Architecture and tectonostratigraphic evolution of the Pescadero Basin Complex, southern Gulf of California: Analysis of high-resolution bathymetry data and seismic reflection profiles

Abstract

The Pescadero Basin Complex (PBC) comprises three distinctive rhomb-shaped pull-apart basins separated by short and highly overlapped transform faults. Multibeam bathymetric data collected from ship at 40-m resolution, combined with the interpretation of three 2D high-resolution multichannel seismic reflection profiles, were used to establish the architecture of the PBC. Detailed mapping and cross-sectional kinematic modeling based on the seismic images of the North Pescadero Basin reveal a highly evolved pull-part geometry, characterized by a well defined ∼1.8 km-wide axial graben extending ∼32 km in a NNE-SSW direction. Among the fundamental elements controlling basin architecture and evolution of the PBC are the geometry of the initial configuration of the master strike-slip fault step-over and fault dynamics, which may cause transients in fault system activity and basin reconfigurations. Structural analyses carried out in this study point out the PBC pull-apart basins developed under sustained transtensional deformation, where the relative motion of the crustal blocks is oblique and divergent to the transforms or principal displacement zones. Cross-cutting relationships between the main fault systems controlling basin's subsidence and evolution, indicate that underdeveloped basin-crossing faults terminate against basin bounding normal faults, suggesting that ongoing pull-apart rifting continues to dominate basin evolution of the PBC. Furthermore, we propose that the undeveloped cross-basin faults of the PBC initiated as synthetic Riedel faults that, with progressive deformation along the divergent-wrench fault zone, rotated clockwise around a vertical axis to acquire their present orientation oblique to the master bounding transforms. Basin-crossing faults with lesser obliquities control the subsidence along the basin-side faulted segments of the narrow graben systems that characterize the plate boundary at the corners of the PBC pull-apart basins. These narrow transtensional synforms may have served as connections facilitating marine waters to flood the PBC during the early stages of formation of the Gulf of California.