Investigating the Antarctic Lithosphere Through Sp Receiver Function Analysis

To better understand the lithosphere of Antarctica, we imaged its lithosphere-asthenosphere boundary (LAB) and crust-mantle transition using Sp receiver functions from teleseismic events analyzed at individual stations and with common conversion point stacking. Results reveal a prominent negative velocity gradient at depths of 70–100 km across much of West Antarctica, consistent with the seismically defined base of the lithosphere identified in prior tomography studies. Beneath the West Antarctic Rift System, lithospheric thicknesses are typically 70–85 km, with isolated zones up to 100 km. These thicknesses do not correlate with the time since significant extension. Rather, they are consistent with ablation of the cooling mantle at the base of the lithosphere caused by later processes, including ongoing asthenospheric flow. Mantle upwelling beneath Marie Byrd Land is one possible driver of asthenospheric flow and is consistent with this region's thin lithosphere, higher topography, and low upper mantle seismic velocities. Lithospheric thicknesses vary significantly along-strike beneath the Transantarctic Mountains, and these gradients in thermal structure indicate variable support for the mountains from a warm buoyant mantle. In the interior of East Antarctica, the absence of Sp phases from depths comparable to the base of the lithosphere seen in tomography suggests a more gradual LAB velocity gradient beneath the thick cratonic lithosphere. In contrast, beneath the margin of East Antarctica that rifted with Australia, clear LAB negative velocity gradients are present at depths of 90–120 km.