CAREER: High-resolution Simulations of Subduction Along the Pacific Rim of Fire

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The theory of plate tectonics predicts the outer layer of the Earth, the lithosphere, is composed of rigid tectonic plates (approximately 100 km thick). These plates are in motion with respect to one another, moving at speeds on the order of 1-20 cm/yr. The interaction of the tectonic plates is characterized by convergent, divergent, and shearing motion, with the majority of deformation (earthquakes, volcanism, and mountain building) concentrated at the plate boundaries. Subduction zones are convergent plate boundaries where the denser oceanic plates bend downward, leaving the Earth’s surface, and descend into the underlying mantle. The majority of the Earth’s subduction zones occur along the Pacific Rim of Fire and are characterized by large-scale earthquake activity where plates slide past one another and by arc volcanoes in the upper plate due to fluids released by the subducting slab as it descends into the mantle. This proposal leverages data-driven model design, high performance computing, and three-dimensional (3D) virtual reality to construct high-resolution 3D models of the Pacific Rim of Fire. The geodynamic models of the Pacific Rim of Fire will investigate a new class of volcanoes that occur at the edges of subduction zones, rather than typical arc volcanoes located above the subducted plate. In addition, the geodynamic models will examine slab-driven mantle flow, addressing outstanding questions of coupling between the tectonic plates and the mantle. In terms of broader impacts, the PI will collaborate with the Space Visualization Lab at the Adler Planetarium in Chicago, IL to develop 3D visualizations of subduction along the Pacific Rim of Fire. These visualizations will enable data exploration as people can tour the plate tectonic boundaries through a series of virtual voyages through the Earth. Furthermore, the subduction zones that flank the Pacific Ocean form major tectonic hazards affecting over 20 countries, including major populations centers, making the high-resolution simulations of this region likely to have a large societal impact. A graduate student and undergraduate students will be trained and actively involved in this research.Subduction at convergent plate margins, characterized by descending oceanic lithosphere and subparallel tracts of oceanic trenches and arc volcanoes, has commonly been distilled into a two-dimensional (2D) paradigm. However, modern subduction systems contain discontinuous slabs that are not infinitely long and over half of the slabs intersect or interact directly with another slab, invalidating the 2D subduction approximation. Furthermore, although arc volcanoes do track subducted slabs at depth in most subduction zones, anomalous volcanoes also systematically occur, not above a slab, but distal to the slab edge forming a pattern not explained by the 2D subduction paradigm. In addition, rock deformation experiments indicate that much of the upper mantle is governed by nonlinear rheology, indicating slab-driven flow at intersecting slabs is not a linear combination of variations on the 2D Newtonian framework. The proposed research will build comprehensive 3D geodynamic models of the entire Pacific Rim of Fire that will allow for systematic comparative analysis of natural subduction zones and move the field into a 3D framework of subduction, rather than the 2D paradigm that has governed the broader research community and undergraduate textbooks. Specifically, the numerical simulations will test two hypotheses. The first hypothesis is that slab edge driven mantle upwelling is a common phenomenon, constrained geometrically by the three-dimensional subduction geometry and physically by the constraints on the motion of density anomalies due to conservation of mass and momentum of viscous flow in the asthenosphere. The second hypothesis is that the shear thinning effects of the dislocation creep deformation mechanism of olivine constrains the lateral extent of non-plate motion aligned shear wave splitting in observed subduction zones, by allowing the localized upper mantle near the subduction zone to decouple from the larger-scale mantle circulation patterns. A data-driven 3D model of the Pacific Rim of Fire will provide the ideal system to constrain these phenomena, because a geographically referenced model can spatially link upwellings in the asthenosphere to specific observed locations of anomalous volcanics along the Pacific Rim of Fire, as well as predict the extent of nonlinear mantle flow which can be directly compared to shear wave splitting observations from the region.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.