¹Nancy L. Chabot,¹Rachel H. Cueva,²Andrew W. Beck,³Richard D. Ash
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13462]
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, 20723 USA
²Department of Petroleum Engineering & Geology, Marietta College, Marietta, Ohio, 45750 USA
³Department of Geology, University of Maryland, College Park, Maryland, 20742 USA
Published by arrangement with John Wiley & Sons

Some of the defining characteristics of the IIG iron meteorite group are their high bulk P contents and massive, coarse schreibersite, which have been calculated to make up roughly 11–14 wt% of each specimen. In this study, we produced two data sets to investigate the formation of schreibersites in IIG irons: measurements of trace elements in the IIG iron meteorite Twannberg and experimental determinations of trace element partitioning into schreibersite. The schreibersite‐bearing experiments were conducted with schreibersite in equilibrium with a P‐rich melt and with bulk Ni contents ranging from 0 to 40 wt%. The partitioning behavior for the 20 elements measured in this study did not vary with Ni content. Comparison of the Twannberg measurements with the experimental results required a correction factor to account for the fact that the experiments were conducted in a simplified system that did not contain a solid metal phase. Previously determined solid metal/P‐rich melt partition coefficients were applied to infer schreibersite/solid metal partitioning behavior from the experiments, and once this correction was applied, the two data sets showed broad similarities between the schreibersite/solid metal distribution of elements. However, there were also differences noted, in particular between the Ni and P contents of the solid metal relative to the schreibersite inferred from the experiments compared to that measured in the Twannberg sample. These differences support previous interpretations that subsolidus schreibersite evolution has strongly influenced the Ni and P content now present in the solid metal phase of IIG irons. Quantitative attempts to match the IIG solid metal composition to that of late‐stage IIAB irons through subsolidus schreibersite growth were not successful, but qualitatively, this study corroborates the striking similarities between the IIAB and IIG groups, which are highly suggestive of a possible genetic link between the groups as has been previously proposed.

¹Christian Vollmer,¹Stella Rombeck,²Julia Roszjar,³Adam R. Sarafian,¹Stephan Klemme
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13453]
¹Institut für Mineralogie, Westfälische Wilhelms‐Universität Münster, Corrensstrasse 24, D‐48149 Münster, Germany
²Department of Mineralogy and Petrography, Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria
³Science and Technology Division, Corning Incorporated, 21 Lynn Morse Rd., Painted Post, New York, New York, 14870 USA
Published by arrangement with John Wiley & Sons

We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta′s crust. The textures range from subophitic to brecciated, porphyritic, and quench‐textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y‐793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post‐magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late‐stage alteration processes that caused deposition of Fe‐rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late‐stage metasomatism model for their formation.

¹O. Pravdivtseva,²F. L. H. Tissot,³N. Dauphas,¹S. Amari
Nature Astronomy(In Press) Link to Article [DOIhttps://doi.org/10.1038/s41550-019-1000-z]
¹Physics Department and McDonnell Center for the Space Sciences, Washington University, Saint Louis, MO, USA
²The Isotoparium, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
³Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, Chicago, IL, USA

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