TECTONICS AND RECONSTRUCTION OF MIDDLE MIOCENE TO RECENT RIFT BASINS IN NORTHEASTERN NEVADA

Assessment of middle Miocene to Recent rift basins in northeastern Nevada reveals that this area experienced three distinct phases of sedimentation and tectonics. The first phase, ~ 16 Ma to ~ 7 Ma, was a period of active extensional tectonism that produced several large, interconnected basins and regional drainage divides. The basins evolved adjacent to a major, ~ 190 km-long, north-northeast-trending paleotopographic high and drainage divide. This topographic high was bounded on the west by the west-dipping, Knoll Mountain-Windermere Hills and Ruby Mountain-East Humboldt Range detachment systems and on the east by the east-dipping, Bell Canyon-Toano fault system. These fault systems produced variable rotation of basin fill, and to the north, they terminated at the Jurassic Contact pluton. The Contact pluton formed part of an easterly-trending paleotopographic high. The drainage divide of this topographic high was situated north of the Contact pluton.

The second phase, ~7 Ma to ~ 3 Ma, is characterized by the cessation of extensional faulting and regional erosion followed by minor Pliocene (?) deposition of alluvial gravel that produced a marked angular unconformity with underlying Miocene basin fill. The third phase involved renewed extensional faulting responsible for the emergence of the modern basins and ranges, and erosion that destroyed or modified drainage divides established in the Miocene. By the third phase, northeast Nevada was a relative topographic high that was eroded into by the Humboldt, Snake River, and Thousand Springs (drains into the Great Salt Lake basin) fluvial systems. Headward erosion from these fluvial systems caused progressive erosion and exhumation of Miocene and Pliocene basinal strata as well as migration of extant Miocene drainage divides. Furthermore, encroachment of these fluvial systems into northeastern Nevada was driven by tectonic subsidence near the eastern and western margins of the Basin and Range Province and in the Snake River Plain in the wake of the Yellowstone hot spot to the north of northeastern Nevada.