9614826 Roeske Recent studies have significantly changed traditional views of the late Proterozoic- early paleozoic paleogeographic reconstructions for Laurentia and Gondwana. Essentially two models are current: eastern North America and western South America were in proximity due to actual collision between Laurentia and Gondwana, or only a rifted portion of North American collided with South America, with a large ocean remaining between the continental masses. This research will test these options by study of a belt of ultramafic and mafic rocks along the west side of the Precordillera which represents the postulated Laurentia- Precordillera ocean. In particular, age dating will address both crystallization and metamorphic ages of these rocks, which differ in each scenario. Results are expected to clarify models for Paleozoic tectonics in southwestern South American by providing information about the ocean basin to the west of the Precordillera terrane and provide the basis for a test between the collisional model and the rifted and drifted terrane model.
