ABSTRACT

This two-year proposal focuses on seismological imaging of lower mantle heterogeneity beneath the Pacific Ocean, and numerical convection simulations to put the seismic imaging into a dynamically consistent framework. Our approach is multidisciplinary, and combines seismological analyses by PI Garnero with geodynamical convection simulations by PI McNamara. Recent seismological work has added great detail to deep mantle structure beneath the Pacific, with evidence for large low shear velocity provinces (LLSVPs) that are denser than and chemically distinct from the surrounding mantle. Smaller scale structure includes ultra-low velocity zones (ULVZs) that may preferentially reside at LLSVP margins. Our high resolution seismological experiments aim to better resolve sharp LLSVP edges that appear to extend well up off the core-mantle boundary (CMB), and associated phenomena that depend strongly on LLSVP and mantle properties, including: ULVZ location and structure, CMB topography in vicinity of LLSVP edge, strong heterogeneity within the LLSVP, and relationship to plume upwelling off the LLSVP top. We are focusing on seismic data from southwest Pacific subduction zones recorded in North American, since they densely sample the LLSVP beneath the Pacific Ocean, especially beneath Hawaii. This is a focus area of the proposed work. The seismic findings will inform and be informed by geodynamic simulations that include LLSVP structures. Particular attention will be given to LLSVP morphology and internal structure in the dynamical calculations, as these features will be seismically imaged. Better imaging and modeling LLSVPs will help move us forward in understanding Earth's thermal and mass transport mechanisms, and hence the driving forces in convection that shape the deep structures. Better understanding the nature of convective flow in Earth's deep mantle, how that flow shapes plausible deep and dense compositional reservoirs, and return flow mass transfer that includes plumes is an underlying motivation in this work.

This work is important for understanding the structure and dynamics of Earth's deep interior. The nature of convective flow in Earth?s deep mantle, how that flow shapes plausible deep and dense compositional reservoirs, and return flow mass transfer that includes plumes is of interest to the vast spectrum of Earth and planetary scientists. The funding is for a geodynamics graduate student who will be trained on an interdisciplinary research project, and a postdoctoral researcher focused on seismic imaging and geodynamics computations. The PIs are experienced at co-mentoring students and postdocs in a cross-disciplinary fashion.

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