HR: 0830h
AN: T21C-0463    [PDF]
TI: Topographic Development and Exhumation of the Santa Cruz Mountains, From Fission Track Data and Deformation and Erosional Modeling
AU: * Hilley, G E
EM: hilley@seismo.berkeley.edu
AF: University of California, Department of Earth and Planetary Sciences University of California McCone Hall, Berkeley, CA 94720-4767 United States
AU: B\"urgmann, R
EM: burgmann@seismo.berkeley.edu
AF: University of California, Department of Earth and Planetary Sciences University of California McCone Hall, Berkeley, CA 94720-4767 United States
AU: Dumitru, T
EM: trevor@pangea.stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences Braun Hall 206 Stanford University, Stanford, CA 94305-2115 United States
AB: Tectonic uplift within and advection of material around restraining bends along strike-slip faults is a controlling factor on the topography in these tectonic environments. We investigate the deformation, exhumation, exposed rock types, and topography within the Santa Cruz Mountains (SCM) along the San Andreas Fault to understand how topography develops in this region due to the presence of an 8$^{o}$ restraining bend. Thermochronologic studies indicate that rock uplift is concentrated within an $\sim$30--40 km long zone to the northeast of the restraining bend. Specifically, reset Apatite Fission Track (AFT) samples in the Sierra Azul portion of the SCM indicate that at least three kilometers of exhumation has taken place in the last ~3 Ma, while un-reset AFT samples southwest of the fault indicate that exhumation has been limited. We modeled the total amount of rock uplift through time experienced by crust moving through this restraining bend using the Poly3D boundary element model. We found that even when rock uplift was maximized by fixing the restraining bend to the northeast plate, it was insufficient to reset AFT samples within the Sierra Azul block. Therefore, active contractional structures that strike parallel to the SAF are apparently required to localize uplift in this area and bring rocks from greater than ~3 km to the surface. We used Digital Elevation Model and Digital Line Graph analyses of the topography to constrain the amount and distribution of basin relief in areas that have undergone large and small amounts of exhumation along the northeast and southwest sides of the fault, respectively. High basin relief and averaged hillslope angles were correlated most strongly with different geologic units, and to a lesser degree, locusts of uplift defined by the AFT data. Therefore, basin relief appears undiagnostic of high uplift rates within this area without accounting for variations in erosional resistance between lithologic units. To understand the relative role of rock erodibility and uplift in the construction of relief in this area, we have coupled a three-dimensional erosional model that considers bedrock incision to the deformation predicted by the mechanical boundary element model. We are using this model to calibrate the erosional parameters required to produce the topography observed in this area. We will then use this model in a forward sense to assess the conditions under which rock erodibilities and/or rock uplift rates dominate the topographic signature in these types of environments.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8010 Fractures and faults
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting