Ultra-high temperature metamorphism of metapelitic granulites from Kondapalle, Eastern Ghats Belt: Implications for the Indo-Antarctic correlation

A suite of quartz and corundum-bearing metapelitic granulites, intruded by layered gabbronorite-pyroxenite-anorthosite at Kondapalle. Eastern ghats Be lt, preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions. in the quartz-bearing associations, the reactions are : (a) biotite + sillimanite + quartz --> garnet + liquid; (b) garnet + sillimanite --> spinel (+ magnet ite) + quartz; (c) Fe(2)Tio(4) + O-2 --> ferrian ilmenite + magnetite; (d) reversal of reaction (b); (e) Fe2O3-rich ilmenite + plagioclase + quartz -- > Fe2O3-poor ilmenite + garnet + O2. Reactions in the corundum-bearing asso ciations are: (f) spinal + biotite + sillimanite --> garnet + liquid; (g) b iotite + sillimanite --> garnet + Ti-rich spinal + corundum + liquid; (h) b iotite + sillimanite --> garnet + corundum + liquid; (i) Fe2TiO4 + FeAl2O4 + O-2 --> ferrian ilmenite + Fe3O4 + Al2O3 (in ilmenite); (j) garnet + coru ndum --> spinal + sillimanite. to examine the paragenetic evolution of the metapelitic granulities, a petrogenetic grid for the KFMASH system at high temperatures and pressures, involving quartz and corundum, was constructed. The sequence of inferred reactions documents an anticlockwise heating cool ing path. Reintegrated compositions of spiral (with > 10 mol % Fe2TiO4) and feldspars indicate ultra-high temperature (UHT) of metamorphism (>1000 deg rees C), comparable with the liquids temperature of the enclosing magmatic rocks. Crystallization pressures inferred for the magmatic rocks and the pr essure constraints imposed by the petrogenetic grid on the metapelite assem blages indicate that the emplacement of the igneous suite and the accompany ing UHT metamorphism occurred in the lower crust (>8 kbar). Reported U-Pb c ooling ages of monazite and allanite from a late pegmatite suggests the UHT metamorphism to be older that 1600 Ma. Te deduced PT history and the absen ce of Grenvillian high-grade metamorphism in the study area provide importa nt constraints on the configuration of East gondwana, in particular on the continuation of the Napier Rayner terrane boundary into the Eastern Ghats B elt.