A seafloor gravity profile across the TAG hydrothermal mound

A series of on-bottom gravity stations were completed across the TAG hydrothermal mound during a dive program with the Japanese Shinkai 6500 submersible. The mound appears as a gravity high (similar to 2 mGal) with respect to the surrounding seafloor, reflecting the high density sulfides of which it is comprised. Three-dimensional modeling of the data shows no evidence of a dense sulfide root extending deep into the seafloor below the mound, which would be associated with a broad, highly altered, stockwork zone. Sulfide thickness appears to be greatest (similar to 50m) to the north of the mound. The thickness decreases sharply to the south, reaching a steady value of about 10m just to the south of the Kremlin area. The mass of sulfides within the mound is estimated at 3 million tonnes. The surrounding basaltic seafloor appears to have a density of 2400 +/-100 kgm(-3), indicating a surficial porosity of between 20-30%.