Magnetotelluric survey across the Vestfold Hills, East Antarctica

Reconstruction of Gondwana depends significantly on geophysical information from Antarctica. In 2009, a magnetotelluric survey was collected across a suggested neoproterozoic suture zone near Davis Station in East Antarctica with the aim of delineating the boundary between the high grade metamorphic Rauer Group and the younger Vestfold Hills. A total of 32 broadband MT measurements were collected covering over 100km extending from the Vestfold Hills south to the Larsmann Hills, including the Rauer Group. Because the survey was collected near the geomagnetic south pole, robust time-frequency analysis was used to estimate times when the non-planar assumption of MT was violated. Interestingly, robust time-frequency analysis locates the best window to estimate the MT transfer function to be 0600-1400 UT, when geomagnetic source field power in the MT dead band is at a maximum. Little effects from source field effects are found for periods smaller than 100 seconds. Presented are the first models of the 3D resistivity structure underlying the Rauer Group, Vestfold Hills and extending to the Larsmann Hills. Ice thickness is characterized well finding a conductive layer just below the ice interpreted as a thin water layer. Conductivity anomalies estimated from 3D inversion of the data correlate well with magnetic data collected by the ADMAP project. The 3D model locates a conductive body underlying the Rauer Group extending to the Larsmann Hills that could be the source of metamorphism, while the lithology under the Vestfold Hills is resistive. This contrast indicates a boundary in the resistivity structure that could be interpreted as a neoproterozoic suture zone, but constraining this interpretation is difficult due to lack of geophysical information of the region. A three-dimensional resistivity block model compared to a 2D slice illustrating the magnetic intensity from the ADMAP project and the phase tensor response of the MT data at a period of 10s. Magnetic highs correlate with the enhanced conductivity structure in the middle crust.