Significance of Small-Scale Structures in the Kolar Schist Belt, South India

Well-preserved small-scale deformational structures in the banded ferruginous quartzite in the Kolar Schist Belt indicate four phases of folding (F₁- F₄ ) , and a shearing movement at low angle to the foliation planes. Both the F ₁ and F ₂ folds are very tight to isoclinal with attenuated limbs and sharp hinges. They are nearly (but not strictly) coaxial, resulting in type-3 interference pattern. The F₃ folds are open and recumbent or gently plunging reclined with axial trend towards NNE-SSW. The folds of the fourth generation (F₄) are of the nature of warps with vertical axial planes striking NE through E to SE. It is suggested that the F₁ folds were originally isoclinal and recumbent/gently plunging reclined with northerly axial trend, coaxially refolded by upright and isoclinal F₁ folds. As the F₂ folds became isoclines further squeezing in the same direction was accommodated by a subhorizontal shearing movement at low angle to the foliation planes. resulting in wide variation in plunge of F₁-F₂ fold axes. The F₁-F₂ folds and mesoscopic shear zones developed due to an E-W subhorizontal compression acting over a protracted period of time. The F₃ folds developed due to gravity induced vertical compression on subvertical foliations. whereas the F₄ folds indicate a longitudinal shortening during the relaxation period at the waning phase offolding episodes.