Regional scale strain variations in Banded Iron Formations of Eastern India: results from anisotropy of magnetic susceptibility studies

Anisotropy of magnetic susceptibility (AMS) data are used as a tool to determine strain variations in different parts of the Banded Iron Formations (BIFs) of the Bonai Synclinorium, eastern India. AMS data of 88 cylindrical cores drilled from 29 samples collected from the limb and hinge parts of mesoscopic scale folds as well as different parts of the entire synclinorium are presented. It is found that the samples from limbs of small-scale folds and also from limbs of the regional scale synclinorium have higher degrees of anisotropy than the hinges. This is inferred to indicate that the limbs accommodated higher strain than the hinges. AMS orientation data are analysed in conjunction with field data. It is concluded that the magnetic fabric developed in the limbs as well as hinges of the BIFs of the study area is related to deformation and is not a manifestation of sedimentary fabric.