REMNANTS OF THE NORTHERN SIERRA-NEVADA PALEOZOIC ISLAND ARC IN WESTERN NEVADA

Allochthonous upper Paleozoic volcanic island-are suites of the U.S. C ordillera have previously been interpreted as parts of a single island are. New lithologic, age, structural, biogeographic, and geochemical data indicate the presence at least of two arcs, one built on a baseme nt with continental crustal affinities including that of the Northern Sierra terrane, and the other built on an oceanic basement including t hat of the Eastern Klamath terrane. In the Garfield Hills, western Nev ada, the Lower Permian Black Dike Formation appears to be a remnant of the Northern Sierra Paleozoic island are. It consists of calc-alkalin e rocks with low-to-negative epsilon(Nd) ratios. Volcanic rocks share similar ages, magmatic affinities, and epsilon(Nd) ratios with lavas o f the Goodhue Formation in the Northern Sierra terrane. Our new data s uggest that these rocks are part of the Northern Sierra terrane, and w e therefore infer that part of western Nevada was originally underlain by a basement with continental crustal affinities.