The seismic structure of the Alaskan crust and upper mantle
Abstract
The contemporary structure of Alaska is the result of a distinct tectonic history of subduction and terrane accretion that controls lithospheric thickness and rheology. To provide new constraints on the structure of the crust and upper mantle beneath Alaska, we combined surface and body wave data to calculate shear velocity profiles (Vs). Synthetic tests of our Bayesian joint inversion illustrate that body waves (Sp receiver functions) enhance the resolution of the velocity changes at the Moho and the lithosphere-asthenosphere boundary, while Rayleigh wave phase velocities provide information about absolute velocities. Resulting Vs profiles reveal important features in the subsurface of Alaska, including: the thickness of the lithosphere, the depth of the Moho, the average velocity in the lithosphere and the minimum velocity in the asthenosphere. From these constraints, we show that in central Alaska, above the shallow slab, the continental lithosphere is thinnest (~60 km) and the asthenosphere has its lowest velocities. The continental lithosphere thickens to the north beneath the Brooks Range and the northern Arctic Alaska terrane, up to 130 km thick, with high lithospheric velocities that are comparable to Archean cratons. This pattern is consistent with a northward decrease in modification of the North American plate lithosphere by slab derived melt and volatiles. Lithospheric and asthenospheric velocities are not significantly different inside and outside of the Denali Volcanic Gap (DVG), but lithospheric thickness increases more rapidly to the north of the DVG, which might shed light on the lack of volcanism in this part of the subduction. In the south, the subducting Yakutat plate is thicker (~100-120 km) than the subducting Pacific plate (~80-90 km), likely due to the addition of the Yakutat crust.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMU010...09G
- Keywords:
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- 0810 Post-secondary education;
- EDUCATION;
- 0815 Informal education;
- EDUCATION