A seismic transect across West Antarctica: Evidence for mantle thermal anomalies beneath the Bentley Subglacial Trench and the Marie Byrd Land Dome

• Main Authors: Lloyd, Andrew J., Wiens, Douglas A., Nyblade, Andrew A., Anandakrishnan, Sridhar, Aster, Richard C., Huerta, Audrey D., Wilson, Terry J., Dalziel, Ian W. D., Shore, Patrick J., Zhao, Dapeng
• Format: Text
• Language: unknown
• Published: ScholarWorks@CWU 2015
• Subjects: West Antarctica; upper mantle; tomography; Bentley Subglacial Trench; Marie Byrd Land; Geology; Geophysics and Seismology; Antarctic; Byrd; West Antarctic Ice Sheet; Whitmore Mountains; Antarc*; Antarctica; Ice Sheet
• Online Access: https://digitalcommons.cwu.edu/cotsfac/148; https://digitalcommons.cwu.edu/cgi/viewcontent.cgi?article=1148&context=cotsfac

West Antarctica consists of several tectonically diverse terranes, including the West Antarctic Rift System, a topographic low region of extended continental crust. In contrast, the adjacent Marie Byrd Land and Ellsworth-Whitmore mountains crustal blocks are on average over 1km higher, with the former dominated by polygenetic shield and stratovolcanoes protruding through the West Antarctic ice sheet and the latter having a Precambrian basement. The upper mantle structure of these regions is important for inferring the geologic history and tectonic processes, as well as the influence of the solid earth on ice sheet dynamics. Yet this structure is poorly constrained due to a lack of seismological data. As part of the Polar Earth Observing Network, 13 temporary broadband seismic stations were deployed from January 2010 to January 2012 that extended from the Whitmore Mountains, across the West Antarctic Rift System, and into Marie Byrd Land with a mean station spacing of ~90 km. Relative P and S wave travel time residuals were obtained from these stations as well as five other nearby stations by cross correlation. The relative residuals, corrected for both ice and crustal structure using previously published receiver function models of crustal velocity, were inverted to image the relative P and S wave velocity structure of the West Antarctic upper mantle. Some of the fastest relative P and S wave velocities are observed beneath the Ellsworth-Whitmore mountains crustal block and extend to the southern flank of the Bentley Subglacial Trench. However, the velocities in this region are not fast enough to be compatible with a Precambrian lithospheric root, suggesting some combination of thermal, chemical, and structural modification of the lithosphere. The West Antarctic Rift System consists largely of relative fast uppermost mantle seismic velocities consistent with Late Cretaceous/early Cenozoic extension that at present likely has negligible rift related heat flow. In contrast, the Bentley Subglacial Trench, a narrow ...