Petrogenetic Model of A-Type Granitoids of the Kullampatti Area, Salem District, Tamil Nadu, India

The late Proterozoic granitoids at Kullampatti are of A-type and comprise three phases: (1) barren phase I (granite-adamellite), (2) fertile phase II (trondjhemite) and (3) rarely-mineralized phase III (pegmatitic granite). They were emplaced within the Archean cratonic granulite terrane of southern India, close to the Moyar-Bhavani-Attur shear zone, and form a consanguinous association with the Suriyamalai or Sankari granite-adamellite batholithic dome. On the basis of their field, tectonic, petromineragraphic and geochemical aspects, a petrogenetic model involving a two-stage melting of an undepleted middle to lower crustal granulitic protolith is envisaged. In this, the first-stage melting led to the formation of an LCT-rich hydrous melt that was removed from the site of its generation, followed by second-stage partial melting of the depleted granulite during post-orogenic or anorogenic environment, resulting in the HCD- and HFS-rich, NYF- and A-type melt that on fractional crystallization, together with hydrothermal activity, led to the formation of these granitoids.