Cenozoic volcanism and two-stage extension in the Salton trough, southern California and northern Baja California

摘要: Pronounced differences in age and geochemistry between Cenozoic volcanic rocks within the Salton trough, southern California northern Baja California, imply their formation two distinct tectonic settings rather than previously proposed single phase of continental rifting. The emplacement Oligocene-Miocene alkaline lavas overlapped with crustal extension basin region during this time. Post-4 Ma subalkaline magmatism related to Gulf California-East Pacific Rise divergent plate margin exploited crust already ruptured Miocene extension. New rare earth element Sr-Nd isotopic data, K-Ar, 40Ar/39Ar, U-Pb ages for basalt, andesite, granophyric granite xenoliths contained buttes rhyolite domes, part post-4 oceanic spreading regime, indicate that they are components a differentiated magmatic system. These data also refute presence crystalline basement beneath trough. We suggest rupture axis trough was more effective