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Title

The Diversity, Petrogenesis, and Geochronology of Granitic Lunar Lithologies

Date of Award

Winter 12-15-2013

Author's School

Graduate School of Arts and Sciences

Author's Department

Earth & Planetary Sciences

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Evolved lithologies such as granite and quartz monzogabbro are rare among lunar samples. These rare samples give insight into the end stages of lunar magmatism of which, given the paucity of these samples, little is known. In lunar samples, evolved lithologies typically occur as clasts or as matrix material in polymict breccias. By studying texturally pristine, monomict lithic fragments of granite from Apollo 12, results are not obfuscated by non-granitic components co-occurring in a breccia. In this dissertation, I study Apollo 12 granitic samples using electron-probe microanalysis and laser Raman spectroscopy and interpret the results in conjunction with results from instrumental neutron activation analysis. Topics include: i) the petrography, mineralogy, and geochemistry of Apollo 12 granite fragment 12032,366-19 and modeling the petrogenesis of granitic samples by the fractional crystallization of a parent melt with a KREEP basalt composition, ii) the geochronology of granite fragment 12023,147-10 by the electron-probe microanalysis of thorite, yttrobetafite and monazite occurring therein, and iii) constraining the pressure and temperature conditions under which six Apollo 12 granitic fragments crystallized based on the identification of the silica polymorph that occur in these samples by laser Raman spectroscopy. I conclude that the samples crystallized rapidly at high temperature and that their petrogenesis involved extended fractional crystallization and likely also required density segregation of crystallizing phases or silicate liquid immiscibility. I also conclude that the age of young (~3.88 Ga) granites including samples 12023,147-10 and 12032,366-19 may imply a relationship to the formation of the Imbrium basin, which is estimated to have formed at 3.90-3.93 Ga. Perhaps fracturing induced in the lunar crust by the impact fostered the ascent of KREEP-rich melts from which granitic samples could crystallize after extended fractional crystallization.

Language

English (en)

Chair and Committee

Randy L Korotev

Committee Members

Thomas J Bernatowicz, Robert F Dymek, Daniel Giammar, Bradley L Jolliff, William B McKinnon

Comments

Permanent URL: https://doi.org/10.7936/K75M63MK

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