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Original article (peer-reviewed)

Journal Tectonophysics
Volume (Issue) 615-616
Page(s) 122 - 141
Title of proceedings Tectonophysics
DOI 10.1016/j.tecto.2014.01.003

Open Access

URL http://www.sciencedirect.com/science/article/pii/S0040195114000109
Type of Open Access Publisher (Gold Open Access)

Abstract

Shear zones are weaker than surrounding rocks. Whether weakening depends on accumulated strain or strain rate is debated. We used a three-dimensional numerical code with a visco-plastic/brittle rheology to investigate the influence of strain and strain-rate weakening (often referred to as velocity weakening) on the evolution of thin-skinned fold-and-thrust belts. Two model setups are used: (i) a uniform setup to recognize the effects of each weakening mode on the structural evolution and dynamics of fold-and-thrust belts and (ii) a dual setup with two adjacent domains of décollement strength to investigate the structural response of laterally varying systems. Strain weakening and velocity weakening lead to remarkably different structural patterns. In particular, strain weakening favours out-of-sequence shear zones whilst some amount of finite plastic strain has to be achieved before the structural development initiates weakening. In contrast, velocity weakening starts with the onset of high strain-rate bands and does not favour out-of-sequence deformation. We also tested separately the influences of shortening velocity, cover sequence thickness and weakening style and amount on the structural evolution of the dual systems. The shortening velocity has a minor effect in strain-weakened models. Velocity weakening and a thinner cover sequence enhance the occurrence of strike-slip shear zones. We conclude that the weakening mode strongly influences the fault patterns and the dynamics of thrust wedges. Inversely, natural fault patterns are keys to discriminate weakening processes.
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