Collaborative Research: Characterization of Subduction Channel Processes - Borehole Sampling at Active Serpentinite Mud Volcanoes on the Mariana Forearc

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The Mariana Trench is the deepest location on Earth, resulting from the subduction of the Pacific Plate under the Philippine Plate. Fluids that were trapped in the pores and minerals of the Pacific Plate are liberated during this subduction. These fluids react with rock in the overriding Philippine Plate to produce a slurry of mud and fluids that are very alkaline (with a pH up to 12.5, more alkaline than Clorox), yet support microbial life that thrives in such extreme environments. The discharge produces the largest mud volcanoes on Earth, some spanning 50 km in diameter and several kilometers in height. Probing the mud volcanoes by sampling fluids from boreholes drilling into them, provides the means to examine processes that occur at depth during subduction. The subduction zone environment is the epicenter for most large earthquakes on Earth, and the fluids that flow through subduction zones can be connected with that earthquake generation. Moreover, the reactions that occur to produce the fluids provide energy that can support a wide variety of microbes, a subseafloor biosphere that is present throughout what has been referred to broadly as a "deep crustal aquifer".The research team proposes to the sample fluids and dissolved gases from this ascending slurry in three mud volcanoes that tap different pressure (depths ranging from 10 to 20 km) and temperature conditions at depth. These ascending fluids discharge from scientific boreholes that were emplaced during International Ocean Discovery Program (IODP) Expedition 366. Prior to sampling these fluids, CORK-Lite instruments will be deployed to enable sampling operations. This infrastructure will also provide for a range of potential experimentation and monitoring efforts that can be used in the future. Specifically, the project will: (i) design, fabricate, and deploy CORK-Lites, (ii) sample discharging fluids with gas-tight and large volume sampling systems, (iii) analyze collected fluids for a range of solutes, dissolved gases, and isotopes, and (iv) measure borehole pressure and fluid discharge rates. The CORK-Lites will be sealed at the end of the field program for future experimentation and monitoring efforts. Results from this effort will test a model of abiotic methane formation, constrain the extent of serpentinization during the initial stages of subduction, set limits on potential microbial metabolic capabilities, and resolve water-rock reactions and solute sources.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.