11:15 〜 11:30
[SCG62-03] Slow grain growth of natural plagioclase: effects of the impurity segregation and dislocation
キーワード：斜長石、粒成長、レオロジー、溶質不純物
Ductile shear zones localized in the crust consist of fine-grained minerals and grain size sensitive creep is predominant, enhancing strain accumulation. Grain size is one of the critical parameters in the rheology of the ductile shear zones. However, it is debated why the plagioclase in the ductile shear zone remains with fine grains, since the grains grow at high temperatures in the lower crust.
Plagioclase is the main constituent mineral of the crust, so that synthesized plagioclase aggregates have been used in previous experiments to study the rheological properties of the crust (Rybacki et al., JGR, 2006: Dresen et al., Tectonophysics, 1996). In grain growth experiments of plagioclase, previous experiments used pure systems (Dresen et al., Tectonophysics, 1996) without chemical impurities and strain. However, the grain growth behaviors of pure systems differs significantly from natural systems. For example, the presence of intracrystalline strain accumulation due to deformation affects the kinetics of post-deformation grain growth (Speciale et al., JGR, 2020). In addition, almost all natural minerals contain chemical impurities, and it is necessary to understand the changes in grain growth behavior by these chemical impurities. Plagioclase grain growth has only been performed in the pure system (anorthite by Dresen et al., Tectonophysics, 1996), and no grain growth experiments have examined the effects of strain or natural composition.
In this study, we established a new method to prepare dense plagioclase aggregates with natural composition that are worthy of investigating the rheology of the crust. Natural labradorite from madagascar was crushed down to 300 nm. Then, we synthetized polycrystals by hot press and investigated their grain growth mechanisms by tube furnace. In the grain growth experiments, much slower grain growth was observed than that in Dresen et al. (1996) using pure anorthite. To evaluate the slow glowth behavior, we analyzed intracrystalline strain and chemical composition. EBSD analysis for the intracrystalline strain in annealed samples show that the intracrystalline strain was removed to some extent by 5 hours. STEM-EDS analysis showed segregation of Fe at the grain boundaries. Therefore, it is possible that chemical impurities at the grain boundaries affected the slow grain growth behavior of this sample with natural composition. In our presentation, intracrystalline strain and solute impurity segregation with effect on grain growth will be discussed.
Plagioclase is the main constituent mineral of the crust, so that synthesized plagioclase aggregates have been used in previous experiments to study the rheological properties of the crust (Rybacki et al., JGR, 2006: Dresen et al., Tectonophysics, 1996). In grain growth experiments of plagioclase, previous experiments used pure systems (Dresen et al., Tectonophysics, 1996) without chemical impurities and strain. However, the grain growth behaviors of pure systems differs significantly from natural systems. For example, the presence of intracrystalline strain accumulation due to deformation affects the kinetics of post-deformation grain growth (Speciale et al., JGR, 2020). In addition, almost all natural minerals contain chemical impurities, and it is necessary to understand the changes in grain growth behavior by these chemical impurities. Plagioclase grain growth has only been performed in the pure system (anorthite by Dresen et al., Tectonophysics, 1996), and no grain growth experiments have examined the effects of strain or natural composition.
In this study, we established a new method to prepare dense plagioclase aggregates with natural composition that are worthy of investigating the rheology of the crust. Natural labradorite from madagascar was crushed down to 300 nm. Then, we synthetized polycrystals by hot press and investigated their grain growth mechanisms by tube furnace. In the grain growth experiments, much slower grain growth was observed than that in Dresen et al. (1996) using pure anorthite. To evaluate the slow glowth behavior, we analyzed intracrystalline strain and chemical composition. EBSD analysis for the intracrystalline strain in annealed samples show that the intracrystalline strain was removed to some extent by 5 hours. STEM-EDS analysis showed segregation of Fe at the grain boundaries. Therefore, it is possible that chemical impurities at the grain boundaries affected the slow grain growth behavior of this sample with natural composition. In our presentation, intracrystalline strain and solute impurity segregation with effect on grain growth will be discussed.