In situ oxygen, magnesium, and silicon isotopic compositions of the FUN inclusion Vigarano 1623-5

1,2Johanna Marin-Carbonne,1Kevin D. McKeegan,3,4Andrew M. Davis,5Glenn J. MacPherson,5Ruslan A. Mendybaev,5Frank M. Richter
Meteoritics & Planetary Science (in Press) Open Access Link to Article []
1Department of Earth, Planetary, and Space Sciences, University of California—Los Angeles, Los Angeles, California, USA
2Institut des Sciences de la Terre, Université de Lausanne, Lausanne, Switzerland
3Department of the Geophysical Sciences, University of Chicago, Illinois, USA
4Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
5Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
Published by arrangement with John Wiley & Sons

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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