The Mesozoic Sierra Nevada Batholith preserves an extensive record of continental-margin arc magmatism which serves as a classic, worldwide model for such tectonic environments. However, about one-third of the batholith actually extends northward from the Sierra Nevada proper into the Basin and Range Province of northwest Nevada, where it has received little study. Extensive recent research on late Cenozoic Basin and Range extension in that region has yielded considerable preliminary information on that portion of the batholith, highlighting three key, related issues that form the focus of this project: 1) Magmatic arc history, 2) Erosion and exhumation 3) Sedimentation and basin formation.
Magmatic arc history
Large plutonic complexes have been discovered in northwest Nevada that are apparently members of the voluminous ca. 95-83 Ma Cathedral Range intrusive suites previously defined in the eastern Sierra Nevada. This is preliminary evidence that the magmatic histories of these two parts of the batholith were similar. In contrast however, geophysical studies in northwest Nevada have shown that the crust beneath the Basin and Range part of the batholith is neither as thick nor as felsic as the crust beneath the southern part of the batholith. This project will document the distribution, age, petrology, and geochemistry of batholithic rocks in northwest Nevada, in order to more rigorously integrate their intrusive history and petrogenesis with other parts of the magmatic arc. Work will include reconnaissance investigations over the entire region and detailed work on key plutonic complexes.
Erosion and exhumation
Erosion has stripped an estimated 3 to 7 km of rock section from the top of batholithic rocks in northwest Nevada during the time interval between Late Cretaceous extinction of the arc and Tertiary (mostly Eocene) formation of the regionally extensive basal Tertiary unconformity. The history of this exhumation is poorly understood and has important implications for paleogeography, paleotopography, crustal thickness and structure, uplift mechanisms, tectonics, and sediment dispersal over a large region. This project will document the post-intrusive cooling and erosional history of this part of the batholith by applying a suite of thermochronometers to sample transects collected across 3-6 km thick tilted sections of batholithic rocks exposed beneath the Tertiary unconformity by Basin and Range normal faulting.
Sedimentation and basin formation
Sedimentation and basin formation: Erosion has stripped huge volumes of rock off of the top of the batholith in northwest Nevada; where did all this material go? Preliminary data suggest that the detritus from this region may have been transported into basins to the north and west, rather than into the Great Valley, suggesting the ancient topographic expression of the batholith in northwest Nevada may have been radically different than the western edge of an Altiplano-like plateau envisaged for the Sierra Nevada proper. This project will characterize the basin sinks for these huge volumes of detritus by using single-grain U-Pb dating of detrital zircon populations from uppermost Cretaceous and lower Tertiary strata in the Great Valley, Sierra Nevada, Warner Range (northeastern California), and Oregon.