DISTRIBUTION AND TECTONIC ENVIRONMENTS OF THE HYDROTHERMAL FIELDS

Up to now, around 490 hydrothermal fields have been reported on the world ocean floor since 1965. Data of the water depth of each of the reported hydrothermal activity fields is collected. The tectonic settings and surface distribution of the reported hydrothermal activity fields are analyzed in this paper. The paper points out that almost all the hydrothermal activity fields distribute within a lower latitude belt between 40°N and 40°S and along oceanic ridges or back arc basins or intra plate volcanoes roughly striking in a north-south direction which are separated from each other by 60 degree along longitude. The water depth of the hydrothermal activity fields varies from several meters to more than 5 000 meters, but mainly between 1 300～3 700 m with average water depth of (2 532) m. Statistic study shows that most of the hydrothermal fields occur at water depth around 2 600 m,and some others occur at (1 700 m)、1 900 m、2 200 m and 3 000 m. Hydrothermal activity occurs within 6 kinds of tectonic settings like axial valley on the spreading ridge, seafloor volcanic crater, spreading ridge without axial valley, continental rifting basin, triple junction ridge and sediment covered back arc basin. The first two tectonic settings are the most favorite tectonic environment to develop hydrothermal activity, and more than half of the total hydrothermal activity fields occur in the axial valley on the spreading ridge. The paper also points out that the hydrothermal activity mainly occurs in the area of active tectonic zone, but the active tectonic zone is not necessarily always the place where hydrothermal field occurred, i.e. the hydrothermal activity is not correlated directly with the tectonic activity, but the magma activity is. The development of the hydrothermal activity is controlled by and occurs after the magma activity,and it is the form of heat releasing of the magma activity