Geotectonic subdivision and areal extent of the Sangun belt, Inner Zone of Southwest Japan

摘要: The Sangun belt has long been considered to be a major coherent glaucophanitic terrane of Permian Triassic age, and paired with the low-P/T  Hida north. However, recent progress in geochronology, metamorphic geology, tectonics revealed that is fact comprised two geologic units different ages contrasting conditions formation. older unit named Renge younger Suo belt. oldest high-P/T  belts Japanese Islands extends from northern Kyushu, through San-in coastal regions, marginal It characterized by 330–280 Ma association glaucophane–schist epidote–amphibolite facies schists. also typically associated meta–ophiolite sequences (470–340 Ma) including serpentinite. 230–160 Ma schists closely related weakly metamorphosed accretionary rocks Akiyoshi Metamorphic series prehnite–pumpellyite pumpellyite–actinolite facies. widespread west Kinki north central Kyushu via Chugoku, but stretches further southwest present Ishigaki-Iriomote southern Ryukyu Arc. Throughout this belt, there are scattered small blocks or lenses meta–ophiolite, whose K–Ar relict hornblendes 590 220 Ma. Bounded low-angle faults thrusts, both define subhorizontal nappes dipping gently geotectonic framework Inner Zone Southwest Japan made up of, south, Hida-Oki, Renge, Akiyoshi, Suo, Maizuru plus ultra-Tamba, Mino-Tamba, Ryoke belts, tectonically downward-younging polarity. This resulted stepwise accretions during Palaeozoic Mesozoic time.