Fault weakening across the frictional-viscous transition zone, Karakoram Fault Zone, NW Himalaya

Wallis, D. and Phillips, RJ and Lloyd, GE (2013) Fault weakening across the frictional-viscous transition zone, Karakoram Fault Zone, NW Himalaya. Tectonics, 32 (5). pp. 1227-1246. ISSN 0278-7407, ESSN: 1944-9194 DOI https://doi.org/10.1002/tect.20076

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Abstract

The mechanical behaviour of antigorite strongly influences the strength and deformation of the subduction interface. Although there is microstructural evidence elucidating the nature of brittle deformation at low pressures, there is often conflicting evidence regarding the potential for plastic deformation in the ductile regime at higher pressures. Here, we present a series of spherical nanoindentation experiments on aggregates of natural antigorite. These experiments effectively investigate the single-crystal mechanical behaviour because the volume of deformed material is significantly smaller than the grain size. Individual indents reveal elastic loading followed by yield and strain hardening. The magnitude of the yield stress is a function of crystal orientation, with lower values associated with indents parallel to the basal plane. Unloading paths reveal more strain recovery than expected for purely elastic unloading. The magnitude of inelastic strain recovery is highest for indents parallel to the basal plane. We also imposed indents with cyclical loading paths, and observed strain energy dissipation during unloading–loading cycles conducted up to a fixed maximum indentation load and depth. The magnitude of this dissipated strain energy was highest for indents parallel to the basal plane. Subsequent scanning electron microscopy revealed surface impressions accommodated by shear cracks and a general lack of dislocation-induced lattice misorientation. Based on these observations, we suggest that antigorite deformation at high pressures is dominated by sliding on shear cracks. We develop a microphysical model that is able to quantitatively explain Young’s modulus and dissipated strain energy data during cyclic loading experiments, based on either frictional or cohesive sliding of an array of cracks contained in the basal plane.

Item Type: Article
Uncontrolled Keywords: NILAREP
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Tectonics
Volume: 32
Page Range: pp. 1227-1246
Identification Number: https://doi.org/10.1002/tect.20076
Depositing User: Sarah Humbert
Date Deposited: 07 Aug 2020 13:43
Last Modified: 07 Aug 2020 13:43
URI: http://eprints.esc.cam.ac.uk/id/eprint/4851

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