Upper mantle structure of central and West Antarctica from array analysis of Rayleigh wave phase velocities

Abstract

The seismic velocity structure of Antarctica is important, both as a constraint on the tectonic history of the continent and for understanding solid Earth interactions with the ice sheet. We use Rayleigh wave array analysis methods applied to teleseismic data from recent temporary broadband seismograph deployments to image the upper mantle structure of central and West Antarctica. Phase velocity maps are determined using a two–plane wave tomography method and are inverted for shear velocity using a Monte Carlo approach to estimate three‐dimensional velocity structure. Results illuminate the structural dichotomy between the East Antarctic Craton and West Antarctica, with West Antarctica showing thinner crust and slower upper mantle velocity. West Antarctica is characterized by a 70–100 km thick lithosphere, underlain by a low‐velocity zone to depths of at least 200 km. The slowest anomalies are beneath Ross Island and the Marie Byrd Land dome and are interpreted as upper mantle thermal anomalies possibly due to mantle plumes. The central Transantarctic Mountains are marked by an uppermost mantle slow‐velocity anomaly, suggesting that the topography is thermally supported. The presence of thin, higher‐velocity lithosphere to depths of about 70 km beneath the West Antarctic Rift System limits estimates of the regionally averaged heat flow to less than 90 mW/m2. The Ellsworth‐Whitmore block is underlain by mantle with velocities that are intermediate between those of the West Antarctic Rift System and the East Antarctic Craton. We interpret this province as Precambrian continental lithosphere that has been altered by Phanerozoic tectonic and magmatic activity.

Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

“…Regional studies (Lloyd et al, ; Shen, Wiens, Anandakrishnan et al, ) report similar findings and also differentiate the Ellsworth‐Whitmore mountains crustal block, as does ANT‐20. Likewise, in the Ross Embayment, ANT‐20 images the slowest regional wave speeds along and in places beneath the Transantarctic Mountains, while revealing moderate anomalies beneath the eastern basins of the Ross Embayment, consistent with a number of regional studies (Brenn et al, ; Graw et al, ; Heeszel et al, ; Shen, Wiens, Anandakrishnan et al, ; Watson et al, ). Finally, ANT‐20 exhibits greater seismic heterogeneity beneath East Antarctica, but it is the sharp boundaries of the fast upper mantle anomalies that are most striking in comparison to the smoother global tomographic models.…”

“…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.…”

Glacial Isostatic Adjustment modelling: historical perspectives, recent advances, and future directions

“…The effect of including plate boundaries -which affect the horizontal transmission of stress -and variations in the thickness and rheology of the lithosphere have also been explored (Latychev et al, 2005a;Kuchar and Milne, 2015). The development of these '3D GIA models' are motivated by (i) convincing evidence for strong lateral variations in rheological properties beneath some regions, including Antarctica 580 (Heeszel et al, 2016); and (ii) the demonstration that consideration of lateral variations in rheology is required to correctly model horizontal deformation (Kaufmann et al, 2005).…”

Altimetry, gravimetry, GPS and viscoelastic modeling data for the joint inversion for glacial isostatic adjustment in Antarctica (ESA STSE Project REGINA)

“…Much progress has been made in reconstructing the ice sheet evolution from geomorphological evidence (Bentley et al, 2014) and inferring the underlying Earth structure from seismic observations Heeszel et al, 2016). However, an independent approach to constraining GIA is to make use of the different sensitivities of the various types of satellite data to recent glacial changes and GIA, respectively.…”