Large scale fold interference in a metamorphic-migmatitic complex

Abstract

In the Precambrian terrain of central Rajasthan, India, interference of folds abounding in the scale of hand specimens and outcrops is confirmed for larger scales also from the map patterns and the distribution patterns of lineations and foliations. The map patterns include double closures and mirror-image type formational boundaries. The axes of the reclined, isoclinal, early folds with a wide variation in attitude often plunge westward or eastward down the dip of the limbs of the later folds. The later upright folds trend north-northeast but plunge variably from subhorizontal to subvertical, depending on their location in the limbs or hinges of the early folds. The s-pole diagrams show the effect of interference by superposed folding in fairly perfect girdles around the lateraxes, in rotation around later axes of partial girdles due to early folding, and in the seemingly haphazard patterns caused by rotation of complete girdles on early fold axes by later folding on north-northeast-striking axial planes. The later axial planes remain the plane of symmetry in the s-pole diagrams so long as they are vertical with a constant strike. The degree of acuteness of the later folding shapes the map patterns and the s-pole diagrams. In all the instances cited, the two sets of axial surfaces are subparallel in strike though not in dip, with the early reclined folds plunging west to west-north-west involved in upright folding on north-northeast-striking axial planes.