The study documents similar petrographic signature between accreted materials of the inner Nankai accretionary prism and submarine fans of the Shikoku Basin. The results are in agreement with the hypothesis of very oblique subduction or strike-slip motion between the northern Shikoku Basin and mainland Honshu from ∼12.2 to 9.2 Ma. Furthermore, results document incorporation of the Kyushu Fan into the inner accretionary prism implying changes in décollement location between ∼6 and ∼2 Ma, likely related to changes in physical properties of hemipelagic intervals