Seismic Tomography of Antarctica and the Southern Oceans: Regional and Continental Models from the Upper Mantle to the Transition Zone

• Main Author: Lloyd, Andrew Jason
• Format: Text
• Language: English
• Published: Washington University Open Scholarship 2018
• Subjects: Antarctica; Tomography; Upper Mantle; Geology; Geophysics and Seismology; Antarctic; Bentley Subglacial Trench; Byrd; Executive Committee Range; Gamburtsev Subglacial Mountains; Marie Byrd Land; The Antarctic; West Antarctica; Whitmore Mountains; Antarc*; International Polar Year
• Online Access: https://openscholarship.wustl.edu/art_sci_etds/1714; https://openscholarship.wustl.edu/cgi/viewcontent.cgi?article=2743&context=art_sci_etds

This dissertation utilizes two tomographic techniques to image the upper mantle and transition zone seismic structure beneath the Antarctic and portions of the southern mid-latitude oceans. The first of these techniques, ray-based relative body wave tomography, is utilized in Chapter 2 and Appendix A to produce regional models of the relative P and S wave velocity structure of the upper mantle beneath both a portion of West Antarctica and the East Antarctic Gamburtsev Subglacial Mountains. Specifically, in West Antarctica we utilize a subset of broadband seismic stations deployed by the Polar Earth Observing Network, which are closely spaced and extend from the Whitmore Mountains, across the West Antarctic Rift System, and into Marie Byrd Land. The resulting tomographic images of the relative P and S wave velocity structure illuminate a zone of seismically slower and thus warmer upper mantle within the West Antarctic Rift System that is localized beneath the Bentley Subglacial Trench, consistent with more recent extension. Thermal models for rift basin evolution suggest this region of focus extension occurred in the Neogene. The slowest relative P and S wave velocity anomaly is observed beneath the Executive Committee Range in Marie Byrd Land, which are consistent with either a upper mantle hotspot or mantle plume. The inferred thermal anomaly from this feature is sufficient to isostatically support the anomalous long wavelength tomography of the Marie Byrd Land volcanic dome, relative to the adjacent West Antarctic Rift System. The second relative body wave tomography study, Appendix A, is carried out using 26 broadband seismic stations deployed as part of the 2007/2008 International Polar Year by the Gamburtsev Mountains Seismic Experiment. The imaged relative P and S wave velocity structure reveals large-scale, small amplitude anomalies (δVp = 1.0%, δVs = 2.0%) in the uppermost mantle. In particular, a velocity gradient is observed along the western flank of the Gamburtsev Subglacial Mountains likely ...