Modification of Flexural Folds by Flattening Process-Examples from the Aravalli Rocks of Zawar Mine Area, Rajasthan

Study of two broadly similar folds from the Aravalli rocks of Zawar Lead-Zinc Mines area south of Udaipur in Rajasthan, shows that the folds are tight to isoclinal with wavelength/amplitude ratio between 0.35 to 0.37. The thickened hinges and the stretched limbs (√λ₂/λ₁=0.3) of the folds, and the weakly convergent pattern of the isogon lines suggest that the folds belong to the flattened parallel type. The axial plane cleavage in the rocks is a crenulation cleavage formed by microfolding and migration of quartz from the limbs, which make an angle less than 40° with the axial surfaces of the microfolds. Although some slip has occurred along the cleavage after it formed, this slippage has not altered the shapes of the folds to any great extent. The folds are thought to have been modified by post-buckling homogeneous strain aided by migration of quartz from the limbs to the hinges of the folds.