Continental Rifting and Rupture
From UNC Tectonic Geomorphology
Continental extension and break up are fundamental to understanding the origin of ocean basins and the mechanics of plate tectonics. The Gulf of California, formed by oblique divergence of the Pacific and North America plates, is a premier example of a young ocean basin where the processes that lead to continental break-up can be closely examined. This projects aims to understand the transition from distributed, moderate- to large-magnitude extension of the North America continent to localized rifting and rupture of continental crust.
The timing and rate of opening of the Gulf of California are well-constrained from prior studies of offset syntectonic volcanic rocks. Present work is focussed on the record of continental extension immediately adjacent to the Gulf of California and its relationship to break-up. Preliminary reconnaissance studies have discovered localized large-magnitude continental extension on both margins of the northern Gulf with localized exhumation of mylonitized footwall rocks. These extensional basins appear to have continued activity through the period of continental break-up nearby. Fault scarps in alluvial deposits indicate that several continental extensional faults remain active even six million years after localization of the plate boundary into the Gulf of California ocean basin.
Ongoing studies in western Sonora aim to characterize the history of multiple extensional basins to gain a synoptic view of continental extensional activity in relation to opening of the ocean basin. These studies include geologic mapping of extensional basins, geochronology of interstratified volcanic rocks, and thermochronology of exhumed footwall basement rocks. These studies will also investigate the magnitude of dextral shear may have also been absorbed within the Sonora margin of the Gulf of California.
