Palghat Gap — A Dextral Shear Zone from the South Indian Granulite Terrain

The origin of Palghat Gap, the most prominent discontinuity in the Western Ghats, is controversial. The rocks of the Gap — hornblende-biotite gneiss, mylonitic augen gneiss, charnockite and amphibolite are characterised by three groups of folds formed during two deformations. Shear indicators like augens, pull-aparts, rootless folds, sheath folds, minor shears and quartz fabric strongly suggest ductile dextral shearing. Kinematic analysis of structural elements supports shearing in a N-S compressional field with XY being subvertical. Features on both mesoscopic and microscopic scales strongly favour Palghat Gap being treated as a ductile shear zone. The present Gap topography is the product of shearing and erosion.