The record of Cenozoic volcanism around the Gulf of California

Abstract

Potassium/argon dating and chemical analyses of major oxides of volcanic rocks in areas adjacent to the Gulf of California provide a stratigraphic record of tectonic and magmatic evolution that has occurred during the past 30 m.y. The important volcanic provinces are: the Pliocene-Holocene Gulf of California dacite; the Pliocene-Holocene west Baja California alkaline basalt-andesite; the Trans-Mexican Volcanic Belt; the “proto-Gulf” basalt from the coast of Nayarit; the late Miocene alkaline basalt of the Commondu Formation found in the Peninsula; the late Miocene basalt-andesite-rhyolite rocks straddling the northern half of the Gulf; the 18- to 22-m.y.-old hornblende andesite belt in the Peninsula of Baja California and the central coast of Sonora; and the Oligocene–early Miocene basalt-rhyolite belt, largely east of the Gulf. Tectonics interpretation suggests that the subduction plane moved westward between Oligocene and middle Miocene time and that active calc-alkaline volcanism continued over a broad area around the northern Gulf even after the trench west of Baja California had been annihilated.