Mode of crustal extension and formation of rift systems in the southern Gulf of California, from 2D seismic reflection data

In this paper, we carried out a kinematic analysis of the Cerralvo Extensional System (SEC), southern Gulf of California, and propose a crustal extension model from the processing and interpretation of 57.4 km of two-dimensional multichannel seismic-reflection data. The seismic image shows that in the SEC the main faults dip eastward with angles between 10-25 degrees forming an asymmetric rift. The amount of horizontal extension measured in Cerralvo is 28.0 km, which corresponds to a crustal thinning factor of 2.0. The average subsidence rate in the SEC is 0.3 mm/yr, which is three times the marine sedimentation documented in this basin (0.1 mm/yr). Along the SEC, the acoustic basement is delimited by a layer with semi-continuous reflectors, which may represent cataclastic and/or myloniticfabrics associated with low-angle normal faults. The penetrative deformation, the development of basins bounded by low-angle normal faults, as well as the magnitude of horizontal extension across the SEC, suggest simple shear deformation resulted in crustal extension since the late Miocene to the present. It is also inferred that the SEC is the eastern continuation of the Los Cabos Block structural system (BLC). Thus, our regional model proposes that in the currently advanced phase of the continental rupture process and the opening of the GC, the BLC and SEC fault systems converge at depth forming a regional detachment surface along the upper crust, causing the hanging wall to rotate to lower dip angles forming asymmetric basins with an eastward tectonic transport. Our results were contrasted with the sea bottom topography to the SEC. Here we inferred that at the western boundary of the Pescadero Norte pull-apart basin, the regional detachment surface must acquire an antilistric geometry characterized by a high angle shear zone through the lower crust. This style of deformation might result in the formation of metamorphic core complexes associated with regional rolling hinge structures.