Presentation Information
[SMP31-P11]Microstructural observation of amphibolite xenoliths in the Tanzawa Mountains.
*Ryota Otake1, Miki Tasaka1 (1.Shizuoka University)
Keywords:
EBSD,Crystallographic preferred orientation,Deformation,Amphibole
The intrusion of plutonic bodies imposes heat and stress on surrounding rocks, producing metamorphism in which contact and regional metamorphism overlap. Previous studies have reported metamorphic temperature estimates based on mineral compositions and the development of deformation texture associated with pluton intrusion. However, there are no existing studies that discuss metamorphism using the results of xenolith microstructural perspective.
In this study, research was conducted in the Tanzawa Mountains of Kanagawa Prefecture. In the Tanzawa region, metamorphic rocks are distributed around the Tanzawa Composite Plutonic Complex, which formed 5-4 Ma. The protolith of these metamorphic rocks is 17-16 Ma. Hornfels is distributed in the Yadoriki area (eastern part of the metamorphic body), while schists are distributed in the Nakagawa River area (southern part of the metamorphic body). The purpose of this study was to clarify the deformation and metamorphic processes during the intrusion of the Tanzawa plutonic complex in this region, targeting xenolith samples contained within the plutonic complex, and surrounding metamorphic rocks (amphibolites). Microstructural analysis, including crystallographic preferred orientation (CPO) and shape preferred orientation (SPO), was performed on these samples using electron backscatter diffraction (EBSD).
Analysis of xenoliths showed that xenoliths collected in the Yorisawa area are rich in amphibole and exhibit weak concentration of CPO and SPO. On the other hand, xenoliths from the Nakagawa River area showed two variations: amphibole-rich xenoliths (Hb-rich xenoliths) and plagioclase-rich xenoliths (Al-rich xenoliths). In Hb-rich xenoliths, subgrain boundaries were observed in amphibole, indicating strong concentrations of CPO and SPO. Conversely, Al-rich xenoliths showed weaker concentrations of CPO and SPO compared to Hb-rich xenoliths.
Amphibolite schists from the southern part of the pluton are characterized by coarse-grained amphibole, well-developed subgrain boundaries, and strong CPO and SPO, indicating that deformation and metamorphism were dominated by dislocation creep driven by stresses associated with tonalite intrusion. Contact metamorphic rocks from the eastern part of the pluton have not yet been sampled at the time of this study.
From the above, microstructural analysis of xenoliths contained in the Tanzawa plutonic complex confirms the concentration of CPO and SPO, and their strengths may depend on the mineralogical ratio. Furthermore, the CPO and SPO of metamorphic rocks may be used as indicators of changes caused by the intrusion of plutonic bodies.
In this study, research was conducted in the Tanzawa Mountains of Kanagawa Prefecture. In the Tanzawa region, metamorphic rocks are distributed around the Tanzawa Composite Plutonic Complex, which formed 5-4 Ma. The protolith of these metamorphic rocks is 17-16 Ma. Hornfels is distributed in the Yadoriki area (eastern part of the metamorphic body), while schists are distributed in the Nakagawa River area (southern part of the metamorphic body). The purpose of this study was to clarify the deformation and metamorphic processes during the intrusion of the Tanzawa plutonic complex in this region, targeting xenolith samples contained within the plutonic complex, and surrounding metamorphic rocks (amphibolites). Microstructural analysis, including crystallographic preferred orientation (CPO) and shape preferred orientation (SPO), was performed on these samples using electron backscatter diffraction (EBSD).
Analysis of xenoliths showed that xenoliths collected in the Yorisawa area are rich in amphibole and exhibit weak concentration of CPO and SPO. On the other hand, xenoliths from the Nakagawa River area showed two variations: amphibole-rich xenoliths (Hb-rich xenoliths) and plagioclase-rich xenoliths (Al-rich xenoliths). In Hb-rich xenoliths, subgrain boundaries were observed in amphibole, indicating strong concentrations of CPO and SPO. Conversely, Al-rich xenoliths showed weaker concentrations of CPO and SPO compared to Hb-rich xenoliths.
Amphibolite schists from the southern part of the pluton are characterized by coarse-grained amphibole, well-developed subgrain boundaries, and strong CPO and SPO, indicating that deformation and metamorphism were dominated by dislocation creep driven by stresses associated with tonalite intrusion. Contact metamorphic rocks from the eastern part of the pluton have not yet been sampled at the time of this study.
From the above, microstructural analysis of xenoliths contained in the Tanzawa plutonic complex confirms the concentration of CPO and SPO, and their strengths may depend on the mineralogical ratio. Furthermore, the CPO and SPO of metamorphic rocks may be used as indicators of changes caused by the intrusion of plutonic bodies.