Uplift of the central transantarctic mountains

Abstract

The Transantarctic Mountains (TAM) are the world’s longest rift shoulder but the source of their high elevation is enigmatic. To discriminate the importance of mechanical vs. thermal sources of support, a 550 km-long transect of magnetotelluric geophysical soundings spanning the central TAM was acquired. These data reveal a lithosphere of high electrical resistivity to at least 150 km depth, implying a cold stable state well into the upper mantle. Here we find that the central TAM most likely are elevated by a non-thermal, flexural cantilever mechanism which is perhaps the most clearly expressed example anywhere. West Antarctica in this region exhibits a low resistivity, moderately hydrated asthenosphere, and concentrated extension (rift necking) near the central TAM range front but with negligible thermal encroachment into the TAM. Broader scale heat flow of east-central West Antarctica appears moderate, on the order of 60–70 mW m−2, lower than that of the U.S. Great Basin.

Seismic Structure of the Antarctic Upper Mantle Imaged with Adjoint Tomography

“…In general, where this anomaly extends beneath the Transantarctic Mountains, the region is characterized by greater width and elevation. 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 ().…”

The feasibility of imaging subglacial hydrology beneath ice streams with ground-based electromagnetics

“…The transmitter can take the form of either a grounded dipole or a large ungrounded loop. From a theoretical point of view, the grounded dipole source is preferred since it produces both transverse electric (TE) and transverse magnetic (TM) polarization modes of the EM field, and thus has a richer structural sensitivity than a loop source, which only generates the TE mode (Chave and Cox, 1982;Ward and Hohmann, 1987). However, since the signal-to-noise ratio of EM data is directly proportional to the current in the transmitter wire, the large loop method is often preferred in areas where high ground contact resistance (e.g.…”

“…A measure of this is provided by the EM skin depth z s , which is the e-folding distance of the induced field in a uniform conductor. The skin depth depends on the resistivity ρ and linear frequency f according to: (Ward and Hohmann, 1987). For a given resistivity, the skin depth relation shows that high-frequency energy attenuates more rapidly and is sensitive to shallow structure, while low-frequency energy can penetrate more deeply.…”

“…EM geophysical techniques use low-frequency (<10 kHz) EM induction that is governed by a vector diffusion equation (Ward and Hohmann, 1987). They have been well developed for tectonic, mineral, hydrocarbon and groundwater Resistivity (ohm-m) Fig.…”

“…Beblo and Liebig (1990) present the first quantitative analysis of Antarctic MT data, describing a suite of four stations collected on Priestly Glacier, North Victoria Land, with encouraging results for investigating sub-ice sedimentary basins. More recent studies have concentrated on using low-frequency MT data to study deep crustal and upper mantle tectonics (Wannamaker and others, 1996(Wannamaker and others, , 2004(Wannamaker and others, , 2012Peacock and Selway, 2016). Although theoretical considerations suggest that departures from the MT plane-wave source-field assumption may be prevalent at the poles due to the presence of the polar atmospheric electrojets (Pirjola, 1998), Beblo and Liebig (1990) showed that MT impedance responses from different time segments remain stationary despite clear variations in source strength associated with the electrojet.…”