Primitive high-Mg andesites (HMA) exhibit low FeO*/MgO (FeO*, total iron) and high Mg# (=100×Mg/(Mg+Fe)), and are thought to be generated by hydrous mantle melting (Kushiro, 1969). HMA, including sanukitoids of the Setouchi volcanic belt, have been recognized in many orogenic belts of various ages, and in several cases, constitute a part of ophiolite (Tatsumi, 2003). Therefore, occurrence of HMA in northern Kamchatka may have important implications on the tectonic setting of the peninsula and/or the melting condition underneath
