EAS Seminar Series-Samer Naif

Description

Long-lived mantle melts trapped at the base of the Cocos plate

Abstract:

Nearly sixty years ago, the discovery of plate tectonics revolutionized our understanding of the thermomechanical structure of Earth’s interior: the lithosphere forms the rigid outer shell of Earth’s surface that comprises several tectonic plates, which move with respect to one another over a ductile (i.e., low viscosity) asthenosphere. Yet debate persists today on the mechanism that is responsible for this viscosity reduction. In this presentation, we will tour the eastern equatorial Pacific seafloor and explore the structure of the lithosphere-asthenosphere boundary at a regional scale. A little over a decade ago, a magnetotelluric geophysical survey discovered a thin electrically conductive channel at the base of the Cocos oceanic plate.

The channel was interpreted to be caused by partially molten silicate rock that may be responsible for lubricating plate motions. Competing hypotheses have since been proposed to explain the electrical anomaly. To resolve which hypothesis is most likely, I revisit the original study and implement two distinct multidisciplinary approaches: 1) thermodynamically coupled Bayesian inversion of the electromagnetic data, and 2) integrating geophysical, geochemical, and drilling observations of the Cocos seafloor. This culminates in a 20-million-year saga of the Cocos plate, rife with past episodes of intraplate magmatism and the involvement of the Galápagos plume. The results reiterate the presence of a partial melt channel and elucidate both its origin and composition.