Very high temperature, moderate pressure metamorphism in the New Russia gneiss complex, northeastern Adirondack Highlands, metamorphic aureole to theMarcy anorthosite

The New Russia gneiss complex in the northeastern Adirondack Highlands of N ew York includes meta-anorthosite gneiss and anatectic gneiss derived from metagabbro, mangerite, and charnockite. Metamorphic conditions during anate xis (850-950 degrees C, highest near the anorthosite, with pressure similar to 750 MPa) are inferred from minerals and textures produced by dehydratio n melting of pargasitic hornblende and from ternary feldspar in anatectic s egregations. The complex abuts and is crosscut by the eastern margin of the similar to 1130 Ma Marcy anorthosite massif. The crosscutting contact, the presence of meta-anorthosite gneiss within the complex and undeformed meta -anorthosite in the massif, and the occurrence of deformed and undeformed a natectic segregations within the New Russia gneisses indicate an approximat e synchroneity of penetrative deformation, very high temperature metamorphi sm, and emplacement of anorthosite with both intrusion and anatexis outlast ing deformation. The position of the New Russia gneisses, the metamorphic g radient within them, and the contemporaneity of anatexis with intrusion of anorthosite imply that the complex is the metamorphic aureole of the Marcy anorthosite.