Structural and tectonic analyses of the Chhotanagpur Gneiss Complex of the Eastern Satpura Orogen, India: Significance for a global model

The Chhotanagpur Gneiss Complex, covering the eastern part of the Satpura Mountain Belt of India, has records of polyphase deformation and metamorphism of Proterozoic Eon. Analysis of structural evolution of the region, combined with the tectonothermal history, has shown that the regional ∼E-W alignment was developed during the second phase of deformation, high-grade metamorphism and magmatism at ∼1500 Ma. The migmatites preserve records of an early phase of deformation, metamorphism and magmatism of >1800 Ma. Relict monazite and zircon grains have two age ranges. The older age (>2531 Ma) represents the Archean cratonization event, and the younger age (∼2216 Ma) corresponds to the first deformation, metamorphism and magmatism during amalgamation of the North Indian Block (Bundelkhand Craton) and the South Indian Block (Bastar and Singhbhum cratons), forming the Satpura Orogen. This Orogeny caused complete reset of the isotopic clock, and initiated it from ∼2000 Ma. A phase of separation (basin opening during 2000–1750 Ma) took place on both the sides of the young orogen. The second orogenic event of ∼1500 Ma has been identified to be the result of amalgamation of the Singhbhum Block and the Chhotanagpur Gneiss Complex, during the Eastern Ghats – Dalma Orogeny Phase I. The second deformation-metamorphism was followed by another phase of extension and basin opening at ∼1200–1100 Ma. The third deformation and metamorphism in the Complex took place during the Eastern Ghats – Dalma Orogeny Phase II of 1100–850 Ma, having the maximum probability at ∼926 Ma. This orogeny developed folds with ∼NNW-SSE to N-S axial traces, nearly orthogonal to the fabric defining the Satpura trend. Records of any block amalgamation of <1800 Ma within the Chhotanagpur Gneiss Complex are not found.