HR: 09:30h
AN: T11G-07    [Abstracts]
TI: What controls the asymmetry of convergent mountain belts?
AU: * Stolar, D B
EM: dstolar@asu.edu
AF: Arizona State University, Box 871404, Tempe, AZ 85287, United States
AU: Hoth, S
EM: shoth@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AU: Whipple, K X
EM: kxw@asu.edu
AF: Arizona State University, Box 871404, Tempe, AZ 85287, United States
AB: Mountain belts formed along convergent plate boundaries often exhibit a significant topographic and structural asymmetry that is correlative with the polarity of subduction and accretion. In general, the side of the orogen on top of the down-going plate, or the pro-side, tends to be wider and less steeply-tapered than the retro-side of the orogen, which is often characterized by a crustal-scale backfold. This asymmetry seems to be relatively invariant of the exact plate kinematics and of orogen-scale climatic influences (e.g., rainshadow). In this work, we investigate the controls on orogen asymmetry through complementary suites of numerical and analogue simulations, restricted to the frictional deformation of the Earth's crust. The analogue experiments demonstrate that asymmetry prevails after an initial symmetric phase of deformation and that growth of the retro- side occurs at a much later stage of orogen evolution. Comparison of analogue experiments with and without isostatic compensation suggests that isostasy significantly increases orogen asymmetry. This result is also observed in the numerical experiments, which are used to investigate the range of behavior between no isostatic compensation and local isostatic compensation. The numerical experiments also demonstrate that the contrast between the internal and basal strengths has an important, although secondary, influence on orogen asymmetry, with higher basal strengths tending to enhance asymmetry. As a whole, our results suggest that structural and topographic asymmetry observed in natural systems is primarily driven by isostasy and not by the polarity of subduction and accretion as commonly believed.
DE: 8108 Continental tectonics: compressional
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting