Geochemical characteristics and possible origins of the southern Closepet batholith, South India

The polyphase Closepet batholith in S India intrudes Archean tonalitic and granitic gneisses in a terrane that grades from amphibolite to granulite grade at the S end of the batholith. Two granite and 2 granodioritic suites are recognized in the batholith. One granite suite from the S 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 distinctice Eu anomaly. This latter group, which is widespread in the S Closepet batholith, can be derived by 20% equilibrium partial melting of a tonalite source (containing hornblende and garnet) that is compositionally similar to S India tonalites near the amphibolite-granulite transition. The 2 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 SE margin of the batholith. -Author