Sustainable thermogenic CH4 and H2 generation in the Nankai Trough subduction zone

Abstract Mud volcanoes, gas plumes, and gas hydrates comprising thermogenic and biogenic CH 4 are widely distributed in the Nankai Trough subduction zone, showing ongoing significant CH 4 activity. However, the source rocks of the thermogenic CH 4 and the geological source of H 2 for microbial CH 4 production remain uncertain. Here, we reveal the timing and amount of the thermogenic CH 4 and H 2 generation in shales and metapelites during diagenesis to metamorphism and estimate their current generation in the Nankai Trough from the movements of the oceanic plate and the accretionary prisms. The results show that the thermogenic CH 4 and H 2 are generated mainly in the underthrust sediments below the décollement. The sustainable H 2 supply from the underthrust sediments can be another potential H 2 contributing to microbial CH 4 production. The findings enhance our understanding of the active CH 4 emission, large-scale gas hydrate formation, and subseafloor biosphere in the oceanic plate subduction zone.