Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada

摘要: Ongoing arc magmatism along western North America was preceded by ancestral that began ca. 45 Ma and evolved into modern volcanism. The southern segment, active from 30 to 3 Ma, adjoins the northern segment in California across a proposed subducted slab tear. east edge of Walker Lane approximates whose products, mostly erupted stratovolcanoes lava dome complexes arrayed crest arc, extend down west flank Sierra Nevada. Southern rocks include potassic, calc-alkaline intermediate- silicic-composition flows, complexes, associated volcaniclastic deposits. Northern are similar other convergent-margin magmatic but compositionally distinct each other. have lower TiO 2 , FeO*, CaO, Na O contents higher K contents, exhibit less compositional-temporal variation. Compositional distinctions between reflect composition thickness crust beneath which magma systems were sourced. rock compositions consistent with generation thin, primitive crust, whereas represent magmas generated fractionated thicker, more crust. Although two segments metal abundances, they metallogenically distinct. Small porphyry copper deposits characteristic significant epithermal precious most commonly segment. These metallogenic differences also fundamentally linked tectonic settings crustal regimes within these evolved.