Tectonic Phases and Crustal Evolution in a Part of the Eastern Chotanagpur Gneissic Complex

The area in and around Jabarban-Belamu (23°25' - 23°29'N, 86° - 86^c05'E) of the Purulia district, West Bengal, bears evidences of polyphase deformation, metamorphism and magmatic activity in the eastern Chotanagpur complex. At least four phases of deformation are imprinted on the rocks since the sedimentation ( ∼ 2300 Ma) of the metasedimentaries up to the last phase of granitic activity (∼800 Ma). A regional north-south compression was responsible for the development of isoclinal or tight F₁ and F₂-foIds with nearly east-west axes and overturning towards south. Ultrametamorphism of the older sediments during the acme of F₁-deformational phase formed the anatectic granitoids and migmatites. Younger plutonic granitoids were emplaced in the axial zones of the F₂-folds. Nearly east-west compression during the third deformational phase caused north-south trending open type cross folds (F₃). Pegmatites and hydrothermal veins were mostly synkinematically emplaced in the ENE-WSW trending shear zone developed during the fourth phase of deformation. These features serve to illustrate the evolution of the Chotanagpur Complex in the Eastern Indian Shield.