METAMORPHISM AND GRANITE GENESIS IN THE HIDAKA METAMORPHIC BELT, HOKKAIDO, JAPAN

Year, pages: 1991, 19 - 32

The Main Zone of the Hidaka Metamorphic Belt is an uplifted crustal section of island arc type. The crust was formed during early Tertiary time, as a result of collision between two arc-trench systems of Cretaceous age. The crustal metamorphic sequence is divided into four metamorphic zones (I to IV), in which zone IV is in the granulite facies. A detailed study of the evolution of the Hidaka Belt, based on a revised P-T-t analysis of the metamorphic rocks, notably a newly found staurolite-bearing granulite, confirms a prograde isobaric heating path, after a supposed event of tectonic thickening of accretion sedimentary and oceanic crustal rocks. During the peak metamorphic event (ca. 52.6 Ma), the regional geothermal gradient attained 30 to 40 °C/km, and the highest P, T condition obtained from the lowest part of the granulite unit is 830 °C, 7kb. In this part, X_H2O of Gt-Opx-Cd gneiss is about 0.15 and that of Gt-Cd-Bt gneiss is 0.4. The P-T-X_H2O condition of the granulite unit is well within a field where fluid-present partial melting of pelitic and greywacke metamorphic rocks take place. This is in harmony with the restitic nature of the Gt-Opx-Cd gneiss in the lowest part of the granulite unit. The possibility that partial melting took place in the Main Zone is significant for the genesis of the peraluminous (S-type) granitic rocks within it. The S-type granitic rocks in this zone are Opx-Gt-Bt tonalite in granulite zone, Gt-Cd-Bt tonalite in amphibolite zone, and Cd-Bt-Mus tonalite in the Bt-Mus gneiss zone. The mineralogical and chemical natures of these strongly peraluminous tonalitic rocks permit us to regard them to have been derived from S-type granitic magma generated by crustal anatexis of pelitic metamorphic rocks in deeper crust.

Osanai, Y., Komatsu, M., Owada, M. 1991. METAMORPHISM AND GRANITE GENESIS IN THE HIDAKA METAMORPHIC BELT, HOKKAIDO, JAPAN. In Geologica Carpathica, vol. 42, no.1, pp. 19-32. 1335-0552.

Osanai, Y., Komatsu, M., Owada, M. (1991). METAMORPHISM AND GRANITE GENESIS IN THE HIDAKA METAMORPHIC BELT, HOKKAIDO, JAPAN. Geologica Carpathica, 42(1), 19-32. 1335-0552.