This project aims to resolve a long-standing controversy regarding the earliest evolution and deep structure of the Precambrian lithosphere of southwestern North America. This area is a globally important field laboratory for studies of the processes that form continents. Current debate has focused on the need to resolve the relative importance of accretion of juvenile arcs versus recycling of older crustal materials, and/or rift-related addition of mafic crust. The objectives of this project are to: 1) resolve the nature of the cryptic Archean and other pre-1.8 Ga lithospheric components in the Mojave Province and elucidate the timing and processes of their incorporation into an assembling 1.8-1.6 Ga orogenic system; 2) discover more definitive piercing points (relative to Australia, Antarctica, etc.) that can be used for supercontinent reconstructions of Nuna (1.8 Ga) and Rodina (1.0 Ga); and 3) provide a comprehensive basement provenance age template in support of the wide array of detrital zircon studies of sedimentary basins of all ages in the Southwest. The approach is to use U/Pb radiometric dating and Hf isotopic characterization of zircons from the oldest rocks in the Southwest. Pilot studies show that these rocks contain still older grains, whose history will be decipherable using these approaches. The research team will analyze inherited zircons from the oldest plutons, which act as probes what was being melted in the lower crust, and detrital zircons from the oldest metasedimentary rocks, which are an indication of eroding source regions and resulting sedimentary basin and depositional systems.
The project involves collaboration between PIs in U.S. academia, the USGS, and Australian collaborators from academia and the mineral industry. The combined datasets will be integrated with several decades of previous work by the PIs and with emerging new geophysical images from the NSF EarthScope experiment. The importance of the work will be a new integrated synthesis of the structure and evolution of the basement architecture of this part of the North American continent that will be useful for many subfields in the geosciences, including tectonics, deep time geologic history of our continent, ground-truth of geophysical interpretations of the subsurface, and applications for minerals exploration. The project also has a strong outreach component that integrates research and education via training of student geoscientists, including minority students, and working with the Parks for informal geoscience education of the public.
