Trace elements in the Allende meteorite—I. Coarse-grained,Ca-rich inclusions |
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| Authors: | Lawrence Grossman R Ganapathy |
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| Institution: | Department of the Geophysical Sciences and Enrico Fermi Institute U.S.A.;Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, U.S.A. |
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| Abstract: | INAA of ten coarse-grained, melilite-spinel-bearing inclusions in the Allende meteorite for Ca, Sc, Hf, Ta, W, Os, Ir, Ru, La, Ce, Sm, Eu, Tb, Dy, Yb, Fe, Co, Cr and Au reveals that all of the refractory elements are enriched by a mean factor of 18.6 relative to their concentrations in Cl chondrites, consistent with a high-temperature condensation origin for the inclusions. Os, Ir and Ru were probably incorporated by the inclusions as tiny nuggets of an alloy in which they were dissolved in cosmic proportion to one another. Sc and Hf entered the inclusions in a separate phase, also in cosmic proportion, accompanied by a fraction of the REE. Bulk REE abundances are independent of the major minerals in the inclusions; yet, data from mineral separates suggest that the REE were partitioned between coexisting melilite and pyroxene according to crystal structure controls. A two-stage model is proposed in which the REE first entered the inclusions as trace, refractory condensate phases and then re-distributed themselves between the crystallizing major phases after the inclusions were melted in the nebula. |
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