Geometry of Superposed Deformations in Hesadi-Tebo Area, Western Singhbhum, Bihar

Abstract

Abstract The study reveals three generations of deformation which have produced two splanes and a host of linear structures with complex geometric relations. All the three fold systems are, however, not equally developed all over the area and the associated structures also regionally vary in orientation and angular relation; this has resulted in diverse geometric patterns in different subareas. The first deformation produced subhorizontal folds (F1) on bedding (S1) with strongly developed axial plane schistosity (S2). These folds are refolded, along with S2, about a set of steeply plunging axes (F2) at high angles with the F1 axes (60° to 90°). The main structural closures defined by Hesadi antiform and Kamrora synform are caused by the second folds (F2). On these structures are superposed a subhorizontal E-W trending set of folds (F3) with northerly dipping axial planes, resulting in dispersal of all the earlier lineations. The F3 folding was also accompanied by shearing in several tracts producing shear cleavage (S3) with downdip striation and groove lineations. The F3 folds show somewhat regular plunge reversals on macroscopic scale forming highly elongated domes and basins. An attempt has been made to restore the original attitudes of the fold systems.