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dc.contributor.authorSchmandt, Brandon, 1984-
dc.date.accessioned2012-02-28T22:56:32Z
dc.date.available2012-02-28T22:56:32Z
dc.date.issued2011-09
dc.identifier.urihttp://hdl.handle.net/1794/11974
dc.descriptionxii, 95 p. : ill. (some col.)en_US
dc.description.abstractVigorous convective activity in the western U.S. mantle has long been inferred from the region's widespread intra-plate crustal deformation, volcanism, and high elevations, but the specific form of convective activity and the degree and nature of lithospheric involvement have been strongly debated. I design a seismic travel-time tomography method and implement it with seismic data from the EarthScope Transportable Array and complementary arrays to constrain three-dimensional seismic structure beneath the western U.S. Tomographic images of variations in compressional velocity, shear velocity, and the ratio of shear to compressional velocity in the western U.S. mantle to a depth of 1000 km are produced. Using these results I investigate mantle physical properties, Cenozoic subduction history, and the influence of small-scale lithospheric convection on regional tectonic and magmatic activity, with particular focus on southern California and the Pacific Northwest. This dissertation includes previously published co-authored material. Chapter II presents a travel-time tomography method I designed and first implemented with data from southern California and the surrounding southwestern U.S. The resulting images provide a new level of constraint on upper mantle seismic anomalies beneath the Transverse Ranges, southern Great Valley, Salton Trough, and southwestern Nevada volcanic field. Chapter III presents tomographic images of the western U.S. mantle, identifies upper mantle volumes where partial melt is probable, and discusses implications of the apparently widespread occurrence of gravitational instabilities of continental lithsophere and the complex geometry and buoyancy of subducted ocean lithosphere imaged beneath the western U.S. In Chapter IV, tomography images are used in conjunction with geologic constraints on major transitions in crustal deformation and magmatism to construct a model for Pacific Northwest evolution since the Cretaceous. Accretion in the Pacific Northwest at 55-50 Ma is suggested to stimulate roll-back of the flat subducting Farallon slab. This change in convergent margin structure is further suggested to drive the short-lived Challis magmatic trend and trigger the southward propagating Eocene-Oligocene transition from the Laramide orogeny to widespread crustal extension and ignimbrite magmatism.en_US
dc.description.sponsorshipCommittee in charge: Eugene Humphreys, Chair; Douglas Toomey, Member; Emilie Hooft Toomey, Member; John Conery, Outside Memberen_US
dc.language.isoen_USen_US
dc.publisherUniversity of Oregonen_US
dc.relation.ispartofseriesUniversity of Oregon theses, Dept. of Geological Sciences, Ph. D., 2011;
dc.rightsrights_reserveden_US
dc.subjectGeophysicsen_US
dc.subjectEarth sciencesen_US
dc.subjectSeismic structureen_US
dc.subjectWestern U.S. mantleen_US
dc.subjectRegional tectonic activityen_US
dc.subjectMagmatic activityen_US
dc.titleSeismic Structure of the Western U.S. Mantle and Its Relation to Regional Tectonic and Magmatic Activityen_US
dc.typeThesisen_US


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