Interaction of extensional, contractional, and strike-slip elements at Mount Diablo and the surrounding eastern Coast Ranges, San Francisco Bay area, California: A model-based analysis

Abstract

This study presents three regional cross sections, a structural map analysis, and a schematic map restoration. The sections are constrained by surface geology and petroleum wells and were developed using model-based methods to be consistent with the regional tectonic context and balancing concepts. Together, these products depict the geometry and kinematics of the major fault systems. Insights from this research include the following. Franciscan complex blueschist-facies rocks in the Mount Diablo region were unroofed west of their current location and subsequently thrust beneath the Great Valley sequence in the mid-Eocene. East Bay structures are complicated by overprinting of Neogene compression and dextral strike-slip motion on a Paleogene graben system. Net lateral displacement between the Hayward fault and the Central Valley varies from 26 km toward 341° to 29 km toward 010° in the southern and northern East Bay Hills, respectively. Uplift above a wedge thrust generates the principal Neogene structural high, which extends from Vallejo through Mount Diablo to the Altamont Ridge. Anomalous structural relief at Mount Diablo is due to strike-parallel thrusting on the crest of a fault-propagation fold formed on the west-verging roof thrust. Uplift that exposes the Coast Range ophiolite in the East Bay Hills is formed by oblique thrusting generated by slip transfer at the northern termination of the Calaveras fault. The Paleogene extensional fault system likely extends farther west than previously documented. An east-dipping branch of that system may underlie the Walnut Creek Valley. Three-dimensional restoration should be applied to constrain geologic frameworks to be used for seismic velocity modeling.

Quaternary-Active Faults and the Role of Inherited Structures in the Sacramento-San Joaquin Delta, Western Central Valley, Northern California

“…Structural geometries from this phase of tectonic history have been preserved in the Coast Ranges by the transition of the convergent plate boundary to a transform margin, rather than being destroyed by processes associated with terminal collision (e.g., Wakabayashi, 2015). This preserved structural architecture likely exerts an influence on the geometry of the modern transform plate boundary system, leading in some cases to reactivation of Late Cretaceous-Paleogene forearc faults to accommodate right-lateral plate motion (e.g., Jachens et al, 1995;Langenheim et al, 2007;Medwedeff , 2021;Unruh et al, 2007).…”

“…The Coast Range Fault, a name applied over a wide geographic region to structures separating Franciscan Complex and Coast Range ophiolite, is a bedrock fault with remnants found as far east as the eastern margin of the Coast Ranges and as far west as the San Andreas Fault. The Coast Range Fault has a complex kinematic history, with various datasets suggesting both thrust and normal displacement across the fault (e.g., Medwedeff , 2021). Juxtaposition of blueschist-grade rocks of the Franciscan Complex against zeolite-grade rocks of the Great Valley Group in the footwall and hanging wall, respectively, of the Coast Range Fault indicates that it may be the structure on which the Franciscan Complex is exhumed (e.g., Jayko et al, 1987;Unruh et al, 2007;Wakabayashi, 2021), though it has also been interpreted as a later, out-of-sequence thrust Ring andBrandon (1994, 1999); Ring (2008).…”

“…Major faults in the Coast Ranges -including the San Andreas; the Hayward and Rodgers Creek; and the Calaveras, Green Valley, and Berryessa Faults -exhibit primarily right-lateral kinematics from the late Neogene to the present, consistent with dextral motion across the plate boundary. Other structures that initiated in the late Neogene include the Diablo Anticline, a fold 20 km wide and 40 km long and located southwest of the Delta, that forms in a restraining step in plate-boundary-parallel faults and is amplified by plate-boundary-normal compression (Graymer and Langenheim, 2021;Medwedeff , 2021).…”

“…In this new tectonic regime, preexisting dip-slip faults were in some cases reactivated as strike-slip or oblique-slip faults (e.g., Jachens et al, 1995;Langenheim et al, 2007;Medwedeff , 2021). Examples include Paleogene-age extensional faults exposed on the north limb of the Diablo Anticline, which reactivated after 10 Ma to accommodate oblique right-lateral displacement and north-south shortening around the restraining bend (Unruh et al, 2007;.…”

“…Both the Kirker Fault and the Los Medanos Fault root into the Clayton-Marsh Creek Fault System to the south (Unruh et al, 2007;Graymer and Langenheim, 2021), which may represent, or reactivate, the basal detachment for the Late Cretaceous to Paleogene extensional graben system (Crane, 1995;Unruh et al, 2007). In the modern tectonic regime, the Clayton and Marsh Creek Faults may connect to the northern end of the Greenville Fault System (e.g., Medwedeff , 2021), but the Quaternary activity of the Clayton and Marsh Creek Faults remains unconstrained.…”