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Metastable Phase Relations in the System Ca(sub O)-Al2(sub O)3-MgO-TiO(sub 2): Applications to Ca- And Al-Rich InclusionsIntroduction: High temperature phases such as corundum, hibonite, grossite, and perovskite are among the earliest phases that condensed in the early solar nebula. Recent work has shown that defect-structured phases occur in some ultrarefractory inclusions as metastable, possibly more kinetically-favored alternatives to the thermodynamically predicted stable phase assemblages [1-4]. For example, Han et al. have shown that non-stoichiometry in hibonite is accommodated by extra "spinel" blocks in the structure instead of the equilibrium assemblages hibonite+corundum or hibonite+spinel. To explore these relations, we have conducted a series of experiments in the system CaO-Al2O3- MgO-TiO2. Here we discuss the compositions and mineralogy of the experimental samples and how they relate to phases in refractory inclusions with a focus on perovskite and spinel. Methods: For the series of annealing studies, a CaO-Al2O3 eutectic melt is allowed to react with a pure alumina crucible at 1,530degC for either 4 hours or 5 days, followed by quenching in air. Later experiments were similar except that additions of 5 wt% MgO, and CaTiO(sub 3) were used to explore the effect of minor elements on the phase assemblages. The experimental conditions resulted in reaction zones approximately 100-300 m wide consisting of a hibonite layer immediately adjacent to the corundum, followed by a grossite layer, and finally krotite with residual quenched melt. For the experiments with Mg, spinel is distributed in all layers but is mainly concentrated in the krotite layer. In the Ti-bearing experiments, perovskite precipitated in association with the krotite and residual melt. In addition to the experiments, we also analyzed perovskite grains in the FUN inclusion SHAL [5] and a large compact type A CAI from Allende. The experiments and refractory inclusions were analyzed using a JEOL 7600F SEM and quantitative analyses were obtained using the JEOL 8530F field-emission electron microprobe.
Document ID
20170007949
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Keller, L. P. (NASA Johnson Space Center Houston, TX, United States)
Han, J. (Lunar and Planetary Inst. Houston, TX, United States)
Date Acquired
August 22, 2017
Publication Date
July 23, 2017
Subject Category
Metals And Metallic Materials
Report/Patent Number
JSC-CN-39716
Meeting Information
Meeting: Meteoritical Society Annual Meeting (METSOC 2017)
Location: Santa Fe, NM
Country: United States
Start Date: July 23, 2017
End Date: July 28, 2017
Sponsors: Lunar and Planetary Inst.
Distribution Limits
Public
Copyright
Public Use Permitted.

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