Superposed Folding in the Northern Part of the Gangpur Series, Orissa

Precambrian metasediments in the northern part of the Gangpur Series, represented by mica schist, phyllite-slate, and schistose quartzite have been investigated over an area of 50 sq km around Lase (22°21' ; 84°45') of Sundargarh district, Orissa. Structural analysis reveals that the earliest folds in bedding (S₁) were reclined in nature, but they have been blurred by the profuse development of axial plane schistosity (S₂). S₂, however, shows upright to slightly overturned folds plunging moderately to E to ESE. The most dominant attitude of S₂ nearly normal to the regional fold axis points to the reclined geometry of the folds in S₁. Non-penetrative fracture cleavage surfaces (S₃) have developed parallel to the axial planes of S₂-folds, generally displacing the folded segments. The S₃-surfaces, however, show appreciable fanning.