ASSEMBLY AND RECYCLING OF COMPONENTS TO FORM THE MOJAVE CRUSTAL PROVINCE

New rock and zircon geochemistry yield a clearer picture of the origins of the Mojave province. The oldest recognized rocks include tholeiitic to aluminous amphibolites chemically similar to enriched MORB or primitive arc basalts, which yield a whole rock isochron of ~1.81 Ga (εNd=+1), implicating an enriched mantle source. Amphibolites are commonly spatially associated with metasediments chemically similar to immature arc-derived greywackes, which contain abundant 1.98-1.8 Ga and lesser Neoarchean detrital zircons. Both Archean and younger detrital zircons have Th/U of 0.3 to 1, fractionated REE [Yb/Sm~100] and modest negative Eu anomalies of ~0.3, suggesting provenance in relatively evolved upper crustal igneous rocks. These data suggest initial crust formation by deposition of greywacke derived from an adjacent slightly older arc source onto thin mafic basement overlying an enriched mantle. This older rock assemblage hosted plutons at 1.79-1.73 and 1.69-1.64 Ga. Both phases are composed of intermediate to felsic metaplutonic rocks containing premagmatic zircons, indicating involvement of older crust similar to the greywacke source. Early phase orthogneisses range from low to high K, but late phase plutons are high K to shoshonitic and relatively enriched in HFSE. Early and late phase plutons have εNd=0 to -3, suggesting a persistently mixed source with greater involvement of early phase plutonic rock in generation of late phase plutons. Metamorphism began about 1.795 Ga and persisted throughout plutonism. The 1.72-1.70 Ga Ivanpah Orogeny corresponds to a time of widespread metamorphism and a change in plutonic character, and thus probably represents either crustal thickening or flattening of the geotherm, causing remelting of arc lower crust. Mylonitization and metamorphism continued until ~1.64 Ga, indicating continued thickening or post-orogenic extension, as mylonites with both east and west vergence are preserved locally. Mojave crust was sufficiently thick and stable to support shallow water sedimentation by early Mesoproterozoic time. Provenance of overlying quartzite-carbonate sequences suggests the province remained in proximity to its ‘Hudsonian' neighbor until rifting and formation of the miogeocline.