Metamorphism and granite genesis in the Hidaka Metamorphic Belt, Hokkaido, Japan

Abstract

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-IV), in which zone 1V 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, af'ter a supposed event of tectonic thickening of accretionary sedimentary and oceanic crustal rocks. During the peak metamorphic event (c. 53 Ma), the regional geothermal gradient attained 33-40"Ckm-', and the highest P-T condition obtained from the lowest part of the granulite unit is 830" C, 7 kbar. In this part, X,,,, of Gt-Opx-Cd gneiss is about 0.15 and that of Gt-Cd-Bt gneiss is 0.4. The P-T-X,,, condition of the granulite unit is well within a field where fluid-present partial melting of pelitic and greywacke metamorphic rocks takes 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 the granulite zone, Gt-Cd-Bt tonalite in the amphibolite zone, and Cd-Bt-Mus tonalite in the Bt-Mus gneiss zone. The mineralogical and chemical nature of these strongly peraluminous tonalitic rocks permit them to be regarded as having been derived from S-type granitic magma generated by crustal anatexis of pelitic metamorphic rocks in deeper crust. And = andalusite Hbl = hornblende Bt =biotite Hc = hercynite Cd = cordierite Kfs = K-feldspar Chl =chlorite Mus = muscovite Co =corundum Opx = orthopyroxene Cpx = Ca-pyroxene Phe =phengite Cum = cummingtonite PI = plagioclase Ep =epidote Qz =quartz Ged =gedrite Sil = sillimanite Gt = garnet St = staurolite. , , ~ ~~

Strain-induced amorphization of graphite in fault zones of the Hidaka metamorphic belt, Hokkaido, Japan

“…1a). The belt exposes a typical cross section of a magmatic arc, and consists of intrusive magmatic rocks and eastwards-dipping metamorphic rocks that have a NNWeSSE trending zonal distribution (e.g., Komatsu et al, 1983Komatsu et al, , 1989Osanai et al, 1991;Toyoshima et al, 1994, Fig. 1b).…”

Crystal bending, subgrain boundary development, and recrystallization in orthopyroxene during granulite-facies deformation

“…The mylonite, constituted principally of elongated (up to a few mm) orthopyroxene (opx) grains embedded in a matrix of small (~50μm) plagioclase grains (details of the microstructure in Raimbourg, Toyoshima, Harima and Kimura (2008)), is characterized by a strong dextral deformation at granulite-facies conditions (T~800 − 900℃ and P~6.1 − 7.2 kbar) (Osanai, et al 1991;Toyoshima, et al 2000), which was completely preserved from lower-grade retrogression described in Kanagawa, et al (2008).…”

Origin of the I- and S-type tonalite magma in the Satsunai-gawa Shichino-sawa river region of the Hidaka metamorphic belt, Hokkaido, northern Japan: Inferences from Sr and Nd isotopic compositions

“…1 2 55 Ma 3 , 1992;Toyoshima et al, 1994;Owada et al, 2003 55 Ma Rb-Sr Owada et al, 1991;, 1992 , 1984;Tagiri et al, 1989;Osanai et al, 1991Osanai et al, , 1992Owada et al, 1991;, 1992;Shimura et al, 1992Shimura et al, , 2004Komatsu et al, 1994;, 1994; Whitney and Evans 2010, 1986Fig. 1a -, 1986 , 1983 Kiyokawa, 1992, Ueda et al, 2001Komatsu et al, 1983 Komatsu et al (1986) and Shimura et al (2004).…”

“…, 1985--, 1985, 1986Shimura et al, 1992-Chappell and White 1974S I , 1986Komatsu et al, 1989;Osanai et al, 1991;, 1992;Shimura et al, 1992Shimura et al, , 2004Shimura et al, S I S , 1986Shimura et al, S I , , 1986, 1992;, 1994;Shimura et al, 2004 …”