Structural pattern in Sukma supracrustal rocks near Nagaras, southern Bastar Craton

Abstract

The Precambrian Sukma supracrustal sequence near Nagaras, southern Bastar Craton, has been mapped as two quartzite lithounits and an intervening undifferentiated unit comprising Mg-Al rich granulite, mafic granulite, amphibolite and hornblende schist. The rocks bear imprints of three phases of deformation. The structures of the first generation are represented by rarely occurring small isoclinal folds (F-1) on bedding (S-0), and pervasive axial planar foliation (S-1). The folds of second generation (F-2) vary from open to close, and upright to locally overturned with NNW-SSE to NNE-SSW striking axial planes. Gentle warps with ESE-WNW striking axial planes represent folds of the third generation (F-3). Superposition of F-3 folds on F-2 folds has resulted in dome-and-basin interference pattern in both small and large scales. The map pattern is elongated in the N-S direction because of control by F-2 folds, and slight concave geometry towards west is the result of F-3 folding.