Gravity anomalies of the Antarctic lithosphere

Abstract

Anomalous free-air gravity signals in and around the Antarctic continent have been reported for some decades. Recent defi nition of the Antarctic gravity fi eld from fi eld-based oversnow traverses and supporting data from Earth-orbiting satellites reveal discrete regions of both negative and positive free-air gravity anomalies. The data from these observations have enabled us to construct a free-air gravity anomaly map of Antarctica. Negative free-air gravity anomalies are found to occur mainly on the Antarctic continent, in particular, in the Wilkes Land, Ross Sea, central continental, and Weddell Sea sectors. Positive free-air gravity anomalies are found to occur mainly in the offshore circumcontinental sectors. While each of these regions of anomalies provides excellent opportunities for further investigation, including identifi cation of the causes of the negative and positive free-air gravity anomalies, special attention is given to the negative free-air gravity anomaly sites of the continent proper. Three potential sources of the negative free-air gravity anomalies are identifi ed: the mantle, lithosphere, and crust. Examination of thermally induced density variations in the mantle based upon seismic tomography, and analysis of mantle-related gravity anomaly wavelengths favor a gravity anomaly source other than the mantle. Examination of the subcrustal lithosphere based on upper-mantle thermal structure, the origin of the lithosphere, and crustal infl uences on the underlying lithosphere, including radiogenic heat, implies that the source of the negative free-air gravity anomalies is less likely to be the subcrustal lithosphere and more likely to be located in the Antarctic crust. Examination of possible crustal features that might account for these anomalies leads to a consideration of subglacial topography and specifi c locales of anomalously low rock density.

Mass extinctions over the last 500 myr: an astronomical cause?

“…Other candidates such as the giant Wilkes Land Crater have been associated with the end Permian extinction; but neither the age of that crater nor its association with the Permian–Triassic events are proven. Its location under the Antarctic ice (Weihaupt ) is a formidable barrier to any further investigation at present.…”

The Wilkes Land Anomaly revisited

“…6a Enlargement of the area of the subglacial topography of the Wilkes Land Anomaly (WLA) shown in Figs 4 & 5. Compiled from Victoria Land Traverse and Adélie Land Traverse ground-based gravity and seismic surveys (after Rouillon 1960, Weihaupt 1961, Weihaupt et al 2010, Weihaupt et al 2012), from airborne radiosound survey (after Steed & Drewry 1982), from airborne gravity and magnetic survey (after Ferraccioli et al 2001) and from the BEDMAP2 dataset (after Fretwell et al 2013). b. Mosaic of RADARSAT imaging of the continental ice sheet surface overlying the WLA, reflecting the subglacial morphology of the craterform structure.…”

“…The subglacial topography of both the WSB and the WLA reported by the VLT has been further confirmed by more recent investigations in the region related to the continental ice sheet, crust, lithosphere and mantle. These include airborne radiosound survey (Steed & Drewry 1982, Lythe & Vaughan 2001), airborne magnetic survey (Ferraccioli et al 2001), airborne gravity survey (Jordan et al 2014) and satellite remote sensing (Reigber et al 2002, Weihaupt et al 2010), as well as WISE/ISODYN British-Italian multidisciplinary surveys involving aeromagnetic, aerogravity, seismic, electrical conductivity and petrologic studies (Bozzo & Ferraccioli 2007). All report the subglacial topography of the WSB and the WLA to be in very good agreement with that of the original VLT ground-based survey.…”

On the detection of the Wilkes Land impact crater

“…A giant impact crater beneath the Wilkes Land ice sheet was first proposed by Schmidt (1962); the hypothesis was developed by Weihaupt (1976), challenged by Bentley (1979) and supported by Weihaupt (2010). The Wilkes Land anomaly or mascon was first reported by von Frese et al (2006Frese et al ( , 2009 analyzing satellite gravity data available at that time.…”