Paleozoic and mesozoic evolution of East-Central California

Abstract

East-central California, which encompasses an area located on the westernmost part of sialic North America, contains a well-preserved record of Paleozoic and Mesozoic tectonic events that reflect the evolving nature of the Cordilleran plate margin to the west. After the plate margin was formed by continental rifting in the Neoproterozoic, sediments comprising the Cordilleran miogeocline began to accumulate on the subsiding passive margin. In east-central California, sedimentation did not keep pace with subsidence, resulting in backstepping of a series of successive carbonate platforms throughout the early and middle Paleozoic. This phase of miogeoclinal development was brought to a close by the Late Devonian-Early Mississippian Antler orogeny, during the final phase of which oceanic rocks were emplaced onto the continental margin. Subsequent Late Mississippian-Pennsylvanian faulting and apparent reorientation of the carbonate platform margin are interpreted to have been associated with truncation of the continental plate on a sinistral transform fault zone. In the Early Permian, contractional deformation in east-central California led to the development of a narrow, uplifted thrust belt flanked by marine basins in which thick sequences of deep-water strata accumulated. A second episode of contractional deformation in late Early Permian to earliest Triassic time widened and further uplifted the thrust belt and produced the recently identified Inyo Crest thrust, which here is correlated with the regionally significant Last Chance thrust. In the Late Permian, about the time of the second contractional episode, extensional faulting created shallow sedimentary basins in the southern Inyo Mountains. In the El Paso Mountains to the south, deformation and plutonism record the onset of subduction and arc magmatism in late Early Permian to earliest Triassic time along this part of the margin. Tectonism had ceased in most of east-central California by middle to late Early Triassic time, and marine sediment deposited on the subsiding continental shelf overlapped the previously deformed Permian rocks. Renewed contractional deformation, probably in the Middle Triassic, is interpreted to be associated with emplacement of the Golconda allochthon onto the margin of the continent. This event, which is identified with certainty in the Sierra Nevada, also may have significantly affected rocks in the White and Inyo Mountains to the east. Subduction and arc magmatism that created most of the Sierra Nevada batholith began in the Late Triassic and lasted through the remainder of the Mesozoic. During this time, the East Sierran thrust system (ESTS) developed as a narrow zone of intense, predominantly E-vergent contractional deformation along the eastern margin of the growing batholith. Activity on the ESTS took place over an extended part of Mesozoic time, both before and after intrusion of voluminous Middle Jurassic plutons, and is interpreted to have been mechanically linked to emplacement of the batholith. Deformation on the ESTS and magmatism in the Sierra Nevada both ended prior to the close of the Cretaceous.