冲绳海槽中部南奄西海丘海底热液活动的若干特征

PROPERTIES OF THE SUBMARINE HYDROTHERMAL MOUNDS IN THE MIDDLE OKINAWA TROUGH

冲绳海槽中部南奄西海丘海底热液活动为弧后盆地型热液活动。在水深 ６５０～７７０ｍ处发育有活烟囱，喷出的热液温度（２７０℃）临近当地沸点（２７５℃），热液 中富含ＣＯ２气泡。稳定同位素研究表明，热液活动与岩浆活动有关。根据热液沉积 物的矿物学及化学特征可将其划分为４种类型，它们是富硅热液沉积物、富硫酸盐 热液沉积物、块状富硫化物热液沉积物和碎屑状富硫化物热液沉积物。热液沉积物 中至少含有２７种矿物，并富集了Ｚｎ，Ｐｂ，Ｃｕ，Ａｇ等成矿元素。

The submarine hydrothermal mounds in the Middle Okinawa Trough may be the shsllowest ones in the world. There are some active smokers in the depression of Minami-Ensei, the Middle Okinawa Trough. Temperature (270 ℃) of the hydrothermal fluids emitted from the smokers is slightly lower than the boiling point (275℃) in situ. The bubbles emerged from the sea floor are rich in carbon, dioxide, and its stable isotopic ratios imply their magmatios origin. According to the mineralogy and geochemistry, the hydrothermal deposits, which contains at least 27 type minerals and rich in Zn.Pb.Cu.Ag, can be divided into 4 types, they are (1) the silicic one. (2)the sulfate-rich one. (3)the massive sulfide-rich one and. (4)the clastic sulfide-rich one.