Crustal Magnetic Anomalies in the Antarctic Region Detected by MAGSAT.

Abstract

Crustal magnetic anomalies in the Antarctic region were studied with the MAGSAT CHRONFIN data of 1790 passes.The GSFC(12/83) model was used to reduce the earth's core field to estimate the residual magnetic field. Obtained residual intensity data in the geomagnetic coordinates were averaged over 1 hour magnetic local time (MLT) and 1° invariant latitude, and then grouped by taking the planetary magnetic activity index (Kp) as a parameter to derive the Mean Polar Disturbance Fields (MPDFs).The obtained MPDF for Kp=20, for example, amounts to 50nT at 85°S and decreases monotonically toward lower latitudes on the dawnside. On the duskside, the MPDF takes a small value of 10nT at 85°S, decreases to a negative peak of -30nT at 78°S, recovers to a smaller positive peak of 20nT at 62°S, and then decreases to zero at further lower latitudes. These characteristic features of the MPDF are attributable to the external fields produced by Sqp currents with occasional eastward electrojet in the ionosphere, which are superimposed by the magnetic field due to the westward ring current in the magnetosphere.The MPDFs for Kp values from 00to 20 were subtracted from the residual intensity data, and the resultant data were averaged for 3° by 3° in latitudes and longitudes to obtain crustal magnetic anomalies at a mean altitude of 450km. The anomaly contours at an interval of 2nT reveal long-wavelength (-500km) crustal magnetic anomaly patterns with a clear correspondence to geologic provinces.The anomalies in the oceanic area are negative for abyssal plains, while they are positive for ridges and plateaus. The tectonically active Scotia Sea microplate region is associated with negative anomalies. Land areas of Antarctica are characterized by three positive anomalies over Enderby Land, Gamburtsev Subglacial Mountains and Wilkes Land. Negative land anomalies are also definitely related to geologic provinces such as Queen Maud Land, Queen Mary Land, etc., but a detailed interpretation of overall magnetic anomaly pattern requires more comprehensive geological and geophysical studies.