P AND S BODY WAVE TOMOGRAPHY OF THE UPPER MANTLE IN CENTRAL AND EASTERN WEST ANTARCTICA

Restricted (Penn State Only)
Author:
Soto, David Romualdo
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 24, 2018
Committee Members:
  • Andrew Arnold Nyblade, Thesis Advisor
  • Charles James Ammon, Committee Member
  • Sridhar Anandakrishnan, Committee Member
Keywords:
  • Geophysics
  • Seismology
  • Antarctica
  • Tomography
  • Rift
  • Tectonics
Abstract:
Relative P- and S-wave travel times from teleseismic earthquakes recorded on the Polar Earth Observing Network (POLENET/ANET) and UK Antarctic Network (UKANET) have been inverted to obtain P- and S-wave velocity models of the upper mantle to depths of approximately 400 km beneath central and eastern West Antarctica. The study area consists of the West Antarctic Rift System (WARS) and four surrounding lithospheric blocks. My models reveal a significant amount of heterogeneity in upper mantle structure. Beneath Marie Byrd Land, low velocity anomalies (up to -1.0% Vp and -2.0% Vs) are interpreted as an upper mantle thermal anomaly possibly from a mantle plume. Fast velocities (0.8% Vp and 1.8% Vs) found in the center of the WARS are interpreted as thicker and colder lithosphere that has not been modified by any tectonic activity since the Mesozoic rifting that formed the WARS. Slow velocities (-0.4% Vp and -0.5% Vs) beneath parts of the Bentley Subglacial Trench are interpreted as thermally altered lithosphere from localized Cenozoic rifting within the WARS. Similarly, slow velocities (-0.5% Vp and -1.2% Vs) beneath Pine Island Glacier (PIG) and the mouth of Thwaites Glacier (TG) are interpreted as rift related anomalies indicating the presence of thin lithosphere and warm asthenosphere that is facilitating the rapid uplift caused by glacial isostatic adjustment (GIA). In contrast, faster velocities beneath the interior of the WARS suggest slower GIA within the interior of TG. Fast velocities imaged beneath the Thurston Island block to the north of PIG suggest that the lithosphere in this area has not been altered since the emplacement of Mesozoic intrusive and extrusive rocks, and that the low velocity region to the south beneath PIG may be locally confined.