Crustal geology of Ellsworth Land and the southern antarctic peninsula from gravity and magnetic anomalies

Abstract

The subglacial geology and crustal structure in Ellsworth Land and the southern Antarctic Peninsula are discussed on the basis of gravity and magnetic anomalies and physiographic, geologic, and limited seismic refraction data. High-amplitude magnetic anomalies with sources close to the base of the ice were found in the southern Antarctic Peninsula. The Jones Mountains area also has many magnetic anomalies whose origin near the base of the ice is consistent with the shallow ‘magnetic basement’ measured in Marie Byrd Land to the southwest. The few magnetic anomalies in a central area of Ellsworth Land suggests a deeper basement, and possibly a thick metasedimentary section associated with that of the Ellsworth Mountains. Several lines of evidence indicate that in spite of some structural similarities the Antarctandean geology of the southern Antarctic Peninsula is not continuous with the Ellsworth Mountains. At one location on the mountainous Antarctic Peninsula where good subglacial topographic control exists from seismic soundings, a detailed study of the terrain effect shows that it is not possible to obtain quantitative information from the gravity data about density variations associated with local lithologie changes. The mean free-air anomaly in Ellsworth Land is +11 mgal, indicating that the area is approximately in isostatic equilibrium. Although high free-air anomalies were observed on several crossings, the southern Antarctic Peninsula is shown to be regionally compensated. Bouguer anomalies suggest that the crust of the Antarctic Peninsula extends several kilometers deeper than that of Ellsworth Land.