Shear zone faulting, volcanism, and basin evolution along a continental margin transform system: San Pedro Basin, offshore Southern California

Abstract

Seismic reflection and multibeam bathymetry data establish the San Pedro Basin fault — San Diego Trough fault (SPBF-SDTF) as a >350 km major dextral shear zone in the Inner California Continental Borderland. This currently active shear zone developed between 600 ka and 1 Ma. Prior to that time, slip on the SDTF was transferred to the Catalina fault (CF), forming the Catalina Ridge restraining bend uplift. Seafloor terraces around Santa Catalina Island and flat-lying sediment sequences in adjacent San Pedro Basin indicate that uplift of Catalina Ridge has stopped. This stoppage is related to near or total abandonment of the CF and localization of right-slip along the SPBF-SDTF system. The youthful SPBF transects San Pedro Basin and bypasses most major restraining bend uplifts associated with older strike-slip fault systems such as the CF or Palos Verdes fault. San Pedro Basin is either a small nested basin or a remnant of a larger, older proto-basin that formed within the broader Inner Borderland (IB) rift. The proto-basin, formed during oblique rifting, included parts of now uplifted areas adjacent to San Pedro Basin, such as Catalina Ridge and Palos Verdes anticlinorium. Deep sediments in San Pedro Basin extend under the northeast flank of Catalina Ridge, and age-correlate with middle Miocene strata on Santa Catalina Island and Palos Verdes Peninsula. Restoration along faults and back-rotation of the Western Transverse Ranges show that most of the 19-10 Ma volcanism of coastal southern California formed chains flanking the proto-basin. Continued rifting inflated the proto-basin and could have formed nested basins within it. The proto-basin was further fragmented into smaller basins as a result of inversion and uplift along restraining segments of major shear zones that developed as the Pacific-North America relative plate motion vector changed. Segmentation due to transtension and transpression has continued has continued until after 1 Ma, and is probably still occurring today, as is evidenced by the young San Pedro Basin.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016