Geochemical characteristics of an ophiolitic complex from Mt. Tenzan area, Saga Prefecture, northern Kyushu

Abstract

The metamorphic complex from the Mt. Tenzan area in northern Kyushu consists mainly of ma fi c rocks with small amounts of siliceous, calc – silicate, and ultrama fi c rocks. These lithofacies can be recognized as an ophiolitic complex. Metamorphosed ma fi c rocks are divided into two types, amphibolites I and II, which are probably derived from supracrustal and intrusive rocks, respectively. The geochemical data of both amphibolites plotted within the fi eld between mid – ocean ridge and island arc basalts; such geochemical features resemble those of back – arc basin basalts. As the metamorphic complex was intruded by Cretaceous granitoids, protoliths of the complex could have been formed prior to the Cretaceous. The protolith lithofacies assemblage and geochemical constraints of the Tenzan metamorphic complex indicate the correlation with the Yakuno ophiolite rather than the Oeyama ophiolite.