Implications of Variable Plate Coupling Versus Plateau Buoyancy on Subduction Dynamics: A Case Study of the Yakutat Plateau in Alaska

The eastern Alaska subduction zone is characterized by flat slab subduction of young lithosphere (30–40 Ma) and subduction-collision of the Yakutat plateau. However, the relative effect of the geometry of the flat slab versus the positive buoyancy of the Yakutat plateau on plate deformation is not well understood. This chapter presents three-dimensional numerical simulations to investigate the effect of thermal buoyancy of the flat slab, subduction interface coupling, and compositional buoyancy of the Yakutat plateau on plate deformation. A tectonic characterization of the Yakutat plateau is presented, based on the synthesis of >20 geologic/geophysical datasets. Analytic calculations examine the thermal versus compositional lithosphere thickness and buoyancy. The 3D numerical simulations implement a simplified plateau anomaly derived from the data synthesis and analytic calculations, and increase coupling at the flat slab, requiring 25,000–48,000 compute hours per simulation. Models with the localized increase in plate coupling and plateau buoyancy provide the best fit to geodetic observations and geologic constraints of uplift and subsidence, but also result in a reduction of downgoing plate speed. The models demonstrate the Yakutat plateau is critical to explain upper-plate deformation in south-central Alaska and imply that localized oceanic plateau subduction can have a significant impact on plate motions.