Late Quaternary tectonism along the Pacific coast of the Californias: a contrast in style

Abstract

Abstract Marine terraces and associated features are examined along 1500 km of coast at the seaward margin of that part of the North American plate that has been captured by the Pacific plate. This coast embraces parts of three morphotectonic provinces, each with its own distinctive tectonic style, namely the southern Coast Ranges, western Transverse Ranges, and northern Peninsular Ranges. Based primarily on the 125 ka shoreline, four magnitudes of late Quaternary deformation are recognized: (1) high uplift rates exceeding 1.0 m per 1000 years; (2) moderate uplift rates between 1.0 and 0.1 m per 1000 years; (3) low uplift rates less than 0.1 m per 1000 years; and (4) variable net subsidence. The highest rates of uplift and subsidence are associated with the intense fold-thrust tectonics of the western Transverse Ranges nearest the Big Bend in the San Andreas fault, and diminish in magnitude to east and west. Moderate uplift rates occur in both the southern Coast Ranges and the northern Peninsular Ranges adjacent to the western Transverse Ranges, commonly associated with block uplift and subsidence between high-angle reverse faults within a broader strike-slip scenario. This suggests that compression and transpression are significant features of these areas and that the continued rotation and relative westward motion of the western Transverse Ranges, within the broader context of shear distributed across the San Andreas fault system, continue to have an impact on regions immediately to the north and south. Uplift diminishes with distance from the Transverse Ranges and is low for Baja California south of Punta Banda. The style of late Quaternary deformation is similar to that defined by earlier Quaternary marine limits, but intensity varies, most notably in the western Transverse Ranges.