Basin Style Variation Along a Transform Fault: Southern Colorado River Delta, Baja California, México

Abstract

The Colorado River Delta is an example of a transtensional plate boundary defined by a series of en-echelon faults along the Gulf of California. Near the gulf’s mouth, the southern segment of the Cerro Prieto transform Fault (CPF) and the listric Pangas Viejas Fault (PVF) outline Montague Basin (MB), which contrasts with the pull-apart basins along the gulf’s axis. In this context, we present a series of seismic reflection profiles and known observations to illustrate the MB subsurface architecture. The imaging findings reveal concentrated deformation within the CPF and PVF regions, which exhibit a high density of faults perpendicular to the major faults. The imaging findings reveal concentrated deformation within the CPF and PVF regions, which exhibit a high density of faults perpendicular to the major faults. At the same time, in the central part of the basin, the seismoreflectors appear largely unaltered and only slightly tilted. The MB covers an area of approximately 250 km², with a length of around 90 km and a width of 30 km between the CPF to the east and the PVF to the west. Based on the data resolution, the basin's depth is believed to be over 5 km. The acoustic basement appears only on the west side of the basin, around 4 km deep. Other important observations include the Yurimori Fault running parallel to the PVF showing significant deformation at the basement level, as well as the Ometepec and La Salina Faults in the southwest oblique to the CPF, which could be the structural link with the Wagner Basin in the Gulf of California. Historical seismicity and one particular seismic profile indicate that deformation in the Indiviso fault occurred before the El Mayor-Cucapah earthquake (2010, Mw 7.2). Although the connection with the gulf’s basins is uncertain, a slight gravimetric high striking NE is observed; this is interpreted as a strike-slip zone, suggesting that the MB could become an overlap gap between marine and terrestrial basins. Our findings provide various controls for fault linkage in a transtensional setting in which continental and oceanic basins interact.