3:30 PM - 3:45 PM
[SCG44-01] New development in the research of quartz c-axis fabric and dynamic recrystallization microstructures: indicators for deformation temperatures and strain rates
It has been known that the physical conditions for deformation can be inferred from microstructures, in particular, those of dynamic recrystallization in quartz. Masuda and Fujimura (1981) have shown that S type (elongated) and P type (polygonal) recrystallized quartz grains are formed under relatively low temperature and fast strain rate, and high temperature and slow strain rate, respectively. Subsequently, Hirth and Tullis (1992) conducted deformation experiments on natural quartzite, and showed that the deformation regime of dislocation creep changed from regime 1 through 2 (subgrain rotation) to 3 (both subgrain rotation and grain boundary migration) with increasing temperature/strain rate, which are defined by the mechanism of dynamic recrystallization in quartz. It should be noted here that regimes 2 and 3 are essentially same as the ones to form S and P type quartz microstructures, respectively. Further, Stipp et al. (2002) showed that the mechanism of dynamic recrystallization in natural quartz aggregates changed from bulging (BLG) through subgrain rotation (SGR) to grain boundary migration (GBM), and correlated them with the experimental regimes 1, 2 and 3.
Sakakibara (1995, 1996) presumed that the transition condition (line) for the regime 2 and 3 and the one for the dominant slip systems are oblique in the space of temperature and strain rate based on the previous experiments. Thus, he predicted that in natural deformation in quartz aggregates, the four combinations of the quartz microstructures and dominant slip systems, S type-basal, S type-prism, P type-basal, P type-prism must exist. Here, when the dominant slip systems are basal, a type-I crossed girdle quartz c-axis fabric forms, while for the case of the dominant prism slip systems a type-II crossed girdle with a Y-maximum quartz c-axis fabric forms (Lister et al., 1978; Takeshita and Wenk, 1988). In fact, Sakakibara (1995, 1996) found the four combinations of the quartz microstructures and dominant slip systems in mylonites constituting the Ryoke southern marginal shear zones in the Kayumi district, Mie prefecture.
Recently, Takeshita (2021) has discussed that the boundary for the SGR/GBM transition in quartz aggregates would be an iso-stress boundary at c. 30 MPa based on the recrystallized grain size paleopiezometer (e.g. Twiss, 1980) and the flow law in natural quartzite (Gleason and Tullis, 1995). Further, Takeshita (2021) argued that the transition of the S type/P type microstructural transition in the Sambagawa quartz schist in fact occurred at the uppermost part of the garnet zone in the Asemi-River route, as Masuda (1982) showed. Whereas the quartz c-axis fabric patterns consistently show type-I crossed girdles throughout the route irrespective of the metamorphic grade except for part of the biotite zone where a type-II crossed girdle with a Y-maximum quartz c-axis fabric sporadically developed (Yagi and Takeshita, 2002). On the other hand, Bui et al. (2023) showed that in mylonites derived from the Ryoke granitoids in the Tsukide district, Mie prefecture most of them show a type-II crossed girdle with a dominant Y-maximum quartz c-axis fabric, whereas the S type/P type microstructural transition occurred in rocks with the same Y-maximum quartz c-axis fabric pattern. There facts suggest that whereas the type I/type II quartz c-axis fabric transition occurred at nearly the same temperature (c. 400 oC), the Sambagawa quartz schist deformed at lower strain rates than the Ryoke granitoids mylonites, based on the idea of Sakakibara (1995, 1996). Accordingly, the precise estimate of the temperature and strain rate conditions has now become possible using the transition of quartz c-axis fabrics (i.e. dominant slip systems) as the thermometer. Further, in this talk, I will try to physically interpret why the transition of dominant slip systems is little dependent on the strain rate, but mostly on the temperature for deformation.
Sakakibara (1995, 1996) presumed that the transition condition (line) for the regime 2 and 3 and the one for the dominant slip systems are oblique in the space of temperature and strain rate based on the previous experiments. Thus, he predicted that in natural deformation in quartz aggregates, the four combinations of the quartz microstructures and dominant slip systems, S type-basal, S type-prism, P type-basal, P type-prism must exist. Here, when the dominant slip systems are basal, a type-I crossed girdle quartz c-axis fabric forms, while for the case of the dominant prism slip systems a type-II crossed girdle with a Y-maximum quartz c-axis fabric forms (Lister et al., 1978; Takeshita and Wenk, 1988). In fact, Sakakibara (1995, 1996) found the four combinations of the quartz microstructures and dominant slip systems in mylonites constituting the Ryoke southern marginal shear zones in the Kayumi district, Mie prefecture.
Recently, Takeshita (2021) has discussed that the boundary for the SGR/GBM transition in quartz aggregates would be an iso-stress boundary at c. 30 MPa based on the recrystallized grain size paleopiezometer (e.g. Twiss, 1980) and the flow law in natural quartzite (Gleason and Tullis, 1995). Further, Takeshita (2021) argued that the transition of the S type/P type microstructural transition in the Sambagawa quartz schist in fact occurred at the uppermost part of the garnet zone in the Asemi-River route, as Masuda (1982) showed. Whereas the quartz c-axis fabric patterns consistently show type-I crossed girdles throughout the route irrespective of the metamorphic grade except for part of the biotite zone where a type-II crossed girdle with a Y-maximum quartz c-axis fabric sporadically developed (Yagi and Takeshita, 2002). On the other hand, Bui et al. (2023) showed that in mylonites derived from the Ryoke granitoids in the Tsukide district, Mie prefecture most of them show a type-II crossed girdle with a dominant Y-maximum quartz c-axis fabric, whereas the S type/P type microstructural transition occurred in rocks with the same Y-maximum quartz c-axis fabric pattern. There facts suggest that whereas the type I/type II quartz c-axis fabric transition occurred at nearly the same temperature (c. 400 oC), the Sambagawa quartz schist deformed at lower strain rates than the Ryoke granitoids mylonites, based on the idea of Sakakibara (1995, 1996). Accordingly, the precise estimate of the temperature and strain rate conditions has now become possible using the transition of quartz c-axis fabrics (i.e. dominant slip systems) as the thermometer. Further, in this talk, I will try to physically interpret why the transition of dominant slip systems is little dependent on the strain rate, but mostly on the temperature for deformation.