Structural framework of the transpressive Mahanadi Shear Zone and reevaluation of the regional geology in the northern sector of the Eastern Ghats Mobile Belt, Eastern India

Abstract

Mahanadi Shear Zone (MSZ) is located in the northern segment of the Eastern Ghats Mobile Belt (EGMB), represented by extensive mylonitization. WNW-trending mylonitic foliation has a moderate-to-steep dip towards NNE. Kinematic indicators such as asymmetric folds, shear bands, quarter structures, suggest dextral ductile shear sense of the dominant strike–slip component and reverse sense of the less prominent dip slip component. Predominance of foliation over lineation indicates flattening strain. Reverse movement and flattening strain confirm shortening. The MSZ is a transpressional zone with simple shear along and pure shear (shortening) perpendicular to the mylonitic fabric. Wide variation in plunge of stretching lineation, presence of back-rotated clasts and 0 < Wk < 1 on two sections oblique to the mylonitic foliation, suggest triclinic symmetry of deformation. This study demonstrates that the width of the MSZ—located in the northern part of the Phulbani Domain—extends beyond 38 km. It covers the entire ‘Tikarpara Domain’ in the north of Phulbani Domain and put the very existence of Tikarpara Domain in question. Lithounits of Phulbani Domain continue to the north across the southern boundary of the MSZ, through Tikarpara Domain and Angul Domain up to the Northern Boundary Shear Zone (NBSZ). It is proposed that the entire area comprising the Phulbani Domain, the MSZ, and the region further north up to the NBSZ, form part of a single domain—Phulbani Domain. MSZ is an outcome of intra-terrane transpression. Thus, this study also questions the credibility of the domainal classification of the EGMB.