Geometry of Fold Structures and Their Interference Patterns in Banded Iron Formation of Eastern Limb of Bonai-Keonjhar Belt, Odisha, India

Abstract

The Bonai-Keonjhar belt of Odisha is famous for its potential iron formation that lies in the western flank of the North Odisha Iron Ore Craton (NOIOC). This horse shoe shaped belt having two limbs form a distinct ‘U’-shaped pattern, which is considered as the youngest Iron Ore Group. Banded Iron Formation (BIF) of the Precambrian age occurs in huge amount in the belt comprising of alternate layers of iron bearing minerals and silica along with iron ores and associated rocks. The abundant lithomembers of the study area that comprise of banded hematite jasper, banded hematite quartzite, banded hematite chert, banded shale and ferruginous shale are un-metamorphosed and lack of any intrusive. The general structural disposition of the rocks of the belt is a synclinorium trending NNE-SSE direction having low plunge towards NNE. The rocks of the area are experienced with prolonged deformations correlated with iron ore orogeny and impact has been manifested in form wide range fold geometry. The structural disposition and pattern of the study area consist of three distinct types of folds, which represent deformation history of the area and individual geometric dissimilarity. One set of folds is found to be open upright folds of symmetric or asymmetric nature. The second set consists of tight isoclinal folds, which are horizontal or overturned. The third set comprises of more open folds with broad warps. Such folds of three generations have been superimposed to produce different types of interference patterns.