Petrology of Early Proterozoic granitoids from the southwestern United States: Implications for genesis and tectonics of the Mojave crustal province.

摘要

uch of the southwestern United States is underlain by Early Proterozoic crust that formed or was accreted to the southern margin of the Archean Wyoming province between about 1.8 and 1.6 Ga. The oldest rocks in the desert mountain ranges of southern California and adjacent Arizona and southern Nevada are of these ages. Commonly these rocks have been affected by Phanerozoic metamorphism, plutonism and faulting. Yet relatively well preserved areas occur, in upper plates of Tertiary detachment faults of metamorphic core complexes or in regions marginal or outside the Colorado River extensional corridor.;Studies of these Early Proterozoic rocks show several stages of crustal development beginning shortly after 1.8 Ga, a time of major orogenesis both in this area and elsewhere in the North American craton. The oldest units exposed occur as lithologically heterogeneous and variably deformed layered gneisses that are interpreted as supracrustal rocks. Although poorly constrained, the age of these gneisses appears to be at least 1.97 Ga. Plutonic rocks that intrude this supracrustal package are characterized collectively as pre-kinematic, syn-kinematic, and post-kinematic, relative to the deformation and high amphibolite to granulite grade metamorphism of the Ivanpah orogeny, which has been tentatively dated at 1.70 to 1.71 Ga. Based on U-Pb dating of zircons, the ages of these three intrusive events are