Coupled 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.
Bibliographical noteFunding Information:
We thank Science Party, captains and crew of COMRA Cruise DY35th, DY40th, and DY43th, the submersible Jiaolong group and the 4500 m Qianlong-II Autonomous Underwater Vehicle team. We thank Lars H Rüpke and Jörg Hasenclever for the numerical modeling code and Fernando J.A.S. Barriga, Maurice A. Tivey, and Honglei Shen for polishing English. We thank F. van der Zwan for her fruitful comments. This work was supported by National Key R&D Program of China under contract no. 2018YFC0309901, 2017YFC0306603, 2017YFC0306803, and 2017YFC0306203, COMRA Major Project under contract No. DY135-S1-01-01 and No. DY135-S1-01-06. All the coauthors give their deep appreciation to R.P. Lowell, who passed away during the revision of this work. His contributions to this paper, however, were seminal, in the absence of which key findings and implications of the study would not have been possible.
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