Deep-seated fluid flow processes, seismic faulting and mud volcanisms in a mature collision zone; The backstop to the Mediterranean Ridge accretionary prism

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Convergent plate margins are important locations of mass transfer processes and tectonic activity. However, the so-called subduction factory has rarely been studied by scientific ocean drilling. It comprises (i) the small loop (where frontal accretionary prism is characterised by mostly dewatering), the intermediate loop several tens to hundreds of kilometres behind the toe (where out-of-sequence-faults and other pathways funnel deep-seated material to the ocean), and (iii) the big loop (where material is either recycled in the mantle, or emitted along the volcanic arc). The intermediate loop has never been drilled by DSDP, ODP or lODP, and only active proposal 555-full3 addresses this area in the Hellenic Subduction Zone (HSZ), Eastern Mediterranean. Three major faults south of Crete, all superbly imaged geophysically and one juxtaposed by an active mud volcano, provide evidence for fluid (and mud) ascent from several km depth in the backstop to the accretionary prism. To assist this 4* proposal in SPC ranking and OTF scheduling, and to test a number of critical hypothesis in subduction factory research linking hydrology and tectonics, we propose: - to carry out a research cruise (RV Poseidon) to deploy flow meters, take gravity cores and collect in situ pore pressure data at the proposed drill sites, - to use existing geotechnical as well geochemical data plus those collected during the cruise and from the fluxmeters to numerically model fluid flow at the boundary between the accretionary complex and its hinterland (i.e. the intermediate loop ofthe subduction factory between Eurasia and Africa), and - to relate physico-chemical processes along the active faults to be penetrated to the geochemical findings from hydrothermal experimenls and long-term deployments.