Tectonics of the Neoproterozoic Southern Granulite Terrain, South India

Geological correlations between South India and adjacent Gondwana fragments are hampered by the lack of a coherent structural framework for India's Southern Granulite Terrain (SGT). This paper is an attempt at delineating its large-scale geometry and Neoproterozoic kinematics and tectonics. The basic regional pattern is that of a high-grade gneissic layering produced during several deformation stages (grouped as D-1), which became refolded during two regionally separated phases of upright folding (D-2a: NNW trending; D-2b: NE trending) and reworked in E- to ESE-trending zones of increased strain (D-3). Of these, the Palghat Cauvery Shear Zone (PCSZ), which marks the boundary between Archaean terrains in the north and Proterozoic belts in the south, may represent a major crustal shear zone, whereas the Achankovil Zone (AZ) is better considered as a high-strain zone characterized by flattening with a reverse component. D-1 structures developed close to the peak of Pan-African high-grade metamorphism. D-2a and D-2b occurred on the retrograde path, partly at supersolidus and partly at subsolidus conditions. D-3 high-strain zones show subsolidus textures. In view of the general clockwise nature with a clear decompressional component of all published P-T paths, we propose that D-2-D-3 Occurred during partial exhumation of the terrain. Correlations with Madagascar are weakened as the AZ is no longer considered a major crustal shear zone, whereas correlations with Sri Lanka are strengthened by the presence of a similar syntactical bend possibly produced by an indentor. (c) 2005 Elsevier B.V. All rights reserved.