Abstract
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.
Highlights
Coupled magmatic and tectonic activity plays an important role in high-temperature hydrothermal circulation at mid-ocean ridges
A concerted effort was undertaken to track the pathway of hydrothermal circulation using a twodimensional (2D) numerical model of circulation in a NaCl-H2O fluid system to verify whether the hydrothermal fluids derived from the depth could circulate up to the seafloor and vent at the observed high temperatures
Our results show that the hydrothermal circulation below the Longqi-1 field is associated with a detachment system penetrating to the depth of 13 ± 2 km below the seafloor, and the hydrothermal fluids could circulate ~6 km deeper than the Moho boundary that is much deeper than those at TransAtlantic Geotraverse (TAG) and Logachev-1 hydrothermal fields on the Mid-Atlantic Ridge (MAR)
Summary
Coupled magmatic and tectonic activity plays an important role in high-temperature hydrothermal circulation at mid-ocean ridges. The chlorine-excess in melt inclusions hosted by basaltic rocks in the South Mid-Atlantic Ridge (MAR) and Gakkel Ridge offers further geochemical clues that hydrothermal alteration reaches lower crustal depths[11] Despite these observations, the origin and depth of the hydrothermal fluids in active high-temperature vent fields at the ultra-slow spreading ridge has not, until now, be investigated in any detail. The Longqi-1 hydrothermal vent field (~49.7°E) in the Dragon Horn region (Fig. 1) of the ultra-slow spreading Southwest Indian Ridge (SWIR) exhibits high-temperature hydrothermal vents associated with a major detachment fault system and has been the subject of recent intensive studies[12], providing an opportunity to examine this problem. Our results show that the hydrothermal circulation below the Longqi-1 field is associated with a detachment system penetrating to the depth of 13 ± 2 km below the seafloor, and the hydrothermal fluids could circulate ~6 km deeper than the Moho boundary that is much deeper than those at TAG and Logachev-1 hydrothermal fields on the MAR
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