Cataclastic and crystal-plastic deformation in shallow mantle-wedge serpentinite controlled by cyclic changes in pore fluid pressures

Ken ichi Hirauchi, Yurina Nagata, Kengo Kataoka, Ryosuke Oyanagi, Atsushi Okamoto, Katsuyoshi Michibayashi

Research output: Contribution to journalArticlepeer-review

Abstract

Episodic tremor and slip (ETS) events in the forearc mantle wedge of a warm subduction zone may reflect mixed brittle–ductile deformation of serpentinite in association with high pore fluid pressures. To understand deformation mechanisms and processes occurring in the hydrated mantle wedge, we examined in the Sanbagawa metamorphic belt, SW Japan, an antigorite serpentinite shear zone derived from mantle wedge that was formed under pressure and temperature conditions that correspond to the ETS regions. The serpentinite underwent multiple extensional (mode I) and extensional–shear (mode I–II) failure events at supralithostatic pore fluid pressures (Pf). Such failure events led to drops in Pf (several MPa) and formation of a distributed ‘fault–fracture mesh’. Antigorite precipitation in the fracture openings contributed to an increase in Pf until the failure condition was reached again, and thereby antigorite kinetics controlled the recurrence interval of seismic events. We also suggest that under the low-Pf conditions that facilitate intracrystalline plasticity rather than cataclasis, the newly precipitated antigorite aggregates (localized along shear bands) deform by dislocation creep at a high strain rate and high shear stress, resulting in the transient, accelerated viscous creep that may characterize slow slip transients.

Original languageEnglish
Article number117232
JournalEarth and Planetary Science Letters
Volume576
DOIs
Publication statusPublished - 2021 Dec 15
Externally publishedYes

Keywords

  • antigorite
  • episodic tremor and slip
  • mantle wedge
  • pore fluid pressure
  • semi-brittle deformation
  • serpentinite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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