The rheology and mode of deformation of serpentinite, especially that of antigorite-bearing rocks, are of prime importance for understanding processes occuring in subduction zones, including the nature of the mantle wedge and the transport of fluids in these systems. Auzende et al (2006) observed in naturally-deformed samples the coexistence of brittle and ductile structures (semibrittle deformation) under blueschist and eclogitic facies conditions. Results from further experimental work also at high T and P conditions, have been differently interpreted: Hilairet et al (2007) argue that deformation of antigorite is ductile while Chernak & Hirth (2010) plead for brittle deformation instead. Here we present detailed microsctructural work on 8 deformation experiments performed in a Deformation-DIA apparatus at conditions covering the stability of antigorite under subduction zone conditions (1 to 3,5 GPa, and 400 to 650°C), thus at conditions overlapping this those reported previously. For each PT condition, we performed two experiments at strain rate of 10-5 and 10-4 s-1. We also investigated samples deformed in a Griggs-type apparatus (Chernak & Hirth, 2010), at P= 1 GPa and T=400°C. TEM characterisation of these samples confirms that, at all experimental conditions tested, deformation is at least partially accommodated by brittle microcracking, primarily along basal planes, and often associated with kinking of serpentinite laths. We also document similar deformation microstuctures from naturally deformed rocks sampled in the Alps. These results confirm a semibrittle mode of deformation, and suggest that existing flow laws for serpentinite do not describe plastic deformation of antigorite. These results also suggest that semibrittle deformation in subduction zones may allow fluid transport through and entrapment within microcracks, that would be precluded in a fully plastic deformation regime.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- 3060 MARINE GEOLOGY AND GEOPHYSICS / Subduction zone processes;
- 6045 PLANETARY SCIENCES: COMETS AND SMALL BODIES / Physics and chemistry of materials