The significance of fractional crystallization in the petrogenesis of Apollo 17 Type A and B high-Ti basalts
1990; Elsevier BV; Volume: 54; Issue: 6 Linguagem: Inglês
10.1016/0016-7037(90)90410-m
ISSN1872-9533
AutoresC. R. Neal, L. A. Taylor, S. S. Hughes, Roman A. Schmitt,
Tópico(s)Paleontology and Stratigraphy of Fossils
ResumoWhole-rock and mineral analyses of 26 “new” Type A and B Apollo 17 basalts are reported. The petrography and mineral chemistry of these basalts are similar to previously reported Apollo 17 basalts. However, these “new” whole-rock data extend the compositional ranges of previously reported Type A and B basalts and require the division of the Type B basalts into Type B1 and B2 varieties. These three types display similar trends when both major and trace elements are plotted against a fractionation index of Cr/La ratio. Major element compositions of basalts from all three types fall on olivine + Ti oxide control lines. The compositional ranges of all three groups can be effectively generated by 40–50% fractional crystallization of observed phenocryst phases. The compositions of three Type A basalts are only generated after 80% fractional crystallization. Previous models of different degrees of partial melting and KREEP assimilation were developed in order to explain the range in La/Sm ratio of the Type B basalts. With the recognition of two types of “B” basalts, these models are no longer valid. This study demonstrates that Apollo 17 Type A, B1, and B2 basalts have a relatively simple petrogenesis, with the only post-magma-generation process being fractional crystallization.
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