Kinematics in a Sheared Granite Outcrop Lacking Stretching Lineation – A Case Study from the Bangriposi Region (Eastern India)

ABSTRACT In this paper, a modus operandi is proposed to carry out kinematic analysis of sheared granitic rocks that have well-developed foliation, but lack a visible stretching lineation. The case of a sheared Mayurbhanj Granite outcrop having alternate foliated leucocratic and melanocratic bands, but no lineation, is discussed. It is demonstrated that Anisotropy of Magnetic Susceptibility (AMS) studies help to identify the kinematic reference frame (XZ of the strain ellipsoid). Therefore, microstructures in thin sections prepared parallel to the latter can provide the correct information about the sense of shear. Following this, we analysed Crystallographic Preferred Orientation (CPO) of quartz c-axis in the leucocratic band sample and established a top-towards-NE sense of shear. Oblique set of fractures in feldspar porphyroclasts in the melanocratic band sample from the same outcrop are inferred to have developed perpendicular to the maximum instantaneous stretching axis (ISAmax) and are kinematically compatible with the same top-towards-NE shearing affecting the leucocratic band. It is concluded that the adopted approach of integrating field, AMS and microstructural studies can help in outcrop scale kinematic analysis of sheared granites.