Advances in Understanding the Lithosphere and Asthenosphere System: A Case Study of Seismological Structure in Alaska

Gama Dantas, Isabella

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Year:: 2022
Contributor:: Gama Dantas, Isabella (creator); Fischer, Karen (Advisor); Dalton, Colleen (Reader); Saal, Alberto (Reader); Tsai, Victor (Reader); Eilon, Zachary (Reader); Brown University. Department of Earth, Environmental, and Planetary Sciences (sponsor)
Genre:: theses
Subject:: Subduction zones; Earthquakes; Earth; Alaska; Receiver Functions; Bayesian Inversion; Lithosphere; Asthenosphere
Extent:: xi, 145 p.

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Abstract:: The system of plate tectonics governs the transport of material between Earth’s interior, hydrosphere, and atmosphere to create a dynamic planetary surface that sustains life. A fundamental component of this system is the behavior of the lithosphere and its relationship with the underlying asthenosphere. Since the early years of plate tectonic theory, we have known that the lithosphere, a layer formed by the crust and the rigid upper mantle, rests above the weaker mantle of the asthenosphere. This arrangement permits the lithosphere to migrate over the more deformable asthenosphere, and this interaction alone has significant ramifications for the Earth and life as we know it today. Despite the importance of this arrangement, there are multiple aspects of the lithosphere, asthenosphere, and their interactions that remain elusive, especially at plate boundaries. In the case of Alaska and many other regions globally, subduction and the lithosphere-asthenosphere system are yet to be fully understood. Subduction zones are regions where one lithospheric plate converges with another, and the resulting earthquakes, tsunamis, and volcanoes can pose significant hazards globally and to local communities. In Alaska, surface signatures range from patterns of deformation observed from GPS and earthquake slip data to features such as terrain uplift, mountain building, and large-scale fault systems. However, these features, together with their relationship to the underlying lithospheric structure are debated and not yet understood in the context of plate tectonics. By studying the lithosphere and asthenosphere in Alaska with seismic waves, this thesis aims to understand the role of plate tectonics in subduction zones and how it influences the deformation and surface processes we observe. Among my many conclusions, these stand out as the most influential new insights. (1) It is not surprising that subduction processes thin the upper plate, but I showed that this interaction extends to higher latitudes in Alaska than previously thought, including thin lithosphere and a low velocity asthenosphere that extends all the way to the Seward Peninsula and the southern margin of the northern Arctic Alaska Terrane. In these far-flung regions, surface magmatism is likely due to decompression melting in upwelling asthenosphere, as opposed to the mantle melting creating by slab-derived fluids that occur closer to the subduction zone. (2) While many studies have shown that the lithosphere beneath the northern Arctic Alaska terrane is relatively thick, my work shows that the transition from thin to thick lithosphere occurs over a surprisingly small horizontal distance, resulting in a steep southern boundary to the thick lithosphere in the north. The high velocity and depth extent of this lithosphere allow its characterization as a “mini-craton.” (3) I also showed that the structure of the upper plate lithosphere is perturbed beneath many of the major fault zones and terrane boundaries in Alaska, and that these signatures persist all the way to the base of the lithosphere. These results support the view that mantle lithosphere can deform in thin concentrated zones of shear.
Notes:: Thesis (Ph. D.)--Brown University, 2022

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Gama Dantas, Isabella, "Advances in Understanding the Lithosphere and Asthenosphere System: A Case Study of Seismological Structure in Alaska" (2022). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:4hbkczzy/

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Earth, Environmental and Planetary Sciences Theses and Dissertations

Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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