Triassic evolution of the arc and backarc of northwestern Nevada, and evidence for extensional tectonism

The early Mesozoic marine province of Nevada includes a shallow marine shelf terrane to the east, the Black Rock arc terrane to the west, and an intervening deep marine basinal terrane. A new integrated analysis of the Triassic record across the northern marine province indicates the following history. From the Early to late Middle Triassic, the province was affected by differential uplift and subsidence, subaerial to basinal sedimentation, and intermittent volcanism. Regional subsidence then occurred in the late Middle to early Late Triassic, leading to marine deposition on top of previously exposed areas. During this time, carbonate deposition occurred in all areas, coarse clastics from nearby basement uplifts were shed into the margins of the province, and volcanism occurred in the basinal and shelf terranes. Regional subsidence then continued in the latest Triassic, as manifested by the accumulation of very thick (up to 6 km) successions of marine strata: but in the Black Rock terrane, these strata consist of volcanogenic arc deposits; whereas, in the shelf and basinal terranes, these strata consist exclusively of continentally-derived clastics. Based on these data, the Black Rock, basinal and shelf terranes are interpreted to have evolved together in the Triassic in an extensional tectonic regime that culminated in the opening of a wide basin between the shelf and a volcanic arc. Extensional tectonism led to differential uplift and subsidence in the early history of the province, regional subsidence and accumulation of thick marine successions across the province in the late Middle to Late Triassic, and progressive isolation of the Black Rock terrane from the basinal and shelf terranes as the extensional basin widened.