EAR-PF Discerning the nature of the oceanic lithosphere-asthenosphere boundary through integration of seismological-scale and laboratory-scale observations

Dr. Joshua Russell has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education activities under the mentorship of Dr. Colleen Dalton at Brown University.

Plate tectonics describes the motion of Earth’s rigid plates (the lithosphere) that overlie the actively convecting asthenosphere, providing a comprehensive framework for understanding the dynamics and evolution of the planet. The ocean basins comprise approximately 70% of Earth’s surface and, due to their geologic simplicity, provide a clear window into plate tectonic processes.

Yet, fundamental aspects of plate tectonics remain poorly understood, such as the chemical and physical characteristics that define the base of the plate and how they vary with plate age. This project aims to reconcile competing hypotheses for the origin and evolution of the oceanic lithosphere-asthenosphere boundary (LAB) by integrating high-resolution seismic imaging of the mantle beneath the Pacific Ocean with recent experimental constraints on the physical properties of olivine, the most abundant mineral in Earth’s mantle.

The education plan consists of 1) developing and delivering an Earth science lesson plan to local elementary school classrooms, 2) mentoring an undergraduate student through a summer research project, and 3) organizing a reading seminar at Brown University on plate tectonics and the LAB.

Recent proliferation of ocean-bottom seismometer (OBS) arrays in the Pacific offers an unprecedented opportunity to characterize the large-scale elastic, anelastic, and anisotropic structure of the upper mantle in detail. This project will utilize surface-wave data from five OBS arrays in the Pacific, ranging in seafloor age from ~6 Ma to ~120 Ma, to develop models of shear velocity, shear attenuation, and seismic anisotropy at each site.

A new technique will be developed for recovering velocity structure in the presence of Love-wave overtone interference that will reconcile conflicting models of radial anisotropy. Seismic observations of shear velocity and attenuation at each site will be directly compared with corresponding laboratory predictions via a newly developed Bayesian framework to yield estimates of mantle temperature, grain size, and melt fraction and their age dependence in the oceanic upper mantle.

This project represents a first effort to integrate seismological-scale and laboratory-scale constraints on mantle anelasticity across several high-resolution OBS arrays in the Pacific basin. In addition to illuminating the mechanism(s) controlling the LAB and its hypothesized age dependence, this work will provide new constraints on the thermodynamic state of the oceanic upper mantle that is key for understanding broader planetary evolution. This fellowship received partial funding from the Geophysics program in the Earth Science division.

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.