5:15 PM - 6:45 PM
[SMP24-P10] Metamorphic conditions and the crustal evolution of the Ryoke belt in Takato-Komagane area, SW Japan
Keywords:the Ryoke belt, metamorphic condition, pseudosection modeling, crystallization depth of granitoids
The Ryoke belt was formed by a large flux of magma pulses into the middle crust in late Cretaceous. To clarify formation process of the Ryoke belt is important to understand evolution of middle crust during the strong igneous activity. In the Takato–Komagane area, extensive metamorphic zones are distributed. This area is a good target to understand condition and evolution of the crust. We will discuss additional results, geothermobarometry for metapelites and granitoids and whole rock chemical composition, after Yoshioka and Takagi (2023) In the northern area (Takato area), we redefine biotite (Bt) zone, sillimanite–K-feldspar (Sil–Kfs) zone and garnet–cordierite (Grt–Crd) zone with increasing the metamorphic grade. In the southern area (Komagane area), Bt zone and K-feldspar–cordierite (Kfs–Crd) zone was defined as already described by Hokada (1998). XRF analysis reveal no significant difference in bulk chemical composition of metapelites between the northern and southern part of the area. This result suggests the difference in the sequence of the mineral zones represents variation of P-T condition in the northern and southern area.
P-T pseudosection modeling is calculated for the Ryoke metapelites in the system MnO-TiO2-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O. It shows the mineral assemblages corresponds to the sequence of Bt zone → Sil–Kfs zone → Grt–Crd zone (northern area), and Bt zone → Kfs–Crd zone (southern area) with increasing temperature at >~300 MPa and <~300 MPa, respectively. Accordingly, the metamorphic pressure was larger in the northern area than in the southern area.P-T condition estimated by geothermobarometry (Hodges and Spear, 1982; Hoisch, 1990) was 739°C, 431 MPa in high grade of Kfs–Crd zone and 754°C, 545 MPa in Grt–Crd zone. Estimated P-T condition from the sample near tourmaline-out isograd in Kfs–Crd zone is similar with tourmaline breakdown condition (>730℃, 400–500 MPa) shown in Kawakami (2004). Amphibole−plagioclase geothermometry and Al in-hornblende geobarometry (Anderson and Smith, 1995; Holland and Blundy, 1994) show that crystallization pressure of Katsuma quartz diorite, Hissori granite and Takato tonalite are 460 ± 44, 322 ± 27 and 365 ± 59 MPa.
We will also discuss the relationship between the metamorphic rocks and granitoids, taking the age data of the granitoids into account.
[Reference]
Anderson, J. L. and Smith, D. R. (1995) Am. Mineral. 80, 549–559.
Hodges, K., V. and Spear, F. S. (1982) Am. Mineral., 67, 1118–1134.
Hoisch, T. D. (1990) Contrib. Mineral. Petrol., 104, 225–234.
Hokada, T. (1998) Island Arc, 7, 609–620.
Holland, T. and Blundy, J. (1994) Contrib. Mineral. Petrol., 116, 433–447.
Kawakami, T. (2004) Trans. R. Soc. Edinburgh: Earth Sci., 95, 111–123.
Yoshioka and Takagi (2023) 130th Annu. Meet. Geol. Soc. Japan, Abstr
P-T pseudosection modeling is calculated for the Ryoke metapelites in the system MnO-TiO2-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O. It shows the mineral assemblages corresponds to the sequence of Bt zone → Sil–Kfs zone → Grt–Crd zone (northern area), and Bt zone → Kfs–Crd zone (southern area) with increasing temperature at >~300 MPa and <~300 MPa, respectively. Accordingly, the metamorphic pressure was larger in the northern area than in the southern area.P-T condition estimated by geothermobarometry (Hodges and Spear, 1982; Hoisch, 1990) was 739°C, 431 MPa in high grade of Kfs–Crd zone and 754°C, 545 MPa in Grt–Crd zone. Estimated P-T condition from the sample near tourmaline-out isograd in Kfs–Crd zone is similar with tourmaline breakdown condition (>730℃, 400–500 MPa) shown in Kawakami (2004). Amphibole−plagioclase geothermometry and Al in-hornblende geobarometry (Anderson and Smith, 1995; Holland and Blundy, 1994) show that crystallization pressure of Katsuma quartz diorite, Hissori granite and Takato tonalite are 460 ± 44, 322 ± 27 and 365 ± 59 MPa.
We will also discuss the relationship between the metamorphic rocks and granitoids, taking the age data of the granitoids into account.
[Reference]
Anderson, J. L. and Smith, D. R. (1995) Am. Mineral. 80, 549–559.
Hodges, K., V. and Spear, F. S. (1982) Am. Mineral., 67, 1118–1134.
Hoisch, T. D. (1990) Contrib. Mineral. Petrol., 104, 225–234.
Hokada, T. (1998) Island Arc, 7, 609–620.
Holland, T. and Blundy, J. (1994) Contrib. Mineral. Petrol., 116, 433–447.
Kawakami, T. (2004) Trans. R. Soc. Edinburgh: Earth Sci., 95, 111–123.
Yoshioka and Takagi (2023) 130th Annu. Meet. Geol. Soc. Japan, Abstr