Petrology and geochemistry of lunar meteorite
MIL 05035
Miller Range (MIL) 05035 is an unbrecciated lunar meteorite discovered in 2005 in the Miller Range Ice Field of Antarctica, and is the sixth low-Ti mare basalt meteorite discovered to date. This meteorite consists of pyroxene and maskelynite, where the pyroxenes are highly zoned from core to rimi, to extreme Fe fractionation. Maskelynites display minor melting and recrystallization textures and are relatively uniform (An94-An91), except for near contact with late-stage mesostasis (An84). Mineral trace-element compositions, especially in pyroxenes, show large ranges of variation suggesting extensive fractional crystallization. The calculated REE melt composition that was in equilibrium with the pyroxene and maskelynite is consistent with pyroxene as the first liquidus phase, followed by plagioclase. This calculated melt composition is also indicative of the highly fractionated nature of the parental melt.
A striking feature of this meteorite is its high abundance of late-stage, pyroxene-breakdown symplectites (intergrowths of Fe-augite, fayalite, and silica), more abundant than in almost all mare basalts. These symplectites possess various textures with different bulk compositions, suggesting formation that is independent of bulk composition. A possible energy source for breakdown of ferro-pyroxenes to form the symplectites is the heat and pressure generated during impact melting.
The petrograpy , bulk chemistry, and mineral compositions of MIL 05035, combining with age data in the literature, suggest it is source-paired with Asuka 881757 and possibly Yamato 793169. These meteorites represent a unique type of low-Ti basalts that is old (~3.8-3.9 Ga) and highly fractionated, and likely formed by partial melting of early mantle cumulates.
Liu et al. (2008) Meteorit. Planet. Sci., submitted.
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Last revised: 3-2008