Upper Mantle Processes and Structures Imaged with Shear-wave Splitting and Ps and Sp Receiver Functions Abt, David L. creator 2009 xiv, 265 p. born digital Thesis (Ph.D.) -- Brown University (2010) Fischer, Karen director Forsyth, Donald reader Parmentier, Edgar reader Saal, Alberto reader Abers, Geoffrey reader Brown University. Geological Sciences sponsor theses The interaction between Earth's relatively rigid tectonic plates and relatively viscous convecting upper mantle fundamentally influences myriad processes ranging from arc and intraplate volcanism to orogenesis and rifting. The work presented here addresses two of the most basic concepts of plate tectonics regarding this interaction: (1) the pattern of upper mantle flow in subduction zones, and (2) the thickness and internal structure of continental lithosphere. Chapters 1-3 are devoted to the observation, modeling, and interpretation of local-S and teleseismic SK(K)S splitting measured by the TUCAN seismic array in the Central American subduction zone. Both the splitting measurements themselves and the tomographic model derived from them demonstrate the need for significant arc-parallel anisotropic fabric, inferred to indicate arc-parallel mantle wedge flow; trends in arc lava radiogenic isotopes (Appendix A) provide independent evidence for the existence of arc-parallel flow. The primary implications of these results are that (1) two-dimensional corner flow models and any predictions derived from them are unlikely to be accurate in southeastern Central America, (2) the three-dimensional and finite lateral extent of subduction probably plays a significant role in determining the pattern of wedge and sub-slab flow, and (3) the degree of coupling between the subducting plate and surrounding mantle may be lower than expected. Chapter 4 presents a receiver function study across North America that uses both Ps and Sp data to estimate the depth of the lithosphere-asthenosphere boundary (LAB), as well as other lithospheric discontinuities. Along with other geophysical data (e.g., heat flow, xenoliths, reflection profiles), the differences in inferred LAB depth between the receiver functions and surface waves and the variation in negative Sp energy indicate that (1) the velocity contrast between lithosphere and asthenosphere in the western U.S. is larger, perhaps due to both elevated temperatures and the presence of asthenospheric partial melt, (2) the velocity gradient at the LAB in cratonic North America likely occurs over more than 30 km and can be explained purely thermally, and (3) significant lithospheric layering likely exists in the central and eastern U.S. shear-wave splitting mantle wedge seismic anisotropy receiver functions lithosphere-asthenosphere boundary TomographyCentral AmericaNorth America RPB 20091218 engEnglish10.7301/Z0SQ8XPMIn CopyrightCollection is open for research.dissertations