HR: 0800h
AN: T21C-0503    [Abstracts]
TI: Effects of Topography on the Curvature of Fold-and-Thrust Belts During Shortening of a 2-layer Model of Continental Lithosphere
AU: * Marques, F O
EM: fomarques@fc.ul.pt
AF: Dep. Geologia and CGUL, Fac. Ciencias, Univ. Lisboa, Edifi-cio C6, Piso 2, Lisboa, 1749-016 Portugal
AU: Cobbold, P R
EM: peter.cobbold@univ-rennes1.fr
AF: Geosciences-Rennes (UMR6118 du CNRS), Campus de Beaulieu, Rennes, 35042 France
AB: We have used analogue experiments to investigate the effects of surface topography on the curvature of fold-and-thrust belts, under conditions of (1) initial relief, but no erosion, and (2) no initial relief, but differential erosion, sedimentation and drainage. In experiments where a 2-layer model lithosphere shortened and thickened in front of an advancing straight piston, the geometry of the developing thrust wedge was highly sensitive to variations in surface topography. In models with an initially flat, horizontal surface, and in the absence of erosion and sedimentation, thrusts were straight, propagated forwards, and nucleated at buckle folds far in front of the advancing piston. Around an initial topographic high (plateau or cone), thrusts tended to be arcuate, forming salients towards the foreland. Initial plateaux and cones tended to behave rigidly, while arcuate thrust slices formed around them. To accommodate differential slip, transfer zones developed on both sides of initial highs. Within the transfer zones, fault blocks rotated about vertical axes and thrusts moved in oblique slip. In models with initially horizontal surfaces, which were subject to differential erosion, sedimentation and drainage, thrusts initially were straight, but then progressively rotated around non-drained, thickened and stronger areas. These worked as indenters, in front of which new thrusts nucleated at curved buckle folds. These thrusts were also curved, their apices being in front of the thickened, non-drained areas. In nature, arcuate structural patterns are to be found around the Altiplano of the Central Andes and around the Tromen volcanic ridge in the Neuquen Basin of northern Patagonia. We infer that these areas behaved in quasi-rigid fashion, protected as they were by their high elevations.
DE: 8104 Continental margins: convergent
DE: 8122 Dynamics: gravity and tectonics
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: Fall Meeting 2005