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Published November 1999 | Published
Journal Article Open

A study of the minor element concentrations of spinels from two type B calcium-aluminum-rich inclusions: An investigation into potential formation conditions of calcium-aluminum-rich inclusions

Abstract

We have conducted an electron microprobe study of minor element distributions among spinels from two type B1 calcium-aluminum-rich inclusions (CAIs): Allende TS-23 and Leoville 3537–2. We show that by maintaining the petrologic context (edge, middle, and center of the inclusion plus their host silicate phase), four populations of spinels are resolvable based on their minor element contents. One population resides within the edge area (mainly mantle melilite) and is characterized by the highest V contents. Unlike Leoville 3537–2, many edge grains from Allende TS-23 also have high-Fe contents (up to 4.0 wt%) and low-Cr values. Based on their V and Ti concentrations (which is positively correlated), middle and center grains define a trend that is divided into three populations: spinels enclosed by melilite, fassaite, and anorthite. The overall range in Ti concentration based on fractional crystallization should be much less than a factor of 2; however, the observed range is considerably larger. The minor element contents of these grains are interpreted as recording alteration, primary fractional crystallization, and a complex igneous history that may involve remelting and recrystallization. From our data, Allende TS-23 has experienced more alteration than Leoville 3537–2, which is consistent with previous petrologic studies of silicates within these objects; yet both objects have likely been remelted (at least one additional melting event, possibly two, postdating the initial formation of these CAIs). By invoking a remelting history, the large range ir Ti concentrations and the different populations of spinels can be explained. Although our data suggest that more than one generation of spinels exist within these objects, we are unable to establish any population of relic spinel grains that predate the initial melting event.

Additional Information

© 1999 The Meteoritical Society. Received 1998 May 29; accepted in revised form 1999 July 1. We would like to thank G. J. MacPherson for the loan of USNM Leoville 3537-2 and L. Grossman for the sample of Allende TS-23. This project was greatly improved by numerous conversations with J. Paque, J. Beckett, G. J. MacPherson, A. Davis, S. Russell, S. Simon, and L. Grossman, A. El Gorsey, R. Ash, and G. Rossman. We also thank D. Ebel and L. Grossman for data used in our condensation figure and P. Carpenter for assistance with the microprobe analysis. The quality of this manuscript was improved by constructive reviews from G. J. MacPherson, M. Ebihara, and associate editor J. S. Delaney, and we thank them. This project was supported by NASA grant NAG5-4319, D. S. Burnett.

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August 22, 2023
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