The Carboniferous tropical paleo-latitude of the Hida Marginal Belt (SW Japan) from pedologic evidence in metapelites

Hiroshi Kamikubo, Sayaka Maki, and Makoto Takeuchi

Petrology and geochemistry of chloritoid-bearing Al-rich metapelites in the Carboniferous Shimozaisho Group (Hida Marginal Belt, Central Japan) reveal the abundance of metamorphic sericite and less quartz than in non-Al-rich metapelites. This indicates that quartz was consumed during a metamorphic reaction as well as the contribution of Si-free aluminous minerals in detritus derived from highly weathered soil. The high CIA (Chemical Index of Alteration) values and high TiO2 contents (up to 2.05 wt. %) in the Shimozaisho metaclasts are comparable to those of modern tropical soils and suggest that tropical climate may have controlled the intense weathering of their protolith source. The volcaniclastic layers that prevail in the Carboniferous formations that overlie thick limestone beds in the Hida Terrane suggest that a stable land surface evolved into the unstable tectonic setting that triggered the detritus supply and mixing of its highly weathered and non-weathered materials. Al-rich metaclastic rock series in Hida Marginal Belt with protolith originating from Late Paleozoic shelf deposits commonly have formed at tropical climate conditions.