Abstract Intra-terrane shear zones (ITSZs), though widespread across Proterozoic mobile belts, remain underexplored in their structural evolution and tectonic significance. This study explores the anatomy of the North Purulia Shear Zone (NPSZ), a ∼E–W trending, steeply dipping ITSZ within the Chotanagpur Granite Gneiss Complex (CGGC), eastern India. Integrated structural, kinematic, anisotropy of magnetic susceptibility (AMS) and microstructural analyses reveal that the NPSZ nucleated within megacrystic granite gneiss during late-Grenvillian tectonism (∼0.9–1.1 Ga), contemporaneous with Rodinia assembly. Field and AMS data demonstrate a sub-simple shear regime with a sinistral strike-slip component and magnetic fabrics transition from mixed oblate–prolate in host gneiss to only oblate in mylonitic zones. Recrystallized quartz grain aspect ratios increase significantly toward the core, coupled with elevated strain rates and decreasing flow stress. Deformation temperatures inferred from microstructural observation coupled with quartz dynamic recrystallization mechanisms suggest dominance of dislocation creep, which implies that the shearing took place at deep crustal level. The absence of precursor fractures or dykes and alignment of feldspar megacrysts suggest that the nucleation of the NPSZ was facilitated by anisotropy produced by the magmatic/sub-magmatic gneissic fabric, where interstitial smaller-sized quartz-rich domains in between K-feldspar megacrysts acted as viscous pathways. These findings not only provide first-order insights into ITSZ nucleation mechanisms but also reaffirm the CGGC as a site of late-Grenvillian crustal thickening related to the suturing of North and South Indian cratons during Rodinia amalgamation. The NPSZ thus emerges as a key intra-terrane tectonic structure recording Rodinia-linked crustal reworking within the Indian shield.
Banerjee et al. (Thu,) studied this question.