Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS splitting analysis

Abstract

Using data from the new Transantarctic Mountains Northern Network, this study aims to constrain azimuthal anisotropy beneath a previously unexplored portion of the Transantarctic Mountains (TAMs) to assess both past and present deformational processes occurring in this region. Shear‐wave splitting parameters have been measured for PKS, SKS, and SKKS phases using the eigenvalue method within the SplitLab software package. Results show two distinct geographic regions of anisotropy within our study area: one behind the TAMs front, with an average fast axis direction of 42 ± 3° and an average delay time of 0.9 ± 0.04 s, and the other within the TAMs near the Ross Sea coastline, with an average fast axis oriented at 51 ± 5° and an average delay time of 1.5 ± 0.08 s. Behind the TAMs front, our results are best explained by a single anisotropic layer that is estimated to be 81–135 km thick, thereby constraining the anisotropic signature within the East Antarctic lithosphere. We interpret the anisotropy behind the TAMs front as relict fabric associated with tectonic episodes occurring early in Antarctica's geologic history. For the coastal stations, our results are best explained by a single anisotropic layer estimated to be 135–225 km thick. This places the anisotropic source within the viscous asthenosphere, which correlates with low seismic velocities along the edge of the West Antarctic Rift System. We interpret the coastal anisotropic signature as resulting from active mantle flow associated with rift‐related decompression melting and Cenozoic extension.

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

“…Since 2001, regional seismic experiments such as TAMSEIS (2001TAMSEIS ( -2003, AGAP/GAMSEIS (2007, ANET/POLENET (2008-present), RIS/DRIS (2014, and TAMNNET (2012TAMNNET ( -2015 have accumulated a tremendous amount of seismic data that have enabled new, higher-resolution investigations of Antarctic crust and mantle structure. Studies have included body wave tomography (Brenn et al, 2017;Hansen et al, 2014;Lloyd et al, 2013Lloyd et al, , 2015Watson et al, 2006), teleseismic surface waves Graw et al, 2016;Heeszel et al, 2013Heeszel et al, , 2016Lawrence et al, 2006a;Vuan et al, 2005), surface waves derived from ambient noise (Pyle et al, 2010), receiver functions (Chaput et al, 2014;Emry et al, 2015;Finotello et al, 2011;Hansen et al, 2009Hansen et al, , 2010Hansen et al, , 2016Ramirez et al, 2016Ramirez et al, , 2017, seismic attenuation (Lawrence et al, 2006b), and shear wave splitting (Accardo et al, 2014;Barklage et al, 2009;Graw & Hansen, 2017). These studies have revealed a number of new details of lithospheric structure, especially at regional scales.…”

Upper Mantle Deformation of the Terror Rift and Northern Transantarctic Mountains in Antarctica: Insight From P Wave Anisotropic Tomography

“…The Nimrod (~1.7 Ga), Beardmore (~625 Ma), and Ross (~500 Ma) Orogenies may have significantly affected the crustal and upper‐mantle structures of this region, but younger geological events, like the Ross Orogeny, may have erased or modified most of structural features from the Beardmore and Nimrod Orogenies (Goodge et al, 2001). Within the TAM, some faults were detected to reactive along NE–SW trending fabrics formed during the Ross Orogeny (Jones, 1997), which is nearly parallel to the fast direction revealed by SWS and Rayleigh wave analyses (Graw & Hansen, 2017; Lawrence et al, 2006). Hence, we suggest that the high‐V zone with positive RAN reflects the deformation pattern formed during the Ross Orogeny.…”

“…The lithospheric mantle exhibiting a positive RAN anomaly has also been revealed beneath North America (Yuan et al, 2011). Due to the extremely slow absolute plate motion of the Antarctic plate (Gripp & Gordon, 2002) and the nearly orthogonal direction between the absolute plate motion and fast direction of azimuthal anisotropy (Graw & Hansen, 2017), it is difficult to attribute the positive RAN to the plate motion alone. Several previous studies have detected a thick and rigid lithosphere beneath this region (Morelli & Danesi, 2004), which would not be prone to deform.…”

“…Many shear wave splitting (SWS) investigations have been made in the study region. Behind the TAM front, the SWS results show that anisotropy occurs in the thick lithosphere, which reflects ancient deformation predating the Ross Orogeny (Graw & Hansen, 2017). In contrast, azimuthal anisotropy with different fast directions along the Ross Sea coastline is attributed to the Cenozoic rifting (Graw & Hansen, 2017).…”

“…Behind the TAM front, the SWS results show that anisotropy occurs in the thick lithosphere, which reflects ancient deformation predating the Ross Orogeny (Graw & Hansen, 2017). In contrast, azimuthal anisotropy with different fast directions along the Ross Sea coastline is attributed to the Cenozoic rifting (Graw & Hansen, 2017). The distinct fast direction observed in the EA interior, near the Belgica Highlands, suggests that the EA comprises multiple cratonic blocks rather than a single block (Barklage et al, 2009).…”