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Basalt generation at the Apollo 12 site. Part 2: Source heterogeneity, multiple melts, and crustal contaminationThe petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and late-stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile.
Document ID
19950031755
Document Type
Reprint (Version printed in journal)
Authors
Neal, Clive R. (Univ. of Notre Dame, Notre Dame, IN United States)
Hacker, Matthew D. (Univ. of Notre Dame, Notre Dame, IN United States)
Snyder, Gregory A. (Univ. of Tennessee, Knoxville, TN United States)
Taylor, Lawrence A. (Univ. of Tennessee, Knoxville, TN United States)
Liu, Yun-Gang (Oregon State Univ. Corvallis, OR, United States)
Schmitt, Roman A. (Oregon State Univ. Corvallis, OR, United States)
Date Acquired
August 16, 2013
Publication Date
May 1, 1994
Publication Information
Publication: Meteoritics
Volume: 29
Issue: 3
ISSN: 0026-1114
Subject Category
LUNAR AND PLANETARY EXPLORATION
Funding Number(s)
CONTRACT_GRANT: NAG9-415
CONTRACT_GRANT: NAG9-63
Distribution Limits
Public
Copyright
Other