THREE-DIMENSIONAL DEVELOPMENT OF THE SEVIER-LARAMIDE OROGEN AS A RESULT OF TERRANE TRANSLATION, COLLISION, AND TRANSLATION

This presentation expands on models of tectonic development of the western United States that invoke a combination of collisions and translations of terranes. In particular, this account considers how Cretaceous-Paleogene deformation is spatially and temporally influenced by previous – and commonly considered as separate– events. The three-dimensional geometry of the Precambrian rifted continental margin plays a major role in segmenting the orogen and focusing contractional deformation. The Intermontane supererterrane likely collides along this continental margin in the Early-Middle Jurassic. Subsequent margin-parallel sinistral movement of the superterrane has two major effects on Early Cretaceous tectonism. First, it causes a zone of contraction in northern Nevada, because the Precambrian transform segments act as a backstop to southward terrane motion. This Early Cretaceous contractional deformation is recorded simultaneously in the Willard thrust, the Raft River-Albion range, the Salmon River “suture” belt, and NW Nevada. Second, the southward momement duplicates the Intermontane superterrane in the coterminous U.S., with the eastward section being the Blue Mountains province. At ~105-100 Ma the Insular superterrane shows major internal contractional deformation indicating the superterrane began colliding by this time. Deformation on the continent is localized in the places where the North America margin protudes westward with respect to margin-parallel dextral transport. Two of the most significant promontories from Precambrian rifting were located in western Idaho and the M0jave region. Deformation associated with the Insular superterrane collison lasts from 100-85 Ma in both the Idaho and Sierra Nevada batholiths: These magmatic arcs accommodate dextral transpressional deformation while the forearc regions remain relatively rigid. Major deformation in the Sevier thrust belt and foreland deposition occurs at this time. At 85 Ma, rapid northward movement of the Insular superterrane initiated. The northward movement causes contractional deformation in regions north of the Garlock fault, including the Colorado plateau. Consistent with other studies, contractional deformation ceased because of a plate motion change at 55 Ma and the Insular superterrane moved north of the conterminous United States.