ANISOTROPIC MAGNETIC-SUSCEPTIBILITY IN THE CONTINENTAL LOWER CRUST AND ITS IMPLICATIONS FOR THE SHAPE OF MAGNETIC-ANOMALIES

Magnetic anisotropy measurements on samples from the lower continental crust were made to test the hypothesis that anisotropy may cause deflection of the peak-to-trough axes of magnetic anomalies caused by mid- to lower crustal sources. Average anisotropy (P') for these samples is 1.5 but can be as high as 3.4. Felsic granulite facies rocks show the highest anisotropy. Magnetic sources with P' equal to the maximum determined in this study can cause azimuthal rotations of magnetic anomalies by up to about 25-degrees, but P' lower than or equal to 1.5 causes no significant rotation. Comparison of the model results to the abnormal shape of some magnetic anomalies in southern Italy indicate that these anomalies cannot be related easily to a strong and coherent AMS of the source rocks. The most probable explanation of such shapes is the existence of a strong remanent magnetization in subsequently rotated source bodies.