In situ oxygen,magnesium, and silicon isotopic compositions of the FUN inclusion Vigarano 1623-5 |
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Authors: | Johanna Marin-Carbonne Kevin D McKeegan Andrew M Davis Glenn J MacPherson Ruslan A Mendybaev Frank M Richter |
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Institution: | 1. Department of Earth, Planetary, and Space Sciences, University of California—Los Angeles, Los Angeles, California, USA;2. Department of the Geophysical Sciences, University of Chicago, Illinois, USA
Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA;3. Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA;4. Department of the Geophysical Sciences, University of Chicago, Illinois, USA |
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Abstract: | Oxygen, magnesium, and silicon isotopic abundances in Vigarano 1623-5 were studied using secondary ion mass spectrometry to investigate correlations between isotopic and petrologic properties of this unique forsterite-bearing FUN inclusion. Vigarano 1623-5 displays large, correlated mass-dependent fractionation effects, tightly linked to mineralogy within distinct petrologic units of the inclusion. The pyroxene-rich and melilite-rich interior parts of the inclusion display highly mass-fractionated isotopic compositions of oxygen, magnesium, and silicon, consistent with Rayleigh distillation during evaporation of a melt with initial oxygen composition close to a solar composition. However, the chemical composition, enriched in magnesium and silicon, suggests a precursor already fractionated by prior melt evaporation. A discontinuous igneous rim was produced by a flash-melting event followed by isotopic exchange in the rim melilite with planetary-like oxygen, mechanical fragmentation, and reassembly with an accretionary rim of heterogeneous materials. Al-rich minerals in 1623-5 show evidence for having crystallized with live 26Al but at less than the “canonical” level of most CV calcium-aluminum-rich inclusions. However, well-defined 26Al-26Mg isochrons are not found and temporal implications are ambiguous. |
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