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Published March 2022 | Supplemental Material + Published
Journal Article Open

Sierra Gorda 013: Unusual CBa‐like chondrite

Abstract

The new metal-enriched anomalous chondrite Sierra Gorda 013 (SG 013) contains two different lithologies. Lithology 1 (L1) is represented by anomalous CBa-like chondrite material containing ~80 vol% of Fe,Ni-metal particles and globules up to 6 mm in size; chondrules and clasts of types POP, BO, and SO (up to 5 mm in diameter); rare sulfides; and shock melted silicate–metal areas. It does not contain any fine-grained matrix. Several chondrules contain chromite–pyroxene symplectites. Lithology 2 (L2) has a recrystallized texture with evenly distributed olivine, pyroxene and plagioclase. L2 does not have any chondrules or sulfides, and contains less Fe,Ni- metal (~25 vol%) than L1. Both lithologies contain reduced olivine (Fa2–4) and pyroxene (Fs3.5), similar to CBa chondrites. Similar to CBa, there is no Ni-Co correlation in the SG 013 metal. Rare sulfides in L1 are enriched in V. Chromite was observed in both lithologies. Oxygen isotope compositions of both lithologies are different but in the range of CBa chondrites. Bulk major and trace element geochemistry of nonporphyritic chondrules and bulk siderophile compositions in metal globules of L1 indicate elemental fractionation during formation of metallic and silicate objects with records of the evaporation process: depletion in moderate and volatile elements with the exception of Cr. Bulk geochemistry of porphyritic chondrules of L1 and the silicate portion of L2 is similar and also indicates evaporation processes. The rare Earth element (REE) distribution of L1 chondrules records a very fractionated signature corresponding to possible differentiated precursor material, while the REE pattern of L2 is primitive chondritic. The formation of SG 013 could be explained by collisions of planetesimals producing an impact plume, the precursor material of which could be chondritic and possibly differentiated. Both lithologies were affected by secondary processes: L1 preserved the traces of shock events and partial melting resulting in formation of symplectites in chondrules, melt pockets, and metal–silicate melt between the metal globules; L2 was affected by shock thermal metamorphism (up to 900 °C) resulting in recrystallization.

Additional Information

© 2022 The Meteoritical Society. Issue Online: 10 March 2022; Version of Record online: 04 March 2022; Manuscript accepted: 22 December 2021; Manuscript received: 26 March 2021. We thank Sergei E. Borisovsky for his help with some BSE images using JEOL JXA-8200(IGEM; Institute of Geology of Ore Deposits,Petrography, Mineralogy and Geochemistry of Russian Academy of Sciences, Staromonetny per. 35, Moscow 119017, Russia). We very appreciate Associate Editor, Kevin Righter, and reviewers, Rhian Jones and Sasha Krot, for their fruitful reviews which helped to improve this paper. This work was partially supported by the Russian Fund of Basic Research (RFBR) (grant #20-05-00117) and it was a part of research contribution of the program #0137-2019-0002. Research at the NationalHigh Magnetic Field Laboratory is supported by theUS National Science Foundation through NSF/DMR-1644779 and the State of Florida, and by NASA Emerging Worlds (#80NSSC18K0595). Data Availability Statement—Data available on requestfrom the authors.

Attached Files

Published - Meteorit_Planetary_Scien_-_2022_-_Ivanova_-_Sierra_Gorda_013_Unusual_CBa‐like_chondrite.pdf

Supplemental Material - maps13786-sup-0001-figs1.pdf

Supplemental Material - maps13786-sup-0002-figs2.pdf

Supplemental Material - maps13786-sup-0003-figs3.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023