Major Late Cretaceous and Tertiary Low-Angle Structures in Southern California
L. T. Silver
California Institute Technology, Pasadena, CA
Probably the most decipherable reflections of the Paleogene (and latest Cretaceous) tectonic rearrangements are the spatial distributions of the Cretaceous and older magmatic arc rocks. The Cretaceous batholiths are systematically but asymetrically zoned, (Silver and Chappell, 1988; Taylor and Silver, 1974). Fragments of these batholithic zones can be recognized by various combinations of chemical and isotopic signatures. Palinspastic restorations of displacements accumulated on the late Miocene to Recent San Andreas- Garlock fault zones produces an intricate but correlable pattern of modified zonation. A simple model suggests westward displacements of batholithis zones up to 100–150 km on older low-angle faults and nappes along a 400+ km length of the continental margin. The southernmost expression includes but is not limited to the Vincent Thrust. The entire width (150km) of the Peninsular Ranges batholith is telescoped into less than 50 km in the eastern Santa Monica and western San Gabriel Mountains. Similar telescoping is evident in the southernmost Sierra Nevada and the restored Salinian block. The timing probably involved recurrent movement episodes between 80– 85 and 18–20 Ma. Orientation of motion sense probably changed significantly during this extended period of time. Some but not all of the major low-angle structures are exposed. Crustal seismic studies (e.g. EDGE-type) at selected positions can help clarify the positions of tectonic discontinuities in the Salinian, Sierra Nevada, Mojave and Transverse Ranges blocks.
AAPG Search and Discovery Article #90904©2001 AAPG Pacific Section Meeting, Universal City, California