Crustal structure of the area around Haag Nunataks, West Antarctica: new aeromagnetic and bedrock elevation data

Five thousand line kilometers of new airborne geophysical data are presented from the area between the Antarctic Peninsula and Ellsworth Mountains. The surveys involved total-field magnetic measurements complemented by simultaneous determinations of ice thickness by radio-echo sounding. The southernmost end of the Antarctic Peninsula shows isolated aeromagnetic anomalies of over 400-nT amplitude which correspond to discrete plutonic bodies. The central area of Fowler Peninsula shows a continuous zone of high-amplitude (600 nT) short-wavelength (5 km) anomalies attributed to metamorphic rocks which outcrop beneath the ice cover. This interpretation is supported by measurements of the magnetic properties of Precambrian rocks exposed at Haag Nunataks. Anomalies of up to 400-nT amplitude and 50-km wavelength suggest a magnetic basement between 5 and 15 km below Evans Ice Stream, Carlson Inlet, Fletcher Promontory, and Rutford Ice Stream. A more subdued magnetic signature to the west of Rutford Ice Stream suggests that the presumed crystalline basement beneath the Paleozoic sediments of the Ellsworth-Whitmore Mountains crustal block may either lie at great depth (>20 km) or have a significantly lower magnetization than the rocks exposed at Haag Nunataks. A correlation of steep bedrock scarps, magnetic anomalies, and depth to magnetic sources indicates major faults delimiting horst and graben structures formed during northeast to southwest extension. The Ellsworth Mountains uplift is attributed to a thermal response of the lithosphere on the flank of this rift system.