Origin Of Isolated Olivine Grains In Carbonaceous Chondrites


Back-scattered electron (A) and cathodoluminescence (B) images of isolated olivine grain NWA 11086 IO12, with dashed line indicating the location of the profile shown in Fig. 6H. The CL shows spectacular oscillatory sector zoning in a central rectangular area. On the lower right, a darker-CL irregularly shaped angular patch seems to indicate an independent olivine grain (enclosing two black-CL metal grains) welded together with the previous one, with subsequent layers with oscillatory zoning swathing both. The irregular outlines may point to fragmentation around the core of the parent olivine.

We report microscopic, cathodoluminescence, chemical and O isotopic measurements of FeO-poor isolated olivine grains (IOG) in the carbonaceous chondrites Allende (CV3), Northwest Africa 5958 (C2-ung), Northwest Africa 11086 (CM2-an), Allan Hills 77307 (CO3.0).

The general petrographic, chemical and isotopic similarity with bona fide type I chondrules confirms that the IOG derived from them. The concentric CL zoning, reflecting a decrease in refractory elements toward the margins, and frequent rimming by enstatite are taken as evidence of interaction of the IOG with the gas as stand-alone objects.

This indicates that they were splashed out of chondrules when these were still partially molten. CaO-rich refractory forsterites, which are restricted to $\Delta^{17}O < -4\permil$ likely escaped equilibration at lower temperatures because of their large size and possibly quicker quenching. The IOG thus bear witness to frequent collisions in the chondrule-forming regions.

Emmanuel Jacquet, Maxime Piralla, Pauline Kersaho, Yves Marrocchi
Comments: 43 pages, 12 figures, accepted to Meteoritics and Planetary Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2101.10073 [astro-ph.EP] (or arXiv:2101.10073v1 [astro-ph.EP] for this version)
Submission history
From: Emmanuel Jacquet
[v1] Mon, 25 Jan 2021 13:39:33 UTC (3,196 KB)
https://arxiv.org/abs/2101.10073
Astrobiology, Astrochemistry

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