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Science 21 December 2007:
Vol. 318. no. 5858, pp. 1910 - 1913
DOI: 10.1126/science.1148494
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Reports

High-Pressure Creep of Serpentine, Interseismic Deformation, and Initiation of Subduction

Nadege Hilairet,1* Bruno Reynard,1 Yanbin Wang,2 Isabelle Daniel,1 Sebastien Merkel,3 Norimasa Nishiyama,2{dagger} Sylvain Petitgirard1

The supposed low viscosity of serpentine may strongly influence subduction-zone dynamics at all time scales, but until now its role could not be quantified because measurements relevant to intermediate-depth settings were lacking. Deformation experiments on the serpentine antigorite at high pressures and temperatures (1 to 4 gigapascals, 200° to 500°C) showed that the viscosity of serpentine is much lower than that of the major mantle-forming minerals. Regardless of the temperature, low-viscosity serpentinized mantle at the slab surface can localize deformation, impede stress buildup, and limit the downdip propagation of large earthquakes at subduction zones. Antigorite enables viscous relaxation with characteristic times comparable to those of long-term postseismic deformations after large earthquakes and slow earthquakes. Antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation.

1 Laboratoire des Sciences de la Terre, CNRS, Ecole Normale Supérieure de Lyon, Université Claude Bernard Lyon 1, 46 Allée d'Italie, 69364 Lyon Cedex 07, France.
2 Center for Advanced Radiation Sources, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA.
3 Laboratoire de Structure et Propriétés de l'Etat Solide, UMR CNRS 8008, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France.

{dagger} Present address: Geodynamics Research Center, Ehime University, Japan.

* To whom correspondence should be addressed. E-mail: nadege.hilairet{at}ens-lyon.fr

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