COMPARISON OF GRANITIC ROCKS FROM NEW ENGLAND AND FROM THE MOON: IMPLICATIONS FOR IGNEOUS PETROGENESIS ON THE MOON

Granitic rocks are a characteristic feature of the Earth’s continental crust, but are rare on other planetary bodies [1]. Nonetheless, granitic rocks (broadly speaking, igneous rocks with K-feldspar and a silica-phase, or glasses with granitic compositions) have been identified on the Moon based on both remote sensing and sample studies [2,3]. On the Earth, granites are linked to fluid water and/or tectonic plate boundaries. On the Moon, however, terrestrial style plate tectonics do not occur and, though H2O may have been active as a chemical component in igneous settings [4], no evidence for liquid water on the Moon has been identified--raising the question: how did granitic rocks form on the Moon?

In this study, we compare granitic rocks from lunar samples with some of the granitic rocks of New England, including S-type granites from the Sebago migmatite area, I-type samples (e.g., Songo pluton), and A-type granites and associated rocks of the White Mountain Magma Suite [5,6]. In addition, we use a database of whole rock compositions maintained by the New Hampshire Geologic Survey. For comparison, we use petrologic data from Apollo 15 quartz monzodiorite (QMD) and granitic melt inclusions (MIs) in clasts of the NWA 773 clan of lunar meteorites [7].

The QMD has moderate Fe#, similar to some terrestrial I-type granites, whereas the NWA 773 clan MIs are Mg-depleted and have AFM whole-rock compositions similar to several S-type granites. Nonetheless, the lunar and terrestrial petrogenetic processes appear to be distinct, with silicate liquid immiscibility playing important roles for both QMD and NWA 773 MIs.

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