Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG53] Science of slow earthquakes: Toward unified understandings of whole earthquake process

Thu. May 24, 2018 1:45 PM - 3:15 PM Convention Hall B (CH-B) (2F International Conference Hall, Makuhari Messe)

convener:Satoshi Ide(Department of Earth an Planetary Science, University of Tokyo), Hitoshi Hirose(Research Center for Urban Safety and Security, Kobe University), Kohtaro Ujiie(筑波大学生命環境系, 共同), Takahiro Hatano(Earthquake Research Institute, University of Tokyo), Chairperson:Mochizuki Kimihiro(Earthquake Research Institute, University of Tokyo), Ando Ryosuke(Graduate School of Science, University of Tokyo)

2:30 PM - 2:45 PM

[SCG53-28] Mixing and reaction of rocks facilitate fluid flow along the forearc slab-mantle interface

*Yasushi Mori1, Miki Shigeno1, Tadao Nishiyama2 (1.Kitakyushu Museum of Natural History and Human History, 2.Kumamoto University)

Keywords:serpentinite mélange, metasomatism, reaction-enhanced permeability, fluid flow, slow earthquakes

The forearc slab-mantle interface in subduction zones is a site of mixing and reaction of crustal and mantle rocks, forming serpentinite mélanges. The studies of exhumed subduction complexes show that extensive fluid flow occurs in the serpentinite mélanges (Bebout and Penniston-Dorland, 2016, Lithos, 240–243, 228–258, and references therein). The fluid flow potentially modifies physical and chemical conditions of rocks along the channels, so it is an important subject for understanding subduction-zone seismicity. For example, redistribution of silica by the fluid flow likely affects elastic properties of rocks and modulates periodic events of slow earthquakes (Audet and Bürgmann, 2014, Nature, 510, 389–392; Fisher and Brantley, 2014, J. Structural Geol., 69, 395–414; Hyndman et al., 2015, J. Geophys. Res. Solid Earth, 120, 4344–4358).

The Nishisonogi metamorphic rocks (a Late Cretaceous subduction complex exposed in Kyushu, Japan) contain serpentinite mélanges, which have been formed at 0.8 GPa and 460 °C. These pressure and temperature conditions are close to those of the forearc mantle corner. The mélanges have a matrix of chlorite-actinolite schist, talc schist and antigorite schist, together with tectonic blocks of meta-sedimentary, mafic and ultramafic rocks. They show various types and degrees of the mixing and reaction of rocks. The isocon analysis indicates that the reactions typically involve a decrease of solid volume and production of fluids. The loss of solid volume possibly reaches dozens percent relative to the initial volume. In addition, the reactions result in mobilization of silica without forming quartz veins. These findings suggest that the serpentinite mélanges are permeable and mechanically weak. The mélanges probably act as fluid flow channels. The fluid flow is favorable to transport silica toward the mantle corner and may induce deep slow earthquakes.