Geology and Structure of the High-Grade Rocks from Punalur-Achankovil Sector, South India

Abstract The Punalur-Achankovil sector is a southwestern segment of the high-grade granulite terrain of South India. It is characterised by charnockite and garnet-biotite. Quartz-feldspar (GBQF) gneiss with minor occurrences of sillimanite and graphitebearing gneiss and basic granulite. Structurally. The terrain has undergone three phases of intense deformation and metamorphism and a late less intense deformation. The first deformation (D1) has disrupted original depositional layering with development of quartzo-feldspathic bands; the accompanying metamorphism (M1) is represented by granulite facies sillimanite-bearing gneiss and basic granulite. The second deformation (D2) resulted in isoclinal folding and the corresponding metamorphism (M2) produced large neosome now represented by the GBQF gneiss. Lithologies representing the D3-M3 event are the charnockite and minor granite bodies developed under high-grade metamorphic conditions; open to tight" asymmetric folds are characteristic of this deformation. The final deformation (D4) is less penetrative and is characterised by open folds. Structural data from the area do not indicate any major shear zone features nor does the region constitute an intercratonic suture belt as suggested earlier. The topographic expression along Achankovil-Punalur represents only a neotectonic lineament.