Comparative petrology, geochemistry, and
petrogenesis of evolved, low-Ti lunar mare basalt meteorites
from the La Paz Icefield, Antarctica
New data are presented for five evolved, low-Ti lunar mare basalt meteorites from the LaPaz icefield, Antarctica, LAP 02205, LAP02224, LAP02226, LAP02436 and LAP 03632. These meteorites have nearly identical mineralogies, textures, and geochemical compositions, and are therefore considered to be paired. The LaPaz basalts contain olivine (Fo64-2) and pyroxene (Fs32Wo8En60 to Fs84-86Wo15En2-0) crystals that record extreme chemical fractionation to Fe-enrichment at the rims, and evidence for silicate liquid immiscibility and incompatible element enrichment in the mesostasis. The basalts also contain FeNi metals with unusually high Co and Ni contents, similar to some Apollo 12 basalts, and a single-phase network of melt veins and fusion crusts. The fusion crust has similar chemical characteristics to the whole rock for the LaPaz basalts, whereas the melt veins represent localized melting of the basalt and have an endogeous origin. The crysstallization conditions and evolved nature of the LaPaz basalts are consistent with fractionation of olivine and chromite from a parental liquid similar in composition to some olivine-phyric Apollo 12, Apollo 15 basalts or lunar low-Ti pyroclastic glasses. However, the young reported ages for the LaPaz mare basalts (~2.9 Ga) and their relative incompatible elmeent enrichment compared to Apollo mare basalts and pyroclastic glasses indicate they cannot be directly related. Instead the LaPaz mare basalts may represent fractionated melts from a magmatic system fed by similar degrees of partial melting of a mantle source similar to that of the low-Ti Apollo mare basalts or pyroclastic glasses, but which possessed greater incompatible element enrichment. Despite textural differences, the LaPaz basalts and mare basalt meteorite NWA 032 have similar ages and compositions and may origiinate from the same magmatic system on the Moon.
Day et al. (2006) Geochim. Cosmochim. Acta 70, 1581-1600.
Full publication: 2006_GCA70_1581.pdf
Last revised: 3-2006