Timing of metamorphism and formation of garnet granite in the Kontum Massif, central Vietnam: Evidence from monazite EMP dating

Abstract

Garnet-bearing granite (Grt-granite) and high-grade pelitic gneisses occur in the Kannak Complex, southern Kontum Massif, central Vietnam. Electron microprobe (EMP) dating of monazite in Grt-granite and garnet-orthopyroxene gneiss (Grt-Opx gneiss) gave ages of ca. 260 Ma from cores and ca. 230 Ma from thin rims. Since most monazite grains are predominately of core composition, the ca. 260 Ma age indicates the timing of high-temperature metamorphism and the formation of Grt-granite. Grt-granite is locally accompanied by coeval intrusions of fine-grained gabbro, which is a candidate for the heat source leading to high-grade metamorphism and partial melting of the crust during the Late Permian.