Constraining the geometry and timing of normal faulting and associated volcanism in the San Gabriel Mountains and its cross-fault correlatives, southern California, U.S.A.

Abstract

The Sierra Pelona anticlinorium of the San Gabriel Mountains has been correlated with the Chocolate Mountains anticlinorium in the Orocopia Mountains. These anticlinoria are associated with Oligocene-Miocene normal faults, but the relationship between the anticlinoria and these faults, and the timing of their development, is unclear. Previous workers have suggested that the Sierra Pelona anticlinorium is the exhumed footwall of a detachment fault, exposed as the Pelona fault. However, kinematic data from the Pelona fault, and its geometric relationship with other faults, indicates that it is actually an antithetic normal fault within the hanging wall of a detachment. Multiple subsequent deformational events have modified the normal-fault system, but sequential palinspastic reconstructions suggest that the anticlinorium is part of a hanging-wall fault block uplifted and warped by isostasy. U-Pb dating of zircon from volcanic units indicates that extension and volcanism initiated concurrently in the San Gabriel and Orocopia Mountains, and on both sides of the anticlinorium. Overlapping chemical compositions of these volcanics underscore their close genetic relationship and potential original proximity. These improved palinspastic reconstructions help constrain the architecture and history of crustal blocks that have been offset by the San Andreas fault system.

AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)