Magnetic anomaly patterns over crustal blocks of the King Edward VII Peninsula, Marie Byrd Land, West Antarctica

Abstract

Within the framework of the GITARA II project an aeromagnetic survey was performed during the GANOVEXVII expedition (1992/1993) over the King Edward VII Peninsula in northwestern Marie Byrd Land (West Antarctica). This region which may represent the eastern flank of the Ross Sea rift system had previously been explored only at reconnaissance level. New total field and upward continued (10 km) magnetic anomaly maps are produced and interpreted here to map and discuss the crustal structure of the Edward VII Peninsula. Tworound-shaped, high-amplitude magnetic anomalies are recognised over the Alexandra Mountains block. The anomalies are difficult to interpret since susceptibility data indicate the prevalence of non-magnetic rocks at the surface. A possible interpretation is that the anomalies are due to Cretaceous mafic intrusives distinct from weakly magnetic Byrd Coast Granite of the adjacent Rockefeller Mountains block. Alternatively the anomalies could be related to buried pluton-sized Devonian Ford Granodiorite intruded by dikes. If Cretaceous in age, the former intrusives revealed from the magnetics could also be responsible for contact metamorphism of the adjacent Alexandra Mountains migmatites. Lower amplitude circular anomalies over the Central Plateau and Prestrud Inlet are likely to be caused by unexposed Devonian Ford Granodiorite which crops out in the Ford Ranges. Elongated high-frequency anomalies of the Sulzberger Bay are similar to those recognised over seismically constrained Cenozoic rift-related volcanics of the Ross Sea. A broad magnetic low over the Sulzberger Ice Shelf may be indicative of a fault bounded graben-like basin with sedimentary infill. Overall recognition of magnetic anomaly patterns and trends reveals segmentation of the Edward VII Peninsula and of the adjacent marine areas in distinct crustal blocks. Faults may separate these blocks and they are interpreted to reflect multiple Cretaceous and maybe Cenozoic crustal extension\uplift phases within this part of the West Antarctic rift system.