Topographic And Geomorphologic Features And Genesis Analyses Of The Hydrothermal Fields And Typical Hydrothermal Vents In The Mid-okinawa Trough

The characteristics of topography and geomorphology of the hydrothermal fields in the Mid-Okinawa Trough are studied with the lasted high-precision deep-water multibeam bathymetric data. And the features of topography and geomorphology of two typical hydrothermal vents are studied with the images obtained by ROV(Remotely Operated Vehicle), combined with the shallow sediment and rock samples. In addition, the different parameters affecting the resolution of the bathymetric data are discussed by taking Seabeam 3012 MBES for example.Results show that the topography is complicated in the study area. There is a rift extending along SW-NE direction, of which the depth ranges approximately from 1500 m to 1800 m. A large amount of knolls exist, with some depressions within them. These knolls can divided into two categories : one is a nearly circular or oval-shaped, larger, linear features is not obvious; the other is some linear seamount chains, more elongated, dagger-like, towering, steep and consistency of various sizes, extending along SE-NE direction, as the expansion direction of the Okinawa Trough, which indicates its formation may result by the back-arc spreading of the trough.The topography of hydrothermal vent in the Iheya North area varies from place to place, within various sizes of chimneys and mounds. The chimneys and mounds are towering, multi-layered eaves, black to dark gray, surrounded by black sulfide and sediments, and associated with hydrothermal communities. While the topography of hydrothermal vent in the Iheya Ridge area is rather smooth, generally as a slope towards the northeast. Hydrothermal fluid at this place is colorless, overflowing from dispersed fissures spread on the hard seafloor. There are little hydrothermal sediments. Differences in geomorphologic features of two hydrothermal vent area is mainly influenced by the strength of hydrothermal activity, Iheya North hydrothermal activity in the early stages, while Iheya Ridge is in late-stage of hydrothermal activity.