Magnetotelluric investigation of the Vestfold Hills and Rauer Group, East Antarctica

Abstract

The Vestfold Hills and Rauer Group in East Antarctica have contrasting Archean to Neoproterozoic geological histories and are believed to be juxtaposed along a suture zone that now lies beneath the Sørsdal Glacier. Exact location and age of this suture zone are unknown, as is its relationship to regional deformation associated with the amalgamation of East Gondwana. To image the suture zone, magnetotelluric (MT) data were collected in Prydz Bay, East Antarctica, mainly along a profile crossing the Sørsdal Glacier and regions inland of the Vestfold Hills and Rauer Group islands. Time‐frequency analysis of the MT time series yielded three important observations: (1) Wind speeds in excess of ∼8 m/s reduce coherence between electric and magnetic fields due to charged wind‐blown particles of ice and snow. (2) Estimation of the MT transfer function is best between 1000 and 1400 UT when ionospheric Hall currents enhance the magnetic source field. (3) Nonplanar source field effects were minimal but detectable and removed from estimation of the MT transfer function. Inversions of MT data in 2‐D and 3‐D produce similar resistivity models, where structures in the preferred 3‐D resistivity model correlate strongly with regional magnetic data. The electrically conductive Rauer Group is separated from the less conductive Vestfold Hills by a resistive zone under the Sørsdal Glacier, which is interpreted to be caused by oxidation during suturing. Though a suture zone has been imaged, no time constrains on suturing can be made from the MT data.

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

“…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. This conclusion is also supported by the lack of source-effect complications in more recent datasets others, 1996, 2004;Peacock and Selway, 2016).…”

“…Due to the high resistivity of firn, the contact resistance of the electric bipoles used to measure the telluric fields can be as high as 1 MΩ leading to enhanced capacitive coupling with the ground, and so specialized ultra-high-input impedance buffer amplifiers and electrodes must be used to minimize these effects (Zonge and Hughes, 1985). Wannamaker and others (2004) and Peacock and Selway (2016) have demonstrated the effectiveness of this approach for measuring electric fields in Antarctica.…”

“…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.…”

Magnetotelluric Constraints on the Temperature, Composition, Partial Melt Content, and Viscosity of the Upper Mantle Beneath Svalbard

“…The MT method assumes that the Earth's magnetic field behaves as a homogeneous plane wave (Cagniard, 1953), but in auroral regions close to the magnetic poles, this assumption may break down (e.g., Hill, 2020; Jones & Spratt, 2002; Peacock & Selway, 2016; Smirnov & Egbert, 2012). We calculated impedance tensors through separate processing of daytime and nighttime data for the long‐period station and found no evidence of temporal changes in the source field (Figure 2b), suggesting that the data are not impacted by non‐planar source field effects.…”

On the Use of Electromagnetics for Earth Imaging of the Polar Regions

“…MT results local to the largest population centre Longyearbyen identified a conductivity structure which is suggested as favourable for geothermal heat storage with a zone of high conductivity in the mid-crust 'sealed' by overlying and surrounding resistive bodies . Elevated heat flow rates ranging from 80 to 130 mW m −2 have been reported for the area (Vagnes and Amundsen 1993;Khutorskoi et al 2009;Slagstad et al 2009;Pascal et al 2011) due to local deep faulting, and a thinned (~ 100 km) lithosphere (Bergh and Grogan 2003) combined with the local conductivity structure makes further evaluation of the areas geothermal resource potential warranted. Further a near-surface resistive layer extending to a depth of ~ 120 m represents the permafrost zone of primarily unconsolidated gravels ; however, there is significant heterogeneity in the thickness of the permafrost layer with a max depth of ~ 250 m and a general thinning westward (towards the coast).…”