METAMORPHIC PETROLOGY AND UNIT DISTRIBITON IN THE OLIVER HILL DOME, EASTERN ADIRONDACK MOUNTAINS, NEW YORK

Recent geologic mapping of the Oliver Hill area in the eastern Adiriondack Mountains has revealed some interesting relationships between various meta-igneous and meta-sedimentary rock units. The area of Oliver Hill is underlain by a structural dome defined by broad arching of the regional foliation. The dome is slightly elongate in the east-west direction, the short direction is about 5 km wide and the long axis is over a distance of about 7 km. Mineral elongation lineations cross the dome at a general trend of 110 parallel to the long axis of the dome. A variety of metaigneous rock units are symmetrically disposed, from core to flank, across the dome. Anorthositic- and gabbroic-gneiss occur in the core of the dome near the top of Oliver Hill. These gneiss bodies are surrounded on all sides by ductilely deformed charnockitic gneiss. Contacts between these units are graditional. The metamorphic mineral assemblages garnet-clinopyroxene-plagioclase, clinopyroxene-hornblende-biotite-plagioclase, and garnet-hornblende-biotite were observed in the gabbroic and charnockitic-gneisses. All the assemblages are consistent with amphibolite facies metamorphism and texturally these assemblages are associated with the foliation that defines the dome. Local metasedimentary rock units include marble, quartzite and calcsilicate gneiss, and these units occur structurally below the metaigneous rocks. The marble contains graphite and phlogopite, while the calcsilicate rocks contain abundant diopside. Previous investigations in the eastern Adirondacks reported on meta-igneous rocks with granulite facies metamorphic mineral assemblages. Intense ductile deformation associated with apparent thrusting in the rocks of Oliver Hill suggests this suite of amphibolite facies meta-igneous rocks is allochthonous relative to the underlying meta-sedimentary rocks.