^1,2,3David Kaeter,¹Martin A. Ziemann,²Ute Böttger,⁴Iris Weber,⁵Lutz Hecht,⁶Sergey A. Voropaev,⁶Alexander V. Korochantsev,⁷Andrey V. Kocherov
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13027]
¹Institute for Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany
²Institute of Optical Sensor Systems, German Aerospace Center, Berlin, Germany
³iCRAG, School of Earth Sciences, University College Dublin, Dublin D04 N2E5, Ireland
⁴Institute of Planetology, University of Münster, Münster, Germany
⁵Museum für Naturkunde, Berlin, Germany
⁶Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia
⁷Chelyabinsk State University, Chelyabinsk, Russia
Published by arrangement with John Wiley & Sons

We present results of petrographic, mineralogical, and chemical investigations of three Chelyabinsk meteorite fragments. Three distinct lithologies were identified: light S3 LL5, dark S4–S5 LL5 material, and opaque fine-grained former impact melt. Olivine–spinel thermometry revealed an equilibration temperature of 703 ± 23 °C for the light lithology. All plagioclase seems to be secondary, showing neither shock-induced fractures nor sulfide-metal veinlets. Feldspathic glass can be observed showing features of extensive melting and, in the dark lithology, as maskelynite, lacking melt features and retaining grain boundaries of former plagioclase. Olivine of the dark lithology shows planar deformation features. Impact melt is dominated by Mg-rich olivine and resembles whole-rock melt. Melt veins (<2 mm) are connected to narrower veinlets. Melt vein textures are similar to pegmatite textures showing chilled margins, a zone of inward-grown elongated crystals and central vugs, suggesting crystallization from supercooled melt. Sulfide-metal droplets indicate liquid immiscibility of both silicate and sulfide as well as sulfide and metal melts. Impact melting may have been an important factor for differentiation of primitive planetary bodies. Graphite associated with micrometer-sized melt inclusions in primary olivine was detected by Raman mapping. Carbon isotopic studies of graphite could be applied to test a possible presolar origin.

¹F. A. J. Abernethy,¹A. B. Verchovsky,¹I. A. Franchi,^1,2M. M. Grady
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13016]
¹Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes, UK
²Department of Earth Sciences, The Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Carbon and nitrogen data from stepped combustion analysis of eight angrites, seven eucrites, and two diogenites, alongside literature data from a further nine eucrites and two diogenites, have been used to assess carbon and nitrogen incorporation and isotope fractionation processes on the angrite parent body (APB), for comparison with volatile behavior on the HED parent body (4 Vesta). A subset of the angrite data has been reported previously (Abernethy et al. 2013). Two separate families of volatile components were observed. They were (1) moderately volatile material (MVM), mostly combusting between ~500 and 750 °C and indistinguishable from terrestrial contamination and (2) refractory material (RM), mainly released above 750 °C and thought to be carbon (as math formula) and nitrogen (as N2 or math formula) dissolved within the silicate lattice, fitting with the slightly oxidized (~IW to IW+2) angrite fO2 conditions. Isotopic fractionation trends for carbon and nitrogen within the plutonic and basaltic (quenched) angrites suggest that the behavior of the two volatile elements is loosely coupled, but that the fractionation process differs between the two angrite subgroups. Comparison with results from eucrites and diogenites implies similarities between speciation of carbon and nitrogen on 4 Vesta and the APB, with the latter being more enriched in volatiles than the former.

¹Ansgar Greshake,²Richard Wirth,³Jörg Fritz,⁴Tomasz Jakubowski,⁵Ute Böttger
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13030]
¹Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
²Helmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Potsdam, Germany
³Saalbau Weltraum Projekt, Heppenheim, Germany
⁴Wroclaw, Poland
⁵Deutsches Zentrum für Luft- und Raumfahrt, Institut für Optische Sensorsysteme, Berlin, Germany
Published by arrangement with John Wiley & Sons

Libyan Desert Glass (LDG) is a SiO₂-rich natural glass whose origin, formation mechanism, and target material are highly debated. We here report on the finding of a lens-shaped whitish inclusion within LDG. The object is dominantly composed of siliceous glass and separated from the surrounding LDG by numerous cristobalite grains. Within cristobalite, several regions rich in mullite often associated with ilmenite were detected. Mineral assemblage, chemical composition, and grain morphologies suggest that mullite was formed by thermal decomposition of kaolinitic clay at atmospheric pressure and T ≥ 1600 °C and also attested to high cooling rates under nonequilibrium conditions. Cristobalite contains concentric and irregular internal cracks and is intensely twinned, indicating that first crystallized β-cristobalite inverted to α-cristobalite during cooling of the SiO₂-rich melt. The accompanied volume reduction of 4% induced the high density of defects. The whitish inclusion also contains several partly molten rutile grains evidencing that at least locally the LDG melt was at T ≥ 1800 °C. Based on these observations, it is concluded that LDG was formed by high-temperature melting of kaolinitic clay-, rutile-, and ilmenite-bearing Cenozoic sandstone or sand very likely during an asteroid or comet impact onto Earth. While melting and ejection occurred at high pressures, the melt solidified quickly at atmospheric pressure.