HR: 17:45h
AN: T24C-08    [Abstracts]
TI: Thermokinematic Modeling of the Effect of Footwall Erosion on Cooling Age Patterns in Detachment Fault Settings
AU: * Robinson, A C
EM: robinson@geo.arizona.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Sciences, University of California Los Angeles, Los Angeles, CA 90024
AU: Yin, A
EM: yin@ess.ucla.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Sciences, University of California Los Angeles, Los Angeles, CA 90024
AU: Lovera, O M
EM: lovera@ess.ucla.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Sciences, University of California Los Angeles, Los Angeles, CA 90024
AB: Determining the kinematics of deformation and exhumation in the footwalls of detachment faults is important in understanding how continental crust behaves during extension. A common method to examine footwall deformation history is to use P-T-t data to constrain the magnitude of exhumation and cooling history in conjunction with structural analysis. However, correctly interpreting cooling age patterns requires knowledge of the thermal evolution of the crust during deformation and exhumation. Previous studies addressing the T-t history of particles exhumed in detachment fault footwalls have focused on particles exhumed along paths directly below the fault surface. As thermal gradients are developed near the fault during exhumation, particles exhumed along paths away from the fault surface experience different T-t paths than those exhumed directly below the fault surface, effecting cooling age and T-t path patterns in deeply eroded footwall terranes. Numerical simulations using a two-dimensional finite-difference thermo-kinematic model were conducted to study the effect of footwall erosion during exhumation on the pattern of footwall T-t paths, and used to predict biotite and muscovite cooling age patterns. Results incorporating footwall erosion with a rolling hinge geometry show a strong affect on cooling age patterns: Instead of a steady increase in age with distance from the fault, erosion of the footwall during exhumation results in constant to slightly decreasing cooling ages with distance from the fault over distances of several km before increasing with distance. The model is used to simulate the cooling age pattern from the footwall of the Kongur Shan normal fault in the eastern Pamir, China, which has experienced large amounts of erosion (>3.5 km) during exhumation. Simulations using initial conditions provided by thermobarometric and geochronologic data require a three stage evolution of exhumation rates from moderate (~7 mm/yr), to slow (~2 mm/yr), to rapid (~10 mm/yr). We suggest changes in exhumation (and extension) rate are a result of 1) the Kongur Shan normal fault lying in the hanging wall of the active Main Pamir Thrust, or 2) variations in exhumation rate are related to changes in climate and erosion.
DE: 1140 Thermochronology
DE: 8020 Mechanics, theory, and modeling
DE: 8109 Continental tectonics: extensional (0905)
DE: 9320 Asia
SC: Tectonophysics [T]
MN: Fall Meeting 2005