Structural geometry of the early Precambrian terrane south of Coimbatore in the “Palghat Gap”, southern India |
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Authors: | K Naha R Srinivasan G K Deb |
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Institution: | (1) Department of Geology and Geophysics, Indian Institute of Technology, 721 302 Kharagpur, India;(2) National Geophysical Research Institute, Uppal Road, 500 007 Hyderabad, India;(3) Present address: Geological Studies Unit, Indian Statistical Institute, 203 Barrackpore Trunk Road, 700 035 Calcutta, India |
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Abstract: | The ENE-plunging macroscopic folds, traced by calc gneiss interbanded with marble and sillimanite schist within the Peninsular
Gneiss around Suganapuram in the ‘Palghat gap’ in southern India, represent structures of the second generation (D2). They have folded the axial planes of a set of D1 isoclinal folds on stratification coaxially, so that the mesoscopic D1 folds range from reclined in the hinge zones, through inclined to upright in the limb zones of the D2 folds. Orthogonal relation between stratification and axial planar cleavage, and ‘M’ shaped folds on layering locate the
hinge zones of the D1 folds, whereas folds on axial planar cleavage with ‘M’ shaped folds are the sites of the D2 fold hinges. Extreme variation in the shapes of the isoclinal D1 folds from class 1B through class 1C to nearly class 2 of Ramsay is a consequence of buckling followed by flattening on layers
of widely varying viscosity contrast.
The large ENE-trending structures in this supracrustal belt within the Peninsular Gneiss in the ‘Palghat gap’ could not have
evolved by reorientation of NS-trending structures of the Dharwar tectonic province to the north by movement along the Moyar-Bhavani
shear zone which marks the boundary between the two provinces. This is because the Moyar and Bhavani faults are steep dipping
reverse faults with dominant dip-slip component.
Deceased |
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Keywords: | Structure Palghat gap early Precambrian granulite terrane southern India |
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