Dehydration‐induced instabilities at intermediate depths in subduction zones. Issue 8 (14th August 2017)

• Record Type: Journal Article
• Authors: Brantut, Nicolas; Stefanou, Ioannis; Sulem, Jean
• Is Part Of: Journal of geophysical research. Volume 122:Issue 8(2017)
• Page Start: 6087
• Page End: 6107
• Publication Date: 2017-08-14
• Subjects: dehydration -- subduction -- intermediate depth -- antigorite -- compaction -- instabilities; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2017JB014357
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We formulate a model for coupled deformation and dehydration of antigorite, based on a porosity‐dependent yield criterion and including shear‐enhanced compaction. A pore pressure and compaction instability can develop when the net volume change associated with the reaction is negative, i.e., at intermediate depth in subduction zones. The instability criterion is derived in terms of the dependence of the yield criterion on porosity: if that dependence is strong, instabilities are more likely to occur. We also find that the instability is associated with strain localization, over characteristic length scales determined by the hydraulic diffusivity, the elasto‐plastic parameters of the rock, and the reaction rate. Typical lower bounds for the localization length are of the order of 10 to 100 for antigorite dehydration and deformation at 3 GPa. The fluid pressure and deformation instability is expected to induce stress buildup in the surrounding rocks forming the subducted slab, which provides a mechanism for the nucleation and propagation of intermediate‐depth earthquakes. Key Points: We model deformation of dehydrating antigorite using porosity‐dependent cataclastic flow Pore pressure instabilities and strain localization arise when the net volume change of the reaction is negative Rapid ductile deformation during instabilities dramatically change the stress in the surroundings, with potential to trigger earthquakes