Group II xenoliths from Lunar Crater Volcanic Field, Nevada
Mosely, John Clark
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Lunar Crater Volcanic Field (LCVF), a Quaternary volcanic field in central Nevada, is characterized by alkali basalts that host megacrysts of clinopyroxene, amphibole and olivine as well as mafic and ultramafic xenoliths. The Group II xenoliths present at LCVF offer insight in to the complex magmatic processes at play beneath the volcanic field, as well as providing context for Tertiary and Quaternary volcanism in the western United States. Petrologic and geochemical analysis of these xenoliths and the constituent phases are consistent with genesis from a magma enriched in Ti and Al. High modal abundance of amphibole, as well as the presence of anomalously OH and Cl rich apatite within the xenoliths could be attributed to melting of a source rock enriched in water and chlorine. The geochemistry of xenoliths at LCVF is similar to that of subduction driven magmatism observed at island arcs and convergent margins but occurs well inland. Mantle enrichment by the dehydration of the shallowly subducted Farallon plate and subsequent melting of this enriched mantle allows for and is consistent with the hydrous xenoliths and the anomalous apatite hosted within them.