Geochemistry of metamorphic rocks from Mizoguchi, western Tottori Prefecture, Japan and its geological significance

Abstract

The Mizoguchi area, Southwest Japan, has been interpreted as a western continuation of the Hida terrane, based on the similarity of the mineralogy and radiometric age of metamorphic rocks. However, new geochemical data show metapelite and metabasite from the Mizoguchi area differ from those of the Hida terrane in the following points. i) Metapelite is relatively rich in Sc compared to La and Th, and show gently inclined chondrite-normalized REE patterns. ii) In discrimination diagrams for basaltic rocks, metabasite plots in the fields of arc tholeiites or N-MORBs; however, they are relatively depleted in light REEs but much richer in LIL elements than N-MORBs. From these geochemical features the Mizoguchi metamorphic rocks are interpreted to have formed in the fore-arc region of an oceanic island arc. This is in contrast to generally accepted continental setting for the Hida area and suggests the two areas are geologically distinct.