Geochemical cycling, tectonic drivers and environmental impacts of CH4-rich mud extrusions in subduction zones

• Role of subduction-related geochemical and tectonic mechanisms in driving CH 4 -rich mud extrusions. • A novel evolution model of CH 4 -rich mud extrusions detailing pre-, syn-, and post-thermogenic geological processes. • Thermogenic CH 4 and clay-rich muds sourced from under-thrusted sediments. • Wedge-top overburden pressure facilitates CH 4 -rich mud migration. • CH 4 -rich mud extrusions significantly influenced global CH 4 emissions and marine ecosystems. Subduction zones are critical interfaces for lithospheric volatile fluxes, where complex tectonic and geochemical interactions facilitate the release of gases and fluids from deep-seated reservoirs within the Earth’s crust. Mud volcanism, as a dynamic manifestation of these processes, contributes CH 4 emissions that influence the global methane budget and impact marine ecosystems. Although ∼2000 CH 4 -rich mud extrusions have been documented in subduction zones globally, the geological origins and subduction-related geochemical and tectonic mechanisms driving these emissions remain poorly understood. This research examines the Makran subduction zone which hosts one of the world’s largest accretionary wedge and extensive CH 4 -rich mud extrusions, as a model system. Integrated geochemical, geophysical, and geological observations reveal that thermogenic CH 4 and clay-rich fluidized muds originate from deeply buried Himalayan turbidites (underthrusted sediments), driven by organic-rich sediment maturation and high fluid overpressure. Key tectonic features, including thrust faults, overburden pressure of wedge-top sediments, normal faults, brittle fractures, and seismicity, facilitate CH 4 -rich mud extrusions into the hydrosphere and atmosphere. The extruded gases are predominantly CH 4 , with minor C 2 H 6 , C 3 H 8 , i-C 4 H 10 , and n -C 4 H 10 while the mud breccia exhibits a chemical composition dominated by SiO 2 , Al 2 O 3 , and Fe 2 O 3 , enriched with trace elements (Rb, Zr, and V) and clay minerals, quartz, and carbonates. Geochemical indicators suggest intense chemical weathering and mature sediments classifying the mud breccia as litharenite and sub-litharenite, indicative of deep burial and compaction. These findings model the evolution of CH 4 -rich mud extrusions through three geological stages: (i) Eocene to Early Miocene pre-thermogenic formation of the CH 4 -rich source, (ii) Middle Miocene to Pliocene syn-thermogenic CH 4 and fluidized mud generation, and (iii) Pleistocene to Recent post-thermogenic CH 4 -rich fluidized mud migration. These findings underscore the critical yet often overlooked role of subduction-related geochemical and tectonic processes in CH 4 generation and emission, with significant implications for the global CH 4 budget and marine ecosystems.