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Figure Caption. Total field anomalies of Figure 6 plotted over topography. Positive anomalies are noted by thin-black lines, the zero-contour line is thickened, and negative anomalies are marked by thin-white on thicker-black lines. Contour interval is 1 nT. Major plate boundaries are noted by thick white lines (e.g., the mid-Atlantic ridge). Two possible western boundaries of the small Okhotsk plate (marked Ok) are dashed and denoted with question marks or X symbols. Large black numbers 1 through 11 are keyed to Table 7. Letter abbreviations are: U=Ural mountains, S=west Siberian craton, K=Kazakhstan block, E=east European craton, IS=Irtysh shear zone (e.g., Sengor et al., 1993), TF=Talasso-Fergana strike-slip fault (e.g., Roecker et al., 1993), TS=Tien Shan mountains.
Arctic and Asia Lithospheric Satellite Magnetic Anomalies*
Douglas Alsdorf1, Patrick Taylor2, Ralph von Frese3,
Robert
Langel2 and James Frawley4
1Dept. of Geological Sci. and INSTOC, Cornell Univ.,
Ithaca, NY
2Geodynamics Branch, Goddard Space Flight Center, NASA,
Greenbelt MD
3Dept. of Geological Sci. and Byrd Polar Research Center,
Ohio State Univ., Columbus, OH
4Herring Bay Geophysics, Maryland, USA
*Physics of the Earth and Planetary Interiors, v. 108, pp. 81-99, 1998
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 also 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 the crustal blocks. If the gradient of this contrast is marking the main Uralian fault, then the fault may extend southward to a latitude coincident with the middle of the Aral sea. Large scale strike-slip fault systems are evident in Asia and are well delineated by the long-wavelength magnetic anomaly field.
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