Tectonic History of Northern Nevada

摘要

Tectonic history of northern Nevada basement begins with amalgamation of the supercontinent Rodinia along the Cheyenne lineament, an east west Paleoproterozoic suture and mobile belt between Archean cratons on the north and Proterozoic terranes on the south. East of Park City, Utah this boundary is a suture, which becomes a widening mobile belt westward into northern Nevada. Rifting of Rodinia, initiated on mantle plumes in the early Neoproterozoic was complete by the end of Neoproterozoic time. In Nevada, continental ductile crust slid east off a plume head and created an orthogonal fracture pattern parallel with and normal to the cratonic boundary. Crustal thinning extended eastward from the continental margin near Winnemucca, Nevada to a hinge line near Salt Lake City. During late Neoproterozoic and much of Paleozoic time continental sediments shed westward onto a rectilinear North American margin and formed a passive platform that mimicked the rifted margin. In these environments carbonate sediments containing a high percentage of quartz silt grains formed favorable hosts for future mineral and gold deposits. Island arcs collided with western North America in late Devonian and late Permian times. This caused oceanic sediments between the island arcs and North America to obduct up to 160 kilometers southeastward over the continent in the Antler orogeny and up to 100 kilometers southeastward in the Sonoman orogeny. Break up of Pangea began in late Triassic time when North America began moving northwestward from South America. Rapid northeastward migration of the subducting slab formed an east-northeast directed flat subduction zone off North America's western coast from Mesozoic through Paleocene time creating a magmatic null. Old, favorably-oriented rift structures bounding Precambrian crustal blocks were reactivated with up-to-the-east reverse motion at this time. The thick skinned deformation may have translated to short-throw, thin-skinned detachment faults, imbricate faults and fault propagated folds associated with these periods of Mesozoic compression. The null was interrupted by two periods of slab roll back, centered at 160 Ma and 92 Ma, which produced a number of back arc intrusions in northern Nevada including stocks at Bald Mountain, Goldstrike and Cortez. Flat subduction ended at 48-45 Ma, after which the slab delaminated from both the north-northeast in Idaho and south-southeast in Mexico over the following 25 Ma.