Geochemical Characteristics and Possible Origins of the Southern Closepet Batholith, South India

The polyphase Closepet batholith in South India intrudes Archean tonalitic and granitic gneisses in a terrane that grades from amphibolite to granulite grade at the southern end of the batholith. Two granite and two granodioritic suites are recognized in the batholith. One granite suite from the southern terminus of the batholith has high Sr, Ba, La/Yb, and Eu/Eu*, and low Sc, Y, Nb, Ta, and total REE and is similar to other granites from along the amphibolite-granulite transition zone that have the characteristics of a fractionally crystallized cumulate. The other granite suite has lower Sr and Ba, higher Sc and Y, and no distinctive Eu anomaly. This latter group, which is widespread in the southern Closepet batholith, can be derived by 20% equilibrium partial melting of a tonalite source (containing hornblende and garnet) that is compositionally similar to South India tonalites near the amphibolite-granulite transition. The two granite groups may have been produced by separate episodes of CO₂ metamorphism. The granodiorites appear to have formed by mixing, in different proportions, of tonalitic and granitic gneisses within and around the southeastern margin of the batholith.