Petrological features of olivine-norite along the Ougon-douro, southern part of the Hidaka metamorphic belt, Hokkaido

Abstract

Small olivine-norite bodies crop out along the Ougon-douro, southern part of the Hidaka metamorphic belt. This outcrop has been visited by many geological excursions since the 1970s. However, the geological relations with the adjacent igneous rocks were unclear because the intrusive boundaries were covered by talus for many years. These boundaries could, however, be observed from 2014 to 2017. The olivine-norite bodies might constitute syn-plutonic dykes in the biotite granodiorite. It mainly consists of orthopyroxene, plagioclase, olivine, amphibole, phlogopite, and clinopyroxene, in order of abundance. They include small amount of chromite, magnetite, titanite, pyrrhotite, pentlandite, and chalcopyrite. Serpentinite and chlorite occur around mafic minerals. The rocks are modally classified as olivine-melanorite to olivine-melagabbronorite. Geochemically, these rocks have negatively sloped chondrite-normalized REE patterns. The Sr and Nd isotope ratios are enriched relative to typical MORB.