East Pacific Rise 13 ¡ã N Near The Sediment Geochronology Study

The samples in the paper were obtained from E271 and E272 site near the East Pacific Rise13°N during the first Chinese hydrothermal sulfide investigation cruise in 2003. The study on the grain-size, mineralogy and chronology of sediment from the East Pacific Rise13°N has been finished, the results show: 1. The sediments are divided into two layers, the upper layer is brown, the under layer is yellow. 2. The minerals in E271 upper layer are Rock salt, Anorthite, Quartz, Illite, Kaolinite, Gypsum and many amorphous materials. The minerals in under layer is Rock salt, Anorthite, Quartz, Talc, Kaolinite and many amorphous materials. The minerals in E272 upper layer are Rock salt, Anorthite, Quartz, Talc, Kaolinite, and many amorphous materials. Compared to the sample from E271 station, no Gypsum in upper layer from E272 station. 3.The contents of U in the two sites are 1-3ppm and between the crust(4ppm) and oceanic crust(1ppm); the contents of Th (2.5-4.5ppm)are higer than that of U and between oceanic crust (4ppm) and upper mantle(0.75ppm). 4. In E271 station, The sedimentation rate of the upper layer (0-36.5cm) is 1.307cm/ka, the age of this segment is 27.9ka; the under layer (36.5-45.5cm) is 0.204cm/ka, the sedimentation time is 44.1ka. The form age of E271 is 72.0ka. The sedimentary environment of E271 site is stable, the sedimentation rate of the E272(0-44.5) is 1.02cm/ka, the sedimentation time is 43.6ka. 5. According to the Spreading rate of the Ridge, there were 21.4km distance between the rise and the E271 site on 27.9ka. Lalou(1985)had studied the ages of the sulphide, and considered that the hydrothermal activities of southeastern seamount occurred at 20.0ka. The formed age of E271 upper layer is closed to the beginning age of hydrothermal activities. In future study, we will find the evidence of the hydrothermal activities and understand its evolution of the time and space.