Polyphase deformation of the rocks of Pakhal Supergroup around Tekulapalli, Khammam District, Andhra Pradesh

摘要

The metasedimentary rocks (phyllite, quartzite and impure marble) belonging to Pakhal Supergroup of Mesoproterozoic age, occurring north/around Tekulapalli, have been involved in folding of four generations, hitherto, not described. The four generations of folding are uniquely exhibited in impure marble. The earliest structure is very tight to isoclinal folds (F_1) on bedding plane (S_0),with a pervasive axial planar cleavage (S_1).They have been affected by co-axial, open to tight, upright F_2 folds with axial plane striking NNE-SSW. As a consequence, the F_1 folds range from recumbent/recline through inclined to upright attitude at different places. Both F_1 and F_2 folds are of buckling origin. Open recumbent folds (F_3) affecting S_1 cleavage and S_1 axial planes, at places F_2 axial planes, represent structure of third generation. The latest structures in the area are upright, conjugate folds and kink bands (F_4) with axial plane striking N-S, E-W and chevron folds with NW-SE-striking axial planes. The F4 structure has formed due to longitudinal shortening in the horizontal direction during the last stage of deformation.