Metamorphism and mode of occurrence of metabasites in the Kamuikotan terrain of the Horokanai Pass area, Hokkaido

摘要: The Kamuikotan tectonic belt is a melange zone in which occur various kinds of metamorphic rocks high pressure and low types. In the Horokanai district, central Hokkaido, type are widely distributed. They can be classified into four kinds, metasediments, grade metabasites, epidote amphibolites, metachert based upon original mineral parageneses. A large part metasediments consist black siliceous shale. metabasites spilitic tuff, pillow lava, massive lava gabbro, those amphibolites basaltic lava. scattered as lenticular bodies sizes metasediments. modes occurrence suggest that basic chert were emplaced olistoliths. assemblage quartz+white mica +chlorite+ graphite±lawsonite±albite+metamorphic aragonite. characterized by widespread lawsonite, pumpellyite, alkali amphibole, pyroxene, These parageneses indicate suffered metamorphism glaucophane schist facies. On other hand, display relic amphibolite assemblages have been partly or entirely modified later emplacement may explained follows. Their component oceanic crust was underthrust beneath older subduction region during Mesozoic time. Rock slices scraped off accreted to pile composing slices. metamorphosed up facies processes. Underthrusting accretion accompanied concurrent intrusion serpentinite with fragments blocks deeper crust. uplifted exposed denudation. clasts reworked subaqueous sliding form an olistostrome clastic sediments. Later all area thus rock observed presently formed.