Miocene to recent structural development of an extensional accommodation zone, northeastern Baja California, Mexico

The Gulf of California Extensional Province in northeastern Baja California contains a major structural transition from a northern domain of widely spaced basins and ranges to a southern domain of closely spaced, NNW-striking high-angle faults. In the northern domain, the western boundary of the province (the Main Gulf Escarpment) is a single listric normal fault, the San Pedro Mártir fault; in the southern domain it is a 5 km wide zone of numerous E-dipping high-angle normal faults. The western half of this structural transition, studied here, does not occur by a single 'transfer fault' but rather by: (1) transfer of displacement from the San Pedro Mártir fault onto multiple fault zones in the footwall, without intervening cross-faults; and (2) increased southward disruption of the hanging wall by WNW-striking strike-slip faults (oblique to the extension direction) and NNW-striking normal faults and extension fractures. This structural transition involves both the hanging wall and the footwall of the escarpment. The lack of a discrete transfer structure is attributed either to insufficient extension (<10%) or to a gradual change in geometry of the basal detachment.