Timing of thermal metamorphism in CM chondrites: implications for Ryugu and Bennu future sample return

Amsellem, Elsa, Moynier, Frédéric, Mahan, Brandon, and Beck, Pierre (2020) Timing of thermal metamorphism in CM chondrites: implications for Ryugu and Bennu future sample return. Icarus, 339. 113593.

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Abstract

Carbonaceous chondrites are often considered potential contributors of water and other volatiles to terrestrial planets as most of them contain significant amounts of hydrous mineral phases. As such, carbonaceous chondrites are candidate building blocks for Earth, and elucidating their thermal histories is of direct importance for understanding the volatile element history of Earth and the terrestrial planets. A significant fraction of CM type carbonaceous chondrites are thermally meta- morphosed or “heated” and have lost part of their water content. The origin and the timing of such heating events are still debated, as they could have occurred either in the first Myrs of the Solar System via short-lived radioactive heating, or later by impact induced heating and/or solar radiation. Since Rb is more volatile than Sr, and some heated CM chondrites are highly depleted in Rb, a dating system based on the radioactive decay of ⁸⁷Rb to ⁸⁷Sr (λ⁸⁷Rb = 1.393 × 10⁻¹¹ yr⁻¹) could be used to date the heating event relating to the fractionation of Rb and Sr. Here, we have leveraged the ⁸⁷Rb/⁸⁷Sr system to date the heating of five CM chondrites (PCA 02012, PCA 02010, PCA 91008, QUE 93005 and MIL 07675). We find that the heating events of all five meteorites occurred at least 3 Ga after the formation of the Solar System. Such timing excludes short-lived radioactive heating as the origin of thermal metamorphism in these meteorites, and relates such heating events to ages of collisional families of C-type asteroids.

Item ID: 62761
Item Type: Article (Research - C1)
ISSN: 1090-2643
Copyright Information: © 2019 Elsevier Inc. All rights reserved.
Funders: European Research Council (ERC), Sorbonne Paris Cité (SPC), chaire d’excellence Sorbonne Paris Cité
Projects and Grants: ERC H2020 framework program/ERC grant agreement #637503 (Pristine), SPC UnivEarthS Labex program, ANR-10- LABX-0023 and ANR-11-IDEX-0005-02, ERC H2020 SOLARYS ERCCoG2017_ 771691
Date Deposited: 23 Jun 2020 22:02
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 50%
02 PHYSICAL SCIENCES > 0201 Astronomical and Space Sciences > 020109 Space and Solar Physics @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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