Mechanics and seismic signature of semi-brittle deformation in antigorite

Date & time

11am–12pm 1 December 2016

Location

Building 61, Jaeger 7, Rm 224, Hales Seminar Room

Speakers

Dr. Emmanuel David (University College London)

Event series

Contacts

 Sebastien Allgeyer

It is well recognised that serpentinites play a major role in subduction zone processes, such as tectonic evolution of the oceanic lithosphere, earthquake nucleation, or recycling of water in the upper mantle. However, it is not yet clearly known how and by which micromechanical process serpentinites deform, and what is their signature on seismic properties.

Deformation experiments were conducted on 90%-rich antigorite polycrystalline serpentinite in the brittle field, under varying conditions of confining pressure, with simultaneous measurements of axial and radial strains, and P and S-wave velocities at various directions with respect to the applied stress. Failure, controlled-failure, and cyclic-loading tests were performed to investigate the strength, dissipation of mechanical energy, seismic signature and resulting microstructures of a suite of antigorite specimens.  

The brittle deformation of antigorite is mostly non-dilatant and accommodated by shear microcracks localised over a very narrow zone near the failure plane – as confirmed by microstructural observations. Antigorite serpentinites display a failure strength as high as for crystalline rocks, and a yield point occurring close to failure. The spectacular absence of any wave velocity evolution during axial compression confirms that microcracking is very localised. Such new results may have strong implications for the understanding of subduction zone dynamics, which remain to be complemented by mechanical tests conducted in the ductile regime.

 

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