This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
This research seeks to investigate and resolve an important controversy in the Mesozoic geologic evolution of the western U.S. Cordillera. Mesozoic processes, including deformation, metamorphism, magmatism, and sedimentation transformed the western U.S. from a largely marine province to an elevated continental landmass. These processes also created a crustal architecture that is critical to the location and character of natural resources (including oil, ore deposits, hydrothermal, and groundwater) and therefore of considerable importance to understand. The controversy addressed by this project concerns two major questions: (1) Did Mesozoic mountain-building occur in a single long-lived episode that started at 160 Ma in western Nevada and propagated eastward into Utah through 65 Ma, or did the region grow during two distinct and unrelated mountain-building episodes (200-160 Ma, and about 120-65 Ma) that were separated by a lengthy period of erosion? (2) Did pre-160 Ma sedimentary basins in Nevada, Utah and Idaho form in response to flexural loading by growing mountains, or did these basins form by other mechanisms during a time when there were no mountain loading the crust?
This project will focus on answering these questions by targeted studies in localities affected by deformation, metamorphism, magmatism and basin formation in northern Nevada, NW Utah and SE Idaho. The main objectives and methods are as follows. (1) Generate tight age constraints for Jurassic deformation. This will be done by U-Pb zircon dating of pre-, syn- and post-tectonic igneous rocks. If the single phase model is correct, deformation should be Late Jurassic (about 160-145 Ma); if the two phase model is correct, deformation will be older than about 160 Ma. (2) Determine the structural and stratigraphic evolution of locations in Nevada where critical relations have been described and disputed, with no current consensus. The goal is to establish a detailed sequence of events that can be linked directly to geochronologic and provenance studies. (3) Constrain the provenance of Jurassic sandstone units by U-Pb dating of detrital zircons. Provenance of sands provides information about paleogeography. If the single phase model is correct, Late Jurassic sediments should be derived from erosion of orogenic highlands to the west. If the two phase model is correct, this should be true for Middle Jurassic sediments instead.
