Polyphase Folding Deformation in the Hutti-Maski Schist Belt, Karnataka

Three phases of folding deformation (F₁, F₂ & F₃) are recognised in the Hutti-Maski schist belt. The first two phases (F₁ and F₂) are quite pronounced producing regional folds whereas the last one (F₃) is of mild intensity. F₁ folding is accompanied by the development of schistosity (S₁) in metabasalt and metasedimentaries, mylonite banding (S_d) in gold quartz veins and minor folds on bedding plane (S_o) and vein quartz. Two major F₁ folds, viz., a syncline and an anticline could be traced in the area on the basis of orientation of pillow structure in metabasalt. Gold mineralisation in Hutti-Maski schist belt is mainly controlled by first phase of folding (F₁) and associated regional metamorphism. F₂ fold shows clear evidence of superposition on F₁. F₁ axial trace is folded by F₂ folds. F₂ folding is accompanied by the development of crenulation or slip cleavage (S₂), minor folds on S₁ and S_d and shear fractures and faults. F₂ fold is represented by two major folds, viz., an antiform and a synform having axial traces along NNW-SSE to NW-SE direction and plunge around 45° to 50° towards Nw to NNW. A time gap between F₁ and F₂ is marked by the intrusion of a granodiorite body. F₃ is developed on the limbs of F₂ folds, and is accompanied by the development of S₃ cleavage and kink band or chevron folds. Axial plane of F₃ fold trends N75°E-S75°W (approx.) with vertical dip. Fold axis (F₃) shows very steep westerly plunge.