Rheology of talc sheared at high pressure and temperature: a case study for hot subduction zones

Abstract

abstract Article history:Received 24 May 2013Received in revised form 8 October 2013Accepted 11 October 2013Available online 24 October 2013Keywords:Torsion experimentsFrictionSlip-partitioningEarthquakeLocalized deformationBrittle–ductile transition Talcisacommon fault-coating mineral occurringina variety oftectonic settingsfromtheimmediatesubsurfacedown to more than 100 km depth along subducting plate interfaces. It is considered to stabilize slip atseismogenic depth. To gain insight into the rheological behavior of talc and related deformation processesalong the subduction interface of hot oceanic slabs, we conducted torsion experiments on intact synthetic talcsamples at 200–600 °C under 100–300 MPa confining pressure at intermediate strain rates (3 × 10 −4 and2.45 × 10 −3 s 1 ) for bulk shear strains up to 12.6.We also conducted stepping strain rate experiments toinvestigate rate and temperature dependence on sliding velocity and slide–hold–slide experiments to explorethe re-strengthening and frictional healing of the sliding zones. The experimental results reveal 1) post-yieldstrain hardening followed by brief weakening episodes and then again strain hardening with increasingdeformation and 2) a gradual transition of friction evolution from velocity-strengthening to velocity-neutral.Microstructural observations coupled with mechanical data suggest that talc rheology combines localized anddistributed deformation, in a state called the brittle–ductile transition, with a predominance of crystal-plasticover cataclastic (brittle to semi-brittle) processes at 600°C and 300MPa confining pressure. These data suggestthat talc cannot accumulate the tectonic stress necessary for earthquake-generating rupture along thesubduction interface. This result concurs with the concept that in weak heterogeneous talc-rich material, strongasperities that can resist the tectonic stress to a greater extent are responsible for the consequential earthquakeoccurrence.© 2014 Elsevier B.V. All rights reserved.