Japan Geoscience Union Meeting 2019

Presentation information

[E] Oral

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

[S-CG50] Intraslab and intraplate earthquakes

Thu. May 30, 2019 9:00 AM - 10:30 AM A02 (TOKYO BAY MAKUHARI HALL)

convener:Saeko Kita(International Institute of Seismology and Earthquake Engineering, BRI), Tomohiro Ohuchi(Geodynamics Research Center, Ehime University), Marcel Thielmann(Bavarian Geoinstitute, University of Bayreuth), Ryo Okuwaki(Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology), Chairperson:Saeko Kita(Building Research Insitute), Tomohiro Ohuchi(Geodynamics Research Center, Ehime University), Marcel Thielmann(University of Bayreuth), Ryo Okuwaki(筑波大学), Thomas Ferrand(UC San Diego)

10:00 AM - 10:15 AM

[SCG50-05] Reaction-induced embrittlement of the lower continental crust

*Alexandre Schubnel1, Sarah Incel2, Julien Gasc1, Nadège Hilairet5, Yanbin Wang3, Feng Shi3, Loic Labrousse4 (1.Laboratoire de Géologie, ENS, 2.University of Oslo, 3.GCECARS, University of Chicago, 4.ISTEP, Sorbonne Université, 5.UMET, Université de Lille)

Keywords:lower crust, Eclogitisation, Granulite

Field observations and geophysical data reveal a causal link between brittle seismic failure and eclogitization of the lower continental crust. We present results from experimental deformation of plagioclase-rich samples at eclogite-facies conditions and quantify the link between rock rheology and the kinetics of the eclogitization reactions. The deformation was ductile both in the absence of reaction and when the progress of eclogitization was fast compared to the imposed strain rate. However, when the reaction rate was relatively slow, the breakdown of plagioclase into nanocrystalline reaction products induced a weakening that triggered seismic failure. Fluid-induced plagioclase breakdown under eclogite-facies conditions is an exothermic reaction accompanied by a negative change in solid volume. This is similar to other mineral transformations that are known to trigger transformational faulting. We demonstrate that mineral reactions lead to brittle deformation in situations where reaction rates are slow compared to the deformation rate. This reaction-induced instability may provide a generic mechanism for embrittlement at depths beyond the normal seismogenic zone.