The deep-rooted serpentinite mud volcanism of the Mariana Forearc

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The applicant formulates two main research goals: determine the spatial and temporal variability in active mud volcanoes edifices of the Mariana forearc and integrate the datasets produced from the laboratory analyses with similar data from deep-seated mud volcanoes in mature accretionary complexes (Mediterranean, Japan). This comparison will allow to establish the function of mud volcanoes in different types of subduction zones and will shed new light on their role as direct windows into the subducting slab. The first part of this proposal is focusing on the Mariana convergent margin, northwestern Pacific Ocean, as an old, cold subduction zone hosting the largest mud volcanoes on earth. During IODP 366, three transects will be drilled on summits and flanks of three mud volcanoes with different dimensions, depths and located at increasing distances from the trench. Particular emphasis of the measurements at MARUM (University of Bremen) will be on determining the relationship between the mud matrix rheology and its mineralogy, by testing the serpentine mud with for uniaxial consolidation and determining its semi quantitative mineralogical composition with a specific attention on the clay fraction, probable responsible for the rheological differences. The applicant is also planning to explore the connection between feeder channel geometry and source of the mud volcanoes products by measuring viscosity, permeability and index properties of both clasts and mud matrix. These measurements will allow linking the mud volcanoes edifices with their deep origins through a preliminary geophysical characterization of the eruption mechanism. The second part consists in integrating the Mariana data with two other areas interested by mud volcanism, the Mediterranean Ridge and the Nankai trough. This is part of a bigger effort to understand the socalled subduction factory by exploiting the occurrence of mud volcanoes as a natural insight into deep processes. These three settings represent regions where the mud volcanoes are rooting in the upper plate or in the downgoing slab at different depths. The drilling campaign on the Mariana forearc is an effort comparable with the ODP 160, when two transect on just as many mud volcanoes of the Mediterranean Ridge accretionary complex were completed. The sediments from ODP 160 have been extensively analyzed with different techniques in the past and constitute the applicant starting point to base a comparative analysis. In addition to that, sediments from MARUM expeditions from both the Mediterranean Ridge and Nankai will be analyzed through most of the same measurements performed during the first part of this proposal to relate these three key areas (as substantially different in geometry) and examine how the rheological behavior of the mud volcanoes products is affecting the fluid and solid balance in subduction zones.