JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

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

[S-CG62] [EE] Dynamics in mobile belts

Tue. May 23, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Robert Holdsworth(Durham University), Jeanne Hardebeck(USGS), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology)

[SCG62-P18] Interseismic plastic deformation in paleo-seismic fault zones under lower crustal conditions at Tonagh Island in the Napier Complex, East Antarctica

*Tsuyoshi Toyoshima1, Norio Shigematsu2, Yasuhito Osanai3, Masaaki Owada4, Toshiaki Tsunogae5, Tomokazu Hokada6 (1.Department of Geology, Faculty of Science, Niigata University, 2.Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 3.Division of Evolution of Earth Environments, Faculty of Social and Cultural Studies, Kyushu University, 4.Graduate School of Science and Engineering for Innovation, Yamaguchi University, 5.Faculty of Life and Environmental Sciences (Earth Evolution Sciences), University of Tsukuba, 6.National Institute of Polar Research)

Keywords:pseudotachylyte, high-strain rate crystal plastic deformation, grain boundary sliding

There are severa; granulite-facies paleo-seismic fault zones (PSF) in Tonagh Island, the Napier Complex, East Antarctica (Toyoshima et al., 1999, 2016). In PSF, alternation of thin ultramylonites, cataclasites, pseudotachylytes, and mylonitized pseudotachylytes occur, showing that multiple generations of pseudotachylytes, cataclasites and ultramylonites.
Two types of granulite-facies ultramylonites occur in PSF: type 1 and 2. Microstructures of recrystallized plagioclase and quartz suggest high-temperature or low-strain rate crystal plastic deformation.
Microstructures of recrystallized quartz in type 2 ultramylonites suggest high-strain rate crystal plastic deformation. Z-maximum c-axis lattice preferred orientation (LPO) patterns for quartz in type 2 ultramylonites suggest a basal slip system dislocation creep and high-strain rate crystal plastic deformation during interseismic periods. There are two alternative posibilities of deformaition mechanisms of quartz in type 2 ultramylonites as follows: (1) Mylonitized quartz layers originated from quartz veins parallel to mylonite foliation. (2) Water weakening occurred during mylonitization of quartz.
Microstructures and LPO patterns of recrystallized plagioclase indicate switch in deformation mechanism from dislocation creep to grain-boundary sliding in type 2 ultramylonites, and also suggest that continuous low strain rate or low differential stress plastic deformation and seismic events alternated. This is imaged acceleration of strain rate or stress relaxation before or after seismic events, respectively. The switch in deformation mechanism from dislocation creep to grain-boundary sliding, associated with the grain-size reduction, attests of the mechanical softening during deformation, which contributed to the localization of the strain within the mylonite, as suggested by Raimbourg et al. (2008).