HR: 1340h
AN: T23C-0582    [Abstracts]
TI: Quantifying the rates of Quaternary deformation in the Peruvian Forearc using in situ produced cosmogenic 10Be and 26Al.
AU: * Hall, S R
EM: shall@es.ucsc.edu
AF: University of California, Santa Cruz, Dept. of Earth Sciences, Santa Cruz, CA 95060 United States
AU: Farber, D L
EM: farber2@llnl.gov
AF: Lawrence Livermore National Laboratory, LLNL, Livermore, CA 94550 United States
AU: Audin, L
EM: laurence.audin@ird.fr
AF: Universite P. Sabatier, Dept. Geologie 38 rue de 36 ponts, Toulouse, 31400 France
AU: Finkel, R C
EM: finkel1@llnl.gov
AF: Lawrence Livermore National Laboratory, LLNL, Livermore, CA 94550 United States
AU: Meriaux, A
EM: meriaux1@mac.com
AF: University of Edinburgh, Institute of Geography, Drummond Street, Edinburgh, EH8 9XP United Kingdom
AB: While the canonical view is that active deformation in the Andes is mostly confined to the eastern slopes in the subandean fold and thrust belt, recent studies have highlighted the existence of active deformation in the central Andean forearc (Audin et al, 2003, Hartley et al., 2000, Husson and Sempere, 2003, Farias et al., 2005). The forearc of southern Peru, between ~14.5{o}S-18{o}S, consists of the Moquegua Basin longitudinal depression which is bound by the Cordillera de la Costa in the west and the Precordillera and main Cordillera Occidental to the east. The well-preserved fan deposits of the Moquegua Formation cover vast areas of up to 5 km{2}. Developed on top of the Moquegua Formation are a series of well-preserved pediment surfaces (Tosdal et al., 1984), along which, abrupt changes in topography, visible changes in drainage incision, and the offset of alluvial terraces indicate recent uplift and/or faulting. We use in situ produced {10}Be and {26}Al to calculate the exposure ages of these surfaces thereby establishing bounds on timing and extent of tectonic activity. Near the town of Mirave in the Locumba river valley (17.4{o}S, 70.8{o}W) we have used satellite imagery and field mapping to identify an active right-lateral reverse fault. The fault vertically offsets an active channel as evidenced by a 2 m scarp and an abandoned surface of river deposits on the upthrown side of the fault. Cosmogenic ages of vertically and horizontally offset abandoned surfaces provide an opportunity to establish slip-rates along this fault. Preliminary data yields an estimated minimum vertical slip-rate of ~0.22 - 1.1 mm per yr. However, this is just one of many newly mapped active strike-slip and reverse faults within the forearc region, which together can be used to establish regional rates of forearc deformation. The presence of significant of deformation within the forearc region suggests present models convergence distribution may underestimate the amount slip locked on the interplate thrust.
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 8175 Tectonics and landscape evolution
DE: 9360 South America
SC: Tectonophysics [T]
MN: Fall Meeting 2005