--> Abstract: Two-Stages of Cenozoic Tectonic Deformation in the California Borderland, by S. M. Howell, I. Sacramentogrilo, J. Washburn, C. Noland, and H. Warren; #90935 (1998).

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Abstract: Two-Stages of Cenozoic Tectonic Deformation in the California Borderland

HOWELL, S. M., I. SACRAMENTOGRILO, J. WASHBURN, C. NOLAND, and H. WARREN, San Diego State University, San Diego, CA

The California borderland has two distinct stages of significant tectonic activity during the Cenozoic era. Miocene crustal extension was once thought to be localized in the Basin and Range region of the southwestern United States. However, now it is believed to have extended hundreds of more kilometers to the west, into the borderland region. Strike-slip faulting associated with the modern San Andreas fault system also extends into the borderland region.

In interpreting seismic reflection profiles about 30 km off the coast of Oceanside, a detachment fault is believed to be present. It is thought to trend approximately NS and dip to the east, parallel to the detachment faults in the Salton Trough and Basin and Range area. Gravity contour maps indicate that a gravity high "ridge" trends parallel to the detachment fault, and is interpreted to be a pre-Cenozoic tilted crustal slab from a system of stacked normal faults, which dip to the east. Rift related volcanic rocks are present in the half-grabens produced by the normal faults.

Since the onset of the San Andreas strike-slip regime, right lateral movement has dominated the borderland region. Numerous strike-slip faults are imaged in the seismic profiles that have spacing intervals which may coincide with the bottom of halfgrabens of the normal faults.

This system of normal and strike-slip faults is characteristic of many other hydrocarbon-bearing basins throughout the world.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California