Evolution of quartz crystallographic preferred orientation (CPO) with increasing strain

抄録

Stress build-up processes within fault zones have been discussed as phenomena that occur during the seismic cycle. Geological studies of this nature are few but bear importance in bridging geophysical and microstructural observations. Methods for investigating stress records in rocks are performed through the application of palaeo-piezometre. This however requires that the rocks are deformed through the dislocation creep mechanism.

Our studies are conducted on the exhumed mylonitic samples from the Ryoke belt along the Median Tectonic Line. The samples contain f-type quartz microstructures and are reported to preserve records of high differential stress deformations. Although deformed under similar temperature conditions close to the brittle-ductile transition, these samples display heterogeneous strain distributions [1], thus suitable to examine stress accumulation processes. However, the samples display trends of the weakening of CPO fabric intensity with increasing strain for the composing quartz crystals. Generally, this phenomenon is accredited to the onset of grain boundary sliding from the dislocation creep mechanism, thus inhibiting the application of the palaeo-piezometre.

Our samples contradicted numerous studies have shown that the CPO fabric intensity increases with strain (e.g. Heilbronner & Tullis, 2006; Muto et al., 2011). Thus, we aim to investigate the effect of strain on the evolution of the CPO fabric intensity and clarify the mechanism involved. The recrystallised fraction of dynamically recrystallised grains is adopted as a proxy for strain evaluated using a newly developed routine to process the EBSD data. Achieving the target enables us to determine sample conditions that are suitable for the application of the palaeo-piezometre, which result will be conducted for the study of stress-strain relationship along the Median Tectonic Line.

[1] Katori et al., 2021. JSG. [2] Heilbronner & Tullis., 2006. JGR. [3] Muto et al., 2011. JGR.