Coordinated Analyses of a Supernova Silicate Grain in the CO3.0 Chondrite Miller Range 07687

Seifert, Laura; Haenecour, P.; Ramprasad, Tarunika; Zega, T. J.

doi:10.1017/s1431927621009776

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“…Two grains were selected from the Fe-rich matrix regions and two grains from the Fe-poor matrix regions to investigate how and to what extent presolar silicate grains are affected by parent-body processing at the TEM scale and to understand their thermodynamic origins. Initial results were reported in Seifert et al (2021aSeifert et al ( , 2021bSeifert et al ( , 2022aSeifert et al ( , 2022b.…”

Section: Introductionmentioning

confidence: 99%

An in situ investigation of the preservation and alteration of presolar silicates in the Miller Range 07687 chondrite

Seifert

Haenecour

Ramprasad

et al. 2023

Meteorit & Planetary Scien

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Dust grains that formed around ancient stars and in stellar explosions seeded the early solar protoplanetary disk. While most of such presolar grains were destroyed during solar system formation, a fraction of such grains were preserved in primitive materials such as meteorites. These grains can provide constraints on stellar origins and secondary processing such as aqueous alteration and thermal metamorphism on their parent asteroids. Here, we report on the nature of aqueous alteration in the Miller Range (MIL) 07687 chondrite through the analysis of four presolar silicates and their surrounding material. The grains occur in the Fe‐rich and Fe‐poor lithologies, reflecting relatively altered and unaltered material, respectively. The O‐isotopic compositions of two grains, one each from the Fe‐rich and Fe‐poor matrix, are consistent with formation in the circumstellar envelopes of low‐mass Asymptotic Giant Branch (AGB)/Red Giant Branch (RGB) stars. The other two grains, also one each from the Fe‐rich and Fe‐poor matrix, have O‐isotopic compositions consistent with formation in the ejecta of type‐II supernovae (SNe). The grains derived from AGB/RGB stars include two polycrystalline pyroxene grains that contain Fe‐rich rims. The SNe grains include a polycrystalline Ca‐bearing pyroxene and a polycrystalline assemblage consistent with a mixture of olivine and pyroxene. Ferrihydrite is observed in all focused ion beam sections, consistent with parent‐body aqueous alteration of the fine‐grained matrix under oxidizing conditions. The Fe‐rich rims around presolar silicates in this study are consistent with Fe‐diffusion into the grains resulting from early‐stage hydrothermal alteration, but such alteration was not extensive enough to lead to isotopic equilibration with the surrounding matrix.

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Section: Introductionmentioning

confidence: 99%