A petrographic and geochemical study of mafic lunar samples from the Apollo 16 site and the new basaltic lunar meteorite from the La Paz Icefield, Antarctica

This dissertation consists of two parts. Chapter 1 reports the bulk composition, mineral compositions, and petrography of a new basaltic meteorite from the La Paz Icefield (LAP), Antarctica. Our observations and measurements support the hypothesis that LAP is lunar and that the stones are paired with each other. In detail, the geochemistry of LAP is unlike that of any previously studied lunar basalt except lunar meteorite NWA 032. The similarities between LAP and NWA 032 are so strong that the two meteorites are almost certainly source-crater paired and may well be two different samples of a single basalt flow. The second part of the dissertation looks at mafic samples from the Apollo 16 site. Chapter 2 discusses the petrography and geochemistry of five new 2--4 mm basalt fragments from the Apollo 16 regolith. Of these new basalts, only one represents a basalt type previously seen at the Apollo 16 site. Chapter 3 reports the major element composition of 280 mafic glasses from six different Apollo 16 soils. These glasses are an approximately equal mixture of basaltic glass and ITE (incompatible-trace-element)-rich glass, with smaller amounts of mare-highlands mixed glass and picritic glass also present. We identified six main glass groups (four basaltic, two ITE-rich) and trace-element concentrations were determined by SIMS on representative glasses from these groups. As there is no evidence for a local origin and scant evidence for a basin-ejecta origin, we infer that the volcanic material (both glass and lithic) in the Apollo 16 regolith originated in the maria nearest the Apollo 16 site, transported there by small to moderate sized postbasin craters. Titanium concentrations derived from Clementine UVVIS data show Mare Tranquillitatis to be the most likely source for the high-Ti basaltic material, Mare Nectaris to be the most likely source for the low-Ti, high-Al, and VLT basaltic material, and a large regional pyroclastic deposit near Mare Vaporum to be the most likely source region for pyroclastic material at the Apollo 16 site. The ITE-rich glasses are likely basin ejecta deposited by the Imbrium impact.