Magmatic record of changing Cordilleran plate-boundary conditions—Insights from Lu-Hf isotopes in the Mojave Desert

Abstract Belts of Cordilleran arc plutons in the eastern part Mojave crustal province, inboard from southwestern North American plate boundary, record major magmatic pulses at ca. 180–160 and 75 Ma smaller 100 20 Ma. This cyclic magmatism likely reflects evolving plate-margin processes. Zircon Lu-Hf isotopic characteristics inherited zircons for different-age may relate magma sources to tectonics. Sources similar age bulk exposed crust (1.6–1.8 Ga) dominated magmas. Rare having εHf(t) values as low −52 indicate that Cretaceous melt also included more ancient components, such Archean-derived detritus supracrustal gneisses Vishnu basin. Some rocks signal contributions mantle lithosphere (in Miocene) or asthenosphere (middle Cretaceous). Temporal shifts pattern this sample Cordillera flux. Hf-isotopic pull-downs suggestive dominantly characterize Jurassic Late flare-ups. The flare-up, occurring near onset flat-slab subduction, produced abundant Proterozoic xenocrystic zircon Hf isotopes implicating derivation largely heterogeneous deep crust. Isotopic pull-ups lower-flux middle Miocene episodes. pulse 105–95 signals but isotopically most juvenile zircons, ranging upward barely positive εHf suspected an contribution. point toward transtension slab retreat causing backarc extension hinterland Cordillera. That possibility raises questions about tectonic environment contemporaneous main Sierra Nevada high-flux closer continental margin.