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 Commondú 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.

First Page Preview

First page PDF preview
You do not currently have access to this article.