Abstract
Gabbroic dikes intruding into Carboniferous-Permian sedimentary rocks of the Hida Gaien belt in the northern part of Takayama City consist of hornblende gabbro and hornblende-clinopyroxene gabbro. On the diagrams SiO2 versus FeO* and V, and FeO*/MgO versus SiO2, the hornblende gabbros show a trend of calc-alkaline magma suite, whereas they have TiO2 concentration as high as mid-ocean ridge basalt (MORB). MORB-normalized high-field-strength element patterns for most hornblende gabbros are similar to those for island arc basalt at the back-arc side and back-arc basin basalt. In addition, one hornblende gabbro with high-K hornblende probably originated from shoshonitic to high-K calk-alkaline magma. These facts suggest that the hornblende gabbro originated from back-arc side of island arc to back-arc basin basaltic magmas. Because the hornblende-clinopyroxene gabbro contains anorthite-rich plagioclase (An=ca. 92) coexisting with moderately evolved clinopyroxene (Mg/(Mg+Fe)=ca. 80), it probably originated from an island arc basaltic magma. Such a diversity of magma types suggests that the Hida Gaien belt was situated in an island arc to a back-arc basin setting in latest Permian time.
