Origin of isolated olivine grains in carbonaceous chondrites

Abstract

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 $Δ^{17}O < -4\permil$ 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.

43 pages, 12 figures, accepted to Meteoritics and Planetary Science

References in corpus (6)

• Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites
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• Northwest Africa 5958: a weakly altered CM-related ungrouped chondrite, not a CI3
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Cited by in corpus (6)

• Formation and evolution of a protoplanetary disk: combining observations, simulations and cosmochemical constraints
• Collisions and compositional variability in chondrule-forming events
• Meteorite petrology versus genetics: Toward a unified binominal classification
• Abundance, Sizes, and Major Element Compositions of Components in CR and LL Chondrites: Formation from Single Reservoirs
• Thermal history of matrix forsterite grains from Murchison based on high-resolution tomography
• Chondrule formation in the outer disk from the primary three-dimensional chemical composition of CM chondrules