Spatial variation of subduction zone fluids during progressive subduction: Insights from Serpentinite Mud Volcanoes

Geological processes at subduction zones control seismicity, plutonism and volcanism, geochemical cycling between the oceans, crust, mantle. The down-going plate experiences metamorphism, associated dehydration fluid flow alters physical properties of interface mantle wedge, as well controlling composition material descending into Any direct study slab evolution during is inhibited by prohibitive depths which these occur. To examine we use serpentinite mud volcanoes in Mariana forearc, that permit sampling materials their pore waters ascend from channel. We present new water chemical data summit flanks three were drilled International Ocean Discovery Program Expedition 366 are reflective reactions within crust early, shallow (<20 km) stages subduction. show, via thermodynamic modelling, our on compositions reflect mineralogical characteristics a predominately basaltic source downgoing Pacific Plate. However, component sedimentary sources likely, especially for those near trench. Other potential slab-derived constituents, such lithospheric serpentinite, carbonate-rich sediments, or seamount basalts with an intraplate character, not required to explain results. Our results indicate progressive lawsonite-epidote mineral transformation boundary ∼250 °C may help drive carbonate destabilisation, despite its apparent stability temperatures projected pressures (∼300 ∼0.6 GPa). New dissolved gas also point primary controls over methane/ethane production channel depths-to-slab increase. findings provide evidence subducting oceanic plate, liberates progressively evolving phase