Application of AMS method in the interpretation of devlopments of high grade metapelitic rocks of Late Neoproterozoic of Shotor Kuh metamorphic complex

Late Neoproterozoic Shotor Kuh metamorphic- igneous complex cropped out in 80 km southeast of Shahrood, include a wide range of igneous and metamorphic rocks such as metapelite, metabasites, metacarbonate, metapsammites and gabbros, olivine gabbros and diorites. In this study, the variations of magnetic parameters of high grade metapelitic rocks have been investigated during the migmatization and granitization processes. The carried out investigations indicate that the average magnetic susceptibilities (Km) decreased from 650 μSI to 3 μSI through the mentioned processes. This decrease is a reflection of the mineralogical and lithological changes, among of the decomposition-dehydration reactions of biotite and the conversion of biotite to orthoclase or muscovite in the transition from gneiss to granite. Garnet, biotite and with a lesser extent, opaque minerals (ilmenite or magnetite) are important magnetic carriers of the studied rocks. The average corrected magnetic anisotropy varies from 1.008 to 1.45 and also the shape parameter values of these rocks vary from-0.44 to 0.96. Based on the interpretation of magnetic fabric, most of the magnetic ellipsoids of gneisses are in oblate shape. The obtained magnetic foliations from the interpretation of magnetic data show a good corresponding with the measured magnetic foliations in the field