Interpretation of ground and aeromagnetic surveys of Palmer Land, Antarctic Peninsula

Abstract

Aeromagnetic data for Palmer Land provide new information on crustal structures of the Antarctic Peninsula. Features shown on the compilation of the Lassiter Coast and Orville Coast are characterized by systems of subparallel regional anomaly zones and lineaments. The magnetic data reveal the widespread presence of an orthogonal pattern of crosscutting linear discontinuities that can be interpreted as a Late Cretaceous/Early Tertiary fracture pattern. The main displacements in the anomaly pattern between the two units are recognized in Wetmore-Irvine glaciers area where the structure of the Antarctic Peninsula changes orientation from SW-NE to S-N. The NW-SE trending transitional zone is probably a transfer zone associated with north-westerly movement of the Lassiter Coast crustal segment relative to the Orville Coast segment. Within the Lassiter Coast a fragment of Pacific Margin Anomaly (PMA), Central Plateau Magnetic Anomaly and East Coast Magnetic Anomaly (ECMA) are mapped. Two-dimensional modelling suggests that PMA is caused by a limited depth body (8 km) consisting of numerous plutons, probably, of different ages, composition and magnetization. The Central Plateau Magnetic Anomaly and the Merrick-Sweeney-Latady zone of the Orville Coast are represented by strong positive anomaly bands that are associated with gabbro-diorite rocks and accompanying plutons intruded near by the border of Mount Poster Formation and Latady Formation. The ECMA are alignments of high-amplitude magnetic anomalies caused by gabbro-diorite bodies, which are located within the framework of the Cretaceous granite-granodiorite plutons. Granite-granodiorite plutons of Lassiter Coast Intrusive Suite are mostly reflected by positive anomalies (100-500 nT). Modelling studies and the character of distribution of the magnetic anomalies suggest that the plutons of Lassiter Coast Intrusive Suite are prominently reflected in magnetic anomalies of regional extent. The plutonic activities during the geological evolution of Palmer Land have been a more important process than what is apparent from rock outcrops. Magmatic activity abruptly diminished westward from the Behrendt Mountains apparently due to a modification of the crustal structure of the Antarctic Peninsula. The area between the Evans Ice Stream and the Behrendt Mountains is possibly underlain by the non-magnetic equivalent of the Haag Nunataks basement, similar to that which has been inferred for the Ellsworth Mountains.