Huaiming Li1 *, Chunhui Tao1, Shili Liao1, Jin Liang1, Weifang Yang2
1 Second Institute of Oceanography, State Oceanic Administration, 310012, Hangzhou, China
2 School of Earth Sciences, Zhejiang University, 310010, Hangzhou, China
Longqi (also named by Dragon Flag) hydrothermal field, regarded as the first active hydrothermal field at the ultraslow spreading ridge, is situated at the southern abyssal hills of the segment 28, the Southwest Indian Ridge (SWIR) between the Indomed (46°E) and Gallieini (53°E) transform faults. The giant, isolated sulfides smokers both active and inactive are distributed along an orientation of about North-South. The active "black smokers" issuing intense, high-temperature fluids are mostly located at the southern area, while the inactive sulfide smokers are found at the northern area. The fresh pillow lava with thin pelagic sediment are observed at the Longqi. However, varity of hydrothermal altered rocks, like altered basalt, serpentinite, and serpentinized peridotite, were found in the area with about 2 km×3 km adjacent to the Longqi field. The Longqi hydrothermal system shows some key characteristics similar to the TAG hydrothermal system at 26°N, the Mid-Atlantic Ridge. We believed that the detachment fault is the main factors controlling the Longqi hydrothermal circulation, which provide hydrothermal fluid with the upflowing pathway. Gabbro intrusion under the detachment fault probably is the heat source. The deposit morphology is mostly controlled by rock type and porosity distribution of the substrate.
