Origin of mafic enclaves and their feldspar phenocrysts in the El Capitan Granite, Yosemite National Park, California

The El Capitan Granite of Yosemite Valley contains abundant mafic enclaves and is adjacent to a large, roughly coeval mafic complex known as the diorite of the Rockslides (DOTR) that has been suggested as an enclave source. However, Na2O and MnO lie above a simple mixing line between the two, precluding mixing as a complete explanation for their bulk compositions. The mafic enclaves also contain large plagioclase crystals similar in size to those in the host El Capitan Granite, yet their compositions are distinct from those in the El Capitan Granite and DOTR. Inclusions of Mn-rich ilmenite distinct to the mafic enclaves are also observed within the plagioclase. These data indicate enclaves did not result from mixing of the El Capitan Granite and mafic rocks of the DOTR, but most likely arose from andesitic magmas that are not otherwise found in the Sierra Nevada batholith.