Fluctuation of chemical compositions of the phase-separated hydrothermal fluid from the North Fiji Basin Ridge

On the central ridge of the North Fiji Basin (southwest Pacific), hydrothermal activities were located in 1989. It was the second discovery of the hydrothermal fluid undergo phase separation. During a dive mission of Shinkai 6500 in 1991, we revisited the hydrothermal area and collected fluid samples from the same anhydrite chimney. Fluid composition of the end member shows no significant changes during this two years. Other fluid ventings 150 m apart show similar chemistry, suggesting that the phase separation and segregation processes occur throughout the hydrothermal area. Small fluctuation in chemical composition of the fluids from two sites is attributed to subseafloor fluid-rock interaction after the phase segregation.