Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains

Abstract

The Transantarctic Mountains (TAMs) are the largest non-compressional mountain range on Earth, and while a variety of uplift mechanisms have been proposed, the origin of the TAMs is still a matter of great debate. Most previous seismic investigations of the TAMs have focused on a central portion of the mountain range, near Ross Island, providing little along-strike constraint on the upper mantle structure, which is needed to better assess competing uplift models. Using data recorded by the recently deployed Transantarctic Mountains Northern Network, as well as data from the Transantarctic Mountains Seismic Experiment and from five stations operated by the Korea Polar Research Institute, we investigate the upper mantle structure beneath a previously unexplored portion of the mountain range. Rayleigh wave phase velocities are calculated using a two-plane wave approximation and are inverted for shear wave velocity structure. Our model shows a low velocity zone (LVZ; ∼4.24 km s −1 ) at ∼160 km depth offshore and adjacent to Mt. Melbourne. This LVZ extends inland and vertically upwards, with more lateral coverage above ∼100 km depth beneath the northern TAMs and Victoria Land. A prominent LVZ (∼4.16-4.24 km s −1 ) also exists at ∼150 km depth beneath Ross Island, which agrees with previous results in the TAMs near the McMurdo Dry Valleys, and relatively slow velocities (∼4.24-4.32 km s −1 ) along the Terror Rift connect the low velocity anomalies. We propose that the LVZs reflect rift-related decompression melting and provide thermally buoyant support for the TAMs uplift, consistent with proposed flexural models. We also suggest that heating, and hence uplift, along the mountain front is not uniform and that the shallower LVZ beneath northern Victoria Land provides greater thermal support, leading to higher bedrock topography in the northern TAMs. Young (0-15 Ma) volcanic rocks associated with the Hallett and the Erebus Volcanic Provinces are situated directly above the imaged LVZs, suggesting that these anomalies are also the source of Cenozoic volcanic rocks throughout the study area.

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.…”

“…The slow wave speed anomaly is much narrower and less pronounced in the central Transantarctic Mountains where the mountains are narrower, lacking volcanism, and where the cold continental lithosphere extends up to the Transantarctic Mountains front (Wannamaker et al, ). Thus, the width and amplitude of the upper mantle slow wave speed anomaly adjacent to the Transantarctic Mountains front correlates well with the broad‐scale structural and tectonic variation along the front, as also discussed in Graw et al (), Brenn et al (), and Shen, Wiens, Stern et al (). Here, we discuss each of these regions individually.…”

“…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, ).…”

“…Thus, the slow upper mantle wave speeds spatially align with Neogene volcanism and are consistent with thin lithosphere as well as the presence of warm mantle that may contain partial melt. Graw et al () and Brenn et al () also find slow upper mantle wave speeds along the northwestern margin of the Ross Embayment and interpreted them as the signature of rift‐related decompression melting.…”

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

“…Using data from a new array of seismic stations, the goal of the current study is to measure the seismic anisotropy beneath the TAMs in Northern Victoria Land, particularly in relation to the mantle velocity structure imaged beneath this region [ Graw et al ., ; Brenn , ]. By measuring shear‐wave splitting parameters (φ and δt), we will better constrain the deformation processes and tectonic fabric in the northern TAMs, ultimately providing improved constraints on the geologic history of this enigmatic region.…”