Discriminating Tectonic and Magmatic Fabrics in the Remal Granite Gneiss: Implications for Terrane Amalgamation Processes in Southeastern Singhbhum, India

Abstract

The Remal granite gneiss body in the southeastern part of the Singhbhum Craton, near its contact with the Rengali Province, preserves two orthogonal penetrative foliations. The subhorizontal foliation defines cross and trough bedding structures, and is characterized by (i) systematic grain-size variation between the layers, (ii) the presence of feldspar laths and (iii) graphic intergrowth textures, confirming that it is primary and of igneous origin (Sign). Sign has a non-planar geometry and shows a spread in orientations, while a later foliation of tectonic origin is defined by alternating biotite-rich and biotite poor bands that define a consistently oriented gneissic foliation (S1). S1 gneissic layering is associated with the alignment of biotite flakes and myrmekite formation, and operated under low grade metamorphic conditions. S1 shows a remarkable similarity in orientation with the shear fabric along the amalgamation front of the Rengali Province with the Eastern Ghats Province further to the south, indicating that strain related to this regional strike-slip event can be identified even in southeastern Singhbhum.