Tectonic Framework of the Great Basin

The Great Basin is bordered on the west by the Sierra Nevada and on the east by the Colorado Plateau and Rocky Mountains. These tectonically different provinces are genetically related; basin and range structure evolved as part of the tectonic development of western North America. The Precambrian framework here is not well known, but northeasterly geosynclinal trends, east- west orogenic trends, and northwesterly fracture zones can be projected from the craton or inferred. Sedimentation in the Cordilleran orthogeosyncline from Cambrian to Devonian time was characterized by an eastern miogeosynclinal (carbonate) and a western eugeosynclinal (siliceous and volcanic) assemblage. In latest Devonian time, the Antler orogenic belt formed by predominantly vertical uplift along the boundary between these assemblages at the continent-ocean basin interface where loading and thermal blanketing changed mineral phases in the mantle. In late Paleozoic and early Mesozoic time, two post-Antler marginal troughs developed in which thick orogenic sediments accumulated. These troughs later became the sites of the Nevadan and Sevier orogenic belts. During late Mesozoic time, an enormous volume of debris was transported from the Nevadan and Sevier orogenic belts eastward into the Rocky Mountain geosyncline and westward into the Pacific geosyncline. About 5 miles of material were eroded from each square mile of source area. The unloading and loading affected crustal and mantle equilibrium. In the source area, crustal break-up, possibly accentuated by magmatism, resulted in basin and range structure. In the Rocky Mountain geosyncline where the crust was thickened, the Rocky Mountains and the Colorado Plateau were uplifted