P- and S-wave velocity structure of central West Antarctica: Implications for the tectonic evolution of the West Antarctic Rift System

Abstract

New P- and S-wave velocity models of the upper mantle from 100 to 400 km depth beneath the central portions of West Antarctica, obtained by inverting relative travel-times from teleseismic earthquakes recorded on Polar Earth Observing Network (POLENET/ANET) and UK Antarctic Network (UKANET) seismic stations between 2007 and 2017, reveal a heterogeneous upper mantle. A low velocity anomaly (−1.0% Vp; −2.0% Vs) imaged beneath Marie Byrd Land is attributed to thermally perturbed upper mantle of possible plume origin, and a low velocity anomaly imaged beneath the Pine Island Glacier and the mouth of Thwaites Glacier is interpreted as a rift-related thermal structure that may include warm mantle flowing from Marie Byrd Land. High velocity anomalies (≤0.8% Vp; 1.5% Vs) imaged in the central portion of the West Antarctic Rift System indicate the presence of lithosphere unmodified by tectonic activity since the Late Cretaceous formation of the rift system. Within the region of high velocities, localized low velocity anomalies beneath parts of the Bentley Subglacial Trench are suggestive of focused Cenozoic rifting. The models also show variable velocity structure beneath the Haag-Ellsworth Whitmore crustal block and low velocities beneath the Thurston Island-Eights Coast crustal block. The heterogenous upper mantle structure of central West Antarctica indicates that upper mantle temperatures could vary by 100 K or more over distances of less than 100 km, which may add complexity to solid earth-ice interactions and influence basal ice sheet conditions.