Arctic and Asia lithospheric satellite magnetic anomalies

Abstract

The polar regions present special problems in magnetic studies because they are largely inaccessible and contain the most disturbed magnetic fields on earth (e.g., effects from auroral phenomena). A processing method, previously developed for south polar satellite magnetic data (e.g., Magsat), is applied to north polar data to separate the core and external fields from the lithospheric anomalies. The core field is removed with a least-squares procedure and Fourier correlation coefficient filtering effectively reduces the external field signatures. As demonstrated by improved correlation coefficients and reduced sum-of-squared differences between passes and between dawn and dusk maps, the processing effectively extracts the static geologic signal from the dynamic noise (e.g., external fields). Quantitative comparisons of the resulting lithospheric anomaly map with previous maps suggest that the processing maintains anomaly amplitude while significantly reducing non-lithospheric energy. The map shows a long-wavelength contrast across the Ural mountains, the suture zone between the east European craton (+4 nT) and the west Siberian platform (−4 nT). This contrast might be indicative of significant petrologic differences between these large crustal blocks. If the steepest portion of the magnetic gradient is marking the main Uralian fault, then the fault may extend southward to a latitude coincident with the middle of the Aral sea. The easternmost section of the intraplate Tien Shan is marked by a +3 nT anomaly whereas the remainder of the mountain belt is not associated with a significant anomaly. This pattern agrees with previous interpretations that suggest the eastern Tien Shan is supported by a lithospheric root and the rest of the belt is held up by a positive buoyancy force, i.e., it lacks a root.