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ArticleDeep high-temperature hydrothermal circulation in a detachment faulting system on the ultra-slow spreading ridge(Nature Research, 2020-03-10) Tao, Chunhui ; Seyfried, William E. ; Lowell, Robert P. ; Liu, Yunlong ; Liang, Jin ; Guo, Zhikui ; Ding, Kang ; Zhang, Huatian ; Liu, Jia ; Qiu, Lei ; Egorov, Igor ; Liao, Shili ; Zhao, Minghui ; Zhou, JianPing ; Deng, Xianming ; Li, Huaiming ; Wang, Hanchuang ; Cai, Wei ; Zhang, Guoyin ; Zhou, Hongwei ; Lin, Jian ; Li, WeiCoupled magmatic and tectonic activity plays an important role in high-temperature hydrothermal circulation at mid-ocean ridges. The circulation patterns for such systems have been elucidated by microearthquakes and geochemical data over a broad spectrum of spreading rates, but such data have not been generally available for ultra-slow spreading ridges. Here we report new geophysical and fluid geochemical data for high-temperature active hydrothermal venting at Dragon Horn area (49.7°E) on the Southwest Indian Ridge. Twin detachment faults penetrating to the depth of 13 ± 2 km below the seafloor were identified based on the microearthquakes. The geochemical composition of the hydrothermal fluids suggests a long reaction path involving both mafic and ultramafic lithologies. Combined with numerical simulations, our results demonstrate that these hydrothermal fluids could circulate ~ 6 km deeper than the Moho boundary and to much greater depths than those at Trans-Atlantic Geotraverse and Logachev-1 hydrothermal fields on the Mid-Atlantic Ridge.