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The Southern Granulite Terrain (SGT) is one of the best-exposed granulite terrains suited to address some fundamental problems concerning the origin and development of granulites. The contact between Dharwar craton and the SGT is marked by a series of crustal zone shear zones like the Moyar Bhavani-Attur shear zone to the south of the regional orthopyroxene isograd. Geochronological studies reveal that the PCSZ forms a major divide between older Archaean granulite crust in the north and the younger supracrustal dominated crust in the south (Harris et al., 1994, 1996; the major Proterozoic domains in India fall in the SGT and comprise of the Nilgiri Block (NB), the Madras Block (MB), the Madurai Granulite Block (MGB) and the Trivandrum Block (TB) (Hariss et al., 1994; Jayananda and Peucat, 1996; Braun and Kriegsman, 2003). The major shear zones demarcating these blocks are, the Moyar shear zone (between the transition zone and the Nilgiri block), the Moyar Bhavani and the Palghat-Cauvery shear zone (between  adras/Nilgiri Blocks and the Madurai Granulite Block) and the Achankovil shear zone the local scenario it can be noticed that the gneisses show wide variations. They are sometimes migmatitic gneisses, garnet-biotite gneisses or simply biotite gneisses. The intrusives are generally elongated or elliptical bodies having sharp contacts with the country rocks and are always associated with major lineaments in the block.The study area has a late orogenic structural evolution produced the main D3 folding, which transposed previous structures into a NE-SW trend. The doubly plunging fold axis produced dome-and basin structures. The attitude of the F3 folds varies from upright or slightly overturned to locally recumbent towards the NW. Granite dikes were intruded along S3 axial
planes. Large D3 fold limbs are often strongly deformed, intensively migmatized and intruded by garnet- and cordierite-bearing granites.The present study involves most of the structures identified for the study area and it has been classified for the different regions. This structures are relates with the major shear zone in the SGT. The temperature variation during the crystallization and the structural trends are also mentioned for this study.

International Journal of Engineering Science Invention ISSN (Online): 2319 – 6734, ISSN (Print): 2319 – 6726 Volume 3 Issue 8 ǁ August 2014 ǁ PP.53-59
Department of Earth Sciences, Annamalai University, Annamalai Nagar
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