Angular Unconformity, Structural Unity Argument and Sargur-Dharwar Relations in Bababudan Basin

Recent mapping by the authors in southern Bababudan has confirmed tbe angular unconformity between the Dharwar cover and Sargur-Peninsular Gneiss basement. The original structural trend of Sargur Group is preserved in an unmodified form in the low strain zone near Kalasapura. In the structural domain of eastern Bababudan with its N-S trends, the underlying Sargur enclaves retain their old N-S orientation but with minor rotation and enhancement during Dharwar overprinting. The apparent structural unity between the basement and cover, therefore, is due to the repetition of a stress regime similar to that of Sargur during the later Dharwar orogeny, which is a common feature of most Archaean cratons. Even in such domains of superposed deformation, the Sargur Group is lithologically distinct from the Dharwar cover rocks and occurs as a train of migmatised enclaves in Peninsular Gneiss, whereas the Dharwar cover forms a large athwart-lying fold belt with mature basal conglomerate preserved in the unaffected parts. These are prima facie evidences for separation of the Sargur and Dharwar into two distinct orogenies. Structural unity per se, divorced from regional stratigraphic considerations, is apt to be grossly misleading in interpreting the geological history of multiple deformed terrains.