Date of Award
Winter 12-15-2018
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
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 demarcates a suture zone between two lithospheric blocks. Our results lend themselves to a Precambrian origin for the high topography of the Gamburtsev Mountains, as opposed to uplift due to Permian/Cretaceous rifting or Cenozoic magmatism.
The second tomographic technique, adjoint tomography, is utilized in chapter 3 to image the upper mantle and transition zone seismic structure beneath Antarctica and the southern oceans. Three-component earthquake waveforms that contain P, S, Rayleigh, and Love waves, including reflections and overtones, recorded by 323 broadband seismic station are utilized along with adjoint tomographic techniques and high performance computing resources to produce tomographic images that approach similar resolution to that of regional studies. Across much of East Antarctica we image thick cold continental lithosphere, however thinner continental lithosphere characteristic of Proterozoic and Phanerozoic orogenic activity is found beneath areas of Dronning Maud Land and the Rayner Province. Slow shear wave speed anomalies delineating regions of mid and late-Cenozoic extension are imaged in the western Ross Embayment and extend seaward beneath the Balleny Islands. Our tomographic image also provides evidence for a mantle plume beneath Marie Byrd Land, Cenozoic subducted slabs and the formation of a slab window along the Antarctic Peninsula. Finally, the slow velocity anomalies along the Amundsen Sea Coast appear connected to deeper anomalies offshore, suggesting a connection to a deeper mantle processes.
Language
English (en)
Chair and Committee
Douglas A. Wiens
Committee Members
James A. Conder, Philip A. Skemer, V. Slava Solomatov, Michael E. Wysession,
Recommended Citation
Lloyd, Andrew Jason, "Seismic Tomography of Antarctica and the Southern Oceans: Regional and Continental Models from the Upper Mantle to the Transition Zone" (2018). Arts & Sciences Electronic Theses and Dissertations. 1714.
https://openscholarship.wustl.edu/art_sci_etds/1714
Comments
Permanent URL: https://doi.org/10.7936/4r3g-rn34