Mantle flow systems associated with slab subduction and absolute plate motion in Alaska constrained by shear wave splitting analyses
"Alaska has long been recognized as a geologically complex region with a sharp contrast in tectonic activity between southern and northern Alaska. While the former is characterized by the subduction of the geometrically varying Pacific-Yakutat plate beneath the North American plate, the latter...
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Scholars' Mine
2021
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| Online Access: | https://scholarsmine.mst.edu/doctoral_dissertations/3023 https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=4028&context=doctoral_dissertations |
| Summary: | "Alaska has long been recognized as a geologically complex region with a sharp contrast in tectonic activity between southern and northern Alaska. While the former is characterized by the subduction of the geometrically varying Pacific-Yakutat plate beneath the North American plate, the latter has a mostly stable cratonic setting. To investigate the mantle flow fields beneath Alaska and understand the influence of the subduction process on regional mantle dynamics, a total of 2790 pairs of well-defined teleseismic shear wave splitting (SWS) measurements recorded from 379 stations are obtained and analyzed. In addition, 247 pairs of SWS results from local earthquake events are measured to isolate contribution of the mantle wedge to the teleseismic shear wave splitting. We obtain well-defined two-layered anisotropy models in three areas in southern Alaska. The observations revealed several mantle flow fields, including trench- parallel flow beneath the Pacific slab, trench-normal flow beneath the flat Yakutat slab, toroidal flow around the Pacific-Yakutat slab edge, absolute plate motion-parallel flow in the stable cratonic area, and deflected flow around the deep continental keel in northern and possibly western Alaska. The presence of a slab edge and conflicting conclusions from previous shear wave splitting studies motivated us for an in-depth analysis of the splitting measurements in southcentral Alaska. The results indicate that the sub-slab flow, which is driven by slab roll-back, may separate into two branches at the edge: One flows anticlockwise to the wedge, and the other continues flowing to the east of the study area"--Abstract, page iv. |
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