PROVENANCE OF JURASSIC ACCRETIONARY COMPLEX MINO TERRANE, INNERZONE OF SW JAPAN: IMPLICATIONS FOR PALEOGEOGRAPHY OF EASTERN ASIA

Japanese Islands are composed of several continental-affiliated blocks and accretionary complexes formed due to the subduction-accretion processes since the late Paleozoic. The Mino terrane, a Jurassic accretionary complex located in the Inner Zone of Southwest Japan is one of Mesozoic accretionary complexes. In this study, provenance of turbidite sandstones and mudrocks from the chert-clastic sequences of the Mino terrane was investigated using sandstone petrography, mineral chemistry, and whole-rock geochemistry of sandstones and mudrocks. Sandstones consist mainly of quartz, plagioclase, K-feldspar, and metamorphic and sedimentary rock fragments. Total feldspar contents are higher than quartz contents, and plagioclase exceeds K-feldspar in amount. Volcanic traces are negligible. The low K₂O/Na₂O (< 1) in sandstone, Eu anomaly in mudrock less negative than PAAS and the paucity of Eu anomaly in sandstone reflect abundant plagioclase in these sediments. Depleted transition metals, fractionated REE pattern, and various provenance diagrams using trace element contents indicate fractionated source terrane for Mino sediments. Factor analysis using geochemical data of sandstone and mudrock reveals the presence of major four factors controlling chemistry of sediments and that the grain size affected much the chemistry of these sediments. Plagioclase composition in sandstone ranges from albite (An₅) to oligoclase (An₃₀), which suggests their derivation from felsic plutonic and metamorphic rocks, while detrital garnet composition indicates high-grade metamorphic source rocks. Poor sorting and the presence of rather fresh feldspar in sandstones support sediment supply from rapidly uplifted source terrane. Predominance of basement signature with lack of volcanic contribution indicates the exposure of uplifted continental basement during deposition of Mino sediments. Precambrian basement rocks in the Korean Peninsula, located in the eastern margin of Asian continent, are the most probable provenance for the Mino sediments. Considering paleogeographic studies, felsic basement rocks of Precambrian Yeongnam massif distributed in the central eastern part of the Korean Peninsula may have supplied immature sediments to the Mino trench.