A large intraplate hydrogen-rich hydrothermal system driven by serpentinization in the western Pacific: Kunlun.

The Kunlun hydrothermal system near the Mussau Trench in the western Pacific consists of 20 large round/oval craters of hundreds of meters in diameter. The total area is 11.1 square kilometers, i.e., over a hundred times larger than the Lost City. Four of the larger craters were prospected using the human occupied vehicle Fendouzhe and have steep walls similar to those of kimberlite pipes, with depths of up to 130 meters. Ecosystems have been observed in smaller pits on the bottom of these pipes. Hydrogen concentrations of ~5.9 to 6.8 millimoles per kilogram in hydrothermal fluids have been obtained using in situ Raman spectra. The estimated total hydrogen flux of Kunlun is 4.8 × 10 moles per year, which is >5% of the estimated global submarine abiotic hydrogen flux. Hydrogen-rich, alkaline fluids generated by serpentinization have formed large-scale carbonate rocks within the pipes below the carbonate compensation depth, and both dolomite and calcite have been identified.