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Insights into Primitive and Evolved Magmatism and Impactor Compositions on the Moon.

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The Moon is the only planetary body, besides Earth, from which there are samples from known locations. Consequently, the Moon is crucial to understanding planetary evolution processes. The Moon has undergone differentiation, where it separated into a crust, mantle and possibly a small core. Since differentiation, impactors have left an indelible imprint on the lunar surface and the Moon has produced both primitive and evolved magmatism. This dissertation reports and examines data from impact melt samples, pyroclastic deposits, and a felsic clast to gain a holistic understanding of lunar evolution. Chapter 2 examines impact melt coats and anorthositic regolith breccia meteorites using highly siderophile elements, trace elements, and whole rock data. Osmium isotopic data provides evidence for impact composition and suggests the impactors that were striking the Moon changed from ordinary to carbonaceous-like impactors with either time or location. Chapter 3 examines two pyroclastic deposits sampled during the Apollo 15 and 17 missions which are the two of the most primitive magmatically derived products from the Moon. Both glassy holohyaline and crystallized beads are analyzed. Crystalline beads exhibit more major, minor and trace element variation than holohyaline beads. The Apollo 74220 holohyaline beads have subchondritic Nb/Ta values as result of the presence of ilmenite in their source. A new bead group within the Apollo 15 beads is identified that has pronounced relative depletions in Sr and Eu for the most incompatible element enriched beads. In Chapter 4, information reported in Chapter 3 is used to further examine moderately volatile element abundances in the Apollo 15 and 17 pyroclastic deposits. The Apollo 15 bead edges have elevated moderately volatile element abundances, likely resulting from syn- or post-eruptive processes. Meanwhile, there is more overlap in the Apollo 17 data between edge and center analyses. Compared to mare basalts, the Apollo 15 and 17 pyroclastic glasses have higher moderately volatile element abundances, implying that the lunar interior is heterogeneous with respect to volatile elements. Chapter 5 examines a felsic clast within Apollo sample 14321. This felsic clast has recently been reinterpreted by some authors to be a terrestrial meteorite. Highly siderophile element systematics in this clast do not resemble that of terrestrial evolved rocks, suggesting that the clast is of lunar origin. The clast contains minerals that are unusual in lunar rocks, which implies that it has experience more oxidizing conditions than typical lunar rocks. The felsic clast likely crystallized at ~4.1 Ga and then experienced an impact event at ~3.8 Ga.

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This item is under embargo until September 16, 2024.