5:15 PM - 6:45 PM
[SMP24-P09] Metamorphic P-T conditions of the Ryoke metamorphic rocks in the eastern part of Matsuyama City, Takanawa Peninsula, Ehime Prefecture, SW Japan.
Keywords:Takanawa Peninsula, Ryoke belt, Metamorphic zoning, Metamorphic P-T conditions, Garnet + Cordierite assemblage, Partial melting
Introduction
Metamorphic rocks and Cretaceous granitoids distributed in the Takanawa Peninsula, Ehime Prefecture, belong to the Ryoke belt. The granitoids in this area are classified into three lithological facies: tonalite, granodiorite, and granite (Ochi, 1982). Based on this classification, zircon U-Pb ages have been determined, and the Yunoyama body in the study area has been dated to 98.8 ± 1.0 Ma (Shimooka et al., 2019).
The metamorphic rocks are distributed as E-W trend metamorphic layer, at the base of the peninsula, and also occur as xenoliths in the granitic body. Metamorphic zoning of the metamorphic bodies and mineral assemblage have been studied by Toriumi et al. (1991) and Miyazaki et al. (2016) (Fig. 1). Highest grade pelitic rocks is composed of Grt, Crd, Kfs, Bt, Ms, Pl and Qz, but the Grt + Crd assemblage has not been clearly reported.
This study discusses metamorphic zoning and metamorphic P-T conditions of metamorphic body at the base of the peninsula in the eastern part of Matsuyama City.
Field occurrences
The metamorphic rocks and granites in this area consist of the metamorphic body at the base of the peninsula in the southeast (hereinafter, M-body), and Bt granite body and Hbl-Bt granite body in the northwest correspond to Yunoyama body and Matsuyama body, respectively Ochi (1982). Both granite bodies are discordantly intruded into the metamorphic layer. Metamorphic rocks also occur in metamorphic xenoblock (hereafter, X-body) in Hbl-Bt granite. In X-body and part of the M-body, Grt + Crd assemblage is observed. The metamorphic rocks of X-body show migmatitic feature. The mineral assemblage is Kfs free, Pl in the leucosome shows oscillatory zoning.
Metamorphic zoning
Metamorphic zoning of M-body and X-body based on mineral assemblages. The metamorphic rocks in this area can be divided into the Bt zone, Crd zone, Kfs zone, Grt zone, and Grt-Crd zone from low to high metamorphism, respectively. The grade of metamorphic bodies in this area increases from the southeast to the northwest from the results in Fig. 1.
Metamorphic P-T conditions
The peak P-T conditions during of the Crd zone is about 150–300 MPa and 540–550 °C, based on calculations from the Grt-Bt geothermometer (Hodges and Spear, 1982) and the GMPB geobarometer (Hoisch, 1991).
The peak temperature conditions during of the Grt-Crd zone is about 670–750 °C, based on calculations from the Grt-Crd geothermometer (Thompson, 1976; Wells, 1979; Perchuk et al., 1985).
Conclusion
These results suggest that M-body was metamorphism in the following order. Regional metamorphism of the Ryoke belt. Contact metamorphism of Bt granite body and Hbl-Bt granite body. Grt zone rocks are Kfs-bearing assemblage. Therefore, it may be produced by the following reaction, Bt + Als + Qz → Grt + Crd + Kfs + H2O (Wei et al., 2004). These occurrences also suggest that this zone has not experienced partial melting.
Metamorphic rocks of X-body are Kfs-bearing free assemblage. Therefore, it may be produced by the following reaction, Bt + Als + Qz + H2O → Grt + Crd + L (Wei et al., 2004). These occurrences also suggest that this zone has experienced partial melting.
References
Hodges and Spear (1982) Amer. Mineral., 67, 1118–1134.
Hoisch (1991) CMP, 108, 43–54.
Miyazaki et al. (2016) Geol map, Matsuyama (2nd ed.). AIST
Ochi (1982) JGSJ, 88, 511–522.
Perchuk et al. (1985) JMG, 3, 265–310.
Shimooka et al. (2019) JMPS, 114, 284–289.
Thompson (1976) AJS, 276, 425–454.
Toriumi et al. (1991) Geology of Japan, Shikoku District. Geology of Japan, Shikoku District Editorial Committee, 6–8.
Wei et al. (2004) JMG, 22, 495–508.
Wells (1979) JP. 20, 187–226.
Metamorphic rocks and Cretaceous granitoids distributed in the Takanawa Peninsula, Ehime Prefecture, belong to the Ryoke belt. The granitoids in this area are classified into three lithological facies: tonalite, granodiorite, and granite (Ochi, 1982). Based on this classification, zircon U-Pb ages have been determined, and the Yunoyama body in the study area has been dated to 98.8 ± 1.0 Ma (Shimooka et al., 2019).
The metamorphic rocks are distributed as E-W trend metamorphic layer, at the base of the peninsula, and also occur as xenoliths in the granitic body. Metamorphic zoning of the metamorphic bodies and mineral assemblage have been studied by Toriumi et al. (1991) and Miyazaki et al. (2016) (Fig. 1). Highest grade pelitic rocks is composed of Grt, Crd, Kfs, Bt, Ms, Pl and Qz, but the Grt + Crd assemblage has not been clearly reported.
This study discusses metamorphic zoning and metamorphic P-T conditions of metamorphic body at the base of the peninsula in the eastern part of Matsuyama City.
Field occurrences
The metamorphic rocks and granites in this area consist of the metamorphic body at the base of the peninsula in the southeast (hereinafter, M-body), and Bt granite body and Hbl-Bt granite body in the northwest correspond to Yunoyama body and Matsuyama body, respectively Ochi (1982). Both granite bodies are discordantly intruded into the metamorphic layer. Metamorphic rocks also occur in metamorphic xenoblock (hereafter, X-body) in Hbl-Bt granite. In X-body and part of the M-body, Grt + Crd assemblage is observed. The metamorphic rocks of X-body show migmatitic feature. The mineral assemblage is Kfs free, Pl in the leucosome shows oscillatory zoning.
Metamorphic zoning
Metamorphic zoning of M-body and X-body based on mineral assemblages. The metamorphic rocks in this area can be divided into the Bt zone, Crd zone, Kfs zone, Grt zone, and Grt-Crd zone from low to high metamorphism, respectively. The grade of metamorphic bodies in this area increases from the southeast to the northwest from the results in Fig. 1.
Metamorphic P-T conditions
The peak P-T conditions during of the Crd zone is about 150–300 MPa and 540–550 °C, based on calculations from the Grt-Bt geothermometer (Hodges and Spear, 1982) and the GMPB geobarometer (Hoisch, 1991).
The peak temperature conditions during of the Grt-Crd zone is about 670–750 °C, based on calculations from the Grt-Crd geothermometer (Thompson, 1976; Wells, 1979; Perchuk et al., 1985).
Conclusion
These results suggest that M-body was metamorphism in the following order. Regional metamorphism of the Ryoke belt. Contact metamorphism of Bt granite body and Hbl-Bt granite body. Grt zone rocks are Kfs-bearing assemblage. Therefore, it may be produced by the following reaction, Bt + Als + Qz → Grt + Crd + Kfs + H2O (Wei et al., 2004). These occurrences also suggest that this zone has not experienced partial melting.
Metamorphic rocks of X-body are Kfs-bearing free assemblage. Therefore, it may be produced by the following reaction, Bt + Als + Qz + H2O → Grt + Crd + L (Wei et al., 2004). These occurrences also suggest that this zone has experienced partial melting.
References
Hodges and Spear (1982) Amer. Mineral., 67, 1118–1134.
Hoisch (1991) CMP, 108, 43–54.
Miyazaki et al. (2016) Geol map, Matsuyama (2nd ed.). AIST
Ochi (1982) JGSJ, 88, 511–522.
Perchuk et al. (1985) JMG, 3, 265–310.
Shimooka et al. (2019) JMPS, 114, 284–289.
Thompson (1976) AJS, 276, 425–454.
Toriumi et al. (1991) Geology of Japan, Shikoku District. Geology of Japan, Shikoku District Editorial Committee, 6–8.
Wei et al. (2004) JMG, 22, 495–508.
Wells (1979) JP. 20, 187–226.