Retrodeformation of a 3D Geologic Model of the Santa Cruz Mountains West of the San Andreas Fault

Abstract:

We present a 3D geologic model of the Santa Cruz Mountains west of the San Andreas Fault, as constrained by surface expressions of geologic units and well data. Topography within this area has been posited to result from the advection of crust into and through a restraining bend in the San Andreas Fault, which bounds this block to the northeast. We seek to use this new geologic model to test whether or not the geologically observed deformation is consistent with this uplift-advection model within the restraining bend. The new geologic model utilizes available data sets to concisely display the geology of the Santa Cruz Mountains as it is understood today. Restoring this 3D geologic model in Move3D illustrates the distribution of vertical and horizontal strain throughout the region, and yields insight into the spatial and temporal history of the uplift and evolution of the Santa Cruz Mountains. However, complexities associated with wide disparity in sediment thicknesses of individual units, and in total accumulated sediment thicknesses of adjacent regional sub-blocks comprising the range, complicate the restoration process. Additionally, the area hosts a number of potential strike-slip faults with unknown or poorly constrained total slip, and these structures may be partially responsible for the large changes in sediment thicknesses observed within this region. Low temperature thermochronometric data from granitic basement expressions associated with Montara Mountain and the Ben Lomond pluton, and from Eocene units exhumed along significant structures in the range, help to constrain structural evolutionary interpretations and regional block relationships. Coupling kinematic and thermo-mechanical models of the Santa Cruz Mountains will aid in understanding the evolution of the range, and in identifying and separating the contributions of regional transpression and restraining bend tectonics to total range uplift and to the production of the topography seen today.