The Crust and Upper Mantle Structure of Central and West Antarctica From Bayesian Inversion of Rayleigh Wave and Receiver Functions

Abstract

We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3‐D shear velocity (Vs) model for the crust and uppermost mantle using a Bayesian Monte Carlo algorithm. The new 3‐D seismic model shows the dichotomy of the tectonically active West Antarctica (WANT) and the stable and ancient East Antarctica (EANT). In WANT, the model exhibits a slow uppermost mantle along the Transantarctic Mountains (TAMs) front, interpreted as the thermal effect from Cenozoic rifting. Beneath the southern TAMs, the slow uppermost mantle extends horizontally beneath the traditionally recognized EANT, hypothesized to be associated with lithospheric delamination. Thin crust and lithosphere observed along the Amundsen Sea coast and extending into the interior suggest involvement of these areas in Cenozoic rifting. EANT, with its relatively thick and cold crust and lithosphere marked by high Vs, displays a slower Vs anomaly beneath the Gamburtsev Subglacial Mountains in the uppermost mantle, which we hypothesize may be the signature of a compositionally anomalous body, perhaps remnant from a continental collision.

Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

“…For example, at 100‐km depth, S40RTS (Ritsema et al, ) depicts shear‐wave speed anomalies no faster than ~2% beneath East Antarctica and near the 1‐D global average beneath West Antarctica. At the same depth, models like SEMUM‐2 (French et al, ) and SL2013sv (Schaeffer & Lebedev, ), which utilize additional Antarctic seismic data, reveal anomalies with amplitudes similar to the pioneering continental‐scale surface wave studies conducted more than 15 years ago (e.g., Danesi & Morelli, ; Ritzwoller et al, ) and begin to just hint at second‐order features that are well resolved in regional studies (e.g., Brenn et al, ; Graw et al, ; Lloyd et al, , ; Shen, Wiens, Anandakrishnan et al, ; Watson et al, ).…”

“…Traditional tomographic studies often rely on synthetic model recovery tests (e.g., Lloyd et al, , ) and in some instances utilize Monte Carlo techniques (e.g., Shen, Wiens, Anandakrishnan et al, ) to assess model recovery and reliability. Both approaches rely on the ability to quickly and efficiently solve the forward and inverse problem.…”

“…We obtain the initial values of these parameters from the ice layer, the three sedimentary layers, and the three crystalline crustal layers of CRUST1.0 (Laske et al, ). However, recent geophysical studies of the Antarctic crustal structure (e.g., An et al, ; Chaput et al, ; O'Donnell & Nyblade, ; Shen, Wiens, Anandakrishnan et al, ) indicate that CRUST1.0 inadequately constrains the Moho topography across the Antarctic continent. This is reflected, in part, by its failure to capture the thinned crust of the West Antarctic Rift System and the thick crustal roots that underlie portions of East Antarctica.…”

“…The deeper continental roots of these regions have in the past primarily been imaged by global‐ and continental‐scale seismic tomography that reveal thick and fast lithosphere (e.g., Danesi & Morelli, ; Ritzwoller et al, ) but do not possess sufficient resolution to delineate tectonic provinces. Aided by additional seismological data, recent studies are now beginning to hint at lithospheric heterogeneity beneath East Antarctica (e.g., An et al, , Heeszel et al, ; Lloyd et al, ; Shen, Wiens, Anandakrishnan et al, ). For example, the mantle lithosphere beneath the Gamburtsev Subglacial Mountains (Figure ) is seismically faster than to the north beneath the Lamber Graben (Heeszel et al, ) and to the south beneath the Polar Subglacial Basins (Heeszel et al, ; Lloyd et al, ).…”

“…Recent continental tomographic inversions (An et al, ; Hansen et al, ) achieve higher resolution, but the greatest insights are gained by still higher resolution regional models. Although these models only reveal patches of the West Antarctic, they indicate variable upper mantle wave speeds that coincide with the West Antarctic crustal blocks (Heeszel et al, ; Lloyd et al, ), distinguish between zones of late Cretaceous/early Cenozoic and late Cenozoic extension within the West Antarctic Rift System (e.g., Heeszel et al, ; Lloyd et al, ; Shen, Wiens, Anandakrishnan et al, ; White Gaynor et al, ), and reveal warmer upper mantle beneath late Cenozoic volcanism (e.g., Heeszel et al, ; Lloyd et al, ; Watson et al, ). The most prominent features include slow wave speeds along the Transantarctic Mountain front and those beneath the Marie Byrd Land volcanic dome.…”