Abstract
Devonian conodonts were newly found from red chert of the Hayachine Belt in southeast Morioka district, Northeast Japan. Hayachine Belt is an accretionary complex composed of deformed clastic rocks and greenstones, also constituting a boundary zone between the North and South Kitakami Belts. The conodont assemblage is characterized by the presence of Palmatolepis indicating Late Devonian age (early Famennian). This is the first report of Devonian oceanic rocks in Japanese Islands, confirmed by fossil occurrence.The conodont-bearing chert occurs with bedded iron ore deposits as a lenticular body within greenstone. Chemical analyses for the greenstone show two rock types, within-plate alkali basalts and MORB to within-plate tholeiites. Tholeiites occurring with iron ore deposits indicate the compositional range of N-MORB to P-MORB. The greenstone of the Hayachine Belt is thus considered to have been formed by ocean-floor and oceanic island volcanisms with hydrothermal activity in Late Devonian time.
