Collaborative Research: The influence of incoming plate structure and fluids on arc melt generation at the Lesser Antilles subduction system

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Subduction zones, where one tectonic plate is pushed beneath another, are known areas of abundant volcanic and seismic hazard. The Antilles islands are the result of such volcanic activity at a subduction zone. As the Atlantic seafloor is pushed down into the earth, it sinks, carrying with it a large, but unknown volume of water that is released, either squeezed from cracks, or lost from minerals as they heat up in the warmer interior of the earth. Released fluids play a role in controlling earthquake generation and enhancing the process of magma generation, with the magma formed moving upwards and feeding the volcanoes that create the islands. This project will use electromagnetic methods to image the Antilles subduction system. These data will be used to identify areas of high fluid content including both water and magma in the oceanic plate that is subducting beneath the Antilles. Broader impacts include international collaborations with Germany and France and support for early career researchers graduate students, and undergraduates. Students from the University of Puerto Rico will participate in the field programs. The Antilles is viewed as an end-member system with subduction of oceanic crust formed at the slow spreading Mid-Atlantic Ridge expected to carry large volumes of water bound within serpentinized upper-mantle. Seismic imaging of the incoming plate shows a high degree of structural variability that suggests that high fluxes of fluids into the mantle wedge will be localized. This project will link these localized areas of high fluid flux to the generation of melts that feed the volcanic arc. Electromagnetic (EM) methods are ideal for characterizing the transport of fluids into a subduction system and the subsequent release of those fluids into the overlying decollement and mantle wedge. EM methods broadly fall into two categories: the passive magnetotelluric (MT) method, which uses naturally occurring signals to look to great depth (up to 200 km or more); and controlled source electromagnetic (CSEM) sounding, in which a transmitter is towed behind a ship and generates an artificial EM signal that is recorded by an array of seafloor instruments. CSEM is useful for quantifying fluids in the crust and uppermost mantle. This project will acquire a MT/CSEM survey across the Antilles subduction system that will test the hypothesis that higher fluid contents stored in the incoming plate results in a substantial water flux into the forearc crust and arc mantle wedge above the downgoing slab. Variations in fluid input along strike will be manifested as variations in mantle conductivity, with regions of high flux being substantially more conductive as a result of the larger volume of fluids released and hydrous melts generated. The field program will consist of two research cruises and land acquisition.This project is supported by the Marine Geology and Geophysics program in the Division of Ocean Sciences and the Geophysics program in the Division of Earth Sciences.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.