The El Muerto "NYF" Granitic Pegmatite, Oaxaca, Mexico, and Its Striking Enrichment In Allanite-(Ce) and Monazite-(Ce)

Abstract

The El Muerto granitic pegmatite, of Grenville (Neoproterozoic) age, part of the Oaxacan Complex in southern Mexico, contains an exceptional development of HFSE-enriched accessory phases. We report here compositional data and textures involving the exotic minerals of this suite, in particular allanite-(Ce), perrierite-(Ce), monazite-(Ce), thorite, fergusonite-(Y), aeschynite-(Y), yttrium-rich betafite, polycrase-(Y), uranopolycrase, niobian rutile and a variant of thorutite. This pegmatite has the earmarks of a NYF suite, but is devoid of F. El Muerto is a member of an anorogenic anorthosite – mangerite – charnockite – granite (AMCG) suite, understood to be emplaced as a result of gravitational collapse of the lower crust following a collision. In common with other suites of anorogenic affiliation, we attribute the unusual enrichment in HFSE to a stage of metasomatic fertilization of a source in the lower to middle crust prior to its melting.