Topographic features of the hydrothermal field and their genetic mechanisms in southern Okinawa Trough

In order to better understand the role of tectonic processes in submarine hydrothermal activity and mineralization in back-arc basins, we documented herewith the multi-beam sounding data from the southern Okinawa Trough and detailedly depicted the topographic features of some hydrothermal fields concerned. Combined with the results in previous publications, we analyzed the genetic mechanisms of the topographic features from the viewpoint of tectonics. Topographic features in all of the hydrothermal fields are formed by submarine volcanism. Nevertheless, features of different hydrothermal fields are essentially depending upon the distinct types of magmatism. The D Knoll was influenced by both the arc and back-arc magmatisms; the A Knolls were formed by multi-source magmatism predominated by arc magmatism; the C Knoll and the B Knolls are part of the Ryukyu Volcanic Arc; and the Yuhua Knoll was generated by the magmatism induced by the post-collisional lithospheric extension. The intensity of the Ryukyu Volcanic Arc magmatism shows a trend of migration both temporally and spatially, which may be attributed to the transition from disperse rifting to the focus rifting. The occurrence of the Tangyin hydrothermal field indicates that the magmatism of the Northern Taiwan Volcanic Zone in the continental slop region is strong enough to drive vigorous hydrothermal circulation. Thus this region is an important target area for hydrothermal surveys in the future.