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Jadamec, M.A., 2009

Three-dimensional lithosphere and mantle dynamics: Models of the subduction-transform plate boundary system in southern Alaska

Bibliographic Reference

Jadamec, M.A., 2009, Three-dimensional lithosphere and mantle dynamics: Models of the subduction-transform plate boundary system in southern Alaska: University of California, Davis, Ph.D. dissertation, 165 p.


The theory of plate tectonics states that the outermost part of the Earth, the lithosphere, is composed of plates that are in motion with respect to one another and that the majority of the deformation associated with this motion is concentrated along the plate boundaries. Numerous studies have examined the dynamics that govern plate boundary deformation in two dimensions (2D). To add to this understanding, 2D analytic models are constructed that quantify the relative role between erosion and gravitational collapse in the decay of topography associated with mountain building. A non-dimensional collapse number is calculated that reduces the problem to two parameters, the erosion coefficient and the viscosity. Very few studies have modeled a regional plate boundary in three dimensions (3D). To better understand the 3D dynamics of plate boundaries, 3D numerical models of the subduction-transform plate boundary in southern Alaska are constructed, and are the first 3D models of their kind to incorporate a subducting plate and overriding plate, use a non-linear rheology and allow the slab to drive the flow without applying a kinematic boundary condition. These are also the first regional models that provide a self-consistent mantle flow-field and seismic anisotropy comparison, as these both require the dislocation creep to be the dominant mechanism. The models suggest the strain-rate-dependent rheology provides a mechanism to partially decouple the mantle flow field from the overriding lithosphere. In the weakened region around the slab, mantle velocities may be a factor or ten times faster than observed plate motions. Model results suggest that, in Alaska, the Wrangell slab likely does not extend below 150 km, and that the Cook Inlet basin is generated in part from the downward pull from the subducting Pacific plate. We develop methodology to incorporates an arbitrarily shaped 3D thin viscous layer, referred to as a plate boundary shear zone, into the existing open source mantle convection code, CitcomCU. Solver parameters are optimized to obtain up to a 30% to speed up in run time for models that use a strain-rate-dependent rheology. 3D immersive visualization is used in model construction and analysis.

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