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

Ilvaite–manganilvaite series minerals in jasper and iron–manganese ore from the Northern Chichibu belt, central Shikoku, Japan

“…It has been well established that manganoan greenalite (so-called 'tosalite' in Yoshimura, 1967) is one of the main hydrous minerals in iron-manganese ores in the Northern Chichibu belt (Yoshimura, 1969;Nakagawa et al, 2011Nakagawa et al, , 2014. Therefore, caryopilite and manganoan greenalite represent the major H 2 O hosts in manganese and iron-manganese ores in the Northern Chichibu belt.…”

“…There are numerous stratiform iron-manganese ore deposits in Jurassic accretionary complexes of SW Japan, namely the Tamba-Mino-Ashio belt in the Inner Zone and the Northern and Southern Chichibu belts in the Outer Zone (Watanabe, 1957;Yoshimura, 1967Yoshimura, , 1969Momoi, 1991;Nakagawa et al, 2011). Because of the scarcity of forearc igneous activities, mineralogy of stratiform ore deposits in the Outer Zone of SW Japan can be understood in the framework of diagenesis to low-grade regional metamorphism.…”

A geochemical constraint on the formation process of a manganese carbonate nodule in the siliceous mudstone of the Jurassic accretionary complex in the Mino Belt, Japan

“…Because the Mn deposit in the Katsuyama section is a stratiform deposit interbedded chert according to Komuro and Waktia (2005), they considered that the input of oxic water into the deep ocean floor to form the bedded Mn deposits at the Katsuyama section. Nakagawa et al (2011) summarized the characteristics of the bedded Mn deposits in the accretionary complexes of Japan and proposed that Mn ores in the Mino Belt originated from Mn nodules or crusts followed by low-grade metamorphism through subduction-accretion processes. These previous studies, however, may not be applicable for our study because the Mn carbonate collected in this study was not in bedded form, but was nodular in appearance and incorporated in siliceous mudstone.…”

“…The occurrence of Mn in the Jurassic accretionary complexes are different for the different source locations considered: the stratiform Mn deposits between the chert beds , the stratiform ferromanganese deposit associated with greenstone , and the distinctive nodules associated with laminae composed of spherules of rhodochrosite aggregations in siliceous mudstone and mudstone (Fujihara, 2009;Suzuki and Ogane, 2004;Minoura et al, 1991). This variable occurrence condition of the Mn deposits is presumably caused by the different origins and different formation processes (Nakagawa et al, 2011).…”

Suture zones and geodynamic processes

“…They also suggest that the subduction processes must have played an important role in the generation of chemically heterogeneous mantle. Nakagawa et al (2011) examine the processes and tectonics of manganese ore formation in the accretionary belts of Japan and suggest that these rocks represent the marker beds in the accretionary tectonics associated with the convergent margin processes in this region. The association of manganese deposits with bedded cherts, cretaceous granitic intrusions, and basalts is interpreted in terms of different scenarios such as hydrothermal process and thermal metamorphism involving subduction-accretionary tectonics.…”