Fold Interference Patterns in the Sausar Group, Northern Nagpur District, Maharashtra, India

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Abstract The Precambrian metamorphic rocks of the Sausar Group of the northern Nagpur district, Maharashtra have a polyphase structural history. Three distinct fold phases (F1-Fs) have affected these rocks. The first folds which are tight to isoclinal structures of general' similar type' are developed throughout the region, while structures related to later deformations show a discontinuous development. The first folds have been refolded into a set of close to tight structures (F2) on axial surfaces oriented close to earlier axial direction and dipping steeply S. The superposition has given rise to Type 3 interference pattern which is manifest both in the map pattern and on the scale of outcrops. Fs fold phase has produced open, nearly upright folds with axial traces running N/NNE and axes plunging generally steeply S., the steep plunges resulting from the superposition of these folds on steeply dipping limbs of early structures. In contrast to the much simpler pattern shown by the map in the domains of major Fs folds, the outcrops reveal on a small scale a conspicuous development of Type 1 interference pattern largely in the hinge zones of the late structures, resulting from the superposition of minor Fs on minor F2 structures. The style of structures of different generations and the pattern of their development in the region seem to suggest that the intensity of deformation has gradually declined from F1 to Fs and that the concentration of fold movements has varied rather rapidly within small areas of the fold belt during later phases causing discontinuous development of related structures.