Geologic and tectonic history of the Gulf of California ( DSDP, Leg 64).

Abstract

Deep sea drilling and associated geophysical surveys have provided samples and data that offer new insight into the nature and timing of the evolution of the Gulf of California. We propose a scenario for the opening of the Gulf that begins about 5.5Ma, when the Pacific-Farallon (Guadalupe) spreading center propagated NE, and right-slip transform motion between the Pacific and North American plates jumped from offshore to the E side of the Peninsular Range batholith to initiate motion on the present San Andreas Fault and opening of the Gulf. Assuming constant 5.6cm/yr displacement between the Pacific and North American plates since that time, the Baja California crustal block and S California Terrace of the Pacific Plate have moved 300km to the NW relative to North America. This is the maximum closure that can be attained in paleogeographic reconstruction of the region by retrofitting along the aximuth of the major Gulf fracture zones. About 300km is also the amount of offset required by Gastila and his colleagues for matching geological phenomena across the Gulf and is the amount required by Matthews, Ehlig, and others for restoring offset along the San Andreas Fault in Central and S California. We do not propose that any of this 300km of opening resulted from formation of an earlier proto-Gulf, but instead postulate opening by a single two-phased process.-from Authors