redox and speciation micromapping using dispersive x ray absorption spectroscopy application to iron in chlorite mineral of a metamorphic rock thin section 1 the first dispersive xanes mapping is presented here the experiments have been conducted at the iron k edge on the dispersive exafs beamline of the european synchrotron radiation facility france the mapping has been performed on a polished thin section of 30 m of a natural metamorphic rock including different types of minerals because of the high x ray absorption due to the thickness of the glass sample holder 1 mm the data have been collected in the fluorescence mode using the so called turbo xafs design the effective spot size was approximately 10 10 microns and an area 390 180 microns in size was mapped improvements of the acquisition process allowed collection of each xanes spectrum in 1 5 s and with a step size of 5 microns so that 2808 spectra with full xanes information were collected then automatic procedures for data reduction and mapping reconstruction were developed using matlab the results are maps of iron content oxidation state and speciation with a 5 m spatial resolution after two dimensional deconvolution subsequent analyses of the reconstructed images provide some quantitative calibrations

μxanes study of iron redox state in serpentine during oceanic serpentinization serpentinization of ultramafic rocks at mid ocean ridges generates significant amounts of h2 ch4 and supports specific biological communities the abiotic h2 production is attributed to the reduction of h2o during serpentinization which balances oxidation of ferrous iron contained in primary minerals mainly olivines and pyroxenes to ferric iron contained in secondary minerals mainly serpentines and magnetite magnetite has thus far been considered as the sole fe3 carrier for estimating bulk h2 production notably because the valence of iron in serpentine minerals and its relationship with both magnetite abundance and serpentinization degree are usually not determined we show that the serpentine contribution to the fe and fe3 budget has a significant effect on h2 production we performed xanes analysis at the fe k edge on thin sections of peridotites with various degrees of serpentinization from odp leg 153 mark region 23 n fe3 fetot in oceanic serpentines is highly variable from 0 2 to 1 at the thin section scale and it is related non linearly to the local degree of serpentinization a typical value of 0 7 is observed above 60 serpentinization the highest values of fe3 fetot observed within or close to late veins suggest that the fe3 fetot in serpentine record the local water rock w r ratio as previously proposed from thermodynamic modeling we estimate that the w r ratio increased from 0 6 to 25 during serpentinization at mark and locally reached 100 in veins mass balance calculations combining all mineral and bulk rock analyses provide the distribution of fe and fe3 as serpentinization progresses serpentine dominates the fe3 budget of the rock over magnetite during the first 75 of serpentinization contributing up to 80 of the total fe3 at later stages serpentine contribution to the fe3 budget decreases down to 20 while magnetite formation exponentially increases iron transfer from serpentine to magnetite balances the bulk fe3 content of the rock that increases almost linearly with the advance of the reaction formation of serpentine accounts for the majority of fe3 and h2 production at early stages of serpentinization at a depth 2 km at mark where the concentration of h2 can reach more than 100 mm according to the low w r h2 production values and depths can vary from one site to another depending on the evolution of the temperature w r ratio inlet fluid composition and favored formation of serpentine vs magnetite at mark fe3 in serpentine represents 15 27 of the total fe contained in a rock serpentinized to more than 80 and accounts for 25 of the total h2 production that is estimated at 325 335 mmol kg of rock the absence of magnetite does not necessarily mean a negligible h2 production even at low t conditions 150 200 c under which the fe and fe3 richest serpentines have been observed serpentine minerals are important fe3 carrier in the altered ocean lithosphere and may affect mantle redox state while dehydrating at depth in subduction zones

petrology chemistry and origin of apollo 15 regolith breccias abstract variations in modal petrology mineral compositions and bulk compositions were determined for ten apollo 15 regolith breccias for comparison with local soils and assessment of the intrasite petrologic variability of the apollo 15 regolith based on the above criteria the breccias are of local origin and mimic the soils from the corresponding sampling stations with the exception of station 2 breccia 15205 this sample formed from an anomalous regolith and although not considered exotic to the site is not representative of the soil at the site kreep basalt and green glass components vary from trace amounts to dominant in the breccias evidence that these materials entered the regolith prior to formation of the breccias breccias from the edge of hadley rille are modally richer in highland fragments than the soils whereas at the base of hadley delta the reverse is true this is explained by the loss of material into the rille to be replaced by basalt derived material making the soils more basalt rich at the base of hadley delta highland material is accumulating and the soils are becoming more highland rich over billions of years these processes have developed differences between the present day evolving soils and fossil non evolving soils represented by the regolith breccias this shows that there has been little change in the geology and the morphology of the apollo 15 site probably since the eruption of mare basalts at the site 3 3 b y

quantification of electron microprobe compositional maps of rock thin sections an optimized method and examples quantification of discrete pressure temperature domains in deformed chlorite white mica bearing metapelites was undertaken on mineral compositions derived by two dimensional microprobe compositional mapping of selected areas of rock thin sections in order to achieve compositional information at sufficient analytical precision spatial resolution and sample coverage within a typical analysis time of 1 day an optimization of measurement methods was necessary the method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of 1 2 wt x ray intensity multiplane maps one map per measured chemical element are translated into concentration multiplane maps utilizing selected conventionally measured spot analyses combined with the castaing approximation for each mineral as this step requires identification of the different minerals present in the mapped area a statistical clustering technique to identify different groups of composition was developed guided by simple petrographic inspection of the thin section to delineate the important minerals in the mapped area finally the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information the reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data the possible use of chemical maps to infer the p t deformation history of metamorphic rocks is illustrated with two samples from the spitzbergen and the sambagawa blueschist facies belts in both samples a strong correlation between structures and chemistry is observed qualitative estimates of p t conditions from the si content of mica and chlorite are in good agreement with their location in microstructures that formed at different times therefore the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity

elastic strain energy and pore fluid pressure control of aftershocks abstract aftershocks are well known however their triggering mechanisms remain unclear the coulomb failure stress change cfs has been widely implemented to understand the spatial distribution of aftershocks here we propose a new metric for evaluating aftershock generation based on the energetics of shear faulting in a prestressed state unlike cfs the new metric depends not only on coseismic stress changes but also on background crustal stresses the energetics based formulation expands the cfs defined on a specific plane into a generalized failure stress defined in a three dimensional space we examined the diagnostic ability of the new metric by applying receiver operating characteristic analysis to 12 175 aftershocks m 0 that followed the 1992 landers earthquake with a realistic background stress field inferred from thousands of earthquake focal mechanisms the new metric was able to discriminate the triggering mechanisms of the aftershocks two thirds were direct responses to coseismic stress changes and one fifth resulted from strength decreases owing to pore fluid pressure increases

experimental evidence for perovskite and post perovskite coexistence throughout the whole d region article i nfo since the phase diagram for fe al bearing mgsio3 compositions at the p t conditions of the core mantle boundary remains ambiguous we investigated the fe distribution among the silicate perovskite pv and post perovskite ppv polymorphs using tandem synchrotron analyses of x ray diffraction and x ray absorption spectroscopy we performed measurements at the fe k edge of the partitioning of iron between pv and ppv up to more than 150 gpa after annealing at about 3300 k we obtain a unique solution for kfe pv ppv of 4 2 0 5 our results evidence that the two silicates should coexist over the whole d region with the main post perovskite phase being largely depleted in fe compared to the perovskite as fe and al have a dominant effect on the phase diagram these new results challenge recent determinations of the temperature profile in the lowermost mantle based on the clapeyron slope of the pv to ppv transition for pure mgsio3 composition also it appears clear that variations in the molar fractions of perovskite and post perovskite phases should be expected radially or laterally in the d region in relation with thermal or compositional heterogeneities this can help explaining the seismological anomalies observed for this mantle region finally we predict a significant increase of the feo activity in the d region which should greatly affect the chemical exchange between mantle and core

chemical variability and origin of agglutinitic glass seemingly pure agglutinitic glass is riddled with many submicrometer sized vesicles and clasts as shown by scanning electron microscopy of ion etched polished grain mounts electron microprobe analyses of agglutinitic glasses that have to be identified with relatively low power optical microscopes are difficult and tend to be biased by very fine grained contaminants energy dispersive x ray analysis edxa of small spots 1 m 1 m of pure agglutinitic glass carefully selected to be free of clasts or vesicles as determined by secondary electron imagery can overcome some of the analytical problems we have performed over 600 edxa of pure glass in 32 large agglutinates from five different apollo landing sites analyses adjacent to or away from clasts do not show any difference in chemical composition and suggest that secondary assimilation of clasts by the primary impact melt has not been a major process affecting the final composition the average glass composition of several agglutinates in any single soil is different from the bulk composition of the soil it is biased toward that of the finest fraction of the soil this is consistent with agglutination models advocating the fusion and or incorporation of the finest soil fraction most of the large multigenerational agglutinates contain small glassy areas or domains that are remarkably homogeneous in chemical composition they may represent the melt from single impact events and their homogeneity indicates that total melting of a microtarget in lunar soils upon micrometeoritic bombardment might be the origin of agglutinitic glass the compositions of these domains are different in different agglutinates and even within single multigenerational agglutinates and bear no systematic relationship to the composition of either the bulk soils or their finest fractions it seems likely that random small targets in lunar soils grains 100 m or less can only produce very small volumes of melt that are not representative of the soil itself the total melting of microtargets is not contradictory to models invoking incorporation or fusion of the finest fraction because such models consider average compositions of several agglutinates with respect to the parent soils they therefore refer to larger scale effects of agglutination a large soil grain if hit directly by a micrometeorite smaller than the grain itself is likely to behave more like a solid target a collection of very fine soil grains if hit by a micrometeorite larger than the collection of the grains will behave as a porous target because porous targets produce relatively more melt than solid targets the average melt composition from a large number of random micrometeoritic impacts is expected to be biased to that of the finest fraction of lunar soils

provenance analysis of muddy sandstones abstract a new approach to determine the precursor grains of detrital and diagenetic clay in sandstones requires a reiterative use of optical microscopy and electron beam microanalysis excluding muddy sandstone successions from analysis of the siliciclastic fill of a basin may lead to incomplete if not erroneous provenance interpretation because of biased samping of the sediments to minimize problems inherent in muddy sandstones we have combined a two tier optical modal analysis with energy dispersive x ray analysis edxa to identify precursors of clay this is a new method of point counting and estimating the mineral compositions of muddy sandstones because we apply the principle of identifying the mineral under the cross hair albeit on a micron scale we call this the new or modified g zzi dickinson method calculations of mass balance type using the results of this new method may be performed to reconstruct the original composition of the parental detrital material we have used muddy siliciclastic rocks outcrop and core samples of siltstones and sandstones from the oligocene intra arc medicine lodge beds of southwestern montana usa for this study eocene volcanic rocks of the challis region and thrusts that have transported pre cenozoic sedimentary and metasedimentary rocks in this region were the sources of the siliciclastic sediments results of modal analysis by the standard gazzi dickinson method and by the new modified gazzi dickinson method using both optical and edxa on a micron scale plot in different clusters in a qfl diagram our results show that the standard gazzi dickinson method is not truly independent of grain size even in the context of provenance analysis on the other hand the modified version has the promise of achievi g truly mineralogical modal petrologic analysis of detrital rocks of any grain size

experimental shock metamorphism of terrestrial basalts agglutinate like particle formation petrology and magnetism hypervelocity impacts occur on bodies throughout our solar system and play an important role in altering the mineralogy texture and magnetic properties in target rocks at nanometer to planetary scales here we present the results of hypervelocity impact experiments conducted using a two stage light gas gun with 5 mm spherical copper projectiles accelerated toward basalt targets with similar to 6 km s 1 impact velocities four different types of magnetite and titanomagnetite bearing basalts were used as targets for seven independent experiments these laboratory impacts resulted in the formation of agglutinatelike particles similar in texture to lunar agglutinates which are an important fraction of lunar soil materials recovered from the impacts were examined using a suite of complementary techniques including optical and scanning electron microscopy microraman spectroscopy and high and low temperature magnetometry to investigate the texture chemistry and magnetic properties of newly formed agglutinate like particles and were compared to unshocked basaltic parent materials the use of cu projectiles rather than fe and ni projectiles avoids magnetic contamination in the final shock products and enables a clearer view of the magnetic properties of impact generated agglutinates agglutinate like particles show shock features such as melting and planar deformation features and demonstrate shock induced magnetic hardening two to seven fold increases in the coercivity of remanence b cr compared to the initial target materials and decreases in low field magnetic susceptibility and saturation magnetization

earliest microbial trace fossils in archaean pillow lavas under scrutiny new micro x ray absorption near edge spectroscopy metamorphic and morphological constraints filament shaped titanite microtextures in early archaean c 3 47 ga metabasalts from the barberton greenstone belt of south africa have been argued to represent earth s oldest microbial trace fossils but petrological data on the environmental conditions that led to the formation of these microtextures are sparse we present here new metamorphic constraints on the equilibrium mineral assemblage containing the titanite microtextures together with fe speciation redox variations in the chlorite matrix surrounding the microtextures and morphospace analysis of the microtextures to test their biogenicity thermodynamic phase diagram modelling using a calculated rock microdomain composition indicated that the titanite mineral assemblage is stable at temperature conditions of t 240 360 c the high resolution quantitative mapping results combined with micro x ray absorption near edge spectroscopy at the fe k edge in chlorite revealed that the titanite microtextures are located in low temperature high xfe3 chlorite bands veins and microdomains supporting an origin as abiotic retrograde mineral cooling textures these new data combined with a late c 2 9 ga u pb date for the titanite are incompatible with the existing biological model which invokes microbial micro tunnel formation followed by titanite infilling and preservation in the early archaean sub seafloor the continuum of titanite morphologies reported herein indicates that titanite morphology cannot be used as reliable evidence in support of a biogenic origin in these metavolcanic rocks it is proposed that the titanite microtextures of purported biogenic origin from other greenstone belts such as the pilbara craton of western australia also deserve to be scrutinized by high resolution petrological investigations

grain size evolution and fractionation trends in an experimental regolith the comminution of blocky planetary surfaces into fine grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles diameter 6 35 mm mass 1 2g vi 1 35 km s initially the target fragments were 2 32 mm in size with a mean diameter of 15 2 mm which was reduced to 0 4 mm after 200 shots for the first 60 shots comminution was linear with cumulative kinetic energy and thus essentially linear with time the comminution efficiency however decreased at later stages this could be due to a change in fracture mechanism from predominantly intergranular to predominantly intragranular and or due to a change in partitioning of the projectile s kinetic energy from collisional fragmentation or large fragments at early times to cratering in a progressively finer grained medium at later stages mineral specific preferential comminution is abundantly observed in the modal make up of various grain size fractions plagioclase comminutes more readily than pyroxenes plagioclase initially present at 54 vol comprises typically 65 70 of the 125 250 m fraction pyroxenes initially at 33 are depleted to 20 25 this fractionation occurs in the earliest samples analyzed and is not a time dependent phenomenon bulk chemical analyses reveal a corresponding increase in al2o3 cao and na2o and a decrease in feo and mgo the finest grain sizes are generally the most severely affected by differential comminution similar if not exactly identical trends are abundantly documented for lunar soil samples these experimental findings illustrate that differential comminution is capable of producing fractionation in the finest grain sizes they diminish the need for prominent lateral and vertical transport of components otherwise foreign to a lunar soil sampling site as postulated by some workers on the basis of multivariate chemical mixing models

the production curve for agglutinates in planetary regoliths models for the production of agglutinates are developed that can be applied to the lunar surface or to any planetary or asteroidal body lacking an atmosphere models are developed using rate equations for progressively more complex situations and range from model 1 which is a simple linear increase of agglutinate content with time to model 4 which includes provision for recycling of existing agglutinates and replenishment and burial of exposed soil model 4 has some aspects of a steady state because depending on the rate constants agglutinate content may be limited to an intermediate value even for long exposure times in an extreme case agglutinate content may be limited to a value near zero these models predict that agglutinates should be low in abundance in areas of thin regolith such as the lunokhod 2 site on the moon and on asteroids the models may also help explain the apparent low agglutinate abundances of lunar regolith breccias and meteorite regolith breccias

evidence for k rich terranes on vesta from impact spherules the howardite eucrite diogenite hed clan is a group of meteorites that probably originate from the asteroid vesta some of them are complex breccias that contain impact glasses whose compositions mirror that of their source regions some k rich impact glasses up to 2 wt k2o suggest that in addition to basalts and ultramafic cumulates k rich rocks are exposed on vesta s surface one k rich glass up to 6 wt k2o with a felsic composition provides the first evidence of highly differentiated k rich rocks on a large asteroid they can be compared to the rare lunar granites and suggest that magmas generated in a large asteroid are more diverse than previously thought

quantitative mapping of the oxidative effects of mantle metasomatism the oxidation state of fe in garnets in a garnet peridotite xenolith from the wesselton kimberlite south africa was quantitatively mapped using x ray absorption near edge structure xanes spectroscopy maps of fe3 fe were produced by recording the fluorescence intensity at discrete energies rather than recording the full spectrum at each point the intensity at each point in the map was quantitatively converted to fe3 fe with reference to a linear calibration derived from garnet standards for which fe3 fe had been determined previously by mossbauer spectroscopy the resolution of these maps approaches that of elemental maps obtained using an electron microprobe the maps reveal zoning in fe3 fe between the core 0 075 and rim 0 125 that correlates with zoning of other elements the rims record an oxidizing metasomatic event in the lithospheric mantle the oxygen fugacity fo2 of this metasomatism is considerably higher than expected from studies of homogeneous garnets that exhibit metasomatic signatures such garnets may represent a re equilibrated average of the original core and metasomatic rim fo2 values metasomatism of the lithospheric mantle may thus have a greater impact on diamond stability than previously thought

x ray digital imaging petrography of lunar mare soils modal analyses of minerals and glasses it is essential that accurate modal i e volume percentages of the various mineral and glass phases in lunar soils be used for addressing and resolving the effects of space weathering upon reflectance spectra as well as for their calibration such data are also required for evaluating the resource potential of lunar minerals for use at a lunar base however these data are largely lacking particle counting information for lunar soils originally obtained to study formational processes does not provide these necessary data including the percentages of minerals locked in multi phase lithic fragments and fused soil particles such as agglutinates we have developed a technique for modal analyses sensu stricto of lunar soils using digital imaging of x ray maps obtained with an energy dispersive spectrometer mounted on an electron microprobe a suite of nine soils 90 to 150 micrometers size fraction from the apollo 11 12 15 and 17 mare sites was used for this study this is the first collection of such modal data on soils from all apollo mare sites the abundances of free mineral fragments in the mare soils are greater for immature and submature soils than for mature soils largely because of the formation of agglutinitic glass as maturity progresses in considerations of resource utilization at a lunar base the best lunar soils to use for mineral beneficiation i e most free mineral fragments have maturities near the immature submature boundary is feo approximately or 30 not the mature soils with their complications due to extensive agglutination the particle data obtained from the nine mare soils confirm the generalizations for lunar soils predicted by l a taylor and d s mckay 1992 lunar planet sci conf 23rd pp 1411 1412 abstract

mineralogical evidence for h2 degassing during serpentinization at 300 c 300 bar abstract hydrogen is produced in large amounts during hydrothermal alteration of peridotite in low spreading rate mid ocean ridges this production is directly linked to reducing conditions in hydrothermal fluids induced by the oxidation of fe2 in primary minerals olivine and pyroxene to fe3 in secondary minerals magnetite and serpentine a better knowledge of iron speciation in serpentine is therefore crucial to the quantification of hydrogen production during the serpentinization process for the first time we have determined the amount of ferric iron in altered peridotite as a function of alteration time we investigated experimentally the alteration of powdered lherzolite in pure water at 300 c 300 bar for each experimental run 0 7 18 34 and 70 days h2 degassing was measured using in situ gas chromatography and the experimental products were analyzed using xrd raman and x ray absorption spectroscopy at the iron k edge in parallel aqueous solutions were analyzed by icp aes our results show quasi complete serpentinization at 70 days with replacement of primary olivine and pyroxene by secondary lizardite and magnetite the fe3 fetotal ratio is linearly dependent on the hydrogen production and ranges from 0 to 0 66 at the end of the experiment our results reveal strong variations in fe3 in serpentine for different alteration times from 0 to 100 of ferric iron including up to 12 of tetrahedral iron hydrogen was produced in three main stages 1 a first stage during which the h2 production rate reaches a maximum at 18 days and is controlled by the crystallization of magnetite 2 an intermediate stage during which serpentine incorporates ferric iron and thus plays a major role up to 50 in the hydrogen formation and 3 a final stage during which magnetite amount increases from 2 to 5 of the mineral assemblage the last alteration stage is accompanied by a slight increase of the fe3 fetotal ratio while the rate of hydrogen production decreases at the end of the experiment consequently variations of the ferric iron contents in natural oceanic peridotites may constitute a good indicator of the hydrogen potential of various ultramafic hydrothermal fields

a statistical approach to estimate the 3d size distribution of spheres from 2d size distributions size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two dimensional 2d circular cross sections of the spheres in random flat planes of a sample such as in thin sections or polished slabs several methods have been devised to find a simple factor to convert the mean of such 2d size distributions to the actual 3d mean size of the spheres without a consensus we derive an entirely theoretical solution based on well established probability laws and not constrained by limitations of absolute size which indicates that the ratio of the means of measured 2d and estimated 3d grain size distribution should be 4 785 actual 2d size distribution of the radii of submicron sized pure fe 0 globules in lunar agglutinitic glass determined from backscattered electron images is tested to fit the gamma size distribution model better than the log normal model numerical analysis of 2d size distributions of fe 0 globules in 9 lunar soils shows that the average mean of 2d 3d ratio is 0 84 which is very close to the theoretical value these results converge with the ratio 0 8 that hughes 1978 determined for millimeter sized chondrules from empirical measurements we recommend that a factor of 1 273 reciprocal of 0 785 be used to convert the determined 2d mean size radius or diameter of a population of spheres to estimate their actual 3d size

oxidation of ch4 to co2 and h2o by chloritization of detrital biotite at 270 5 c in the external part of the central alps switzerland abstract the upper end of the ch 4 zone in the external part of the central alps of switzerland results from an oxidation reaction of methane into water and carbon dioxide at 270 5 c tarantola a mullis j vennemann t dubessy j de capitani c 2007 oxidation of methane at the ch 4 h 2 o co 2 transition zone in the external part of the central alps switzerland evidences from stable isotope investigations chemical geology 237 329 357 petrographic investigations of the north helvetic flysch revealed the presence of detrital biotite muscovite and chlorite in the ch 4 zone at the transition from the methane to the water zone the sudden increase of co 2 in the fluid is associated with the formation of chlorite and muscovite in replacement of detrital biotite in the h 2 o zone biotite is entirely replaced by chlorite muscovite interlayered stacks mossbauer spectroscopy showed a minimum decrease of x fe 3 from 0 18 to 0 09 within the sheet silicate fraction at the transition from the ch 4 to the h 2 o co 2 dominated fluid zone detrital biotite of the investigated host rocks incorporates at the same conditions larger amounts of fe 3 than chlorite in its structure and x fe 3 biotite x fe 3 new chlorite x fe 3 detrital chlorite the reaction of chloritization of detrital biotite is interpreted as a fluid controlled mineralogical isograde at 270 5 c marking the transition from the low to the high grade anchizone and allowing the oxidation of up to 36 moles of ch 4 per cubic meter of rock

the nature and origin of rims on lunar soil grains abstract space weathering processes that operate in the lunar regolith modify the surfaces of lunar soil grains transmission electron microscope analysis of the lunar soil grains from the fine size fraction of several lunar soils show that most grains are surrounded by thin 60 200 nm thick rims the microstructure and chemical compositions of the rims can be used to classify rims into four broad categories amorphous inclusion rich multiple and vesicular amorphous rims are noncrystalline generally lack crystalline inclusions show evidence for preferential sputtering of cations and are produced largely by solar wind irradiation damage inclusion rich rims contain abundant nanometer sized grains of fe metal as randomly dispersed inclusions or as distinct layers embedded in an amorphous silica rich matrix inclusion rich rims are compositionally distinct from their host grains and typically contain accumulations of elements that are not indigenous to the host inclusion rich rims are formed largely by the deposition of impact generated vapors with a contribution from the deposition of sputtered ions a continuum in the chemical and microstructural properties exists between typical amorphous rims and typical inclusion rich rims multiple rims consist of a distinct radiation damaged layer up to 50 nm thick that is overlain by vapor deposited material of comparable thickness vesicular rims are compositionally similar to their hosts and are characterized by an abundance of small the formation of rims on lunar soils is complex and involves several processes whose effects may be superimposed from this study it is shown that one process does not dominate and that the relative importance of vapor deposition is comparable to radiation damage in the formation of rims on lunar silicate grains the presence of rims on lunar soil grains particularly those with nanometer sized fe metal inclusions may have a major influence on the optical and magnetic properties of lunar soils

an experimental investigation of agglutinate melting mechanisms shocked mixtures of sodium and potassium feldspars we report the results of an experiment designed to test the validity of the model for agglutinate formation involving fusion of the finest fraction or f3 papike et al 1981 impact glasses were formed from various mixes of orthoclase and albite powders which were used as analogs for soils with chemically contrasting coarse and fine fractions shock pressures ranged from 31 8 gpa to 78 0 gpa 318 780 kbar results show that the composition of the finest soil fraction is the dominant factor in displacing the composition of the impact melt agglutinate glass from that of the bulk other factors are degree of shock amount of melt and volatile loss a soil with no fine fraction displays only the effects of volatile loss whereas in other runs the glasses are compositionally displaced away from the bulk and toward the finest fraction as predicted by the model the lower pressure melts are the most fractionated higher pressure is accompanied by increased melting causing glass compositions to approach the bulk in general the systematics predicted by the model are observed and it appears that the fusion of the finest fraction model is valid

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

moderate velocity oblique impact sliding production of shocked meteorite textures and palaeomagnetically important metallic spherules in planetary regoliths we detail the production of metallic spherules in laboratory oblique shock impact experiments and their applicability 1 to textures in a partly shock melted chondritic meteorite and 2 to the occurrence of palaeomagnetically important fine iron or iron alloy particles in the lunar regolith samples recovered from 29 44 gpa 800 ns experiments revealed melting and textures reminiscent of metallic spherules in the yanzhuang h chondrite including dumbbell forms and other more complex morphologies our experiments demonstrate that metallic spherules can be produced via oblique impact sliding at lower velocities 1 85 km s 1 than are generally assumed in previous work associated with bulk shock melting and that oblique impact sliding is a viable mechanism for producing spherules in shock induced veins in moderately shocked meteorites significantly our experiments also produced fine metallic iron alloy spherules within the theoretical narrow size range a few tens of nanometers for slightly ellipsoidal particles for stable single domain ssd particles which are the most important palaeomagnetically since they can record lunar and planetary magnetic fields over geological time periods the experiments also produced spherules consistent with superparamagnetic sp and multidomain md particle sizes the fine ssd and sp particles on the lunar surface are currently thought to have been formed predominantly by space weathering processes our experiments suggest that oblique shock impact sliding may be a further means of producing the ssd and sp iron or iron alloy particles observed in the lunar regolith and which are likely to occur in the regoliths of mercury and other planetary bodies

systematic global mixing and melting in lunar soil evolution 1 we present a revised model of soil evolution constrained by the recent lscc data for lunar soils in addition to an observed universal increase in feldspathic components in the finer fractions of soils taylor et al 2001 2003a 2003b both differential melting and lateral mixing processes appear to be required during the evolution of lunar soils we propose mare highland mixing of a significant glass component along with a preferential melting sequence for agglutinitic glass formation of glass plagioclase pyroxene ilmenite

the effects of space weathering on apollo 17 mare soils petrographie and chemical characterization the lunar soil characterization consortium a group of lunar sample and remote sensing scientists has undertaken the extensive task of characterization of the finest fractions of lunar soils with respect to their mineralogical and chemical makeup these compositional data form the basis for integration and modeling with the reflectance spectra of these same soil fractions this endeavor is aimed at deciphering the effects of space weathering of soils on airless bodies with quantification of the links between remotely sensed reflectance spectra and composition a beneficial byproduct is an understanding of the complexities involved in the formation of lunar soil several significant findings have been documented in the study of the 2x whereas the abundance of agglutinitic glass increases by only 10 15 this is evidence for a large contribution from surface correlated nanophase fe0 to the is feo values particularly in the 10 m size fraction the surface nanophase fe0 is present largely as vapor deposited patinas on the surfaces of almost every particle of the mature soils and to a lesser degree for the immature soils keller et al 1999a it is reasoned that the vapor deposited patinas may have far greater effects upon reflectance spectra of mare soils than the agglutinitic fe0

new high precision p t estimates for oman blueschists implications for obduction nappe stacking and exhumation processes oman blueschists and eclogites lie below the obduction nappe of the semail ophiolite in one of the key areas on earth for the study of plate convergence here new metamorphic and tectonic constraints are provided for the central yet poorly constrained hulw unit sandwiched between the low grade units 10 kbar 300 c and the as sifah eclogites pmax 23 kbar tmax 600 c tweequ multi equilibrium thermobarometry using both compositional mapping and spot analyses and raman spectroscopy of carbonaceous material yield a high precision p t path for the hulw and as sheikh units and reveal that they shared a common p t history in four stages i a pressure decrease from 10 12 kbar 250 300 c to 7 9 kbar 300 350 c ii almost isobaric heating at 8 10 kbar from 300 350 c to 450 500 c iii a pressure decrease at moderate temperatures 450 500 c and iv isobaric cooling at 5 6 kbar from 450 500 to 300 c no significant pressure or temperature gap is observed across the upper plate lower plate discontinuity to the north and west of the hulw unit the combination of tectonic and p t data constrains the stacking chronology of the three main metamorphic units comprising the saih hatat window i e the ruwi quryat the hulw as sheikh and the diqdah as sifah units these results strengthen the view that the tectonic and metamorphic data are conveniently accounted for by a simple n vergent continental subduction of the passive arabian margin below the obduction nappe along a cold p t gradient

p t deformation fe3 fe2 mapping at the thin section scale and comparison with xanes mapping application to a garnet bearing metapelite from the sambagawa metamorphic belt japan quantitative x ray maps of composition from a chlorite k white mica albite quartz and garnet bearing thin section from a sambagawa blueschist facies metapelite were combined with a multiequilibrium calculation method to calculate a p t fe3 fe2 deformation map at the millimetre scale the studied sample was chosen because elongated chlorite crystallization tails pressure shadows rimmed by phengite are present which is an appropriate assemblage for the quantification of the p t evolution chlorite temperature and fe3 content maps were calculated by successive iterations for each pixel analysis of fe3 until convergence of the four chlorite quartz h2o equilibria that can be written using the fe and mg amesite clinchlore daphnite and sudoite chlorite end members the calculated map of fe2 fe3 in chlorite is in good qualitative agreement with the in situ mapping of this ratio using xanes x ray absorption near edge structure techniques the temperature map indicates that high temperature chlorite zones with low fe3 contents alternate with lower temperature zones and higher fe3 contents in the crystallization tail late fractures perpendicular to the elongation axis of the tail are filled by very low temperature chlorite 250 c showing fe3 fetotal up to 0 4 groups of chlorite and mica pixels were then identified based on compositional and structural criteria and a p tdeformation map was calculated using representative analyses of these groups the calculated p tdeformation map suggests that in contrast to chlorite the composition of most mica did not change significantly during exhumation mica reequilibrated in late ew shear bands only ew shearing was already active at 0 1 gpa 500 c which corresponds to the peak temperature and probably pressure conditions at reduced redox conditions the intensity of deformation probably decreased with decrease in temperature to 350 400 c at this temperature a second main deformation event corresponding to a further ew stretching occurred and was still active below 250 c and more oxidizing conditions these results indicate that the scale at which p t data can be obtained is now close to the scale of observation of structural geologists a close link between deformation and mineral reaction is therefore possible at the microscopic scale which provides information about the relationship between deformation and mineral reactivity the modalities of deformation with time and the p t conditions at which it occurred

magnetic signatures of serpentinization at ophiolite complexes we compare magnetic properties of 58 variably serpentinized peridotites from three ophiolite complexes pindos greece oman chenaillet france and the mid atlantic ridge near the kane fracture zone mark the pindos and oman sites show low susceptibility and remanence k 250 3008c occurring at the axis i e chenaillet similar to serpentinites from magmatically poor mid ocean ridges from lower temperature serpentinization 200 2508c likely occurring off axis and possibly during obduction i e pindos and oman at both settings serpentinization can result in significant hydrogen release

on the origin of impact glass in the apollo 16 regolith this study addresses the issue of what fraction of the impact glass in the regolith of a lunar landing site derives from local impacts those within a few kilometers of the site as opposed to distant impacts 10 or more kilometers away among 10 323 fragments from the 64 210 lm grain size fraction of three apollo 16 regolith samples 14 are impact glasses that is fragments consisting wholly or largely of glass produced in a crater forming impact another 16 are agglutinates formed by impacts of micrometeorites into regolith we analyzed the glass in 1559 fragments for major and minor element concentrations by electron probe microanalysis and a subset of 112 of the fragments that are homogeneous impact glasses for trace elements by secondary ion mass spectrometry of the impact glasses 75 are substantially different in composition from either the apollo 16 regolith or any mixture of rocks of which the regolith is mainly composed about 40 of the impact glasses are richer in fe mg and ti as well as k p and sm than are common rocks of the feldspathic highlands these glasses must originate from craters in maria or the procellarum kreep terrane of the feldspathic impact glasses some are substantially more magnesian greater mgo feo or have substantially lower concentrations of incompatible elements than the regolith of the apollo 16 site many of these however are in the range of feldspathic lunar meteorites most of which derive from points in the feldspathic highlands distant from the procellarum kreep terrane these observations indicate that a significant proportion of the impact glass in the apollo 16 regolith is from craters occurring 100 km or more from the landing site in contrast the composition of glass in agglutinates on average is similar to the composition of the apollo 16 regolith consistent with local origin 2010 elsevier ltd all rights reserved

heterogeneous agglutinitic glass and the fusion of the finest fraction f3 model evidence in favor of the model fusion of the finest fraction f3 for the origin of lunar agglutinitic glass has been accruing they include 1 theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains 2 experimental results of impact shock albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith and 3 new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed we add another reason in support of the f3 model finer grains of lunar soils are also much more abundant hence electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the moon this further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts new backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction even by more than an order of magnitude for some components additionally we show how an ilmenite grain upon impact would produce tio2 rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction we propose an addition to the f3 model to accommodate these observations i e that micrometeorite impacts indiscriminately melt the immediate target regardless of grain size or grain composition we therefore suggest that 1 agglutinitic glass is the sum of a the melt produced by the fusion of the finest fraction of lunar soils and b the microvolume of the indiscriminate target which melts at high shock pressures from micrometeoritic impacts and that 2 because of the small volume of the melt and incorporating cold soil grains the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition for example that of the finest fraction

an experimental investigation of agglutinate melting mechanisms shocked mixtures of apollo 11 and 16 soils mixtures of chemically contrasting lunar soils from a 11 and a 16 have been shocked at pressures ranging from 18 2 62 0 gpa 182 620 kb other than the generation of impact melts modal and textural changes caused by shock include destruction of pore space and fused soil clasts and conversion of plagioclase to maskelynite the loss of the fused soil component in these runs indicates that low agglutinate contents in shocked and or compacted regolith breccias cannot be considered by themselves to be evidence of formation from immature regolith from the petrographic and chemical data it appears that the impact glass formed mainly from the fine fraction and the fused soil component in the target with relatively minor contributions from the other coarse clasts the impact glasses exhibit the same chemical enrichments and depletions as their corresponding fine fractions and plot on or near a mixing line between the bulk and fine fraction of the soil in which they were formed from this as well as several other studies it appears that the fusion of the finest fraction f3 model is valid and that it accurately predicts the chemical systematics of impact glass formed from lunar soil in addition fusion of agglutinates present in the target soil is an important process

impact induced thermal effects in the lunar and mercurian regoliths while the moon and mercury are similar objects in a geomorphologic sense they also possess important differences particularly in the context of small scale impact phenomena not only is the surface of mercury notably hotter than that of the moon but the impact flux is also more intense at mercury due to higher impact velocities and a greater spatial density of micrometeoroids by extrapolating the terrestrial micrometeoroid flux to the moon and mercury it is found that the impact rate at mercury is 5 5 times greater and the mean impact velocity more than 60 percent higher than at the moon a model of impact melting and vaporization applied to the lunar and mercurian environments indicates that almost 14 times more impact melt and over 20 times more vapor are generated per unit time in the mercurian regolith although the surface temperature plays a role in determining the melt and vapor volumes the difference in impact velocity appears to be markedly more important average craters formed by identical projectiles under the two velocity distributions on the two planets should be very similar in size because differences in the kinetic energy of the average impactors will be offset by the differences in gravitational acceleration as a result variations in regolith mixing should depend more on the actual impact rates than on disparities in excavated volumes each average impact on mercury however will produce more than twice as much impact melt as its lunar counterpart introducing more glass into the mercurian regolith although substantial quantities of impact vapor are produced on both planets mixing of the regolith should occur quickly enough in each case to spread the deposited vapor over large surface areas the resulting vapor coatings should be negligibly small for most purposes a much larger agglutinate population should exist on mercury and individual agglutinates should be similar to those of the lunar highlands reflectance spectra and visual albedos indicate that the mercurian crust possesses relatively small quantities of fe perhaps similar to those of apollo 16 light and dark matrix breccias laboratory studies have demonstrated that as the magnetic fractions which are correlated with agglutinate abundances of soils derived from these breccias increase the differences in 0 565 mm visible light reflectivity between the soils diminish should the regional variations in fe content of the mercurian crust be similar to those of these apollo 16 samples then the intense agglutination environment could account for the lack of optical contrast across the mercurian surface at the same time the very large fraction of impact glass in the regolith would imply that most pyroxenes have been fused and incorporated into these glasses seriously attenuating the fe2 crystal field absorption near 0 9 mm supporting this picture are the most recently published spectral observations of mercury which provide little or no evidence of such an absorption feature

from static alteration to mylonitization a nano to micrometric study of chloritization in granitoids with implications for equilibrium and percolation length scales strain accommodation in upper crustal rocks is often accompanied by fluid mediated crystallization of phyllosilicates which influence rock strength and shear zone formation the composition of these phyllosilicates is frequently used for pressure temperature time constraints of deformation events although it is often highly heterogeneous even in mylonites this study investigates the reactions producing a phyllosilicate chlorite in and below grenschist facies conditions and the variations in chlorite composition along a strain gradient in the variscan bielsa granitoid axial zone pyrenees compositional maps of chlorite including iron speciation are compared to nanostructures observed by transmission electron microscopy in increasingly strained samples and related to mechanisms of fluid percolation in the bielsa granitoid altered at the late variscan alpine age shear zones are found with high strain gradients the undeformed granitoid exhibits local equilibria pseudomorphic replacement and high compositional heterogeneities in chlorite this is attributed to variable reaction mechanisms at nanoscale and element supply little interconnected intra and inter grain nanoporosity and isolation of fluid evolving in local reservoirs in samples with discrete and mm sized fractures channelized fluid triggered the precipitation of homogeneous alpine chlorite in fractures preserving late variscan chlorite within the matrix in low grade mylonites where brittle ductile deformation is observed micro and nanocracks and defects allows the fluid percolating into the matrix at the scale of hundreds of m this results in a more pervasive but incomplete replacement of late variscan chlorite by alpine chlorite despite the high strain in studied granitoids deformed under greenschist facies conditions local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according reaction mechanisms and element mobility controlled by i matrix fracture porosity contrasts at nanoscale and ii the location and interconnection of nanoporosity between crystallites of phyllosilicates this preservation influences our ability to reconstruct the pre and syn kinematic metamorphic history of granitic rocks in low grade units of orogens

aluminum speeds up the hydrothermal alteration of olivine the reactivity of ultramafic rocks under hydrothermal conditions controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets on earth hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere this process also has key emerging societal implications such as the production of hydrogen as a source of carbon free energy to date the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates here we use in situ diamond anvil cell experiments and show that the presence of aluminum in hydrothermal fluids increases the rate of olivine serpentinization by one to two orders of magnitude aluminum increases the solubility of olivine and enhances the precipitation of aluminous serpentine after two days olivine crystals were fully transformed to aluminous serpentine under conditions typical for natural hydrothermal environments i e 200 and 300 c 200 mpa this result motivates a re evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings this discovery also opens the potential of the serpentinization reaction for industrial scale production of hydrogen at economically feasible timescales and temperature