Manganese formations in the accretionary belts of Japan: Implications for subduction–accretion process in an active convergent margin

In the accretionary complexes of Japan, many bedded manganese and iron–manganese ore deposits occur, especially in the Jurassic complexes such as the Chichibu, Tamba, Mino, Ashio and Northern Kitakami belts. The manganese ores in these Jurassic accretionary complexes probably formed from manganese nodule/crust-bearing siliceous sediments on deep-sea floor and were subsequently converted to the manganese ores by metamorphism during the subduction–accretion process. Some of the deposits also show the signatures of younger granitic intrusions. The manganese formations now incorporated within these belts are marker beds of accretionary tectonics associated with plate tectonic processes in convergent margins.

► Chert-hosted manganese deposits occur in many localities within the accretionary complexes of Japan.
► The ores were manganese nodule/crust-bearing siliceous sediments on deep-sea floor.
► They were converted by metamorphism through subduction–accretion process.