Geochemistry of Mesozoic plutons, southern Death Valley region, California: Insights into the origin of Cordilleran interior magmatism

Abstract

Mesozoic granitoid plutons in the southern Death Valley region of southeastern California reveal substantial compositional and isotopic diversity for Mesozoic magmatism in the southwestern US Cordillera. Jurassic plutons of the region are mainly calc-alkaline mafic granodiorites with eNdi of –5 to –16, 87Sr/86Sri of 0.707–0.726, and 206Pb/204Pbi of 17.5–20.0. Cretaceous granitoids of the region are mainly monzogranites with eNdi of –6 to –19, 87Sr/86Sri of 0.707–0.723, and 206Pb/204Pbi of 17.4–18.6. The granitoids were generated by mixing of mantle-derived mafic melts and pre-existing crust – some of the Cretaceous plutons represent melting of Paleoproterozoic crust that, in the southern Death Valley region, is exceptionally heterogeneous. A Cretaceous gabbro on the southern flank of the region has an unusually juvenile composition (eNdi –3.2, 87Sr/86Sri 0.7060). Geographic position of the Mesozoic plutons and comparison with Cordilleran plutonism in the Mojave Desert show that the Precambrian lithosphere (craton margin) in the eastern Mojave Desert region may consists of two crustal blocks separated by a more juvenile terrane.