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Brittle-ductile analogue modelling of piedmont arcs: the influence of pushing-from-behind in gravity-driven models

A. Jiménez-Bonilla, A. Crespo-Blanc, J.C. Balanyá, I. Expósito and M. Díaz-Azpiroz

Abstract: 

We performed analogue experiments to investigate the genesis and the progressive formation of piedmonts. A silicone-sand parallelepiped was bounded by wood strips. The central part of the front strip was removed to permit the analogue material to flow through a gate, by gravity only in the first experiment, and also pushed from behind in the second one. In both cases, a piedmont arc formed in front of the gate, whose end points represented the arc tips of natural piedmonts. Deformation in the brittle layer (sand) was mostly accommodated by normal faults in the first experiment, versus oblique-slip faults in the second experiment. Extension separated blocks that rotated in opposite directions. In the piedmont, arc-parallel and arc-perpendicular stretching was observed. Our results can be applied to toe thrust belts or collapsed foreland fold-and-thrust belts, floored by evaporites and/or overpressured shale formations.