R8: Metamorphic rocks and tectonics

[R8-01] Fault formation mechanism in brittle-plastic transition regime

*Jun-ichi Ando¹, Hirotoshi Kotama¹, Kaushik Das¹, Dyuti Prakash Sakar¹, Gautam Ghosh³, Naotaka Tomioka² (1. Hiroshima Univ., 2. JAMSTEC, 3. Presidency Univ.)

Keywords:Fault, Mylonite, Brittle-plastic transition zone, Phyllosilicate mineral, Microstructure

Based on microstructural observations of mylonitic rocks along the main central thrust in India, we are investigating the faulting process in the brittle-plastic transition zone. Our results suggest that the key phenomena are mylonitization of the rock due to the fluid penetration and a change in the deformation mechanism from dislocation creep to diffusion creep, which reduces the strength of the rock and causes stress concentrations. And we believe that the stress concentration generated a nucleus of fracture in the phyllosilicate mineral, which led to the formation of the fault.