[S-CG52] Dynamics in mobile belts

[SCG52-05] Evolution of quartz microstructure during dynamic recrystallisation

*Thomas Jing Yi Yeo^1,2, Norio Shigematsu², Takuma Katori³ (1.Department of Earth and Planetary Science, Graduate School of Science, Tokyo University , 2.Research Institute of Earthquake and Volcano Geology, Geological Survey of Japan, National Institute of Advance Industrial Science and Technology, 3.Fossa Magna Museum)

Keywords:dynamic recrystallisation, crystallographic preferred orientation (CPO), electron backscattering diffraction (EBSD) , microstructure

It is known that the recrystallised fraction is dependent on the strain applied, and possibly can be used to evaluate strain (Cross and Skemer, 2019). Fabric intensity of quartz crystallographic preferred orientation (CPO) evolves with increasing strain (Heilbroner and Tullis, 2006; Muto et. al, 2011). Conversely, it is also documented that fabric intensity of quartz is very weak in strongly deformed ultramylonite (Okudaira and Shigematsu, 2012; Kilian et al., 2011).

The aim of this study is to investigate the effect of strain on fabric intensity of quartz CPO. We use the recrystallised fraction as a proxy of strain. The mylonite samples collected from the Median Tectonic Line, Mie, Japan display large variations in both recrystallized fraction and CPO fabric intensity within a short distance. We consider this phenomena to have occurred at similar deformational conditions.

Within this study, quartz crystallography data were collected from EBSD analysis whilst the dynamically recrystallised and relict grains are separated through applying a newly developed clustering technique. The M-index of both the relict and recrystallised grains are compared to discuss the changes in the fabric intensity in relation to recrystallised fraction. Evaluation of the effect of increasing recrystallised fraction on the possible changes in deformational mechanism will also be discussed.