Abstract
Diving surveys were performed in the North Fiji Basin, Southwest Pacific, using deep-sea submersible Nautile and her mothership Nadir under the framework of the Japan-France Joint Research Project STARMER. Three diving sites were selected based on the results of previous cruises; two along the N15E central spreading axis of the basin and one at the triple junction of three rift axes. In the first diving site (16°59'S;173°55'E), an active white smoker which is called "White Lady" was found. It expels clear, low salinity, hydrothermal solution (T=285°C). We believe that the solution is the vapor condensate of boiled solution. The chimney mostly consists of anhydrite and is built on top of extinct sulfide chimneys which are composed of pyrite, marcasite, wurtzite, chalcopyrite, and covelline. Seepage of low temperature hydrothermal solution was also observed along the fault scarps of the central graben.
In the second site (16°58'S; 173°55'E), which locates about 1 km north of the previous one, huge hydrothermal area, more than 1 km long, of "dead" sulfide chimney forest was observed. This hydrothermal site could be the largest one in western Pacific area. Those chimneys are about 15 m in height, 5 m in bottom diameter and are composed mainly of dendritic aggregate of marcasite. The northeast rift system in the third site (16°45'S; 174°05'E) is suggested to be tectonically active. A cross section of oceanic crust was observed on a cliff face 1000 m in height.
