Structural characteristics of the Altar Basin, Northwest Sonora, Mexico

摘要

Eight two-dimensional, multichannel seismic reflection lines were acquired, processed, and interpreted to study the structure of the Altar Basin, which is part of the Salton Trough tectonic province. We identified two basin-bounding zones characterized by different degrees of strain: the Cerro Prieto-Altar deformation zone (CPADZ) and the Altar-Caborca deformation zone (ACDZ). The CPADZ is bounded on the west by the Cerro Prieto fault and on the east by the Altar fault. To the north, the strike of both faults changes slightly from a NW to more NNW direction. In the CPADZ, the thickness of the crust decreases southward towards the Gulf of California, and is associated with a deformation-developing fault. The CPADZ has a rotation component orientating these faults in an oblique direction to the Cerro Prieto fault, whereas within the ACDZ, a geometric coherence of synthetic and antithetic faults exists, creating horsts and graben striking N37° W. The Altar fault is recognized by basement interruption, with a vertical component of ~1 km, striking at N37° W and dipping 83° SW. On the northeastern side of the Altar Basin, the basement configuration shows that the minimum time of basement record (~0.4 s of two-way travel time) and the time curve gradient decrease in the NE-SW direction. The depocentre is ~6 km deep in the central-west portion of the basin. We identified a graben between the Rosario and Tinajas Altas mountains (Rosario Basin). The extension—connection of the Altar and Rosario basins to the south is not well defined;;nevertheless, these basins could represent the link between the Colorado River and the Gulf of California during the late Miocene, whereas this link was abandoned in the Pliocene as subsidence migrated towards the northwest into the Cerro Prieto and Laguna Salada basins.