BUILDING THE CONTINENTAL LITHOSPHERE: THE HISTORY OF THE CONTIGUOUS U.S. AS PRESERVED IN CRUST AND LITHOSPHERIC MANTLE STRUCTURES

Hopper, Emily

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Year:: 2016
Contributor:: Hopper, Emily (creator); Fischer, Karen (Director); Forsyth, Donald (Reader); Hirth, Greg (Reader); Parman, Stephen (Reader); Wagner, Lara (Reader); Brown University. Geological Sciences (sponsor)
Genre:: theses
Subject:: Receiver functions; Wavefield migration; Asthenosphere; Seismology; Lithosphere; North America
Extent:: xx, 235 p.
DOI: https://doi.org/10.7301/Z0DJ5D22

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Abstract:: The lithosphere, the plate in ‘plate tectonics’, preserves a record of past and present tectonic processes in its internal structures and its boundary with the underlying asthenosphere. This dissertation uses scattered waves, largely common conversion point stacked Sp converted waves locally supplemented with a more formal wavefield migration, to image such structures in the crust and lithospheric mantle of the contiguous U.S. In the tectonically youngest western U.S. (Chapter 1), a shallow, sharp velocity gradient at the base of the lithosphere suggests a boundary defined by ponded melt. The lithosphere thickens with age of volcanism, implying the lithosphere is a melt-mitigated, conductively cooling thermal boundary layer. Beneath older, colder lithosphere where melt fractions are much lower, the velocity gradient at the base of such a layer should be a diffuse, purely thermal boundary. This is consistent with observations in the eastern U.S. (Chapter 2), where the boundary is locally sharp in areas of inferred enhanced upwelling only; and in the cratonic interior (Chapter 5), where the boundary is transparent to Sp waves. However, observations from the eastern U.S. indicate further complexity. Variations in current lithospheric thickness linked to Proterozoic rift boundaries suggest tectonic inheritance is significant at a lithospheric scale (Chapter 2). The preservation of relict tectonic structures like this gives insight into mechanisms of ancient deformation, with observations presented here emphasizing the importance of lateral accretion. A crustal suture in the southeastern U.S. generated by the final collision in the formation of the Appalachians is observed as a long, low-angle, dipping structure, accommodating several hundred kilometers of shortening (Chapter 3). The geometry of this feature is confirmed using an independent dataset and a wavefield migration technique that more accurately retrieves dips (Chapter 4). Ancient lateral accretion within the lithospheric mantle is preserved as dipping structures associated with relict subducted slabs from Paleoproterozoic continental accretion (Chapter 5). These observations suggest that lateral accretion is integral to the cratonic root formation process.
Notes:: Thesis (Ph.D. -- Brown University (2016)

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Rights: In Copyright
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Citation

Hopper, Emily, "BUILDING THE CONTINENTAL LITHOSPHERE: THE HISTORY OF THE CONTIGUOUS U.S. AS PRESERVED IN CRUST AND LITHOSPHERIC MANTLE STRUCTURES" (2016). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0DJ5D22

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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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