HR: 0800h
AN: S41A-0939    [Abstracts]
TI: The study of active submarine volcanoes and hydrothermal vents in the Southernmost Part of Okinawa Trough
AU: * Lee, Y
EM: M91860004@mail.ntou.edu.tw
AU: Tsai, C
EM: chtsai@oc.gep.ncu.edu.tw
AU: Lee, C
EM: leecs@mail.ntou.edu.tw
AB: The study area is located in the Southernmost Part of Okinawa Trough (SPOT), which is a back-arc basin formed by extension of Eurasian plate. Previous research indicated two extensional stages in SPOT area. Many normal-fault structures were come into existence during both extensional processes. The SPOT is presently in an activity tectonic episode. Therefore, the area becomes a frequent earthquake and abundant magmatism. The purpose of this study is to discuss which relationship between tectonics, submarine volcanoes and hydrothermal vents in SPOT area. The investigations are continued from 1998 to 2004, we have found at least twelve active hydrothermal vents in study area. Compare the locations hydrothermal vents with fault systems, we find both of them have highly correlated. We can distinguish them into two shapes, pyramidal shape and non-pyramidal shape. According to plumes height, we are able to divide these vents into two groups near east longitude $122.5\deg$. East of this longitude, the hydrothermal plumes are more powerful and west of it are the weaker. This is closely related to the present extensional axis (N$80\deg$E) of the southern part of the Okinawa Trough. This can be explained the reason of why the more powerful vents coming out of the east group. The east group is associated with the present back-arc spreading system. West of $122.5\deg$, the spreading system are in a primary stage. The andesitic volcanic island, the Turtle Island, is a result of N$60\deg$E extensional tectonism with a lot of faults. Besides the pyramidal shape, this can be proved indirectly. The vents located in the west side were occurred from previous extensional faults and are weaker than the eastern. Therefore, we suggest that if last the extension keeps going on, the hydrothermal vents located at the west side of the longitude $122.5\deg$ will be intensified.
DE: 8424 Hydrothermal systems (8135)
DE: 8109 Continental tectonics--extensional (0905)
DE: 5480 Volcanism (8450)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting