This belt is located along the northwestern margin of the South Kitakami Belt (Ehiro and Suzuki, 2003; Uchino et al., 2005) in Northeast Japan. This is the oldest of the non-metamorphosed accretionary complexes in Japan, formed during Early Carboniferous accretion. It is composed of sandstone, mudstone, felsic tuff and basalt. It is characterized by the dominant presence of felsic volcanic rocks, unlike the other accretionary complexes in Japan. The sandstone contains detrital grains of volcanic arc origin, and the conglomerate yields pebbles of low-temperature and highpressure metamorphic (347–317 Ar–Ar age) and ultramafic rocks. These grains and pebbles were derived from the South Kitakami Belt (Uchino et al., 2008). This accretionary complex is the protolith of the metamorphic rocks of the Nagato-Renge Belt (Uchino et al., 2005; Kawamura et al., 2007).