ABSTRACT: Phanerozoic Plate Tectonics and Paleogeographic Reconstructions

Paul J. Umhoefer

Continental geologic and paleomagnetic data and plate motion models allow the reconstruction of preliminary plate tectonic maps of the western North American margin, which account for most of the geologic relations. The Late Triassic to Middle Jurassic (230-170 Ma) stage had multiple volcanic arcs, most of which collided with North America in the Middle Jurassic after closure of the Slide Mountain, Cache Creek, and other oceanic basins. The Middle Jurassic to Early Cretaceous (170-130 Ma) stage was dominated by sinistral-oblique tectonics as North America rapidly moved poleward, including the formation and destruction of transform-rift and back-arc basins in the Klamaths and Sierra Nevada. The middle Cretaceous (130-85 Ma) stage was dominated by at least two magmatic arcs and the final collision of the Insular superterrane to North America from California to northwestern Canada. Major thrust belts and coeval plutonic rocks are found all along the Insular terrane and within the western edge of middle Cretaceous North America. The Late Cretaceous to early Tertiary (85-60 Ma) stage had two distinct tectonic regions. The southern region was a central Andean-like margin caused by the subduction of the Farallon plate beneath North America. The thick-skinned Laramide foreland lay to the east. The northern region included dextral-slip faults, a narrow magmatic arc, and regional uplift caused by the rapid, oblique convergence of the Kula plate against North America. The boundary between the two regions moved rapidly north from California to its current position in the Columbia embayment.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990