^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

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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.