飛騨外縁帯上広瀬層にみられる電気石の産状と化学組成

Abstract

Tourmaline-bearing hydrothermal veins and metamorphic tourmalines occur in the Kamihirose Formation, circum-Hida terrane. The Kamihirose Formation was intruded by the Funatsu granitic rocks and underwent the contact metamorphism. Two types of tourmaline-bearing hydrothermal veins were distinguished: (1) tourmaline vein, which consists mostly of tourmaline with quartz and minor apatite; (2) potassium feldspar vein, which consists mostly of orthoclase with quartz, plagioclase and acicular tourmaline. Metamorphic tourmalines are found in sandstone and tonalite porphyry and tuffaceous sandstone clast of conglomerate. There are three types of sandstones that yield metamorphic tourmalines: black, white and acidic tuffaceous sandstones. In the black sandstone, the metamorphic tourmalines occur in shale fragments and occur as overgrowth on detrital tourmalines, whereas, in the white sandstone, those occur in acidic tuff fragments. In the acidic tuffaceous sandstone, metamorphic tourmalines occur in the tuffaceous matrix. The electron-microprobe analyses of tourmalines revealed the facts as follows ; (1) The tourmalines from the Kamihirose Formation are members of schorl-dravite solid solutions. (2) The tourmalines in the hydrothermal veins probably contain Fe3+, which substitutes for Al. (3) The metamorphic tourmalines have a wide compositional range reflecting various chemical features of host rocks.