Origin and resource potential of hydrothermal H2 and CH4 degassing along the Xianshuihe strike-slip fault, eastern Tibetan Plateau: Insights from H2-H2O-CH4-CO2 isotope geochemistry

The exploration of natural H2 and CH4 in geothermal systems has gained attention due to their potential as low-carbon, high-temperature energy sources. These gases are commonly found in tectonically active regions, such as the Tibetan Plateau, but their origins remain poorly understood. This study investigates the hydrogeological and geochemical processes behind H2 and CH4 formation in the seismically active Xianshuihe Fault Zone (XSHF) on the eastern Tibetan Plateau, focusing on isotopic exchanges in the H2-H2O-CH4-CO2 system. We highlight the presence of H2 and CH4 in hydrothermal volatiles from continental orogenic belts lacking mafic or ultramafic rocks. Our findings show that: (1) H2 is primarily produced by the hydrolysis of silicate minerals on fault surfaces, driven by geothermal circulation in regions with strong seismicity; (2) CH4 forms from the thermal metamorphism of organic matter in sediments, not abiotic processes; (3) the Kangding Yulingong geothermal system hosts a thermal reservoir at 2 km depth, with a well (2006 m) directly penetrating the reservoir, a novel discovery. While large-scale gas reservoirs are limited, the study highlights the potential of geothermal H2 and CH4, contributing insights for exploring renewable energy in continental orogenic regions worldwide.