Abstract
Geological characteristics of the Ryukyu Island Arc are overviewed and geology and its development of Okinawa Island in Central Ryukyus are described. Ryukyu Arc extends for ∼1200 km from Kyushu to Taiwan, which has been divided into three segments (North, Central, and South Ryukyus) with tectonic boundary of the Tokara Strait in the north and Kerama Gap in the south. The northern part of Okinawa Island consists of older (Permian to Eocene) basement rocks, which form zonal structure from west to east along the extension of Ryukyu Arc; these are products of accretionary processes associated with plate subduction. Southern Okinawa Island is composed of younger (late Miocene to Quaternary) Formations. Drastic change in oceanic environment from `muddy' sea for the Shimajiri Group to `coral reef' sea for the Ryukyu Limestone at lower to middle Pleistocene was caused by crustal movement (Shimajiri Movement), which involved the formation of a young back-arc basin (Okinawa Trough). After the deposition of Ryukyu Limestone during upper Pleistocene to Holocene, the Uruma Movement, involving block faulting, took place and resulted in the present island arc configuration.
