Deformational history of the Precambrian Kolar Schist Belt, South India: Constraints for the tectonic evolution

In the Kolar Schist Belt well-preserved small-scale diastrophic structures suggest four phases of folding (F₁ — F₄). The near coaxial F₁ andF₂folds are both isoclinal with long-drawn out limbs and sharp hinges. The axial planes of bothF₁andF₂folds are subvertical with N-S strikes; these control the linear outcrop pattern of the Schist belt. The later folds (F₃and F₄) are important in small-to-intermediate scales only and are accommodation structures formed during the relaxation period of the early folding episodes. Mesoscopic shear zones, post-F₂ but pre-F₃ in age, are present in all the rock types in this area. The F₁ and F₂ folds and the mesoscopic shear zones were formed during a continuous E-W subhorizontal compression. Available geochemical and isotopic data show that the Kolar Schist Belt with ensimatic setting is bounded by two granitic terrains of contrasting evolutionary histories. This, together with E-W subhorizontal compression over a protracted period of time, strengthens the recent suggestions that the Kolar Schist Belt represents a suture. This belt then marks the site of a continent-continent collision event of late Archaean-early Proterozoic age.