Lithospheric and Asthenospheric Seismic Anisotropy at Collisional and Passive Margins

MacDougall, Julia

Full Metadata

Overview

Year:: 2014
Contributor:: MacDougall, Julia (creator); Fischer, Karen (Director); Forsyth, Donald (Reader); Parman, Stephen (Reader); Parmentier, Edgar (Reader); Kincaid, Chris (Reader); Brown University. Geological Sciences (sponsor)
Genre:: theses
Subject:: Seismic anisotropy; passive margins; Subduction zones
Extent:: 16, 214 p.
DOI: https://doi.org/10.7301/Z08C9TMR

Files

Description

Abstract:: Seismic anisotropy in olivine and orthopyroxene mineral crystals enables us to infer first-order flow characteristics in the asthenospheric mantle and the preserved tectonic history in the lithospheric mantle of continental plates. This work focuses on the observed seismic anisotropy within both the lithospheric and asthenospheric mantle in the southern South American subduction zone, the southeastern United States, and the Hindu Kush-Pamir region. Because these three study areas represent different tectonic environments, their patterns and sources of seismic anisotropy are diverse. Chapter 1 is devoted to the observation, modeling, and interpretation of local S and teleseismic SK(K)S shear-wave splitting results in the southern South American subduction zone. We theorize that the observed shear-wave splitting in the asthenospheric mantle indicates a combination of flow through a slab gap, the presence of the flat Pampean slab segment, and rollback of the subducting Nazca slab. In Chapter 2, we examine the effects of those flow drivers on asthenospheric mantle flow using a subduction zone laboratory tank model. With this apparatus, we can replicate some of the flow patterns discussed in Chapter 1, including the strong pull of mantle wedge material towards the shallowly-dipping slab, analogous to the Pampean flat slab segment. In Chapter 3, we use Pn phases from regional earthquakes in the southeastern United States to constrain lateral variation and azimuthal anisotropy in uppermost mantle P-wave velocities. In particular, mantle P-wave velocities are significantly lower beneath the Blue Ridge Mountains, suggesting that mantle structure may contribute to supporting the higher elevations. We also measure azimuthal anisotropy in this region in Chapter 4, but here, we use S-waves to measure SK(K)S shear-wave splitting. Because of the close station spacing and the density of shear-wave splitting data, we are able to define distinct lithospheric mantle anisotropy signatures that vary between accreted terranes. Lastly, in Chapter 5, we conduct a shear-wave splitting study in the Hindu Kush-Pamir region, where the SK(K)S splitting is primarily sampling asthenospheric mantle flow induced by absolute plate motion of the Eurasian Plate. The shallow upper plate mantle, as sampled by local S waves, is not strongly anisotropic.
Notes:: Thesis (Ph.D. -- Brown University (2014)

Content

Access Conditions

Rights: In Copyright
Restrictions on Use: Collection is open for research.

Citation

MacDougall, Julia, "Lithospheric and Asthenospheric Seismic Anisotropy at Collisional and Passive Margins" (2014). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z08C9TMR

Relations

Collection:

Earth, Environmental and Planetary Sciences Theses and Dissertations

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