The proto-Gulf of California

Extensional zones behind trench-arc systems lying along continental edges take the form of volcano-tectonic rift zones. These are characterized by ignimbrite sheets errupted simultaneously with, but behind, the andesite centers. Slightly later, a trough with basin-range structures is formed by crustal extension. The known geology of the Gulf of California region indicates that a trench, andesite chain, and ignimbrite province co-existed in Mid- to Late Tertiary time in the same tectonic pattern as observed in trench-arc systems. Extension and formation of a broad volcano-tectonic rift zone, the proto-Gulf of California, occurred in Mid- to Late Miocene time, creating a zone of weakness subsequently used for strike-slip faulting and inter-plate extension.