Depth-varying azimuthal anisotropy and mantle flow in the Patagonian slab window
DOI:
https://doi.org/10.26443/seismica.v4i2.1670Abstract
Subduction of spreading ridges forms slab windows which perturb the local structure and dynamics of the upper mantle. Slab windows may alter the pattern of mantle flow and serve as portals for the exchange of mantle material between upper mantle reservoirs that are otherwise separated by the boundary of the subducting slab. Here, we use Rayleigh waves to derive an azimuthally anisotropic regional seismic velocity model for the Patagonian slab window and use the anisotropy model to infer patterns of upper mantle flow and deformation. Anisotropic fast directions are primarily trench-parallel in the upper ~40 km of the mantle throughout the region, likely reflecting the history of subduction and compression along the South American margin. At greater depths sensed by long-period Rayleigh waves, fast directions within the youngest part of the slab window are consistent with cross-basin mantle flow between the Atlantic and Pacific, as previously suggested by shear wave splits. Overall, the anisotropic velocity model reveals complex, depth-dependent patterns of mantle deformation and flow within the Patagonian slab window.
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