Abstract
The geological and structural contrast between the north and central Ryukyus and the south Ryukyus has been significant since the Late Mesozoic. The difference seems to correspond to that of the nature of the Philippine Sea floor facing the Ryukyus, i.e. the Daito Ridges and Amami plateau to the north and deeper basin to the south. The north and central Ryukyus were a separate tectonic unit from the south Ryukyus from the Late Mesozoic to Middle Tertiary. Subsequently they have united to form an island arc as the island groups shifted southeastwards with different rates in the Late Tertiary to Quaternary.
