9J (2025-2026): Collaborative Research: Quantifying melt in the mantle and controls on lithosphere-asthenosphere dynamics and intraplate magmati

• whoi.edu

This project will utilize passive-source seismic and magnetotelluric imaging to quantify the seismic velocity and electrical resistivity structure of the Cocos Plate lithosphere and asthenosphere. A co-located array of ocean-bottom seismic and electromagnetic receivers will be deployed over a 500 km by 500 km section of the Cocos Plate on both sides of the Nicaragua Fracture Zone (NFZ). The seafloor in the survey area shows abundant evidence of past intraplate magmatism, including elevated seafloor bathymetry, numerous seamounts significantly younger than the plate age, and prominent volcanic sills within the sediment column. The presence of a partial melt channel at the lithosphere-asthenosphere boundary is clearly imaged by a previous small-scale magnetotelluric profile. Observations from this study will provide new insights on the dominant controls on asthenosphere rheology and the mechanisms that produce intraplate magmatism by addressing the following key questions: (1) What is the spatial and depth extent of the high-melt region? Does the bathymetry contrast across the NFZ reflect a change in melt content and/or volcanic productivity? (2) What is the seismic signature of the previously inferred melt-rich channel? Are seismic observations consistent with magnetotelluric results and how can they be calibrated to each other? Given this calibration between melt content and velocity, what does it imply for the weakening mechanisms in the asthenosphere globally? (3) Does the mantle fabric change across the NFZ, both within and below the lithosphere? Does the implied flow field suggest a Galápagos plume influence on past seafloor spreading, and/or recent melt productivity beneath the plate?

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