Anatexis and chemical evolution of pelitic rocks during metamorphism and migmatization in the Hidaka metamorphic belt, Hokkaido.

Abstract

The southernmost Hidaka metamorphic belt consists mainly of cordierite tonalite intrusions and pelitic metamorphic rocks ranging from the greenschist to the granulite facies. Anatectic migmatites are common in the higher amphibolite and granulite facies zones. Compositional changes in major, rare earth elements and some other trace metals are so small that they are undetectable among the pelitic metamorphic rocks of zones A + B + C and D, but they are large enough to be detected in the higher am phibolite (zone D) to the granulite facies rocks (zone E). The enrichment of Fe, Mg, Na, Eu, and Sc, and the depletion of K, P, La, Ce, Nd, Cs and Rb are statistically significant in pelitic granulites, while heavy REEs are very variable. The chemical variation of pelitic granulite was derived from the accumulation of plagioclase +garnet. This suggests that more than 50-60% of the total volume of pelitic granulite was melted to produce a large amount of tonalitic magma, leaving pelitic granulite as a restite.Migmatites of the higher amphibolite facies are anatexites, and their K, P, Cs, Rb and light REE content is the same as that of lower grade metamorphic rocks. Migmatites of the higher amphibolite facies melted incipiently to segregate only a small amount of melt, and could not produce a large magmatic mass such as the cordierite tonalites.Cordierite tonalites are S-type granites, and their major elements, Cs, Rb and light REE concentra tions are similar to those of lower grade metamorphic rocks. The chemical variation of cordierite tonalites is explained by the extraction of plagioclase +garnet from a tonalitic magma and the variation of original sedimentary rocks. The small chemical difference between the cordierite tonalites and the lower grade metamorphic rocks suggests that the former was derived from a massive melting of meta pelites or that much of the restite is retained. The material migration among higher amphibolite facies rocks, pelitic granulites, migmatites and cordierite tonalites took place through mineral /melt interac tion in the lower crust.

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).…”

Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

“…subhorizontal crustal displacement (D2) by Komatsu et al (1989). The granitic rocks are almost S-type tonalites formed by anatexis in the deep crust (Tagiri et al 1989;Osanai et al, 1991;Shimura et al 1992), and intruded into the decollement and shear zones (Toyoshima 1991;Shimura 1992). Komatsu et al (1994) showed that granulite facies gneisses underwent decompression under increasing temperature conditions during the peak metamorphic and deformation stage (D,) and suggested that the unloading was caused by extensional doming due to intrusion and underplating of mafic magma.…”

日高変成帯主帯に分布する高変成度角閃岩類の原岩推定および北部日高帯緑色岩類との比較

“…and Katsushima, 1986;, 1987Miyashita andYoshida, 1988, 1994;Miyashita and Watanabe, 1988;, 1990, 1994, 1992 , , 1985;Osanai et al, 1986Osanai et al, , 1991Osanai et al, , , 1997 Fig Amphibolites from the Main zone of Hidaka metamorphic belt are distributed in zones and b . In this study, central and southern areas of the Main Zone were studied and the southern area was subdivided into northern and southern parts.…”

“…H2O , , 1982H2O , , , 1986H2O , , 1985H2O , , Osanai et al 1986H2O , , , 1991H2O , , 1986 3 Fig : schlieren structure composed of Opx tonalite and Opx amphibolite Zone in Nanashino-sawa river , e: agmatite structure of Opx amphibolite intruded by Opx tonalite Zone in Benikaru-zawa river , f: gneissose brown-Hbl amphibolite Zone in Ogawara-zawa river , g: thin Grt amphibolite layer within Opx amphibolite Zone in Sasshibichari river , h: banded green-Hbl amphibolite Zone in Nanashino-sawa river , i: dolerite intruding to shale Shimokawa area , j: pillow lava composed of Cpx-basalt Nupun-Tomuraushi river in Tomuraushi area , k: gneissose amphibolite Uchino-sawa river in Ochiai area l: boundary between greenschist and slate Kanano-sawa river in Ochiai area . Table 1 Table 2 Fig Table 2 SrI Nd NdI , 1984;Tagiri et al, 1989;, 1999 NdI , 1993;Kiminami et al, 1994;Watanabe and Iwata, 1987N-MORB Maeda and Kagami, 1996, 1990Maeda and Kagami, 1996; , …”

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