HR: 16:15h
AN: T34B-02    [Abstracts]
TI: Recent Contractile Deformation in the Forearc of Southern Peru: A Geomorphologic Analysis And 10Be Surface Exposure Ages
AU: * Hall, S
EM: shall@pmc.ucsc.edu
AF: University of California, Santa Cruz, Dept. of Earth Sciences, Santa Cruz, CA 95060, United States
AU: Farber, D L
EM: dfarber@ucsc.edu
AF: University of California, Santa Cruz, Dept. of Earth Sciences, Santa Cruz, CA 95060, United States
AU: Farber, D L
EM: dfarber@ucsc.edu
AF: Lawrence Livermore National Laboratory, 4000 East Ave., Livermore, CA 94550, United States
AU: Audin, L
EM: laurence.audin@ird.fr
AF: IRD-LMTG-UNIVERSITE DE, Lima, Peru, TOULOUSE-CNRS-OMP, 001, France
AU: Finkel, R
EM: finkel1@llnl.gov
AF: Lawrence Livermore National Laboratory, 4000 East Ave., Livermore, CA 94550, United States
AB: The style, amount, and timing of deformation along the margins of the Altiplano are important components of our working model of the formation and maintenance of this high elevation plateau. While much of the convergence- related shortening is accommodated along the eastern margin in the Subandean fold and thrust belt, a significant amount of uplift and crustal thickening has occurred in the western margin during the past ~20 Myr. In addition to ancient uplift and deformation, various styles and amounts of Recent deformation that reflect the current lithospheric state of stress have been documented within the forearc. Some of the first order variables that affect the state of stress and therefore the style of deformation within the forearc of the western margin include: 1) the variable dip of the subducting slab along the South American margin, 2) the orientation of convergence relative to the margin, and 3) the subduction of aseismic ridges (e.g., Nazca Ridge). Other potential influences on the state of stress include addition of material to the western margin through lower-mid crustal flow, subduction erosion, and magmatic additions. In southern Peru, previously documented active deformation in the forearc includes coastal normal faults trending perpendicular to the trench, and transform faults oriented parallel to the trench, including the left-lateral Incapucio fault system, of the Precordillera. Our new field mapping and geochronologic studies in the Longitudinal Basin and Precordillera of southern Peru reveal recent contractile deformation along structures trending sub-parallel to the trench. Here, a southwest propagating anticline related to a blind thrust deflects the active stream channels within the Pampa Cabeza de Vaca region. Incision along the active drainages is localized to areas near active structures and has produced strath terraces that provide datable geomorphologic markers to quantify incision rates and constrain the timing of deformation. Cosmogenic 10Be surface exposure ages from a set of three distinct abandoned terraces in the Pampa Cabeza de Vaca region yield ages ranging from ~35-550ky and incision rates of ~0.04-0.09mm/yr. Thus, the contractile deformation within this region has been active for at least the last 500ky and is plausibly presently active. The documentation of recent contractile deformation within the forearc of southern Peru stylistically contrasts with previously held view active deformation in this region is dominated by extensional topographic collapse. Moreover, active shortening within the Peruvian forearc bears on our models of how the Altiplano plateau is currently being maintained along the western margin. Indeed, by identifying and quantifying active deformation within the Peruvian forearc, we can begin to address the potential links between surface processes related to climate and active tectonics, and the dynamics of the lithosphere.
DE: 8104 Continental margins: convergent
DE: 8107 Continental neotectonics (8002)
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting