Iron redox works well for constraining oxygen fugacity (f(O2)) in terrestrial igneous materials due to the relatively high f(O2) of the Earth's atmosphere, crust, and upper mantle [f(O2 )>= quartz-fayalite-magnetite(QFM), where there are large changes in Fe2+/Fe3+ with relatively small changes in f(O2). At f(O2) values 4s transition and then uses that redox couple to estimate f(O2) as a function of temperature and composition. Here, that method is compared to an alternate approach of predicting f(O2) directly from the spectra of experimentally homogenized glasses of geological relevance without an intermediate step of attempting to discern Cr2+/Cr3+. In this study, partial least-squares (PLS) multivariate (MVA) regression models were trained on the whole XAS energy spectral range, and accuracy was quantified using root mean square error (RMSE). MVA results showed significantly higher accuracy (RMSE-C of +/- 0.75 log units) for predicting f(O2 )Delta IW relative to known experimental conditions relative to the two-step method, which yielded RMSE-C of +/- 2.75 to +/- 7.65 log units for our data set vs. those of Berry and O'Neill (2004) and Berry et al. (2006), respectively. The MVA results calibrate a new Cr oxybarometer for use in low-f(O2) glasses with a cross-validated (RMSE-CV) accuracy of +/- 0.84 log units f(O2) relative to a standard oxygen buffer. Finally, the new Cr oxybarometer was applied to lunar glasses, both volcanic and impact metamorphosed, to assess the range in oxidation conditions the materials experienced during formation. Lunar volcanic glasses cluster similar to IW +/- 1, close to that of previous studies while agglutinates and lunar impact melts record a wide range of f(O2) values using Cr oxybarometry.

This study describes the application of new synchrotron X-ray fluorescence (XRF) and diffraction (XRD) microtomographies for the 3-D visualization of chemical and mineralogical variations in unsectioned extraterrestrial samples. These improved methods have been applied to three compositionally diverse chondritic meteorite samples that were between 300 and 400 mu m in diameter, including samples prepared from fragments of the CR2 chondrite LaPaz Icefield (LAP) 02342, H5 chondrite MacAlpine Hills (MAC) 88203, and the CM2 chondrite Murchison. The synchrotron-based XRF and XRD tomographies used are focused-beam techniques that measure the intensities of fluorescent and diffracted X-rays in a sample simultaneously during irradiation by a high-energy microfocused incident X-ray beam. Measured sinograms of the emitted and diffracted intensities were then tomographically reconstructed to generate 2-D slices of XRF and XRD intensity through the sample, with reconstructed pixel resolution of 1-2 mu m, defined by the resolution of the focused incident X-ray beam. For sample LAP 02342, primary mineral phases that were visualized in reconstructed slices using these techniques included isolated grains of alpha-Fe, orthopyroxene, and olivine. For our sample of MAC 88203, XRF/XRD tomography allowed visualization of forsteritic olivine as a primary mineral phase, a vitrified fusion crust at the sample surface, identification of localized Cr-rich spinels at spatial resolutions of several micrometers, and imaging of a plagioclase-rich glassy matrix. In the sample of Murchison, major identifiable phases include clinoenstatite- and olivine-rich chondrules, variable serpentine matrix minerals and small Cr-rich spinels. Most notable in the tomographic analysis of Murchison is the ability to quantitatively distinguish and visualize the complex mixture of serpentine-group minerals and associated tochilinite-cronstedtite intergrowths. These methods provide new opportunities for spatially resolved characterization of sample texture, mineralogy, crystal structure, and chemical state in unsectioned samples. This provides researchers an ability to characterize such samples internally with minimal disruption of sample micro-structures and chemistry, possibly without the need for sample extraction from some types of sampling and capture media.

IN THE LUNAR BASALTIC METEORITE ELEPHANT MORAINE 96008. M. Wadhwa1, A. G. Distel1, J. Davidson1,2, S. R. Sutton3,4, A. Lanzirotti4, 1School of Earth and Space Exploration (SESE), Arizona State University (ASU), 781 E. Terrace Rd, Tempe AZ 85287-6004, USA, 2Buseck Center for Meteorite Studies, SESE, ASU, Tempe AZ 85287, USA, 3Department of the Geophysical Sciences and 4Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, IL 60637, USA,

Magmatic oxygen fugacity (f(o2)) exerts a primary control on the discrete vanadium (V) valence states that will exist in quenched melts. Vanadium valence proxies for f(o2), measured using X-ray absorption near-edge spectroscopy (XANES), can provide highly sensitive determinations of the redox conditions in basaltic melts. However, X-ray beam-induced changes in V speciation will introduce uncertainty in the calculated average V valence (V*) that must be properly evaluated to make meaningful interpretations of the igneous evolution of the system. The study presented here showed that beam-induced modifications in V speciation are observed in silicate glasses that are dependent on the radiation dose rate used during analysis. Changes in V speciation are observed to be most pronounced at the highest flux density tested, 9.25 X 10(11) ph/s/mu m(2) (photons per second per square micrometer), with rapid changes occurring in the first 200 s of analysis. The high-dose rate conditions result in changes in calculated V* similar to 0.3 valence unit for the most oxidized glass analyzed (V* = 4.94), which can correspond to similar to 0.5 log unit reduction in calculated f(o2). However, at flux densities <= 1.13 X 10(9)ph/s/mu m(2), measured changes in V* were found to be <= 0.03 for all standard glasses analyzed. The degree of reduction observed during analysis is also found to be progressively smaller as the initial V* of the glass decreases, such that magmatic glasses with V* values <= 3.7 show no statistically significant change in calculated valence during analysis at any flux density tested. For most terrestrial magmatic glasses, where V* is found to be <4, beam-induced changes in V* can be effectively minimized (<0.04), within analytical uncertainty of the XAFS analysis, by limiting flux densities to be <= 1 X 10(9)ph/s/mu m(2).

ELEPHANT MORAINE 96008: IMPLICATIONS FOR REDOX CONDITIONS AND MAGMATIC PROCESSES ON THE MOON. M. Wadhwa1, S. R. Sutton2,3, A. Lanzirotti3, A. G. Distel1, and J. Davidson1,4, 1School of Earth and Space Exploration (SESE), Arizona State University (ASU), 781 E. Terrace Rd, Tempe AZ 85287-6004, USA, 2Department of the Geophysical Sciences and 3Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, IL 60637, USA, 4Buseck Center for Meteorite Studies, SESE, ASU, Tempe AZ 85287, USA.

GeoSoilEnviroCARS (GSECARS) is a comprehensive analytical laboratory for Earth and environmental science research using X-ray beams from the Advanced Photon Source, Argonne National Laboratory. State-of-the-art instruments are available for (1) high-pressure/high- or low-temperature diffraction, total scattering, and spectroscopy (Brillouin, Raman, and VIS-IR) using the laser heated diamond anvil cell (DAC); (2) high-pressure/high-temperature diffraction, scattering, and imaging as well as acoustic emission (AE) and ultrasonics using the large-volume press (LVP); (3) powder, single crystal, and surface/interface diffraction; (4) X-ray absorption fine structure spectroscopy; (5) X-ray fluorescence microprobe analysis; and (6) microtomography. Experiments are facilitated by senior level staff who collaborate on all aspects of the analytical work including experiment design, sample preparation, data collection, data interpretation, and publication preparation. Both technical and scientific synergies occur as a result of the intimate association of the various techniques and scientists experienced in the applications of synchrotron radiation to Earth, environmental, and planetary science problems. The facility includes state-of-the-art instrumentation designed and built in-house, including custom X-ray optics, online and offline laser-based systems, specialized sample environments and positioning systems, as well as pixel-array and multi-crystal energy dispersive X-ray detectors, which are available to be shared among the experimental stations.

HYDROGEN ISOTOPES, WATER ABUNDANCES, AND IRON VALENCE OF PYROXENE IN THE REGOLITH BRECCIA NORTHWEST AFRICA 7034. J. Davidson1,2,*, M. Wadhwa2, S. Sutton3, and R. L. Hervig2, 1Buseck Center for Meteorite Studies, Arizona State University (ASU), Tempe, AZ 85287, USA. 2School of Earth and Space Exploration, ASU, Tempe, AZ 85287, USA. 3Department of the Geophysical Sciences and Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, IL 60637, USA. *Email: jdavidson@asu.edu

Large impact‐melt pockets in shergottites contain both Martian regolith components and sulfide/sulfite bleb clusters that yield high sulfur concentrations locally compared to bulk shergottites. The regolith may be the source of excess sulfur in the shergottite melt pockets. To explore whether shock and release of secondary Fe‐sulfates trapped in host rock voids is a plausible mechanism to generate the shergottite sulfur bleb clusters, we carried out shock recovery experiments on an analog mixture of ferric sulfate and Columbia River basalt at peak pressures of 21 and 31 GPa. The recovered products from the 31 GPa experiment show mixtures of Fe‐sulfide and Fe‐sulfite blebs similar to the sulfur‐rich bleb clusters found in shergottite impact melts. The 21 GPa experiment did not yield such blebs. The collapse of porosity and local high‐strain shear heating in the 31 GPa experiment presumably created high‐temperature hotspots (~2000 °C) sufficient to reduce Fe3+ to Fe2+ and to decompose sulfate to sulfite, followed by concomitant reduction to sulfide during pressure release. Our results suggest that similar processes might have transpired during shock production of sulfur‐rich bleb clusters in shergottite impact melts. It is possible that very small CO presence in our experiments could have catalyzed the reduction process. We plan to repeat the experiments without CO.

We have performed a coordinated focused ion beam (FIB)-scanning and transmission electron microscopy (S/TEM), electron probe microanalysis (EMPA)-synchrotron X-ray fluorescence (SXRF) microprobe study to determine phase-specific microstructural characteristics and high-resolution in situ trace element concentrations of primary pyrrhotite, pentlandite, and associated metal grains from chondrules in CM2 and CR2 carbonaceous chondrites. This work is the first of its kind to link trace element chemical and microstructural observations in chondritic sulfides in an attempt to determine formation mechanisms and conditions of primary sulfides in these meteorite groups. SXRF microprobe analyses allowed the concentrations of the minor and trace elements, Co, Cu, Ge, Zn, and Se to be quantified, in addition to Fe and Ni, at a spatial resolution of 2 microns. The similarity between the CM and CR PPI sulfide trace element patterns provides evidence for a common formation mechanism for this type of sulfide grain in both meteorite groups. In addition, the SRM sulfide and metal have comparable trace element patterns that indicates a genetic relationship between the two, such as sulfidization of metal. Enrichments in Ni, Co, Cu, and Se are consistent with the chalcophile/siderophile behavior of these elements. The observed depletions in Ge suggest that it may have been lost by evaporation or else was never incorporated into the metal or sulfide precursor materials. The depletion in Zn may also be attributable to evaporation, but, being partially lithophile, may also have been preferentially incorporated into silicates during chondrule formation. Trace element concentrations support crystallization from an immiscible sulfide melt in chondrules for formation of the PPI grains and sulfidization of metal for the origin of the SRM grains.

CHONDRITE: FURTHER INSIGHTS FROM LA-ICP-MS TRACE ELEMENT ANALYSIS AND Cr, Ti, AND V VALENCE STATE MEASUREMENTS BY XANES. A. J. Brearley, J. M. Johnson, R.D. Ash, and S.R. Sutton Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA (brearley@unm.edu), Department of Geology, University of Maryland, College Park, MD20742, USA; CARS & Dept. Geophysical Sci., 5734 S. Ellis Ave., The University of Chicago, Chicago, IL 60637, USA

OLIVINES AND PYROXENES. S. R. Sutton1,2, A. Lanzirotti1, M. Newville1, A. J. Brearley3, E. Dobrica3, O. Tschauner4.1Center for Advanced Radiation Sources (CARS), 2Dept. Geophysical Sci., 5734 S. Ellis Ave., The University of Chicago, Chicago, IL 60637, USA (sutton@cars.uchicago.edu); 3Dept. Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131; 4Dept. Geoscience, University of Nevada, Las Vegas, NV 89154.

X‐ray absorption fine structure (XAFS) spectroscopy methods have been applied to focused ion beam (FIB) produced sections of olivine and pyroxene for determining the valence states of Ti, V, and Cr and inferring oxygen fugacities of formation for each element. High‐quality XAFS spectra were obtained for all three elements for analytical voxels of ~10 pg and usable spectra down to the pg level are achievable. The extraterrestrial samples studied here were olivine and pyroxene from chondrules in Semarkona (LL3.00), olivine from chondrules in Kainsaz (CO3.2), and an olivine and a pyroxene grain from two Antarctic micrometeorites (AMM). The general agreement between calculated thin section and FIB section valences strongly suggests that there is negligible alteration of Ti, V, and Cr valences during FIB sectioning. The inferred oxygen fugacities for the AMM olivine support an equilibrium igneous history similar to results seen for some achondrites. For the pyroxene, highly reduced Cr, coupled with relatively oxidized Ti, suggests an origin in a mildly metamorphosed chondritic parent body. These results demonstrate that this FIB and micro‐XAFS approach is promising for establishing the oxidation states of minute monomineralic grains of diverse extraterrestrial origins, including materials from sample‐return spacecraft, such as the Stardust, OSIRIS‐REx, Hayabusa, and Hayabusa2 missions.

OLIVINE. S. R. Sutton1,2, A. Lanzirotti1, M. Newville1, A. J. Brearley3, E. Dobrica3, O. Tschauner4.1Center for Advanced Radiation Sources (CARS), 2Dept. Geophysical Sci., 5734 S. Ellis Ave., The University of Chicago, Chicago, IL 60637, USA (sutton@cars.uchicago.edu); 3Dept. Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131; 4Dept. Geoscience, University of Nevada, Las Vegas, NV 89154.

CHONDRITES. S. B. Simon, S. R. Sutton, A. J. Brearley, A. N. Krot, and K. Nagashima.Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131(sbs8@unm.edu). Dept. Geophysical Sci., The University of Chicago, Chicago, IL 60637. Center for Advanced Radiation Sources (CARS), The Univ. of Chicago. Dept. Earth and Planetary Sci., Univ. of New Mexico. HIGP/SOEST, Univ. of Hawai’i, Honolulu, HI. Geosci. Inst./Mineralogy, Goethe University Frankfurt, Germany.

GeoSoilEnviroCARS (GSECARS) is an earth-science-driven X-ray synchrotron facility at the Advanced Photon Source of the Argonne National Laboratory. As a national user facility, we provide users with access to the high-brilliance hard X-rays from this third-generation synchrotron light source. The multi-anvil, large-volume high-pressure facility at the bending magnet beamline (13-BM-D) runs a unique setup permitting an unusually wide range of high-pressure and high-temperature experiments combined with X-rays and other in-situ probing techniques. It has been a great asset for the high-pressure earth science community since its inception in 1997. A series of upgrades and updates occurred in the 2010s. Here we provide a detailed description of the current large-volume press (LVP) setup at 13-BM-D, including hardware, software, and all experimental capabilities. Examples of scientific studies that were performed at GSECARS utilizing the new LVP system are also reported.

THE ANALYSIS OF PICOGRAM MATERIALS RETURNED BY SAMPLE-RETURN MISSIONS. A. Lanzirotti1, M. Newville1, S. R. Sutton1,2, M. Koker1, A. J. Brearley3, E. Dobrica3, O. Tschauner4.1Center for Advanced Radiation Sources, Univ. of Chicago, Chicago, IL 60637 (lanzirotti@uchicago.edu), 2Dept. Geophysical Sci., 5734 S. Ellis Ave., The University of Chicago, Chicago, IL 60637, USA; 3Dept. Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131; 4Dept. Geoscience, University of Nevada, Las Vegas, NV 89154.

Arsenic (As) is a potent carcinogen and the most common metal(loid) contaminant in drinking water sources globally. In acidic, Fe-rich systems, nanocrystalline Fe(III) precipitates (Fe(III)(NP)) are the main scavengers of As. However, the redox cycling of Fe(III)(NP) highly enhances As mobility and bioavailability. Notably, the irreversible release of As in runoff resulting from reductive dissolution of Fe(III)(NP) makes the effective remediation of As an ongoing environmental challenge. Here, we show for the first time that detrital clay minerals originating from the partial weathering of coal mining waste substantially increased total As uptake by acid mine drainage (AMD) sediments. The As immobilization mechanisms by the AMD sediments were investigated by the combined use of microbial community structure characterization (16S rRNA), chemical extractions, and synchrotron-based X-ray fluorescence (XRF), diffraction (XRD), and absorption (XANES). The use of an X-ray spot size as small as one micrometer allowed a detailed examination of the heterogeneous AMD sediments. Our results suggest that during sustained redox cycling of iron in Fe(III)(NP)-clay mixed-mineral systems, the clays controlled As mobility by (1) enhancing heterogeneous precipitation of Fe(III)(NP) under oxic conditions, which then adsorbed or incorporated As; and (2) facilitating the transfer of As from Fe(III)(NP) to clay during microbially mediated reduction of Fe(III)(NP) coatings under anoxic conditions. Designing remediation strategies that incorporate clay could become a promising low-cost strategy for As remediation in mining-impacted areas.

X-ray absorption fine structure (XAFS) spectroscopy has proven to be a valuable tool in defining valence states of multivalent elements in minerals and glasses that can then be used as oxybarometry proxies. First row transition multivalent elements Ti, V, Cr, and Fe are common targets. Micro-XAFS provides wide coverage of oxygen fugacity on all minerals and glasses, with high spatial resolution, trace level sensitivity, and no stoichiometry constraints. This method has been applied to an extensive array of geochemical problems including heterogeneity of terrestrial mantle sources, effects of volatile degassing of magmas, evolution of lunar melts, metamorphism of chondrites, and relationships between achondrites. Valence states alone can be insightful indicators of oxidation, such as the presence or absence of Ti3+ and the effects of metamorphism on asteroidal parent bodies. Importantly, XAFS can be extended to infer oxygen fugacity of parent melts by calibrating with laboratory experiment products under controlled conditions. When valence measurements or oxygen fugacity determinations are undertaken on non-cubic minerals, careful calibration data using oriented samples as well as knowledge of valence-specific partition coefficients are needed. XAFS offers the ability to apply multiple oxybarometers (e.g., Ti, Cr, and V valence proxies) to individual, potentially zoned, mineral grains. Challenges include corrections for orientation effects, X-ray beam-induced modifications, and the sparcity of valence-specific partition coefficient measurements. In some cases, application of statistical and machine-learning methods based on linear algebra such as principal component analysis (PCA), partial least-squares (PLS) analysis, and least absolute shrinkage and selection operator (Lasso) regressions can help to identify and compensate for some of external factors complicating XAFS analysis.