Earth and Planetary Sciences ETDs

Publication Date

9-9-2010

Abstract

Crystallization of the Lunar Magma Ocean has been empirically modeled and its products inferred from sample observations, but it has never been fully tested experimentally. Presented in this study is the first experimental simulation of lunar differentiation. Two end-member bulk Moon compositions are considered: one enriched in refractory lithophile elements relative to Earth and one with no such enrichment. A "two-stage" model of magma ocean crystallization based on geophysical models is simulated and features early crystal suspension and equilibrium crystallization followed by fractional crystallization of the residual liquid. An initially entirely molten Moon is assumed. The study presented below focuses on the early cumulates formed by equilibrium crystallization, differences in mantle mineralogy resulting from different bulk Moon compositions and the implications for the source regions for secondary lunar magmatism. There are significant differences in the crystallization sequence between the two bulk compositions. Refractory element enriched bulk Moon compositions produce a deep mantle that contains garnet and minor Cr-spinel in addition to low-Ca pyroxene and olivine. Compositions without refractory element enrichment produce low-Ca pyroxene bearing dunite mantles without an aluminous phase such as garnet. The differences in bulk composition are magnified in the residual melt and the TWM residual will produce plagioclase and ilmenite earlier and in greater quantities. Both compositions produce Mg-rich early cumulate piles that extend from the core-mantle boundary to ~355 km depth, if 50% equilibrium crystallization and whole Moon melting are assumed. Although they physically encompass the depth of the low-Ti green glass source, mantle lithologies such as these provide poor fits for the green glass source regions. They are both too Mg-rich and Al- and Ca-poor. Thus, additional processes such as cumulate mixing must be called upon to create the green glass source at the appropriate depths. However, these early LMO cumulates provide good fits for the source regions for a component of the high-Mg*, Ni- and Co-poor parental magmas of the Mg-suite cumulates. These LMO cumulates could generate partial melts meeting the criteria of the Mg-suite parent by KREEP hybridization induced melting in the source and/or decompression melting followed by assimilation of a high-Al component.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Advisor

Shearer, Charles K.

First Committee Member (Chair)

Draper, David S.

Second Committee Member

Agee, Carl B.

Third Committee Member

Brearley, Adrian J.

Project Sponsors

National Aeronautics and Space Administration

Language

English

Keywords

Moon, Magma ocean, Experimental Petrology, Planetary Science, Mg-suite, Mare basalts, Lunar mantle, Magma, Basalt, Giant impact

Document Type

Thesis

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