron diffraction and cathodoluminescence spectroscopy the sixteen crystals found all occur within loose and elongate submillimeter sized clusters and one cluster is present in each of the two thin sections studied orientation determinations using ebsd show that the c axes of aragonite crystals within each cluster lie roughly in a plane itself aligned approximately parallel to the long axis of the host cluster aragonite is inferred to have crystallized after calcite but before completion of static impact related compaction the clusters developed by growth of aragonite within films of aqueous fluids that had a relatively high mg ca ratio these fluids were focused within zones of high porosity and permeability along a weak compactional fabric in the matrix and this fabric is also likely to have influenced the orientations of aragonite crystals as they grew these results suggest that aragonite probably occurs in most of those carbonaceous chondrites that have undergone moderate degrees of parent body aqueous alteration and may provide further insights into the evolution of pore fluid compositions and volumes and the chronology of asteroidal evolution

europa s differentiated internal structure inferences from four galileo encounters radio doppler data from four encounters of the galileo spacecraft with the jovian moon europa have been used to refine models of europa s interior europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice liquid outer shell but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice liquid shell the size of a metallic core is uncertain because of its unknown composition but it could be as large as about 50 percent of europa s radius the thickness of europa s outer shell of water ice liquid must lie in the range of about 80 to 170 kilometers

a comparative analysis of potential biosignatures in basalt glass by fib tem abstract bulk analyses of fresh and altered subseafloor basalts have elucidated the large scale geochemical fluxes that result from water rock interactions which ultimately affect both seawater and mantle compositions but these analyses do not provide insights into the physical and chemical processes occurring on the scale of microorganisms micron sized tubules that may represent microbial boring into basalt glass are ubiquitous throughout the seafloor and can potentially be preserved over geological time these putative biosignatures give clues into the history of life on earth and may be significant for the search for life on other planets however their formation and mineralization are still poorly understood we have used a combination of focused ion beam fib milling and transmission electron microscopy tem to analyze the textural and geochemical characteristics of tubular alteration features from four basalt glass samples representing different sample locations collection depths and ages including one sample from the cretaceous troodos ophiolite high resolution tem imaging consistently identified platy layers of partially crystalline material infilling the tubules the lattice spacings and diffraction patterns showed that this material comprises a mix of two layer and three layer silicates closer inspection of the contact point between the tubules and the surrounding basalt glass commonly revealed a thin leached rim around the tubules electron energy loss spectroscopy mapping demonstrated that these rims are depleted in everything but si and o which implies that they are formed by a leaching process likely the incongruent dissolution of the glass during formation of the tubule the infilling material is depleted in ca and enriched in k and in most cases also enriched in fe which is consistent with their identification as fe bearing phyllosilicates these observations are consistent across the samples which implies that the processes that form and mineralize tubular glass alteration features are similar throughout the oceanic subsurface and through time

alteration of submarine basaltic glass from the ontong java plateau a stxm and tem study frequent observations of tubular to vermicular microchannels in altered basalt glass have led to increasing appreciation of a possible significant role of microbes in the low temperature alteration of seafloor basalt we have examined such microchannel alteration features at the nanoscale in basalt glass shards from the ontong java plateau using a combination of focused ion beam milling transmission electron microscopy and scanning transmission x ray microscopy three types of materials were found in ultrathin cross sections cut through the microchannels by fib milling fresh basalt glass amorphous si rich rims surrounding the microchannels and palagonite within the microchannels x ray absorption spectroscopy at the c k edge and fe l2 3 edges showed the presence of organic carbon in association with carbonates within the microchannels and partial oxidation of iron in palagonite compared with basalt glass although these observations alone cannot discriminate between a biotic or abiotic origin for the microchannels they provide new information on their mineralogical and chemical composition and thus better constrain the physical and chemical conditions prevailing during the alteration process 2007 published by elsevier b v

compositional and microtextural zoning in alkali feldspars from the shap granite and its geochemical implications alkali feldspar phenocrysts in the lower devonian shap granite are compositionally and microtexturally zoned most of each phenocryst has exsolved to form microperthite with an approximate bulk composition of or 72 ab 28 an but sub millimetre wide zones within the phenocrysts with an approximate bulk composition or 69 ab 30 an 1 have exsolved to cryptoperthite the sub optical scale of exsolution microtextures in the narrow an rich zones is due to ca al coupling which slows rates of interdiffusion during exsolution relative to an poor volumes of feldspar this form of coupled compositional microtextural zoning has not been described previously from or rich alkali feldspars using electron microscopy but we have seen other examples and predict that it is common cryptoperthite zones are of particular importance because they will have trace element and isotopic compositions least altered subsequent to growth in the magma of any microtextures in alkali feldspars and so will be the most rewarding targets for chemical analysis

microscopy study of biologically mediated alteration of natural mid oceanic ridge basalts and magnetic implications 1 microbial communities have been shown over the last few years to be a significant component of the subseafloor crustal environment however their role in the low temperature alteration of seafloor basalts remains an open question among the diversity of microorganisms that can contribute to oceanic rock weathering sulfate reducing bacteria have been suggested based on sulfur isotope studies to be major actors previous laboratory experiments conducted on basalt samples from the juan de fuca ridge incubated with model sulfate reducing bacteria for several months showed that bacterial activity can play a role in the decrease of seafloor magnetic signal in this paper we characterized alteration features at the nanoscale in one of these basalt samples in order to better understand the mechanisms of the magnetic signal decrease for that purpose we used a combination of focused ion beam milling transmission electron microscopy and scanning transmission x ray microscopy fossilized microbial cells and phyllosilicates were evidenced at the surface of the sample within the sample alteration rims mostly composed of fe and s and measuring 100 300 nm in thickness were observed around titanomagnetites crystals that bear most of the magnetic signal in contrast these features were not observed on noninoculated control samples this study offers a detailed view of the specific mineral assemblages formed in the presence of model sulfate reducing bacteria that can be looked for in the oceanic crust these observations contribute to understand the potential role of microbes in the alteration of the oceanic crust