¹Roberts Blukis, ²Rudolf Rüffer, ²Aleksandr I. Chumakov, ¹Richard J. Harrison
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12841]
¹Department of Earth Sciences, University of Cambridge, Cambridge, UK
²European Synchrotron Radiation Facility, Grenoble, France
Published by Arrangement with John Wiley & Sons

Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using 57Fe synchrotron Mössbauer spectroscopy. Spatial resolution of ~10–20 μm was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1 h. Spectra were recorded every 5–10 μm, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the “cloudy zone.” Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X-ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed.

¹C.J. Renggli, ¹P.L. King, ¹R.W. Henley, ¹M.D. Norman
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.03.012]
¹Research School of Earth Sciences, Australian National University, ACT 2601, Australia
Copyright Elsevier

Transport of metals in volcanic gases on the Moon differs greatly from their transport on the Earth because metal speciation depends largely on gas composition, temperature, pressure and oxidation state. We present a new thermochemical model for the major and trace element composition of lunar volcanic gas during pyroclastic eruptions of picritic magmas calculated at 200-1500 °C and over 10-9-103 bar. Using published volatile component concentrations in picritic lunar glasses, we have calculated the speciation of major elements (H, O, C, Cl, S and F) in the coexisting volcanic gas as the eruption proceeds. The most abundant gases are CO, H2, H2S, COS and S2, with a transition from predominantly triatomic gases to diatomic gases with increasing temperatures and decreasing pressures. Hydrogen occurs as H2, H2S, H2S2, HCl, and HF, with H2 making up 0.5 to 0.8 mole fractions of the total H. Water (H2O) concentrations are at trace levels, which implies that H-species other than H2O need to be considered in lunar melts and estimates of the bulk lunar composition. The Cl and S contents of the gas control metal chloride gas species, and sulfide gas and precipitated solid species. We calculate the speciation of trace metals (Zn, Ga, Cu, Pb, Ni, Fe) in the gas phase, and also the pressure and temperature conditions at which solids form from the gas. During initial stages of the eruption, elemental gases are the dominant metal species. As the gas loses heat, chloride and sulfide species become more abundant. Our chemical speciation model is applied to a lunar pyroclastic eruption model with isentropic gas decompression. The relative abundances of the deposited metal-bearing solids with distance from the vent are predicted for slow cooling rates (< 5 °C/s). Close to a volcanic vent we predict native metals are deposited, whereas metal sulfides dominate with increasing distance from the vent. Finally, the lunar gas speciation model is compared with the speciation of a H2O-, CO2- and Cl-rich volcanic gas from Erta Ale volcano (Ethiopia) as an analogy for more oxidized planetary eruptions. In the terrestrial Cl-rich gas the metals are predominantly transported as chlorides, as opposed to metallic vapours and sulphides in the lunar gas. Due to the presence of Cl-species, metal transport is more efficient in the volcanic gas from Erta Ale compared to the Moon.

¹P. Vernazza et al. (>10)*
The Astronomical Journal 153, 72 Link to Article [https://doi.org/10.3847/1538-3881/153/2/72]
¹Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
*Find the extensive, full author and affiliation list on the publishers website

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Paul H. Warren, ^1,2Junko Isa, ²Mitsuru Ebihara,³Akira Yamaguchi, ^4,5Bastian Baecker
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12827]
¹Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
²Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, Japan
³Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
⁴Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
⁵NASA Marshall Space Flight Center, Huntsville, Alabama, USA
Published by arrangement with John Wiley & Sons

The unique occurrence of abundant (~1 vol%) near-pure-Fe metal in the Camel Donga eucrite is more complicated than previously believed. In addition to that component of groundmass metal, scattered within the meteorite are discrete nodules of much higher kamacite abundance. We have studied the petrology and composition of two of these nodules in the form of samples we call CD2 and CD3. The nodules are ovoids 11 (CD2) to 15 (CD3) mm across, with metal, or inferred preweathering metal, abundances of 12–17 vol% (CD2 is unfortunately quite weathered). The CD3 nodule also includes at its center a 5 mm ovoid clumping (6 vol%) of F-apatite. Both nodules are fine-grained, so the high Fe metal and apatite contents are clearly not flukes of inadequate sampling. The metals within the nodules are distinctly Ni-rich (0.3–0.6 wt%) compared to the pure-Fe (Ni generally 0.01 wt%) groundmass metals. Bulk analyses of three pieces of the CD2 nodule show that trace siderophile elements Ir, Os, and Co are commensurately enriched; Au is enriched to a lesser degree. The siderophile evidence shows the nodules did not form by in situ reduction of pyroxene FeO. Moreover, the nodules do not show features such as silica-phase enrichment or pyroxene with reduced FeO (as constrained by FeO/MgO and especially FeO/MnO) predicted by the in situ reduction model. The oxide minerals, even in groundmass samples well away from the nodules, also show little evidence of reduction. Although the nodule boundaries are generally sharp, groundmass-metal Ni content is anti-correlated with distance from the CD3 nodule. We infer that the nodules represent materials that originated within impactors into the Camel Donga portion of the eucrite crust, but probably were profoundly altered during later metamorphism/metasomatism. Origin of the pure-Fe groundmass metal remains enigmatic. In situ reduction probably played an important role, and association in the same meteorite of the Fe-nodules is probably significant. But the fluid during alteration was probably not (as previously modeled) purely S and O, of simple heat-driven internal derivation. We conjecture a two-stage metasomatism, as fluids passed through Camel Donga after impact heating of volatile-rich chondritic masses (survivors of gentle accretionary impacts) within the nearby crust. First, reduction to form troilite may have been triggered by fluids rich in S2 and CO (derived from the protonodules?), and then in a distinct later stage, fluids were (comparatively) H2O-rich, and thus reacted with troilite to form pure-Fe metal along with H2S and SO2. The early eucrite crust was in places a dynamic fluid-bearing environment that hosted complex chemical processes, including some that engendered significant diversity among metal+sulfide alterations.

¹Carles E. Moyano-Cambero, ¹Josep M. Trigo-Rodríguez, ²M. Isabel Benito, ³Jacinto Alonso-Azcárate, ⁴Martin R. Lee, ⁵Narcís Mestres, ^6,7Marina Martínez-Jiménez, ¹Francisco J. Martín-Torres, ⁸Jordi FraxedasMeteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12851]
¹Institute of Space Sciences (IEEC-CSIC), Campus UAB, Cerdanyola del Vallès, Barcelona, Spain
²Departamento de Estratigrafía-IGEO, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid-CSIC, Madrid, Spain
³Fac. de Ciencias Ambientales y Bioquímica, Universidad de Castilla-La Mancha, Toledo, Spain
⁴School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 800, UK
⁵Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, Barcelona, Spain
⁶Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla, Granada, Spain
⁷Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Kiruna, Sweden
⁸Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, Barcelona, Spain
Published by arrangement with John Wiley & Sons

Martian meteorites can provide valuable information about past environmental conditions on Mars. Allan Hills 84001 formed more than 4 Gyr ago, and owing to its age and long exposure to the Martian environment, and this meteorite has features that may record early processes. These features include a highly fractured texture, gases trapped during one or more impact events or during formation of the rock, and spherical Fe-Mg-Ca carbonates. In this study, we have concentrated on providing new insights into the context of these carbonates using a range of techniques to explore whether they record multiple precipitation and shock events. The petrographic features and compositional properties of these carbonates indicate that at least two pulses of Mg- and Fe-rich solutions saturated the rock. Those two generations of carbonates can be distinguished by a very sharp change in compositions, from being rich in Mg and poor in Fe and Mn, to being poor in Mg and rich in Fe and Mn. Between these two generations of carbonate is evidence for fracturing and local corrosion.

¹Patrick Weber, ²Beda A. Hofmann, ³Tamer Tolba, ³Jean-Luc Vuilleumier
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12847]
¹Hôpital Neuchâtelois, Service de Radiothérapie, La Chaux-de-Fonds, Switzerland
²Naturhistorisches Museum der Burgergemeinde Bern, Bern, CH-3005, Switzerland
³Albert Einstein Center for Fundamental Physics, LHEP, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

/enhanced/static/common/js/patches/ie.js?version=1.13.3
<!–

^1,2E. BUCHNER , ^3,4M. SCHMIEDER
Geological Magazine (in Press) Link to Article [DOI: https://doi.org/10.1017/S0016756816001357]
¹HNU – Neu-Ulm University, Wileystraße 1, D-89231 Neu-Ulm, Germany
²Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstraße 18, D-70174 Stuttgart, Germany
³USRA – Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston TX 77058, USA
⁴NASA–SSERVI

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Agnese Fazio, ¹Ulrich Mansfeld, ¹Falko Langenhorst
Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12849]
¹Analytische Mineralogie der Mikro- und Nanostrukturen, Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Jena, Germany
Published by arrangement with John Wiley & Sons

Coesite is one of the most common and abundant high-pressure phases occurring in impactites. The mechanism of formation of coesite and its postshock evolution is revisited in this paper based on Raman microspectroscopy, and scanning and transmission electron microscopy of a coesite-bearing suevite from the Ries impact structure. Our data indicate that coesite forms through a single process, i.e., by crystallization from high-pressure silica melt, and that its formation is related to fluid inclusions in precursor quartz. During the postshock phase, coesite aggregates are partially modified by annealing and interactions with fluids. In an early stage of the postshock evolution, coesite is back-transformed to quartz and the surrounding diaplectic glass devitrifies into β-cristobalite, which transforms into α-cristobalite and then into microcrystalline quartz during subsequent stages of the postshock evolution. Altogether these postshock modifications result in a significant volume loss and extensional fracturing. During a late postshock stage, the fractures are filled with clay minerals due to circulation of hydrothermal fluids.

¹Bhaskar J. Saikia,²Gopalakrishnarao Parthasarathy,³Rashmi R. Borah
Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12850]
¹Department of Physics, Anandaram Dhekial Phookan College, Nagaon, India
²CSIR-National Geophysical Research Institute, Hyderabad, India
³Department of Physics, Nowgong College, Nagaon, India
Published by arrangement with John Wiley&Sons

We present here the Raman spectroscopic study of silicate and carbonaceous minerals in three ordinary chondrites with the aim to improve our understanding the impact process including the peak metamorphic pressures present in carbon-bearing ordinary chondites. The characteristic Raman vibrational peaks of olivines, pyroxenes, and plagioclase have been determined on three ordinary chondrites from India, Dergaon (H5), Mahadevpur (H4/5), and Kamargaon (L6). The Raman spectra of these meteorite samples show the presence of nanodiamonds at 1334–1345 cm−1 and 1591–1619 cm−1. The full-width at half maximum (FWHM) of Raman peaks for Mahadevpur and Dergaon reflect the nature of shock metamorphism in these meteorites. The frequency shift in Raman spectra might be because of shock effects during the formation of the diamond/graphite grains.

^1,2Ying Sun, ²Lin Li, ³Yuanzhi Zhang
Earth and Planetary Science Letters 465, 48-58 Link to Article [http://dx.doi.org/10.1016/j.epsl.2017.01.019]
¹College of Geoexploration Science and Technology, Jilin University, Changchun 130062, China
²Department of Earth Sciences, Indiana University–Purdue University Indianapolis, 723 W. Michigan St, SL118, Indianapolis, IN 46202, USA
³Key lab of Lunar Science and Deep-exploration, Chinese Academy of Sciences, Bejing 100012, China
Copyright Elsevier

Mg-spinel bearing lithologies, lacking abundant mafic materials, have been discovered with images acquired by the Moon Mineralogy Mapper (M3) aboard Chandrayaan-1. We conducted a systematic screening of lunar crater central peaks for the presence of Mg-spinel to address its distribution and petrogenesis. 38 Mg-spinel bearing crater central peaks were identified in this study out of 166 craters investigated. The results suggest that Mg-spinel is common in the lunar crust and appears to be extensive in the middle part of the lunar crust underneath Procellarum KREEP Terrane (PKT). Mg-spinel neither exclusively originated from deep layers (>10 km) nor necessarily coexist with the appearance of olivine or pyroxene. 15 Mg-spinel bearing central peaks originated from depth less than 10 km. Nine investigated central peaks only contain Mg-spinel and plagioclase without any detectable mafic materials. All those observations imply that the origin of Mg-spinel is possibly related to Mg-suite plutonism and assimilation between high Mg′ magma with anorthositic crust. The extensive distribution and Mg-suite related petrogenesis indicates that Mg-spinel bearing lithologies might represent a new member of Mg-suite rocks.