Discovery of Extensive Hydrothermal Fields in the Wallis and Futuna Back-Arc Environment (SW Pacific)

The EEZ of Wallis and Futuna is located west of the collision zone between the Pacific plate and the Australian plate. In this area, at the north of the Tonga Trench, the fastest plate movement in the world is recorded (24 cm / year). An area of 350x250 km has been explored between 2010 and 2013. Of the 52 200 km(2) mapped, almost 60% consist of recent volcanism occurring as ridges (Western part) and volcanoes (Eastern part). This area, volcanically and tectonically complex, occurs between the northern end of the Tonga trench and the regional north Fiji transform fault. Lavas are basalt, andesite, dacite and some rhyolite. Ten hydrothermal fields have been discovered. Three fields are active (T degrees up to 345 degrees C) and associated with sulfide mineralization. Some fields comprises several hundreds of individual deposits with sizes varying between 10 m and 150 m in diameter. Hydrothermal deposits are of four types: Mnoxides, Fe-Si, Si-Ba, and massive sulfides. Sulfides are generally enriched in Cu, Zn, Au and Ag compared to mid ocean ridge deposit associated with basaltic rocks. Due to the number of hydrothermal sites, this unusual area of extensive hydrothermal activity is for the moment incompletely sampled by submersible.