JpGU-AGU Joint Meeting 2017

講演情報

[EE] ポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG62] [EE] 変動帯ダイナミクス

2017年5月23日(火) 15:30 〜 17:00 ポスター会場 (国際展示場 7ホール)

コンビーナ:深畑 幸俊(京都大学防災研究所)、Robert Holdsworth(Durham University)、Jeanne Hardebeck(USGS)、岩森 光(海洋研究開発機構・地球内部物質循環研究分野)

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

*豊島 剛志1重松 紀生2小山内 康人3大和田 正明4角替 敏昭5外田 智千6 (1.新潟大学理学部地質科学科、2.産業技術総合研究所活断層・火山研究部門、3.九州大学大学院比較社会文化研究院環境変動部門、4.山口大学理工学研究科地球科学分野、5.筑波大学生命環境系地球進化科学専攻、6.国立極地研究所)

キーワード: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).