The kinematic significance of small-scale structures from a part of Singhbhum thrust-belt, Central Singhbhum, Eastern India

Abstract

The wide zone of shearing demarcating the thrust-belt in central Singhbhum is characterized by the presence of a single set of shear planes (ab-plane). The dominant linear structures present on these planes-mineral lineation, streaking, grooving, major axis of deformed pebbles and axis of small-scale folds and puckers-are all parallel to striae on slickensides, and thus indicate the direction of tectonic transport. The small-scale folds in the direction of tectonic transport appear to have formed due to non-collinear movements; while the deformed pebbles indicate that they were stretched and flattened on the same surface. The c-axes of quartz, measured from quartzites affected by mylonitization, form girdles with their axes parallel to mineral lineation in the shear-zone. The thrust was not clean-cut in nature, but was manifested by mylonitization and shearing of the rocks distributed over a wide region. The attitudes of some of the overturned folds on the shear planes, flexing α-lineations, suggest an oblique-slip movement during shearing.