HR: 1340h
AN: T23D-1653    [Abstracts]
TI: Asymmetrical Growth of Footwall Topography in the Cordillera Blanca, Peru: Implications for Normal Fault Control on Landscape Evolution
AU: * Giovanni, M K
EM: mkgiovan@ucalgary.ca
AF: University of Calgary, Dept. of Geoscience, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada
AU: Horton, B K
EM: horton@mail.utexas.edu
AF: University of Texas, Austin, Dept. of Geological Sciences, 1 University Station C1100, Austin, TX 78712, United States
AB: Morphometric parameters and hypsometry of the >5-km-high Cordillera Blanca in Peru provide insights into the topographic evolution of the uplifted footwall of an active, high-magnitude-slip, low-angle normal fault within a contractional orogenic belt. The modern tectonic activity, mappable fault trace, high relief, and uniform footwall lithology make the Cordillera Blanca an ideal locality to test models for the evolution of topography related to normal faulting. Most models for normal fault growth suggest a tectonic and geomorphic symmetry in which maximum slip and maximum surface uplift occur along the central segments of the fault, with net slip, footwall uplift, and hangingwall subsidence diminishing along strike toward the fault tips. A digital elevation model (DEM) of the Cordillera Blanca permits extraction of important geomorphic metrics for footwall transverse drainages and the hanging-wall axial river, including hypsometry, drainage area, drainage length, relief, channel gradient, surface slope, aspect ratio, and longitudinal profile. These data reveal a pronounced asymmetry in which footwall relief, exposed fault relief, channel gradient, and surface slope are greatest along the northern fault segment and become systematically lower southward along strike. In contrast to most models for normal fault growth, largely based on late Cenozoic systems in the Basin and Range province of the western United States, the Cordillera Blanca demonstrates that abrupt and significant along-strike variations in displacement and footwall uplift are possible in major normal fault systems. The causes of an asymmetric distribution of fault slip and footwall topography in the Cordillera Blanca may be related to: (a) mechanical coupling between the subducting flat Nazca slab and the overriding South American plate; (b) gravitational collapse of overthickened crust along reactivated thrust faults; (c) climatic processes linked to the effect of glacial erosion in the footwall and/or fluvial incision in the hanging wall; or (d) a combination of rapid erosional processes and batholith intrusion that removed the strong upper crust and thermally weakened the remaining crust, allowing extension and exhumation along the Cordillera Blanca normal fault.
DE: 8104 Continental margins: convergent
DE: 8109 Continental tectonics: extensional (0905)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting