ABSTRACT

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

The thin, rocky shell of the Earth, the lithosphere, is broken into a mosaic of thin plates that are inconstant motion. Along some boundaries between plates, one slides beneath the other and is consumed in a process known as subduction. Most of great earthquakes and violent volcanic eruptions occur at subduction zones. Both of these processes are significantly affected by the amount of water that is carried into the interior with the downgoing plate, but these processes remain poorly understood because the amount of water entering the subduction system remains poorly constrained. A major carrier of water is the mineral serpentine, and one of the major uncertainties is the volume of water that is being carried into the subduction system by serpentinized upper mantle. Electromagnetic geophysical methods are sensitive to the presence and concentration of water at depth in the Earth. This project consists of a large-scale electromagnetic experiment along a 300 km profile off Nicaragua in a region that shows evidence for substantial fault related fluid circulation in the crust and possibly in the upper mantle, and high Ba/La ratios and water contents in adjacent onshore volcanics suggesting a strong slab fluid input into the arc-melting. This survey will combine controlled-source electromagnetics (CSEM) with broadband and long period magnetotellurics (MT) to provide a comprehensive picture of the conductivity structure from the seafloor to the upper mantle, representing the entire input into this part of the Central American subduction zone. In addition to the societal relevance of improving our understanding of processes that produce earthquakes and volcanic eruptions, this project will promote international scientific cooperation and support two Ph.D. students.

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