Timing of high-grade metamorphism in the Kontum Massif, Vietnam: Constraints from zircon–monazite multi-geochronology and trace elements geochemistry of zircon–monazite–garnet

Abstract

Metamorphic rocks in the Kontum Massif, including the Kannak, Ngoc Linh and Kham Duc Complexes are characterized by amphibolite- to granulite-facies metamorphism and their mono- versus poly-metamorphic evolution is a matter of debate. In this study, we constrained on the timing of high-grade metamorphism in this massif by combining laser ablation inductively coupled plasma mass spectrometry U–Pb zircon and electron microprobe chemical U–Th–Pb monazite ages with geochemical relation of trace elements between zircon–monazite–garnet. The results indicated that the analyzed pelitic and mafic granulites in the western Kannak Complex experienced the high temperature metamorphism at ca. 250 Ma with subsequent decompression. However, in the western Ngoc Linh Complex two high-grade metamorphic events were recorded in one of analyzed pelitic gneisses. The first high temperature metamorphism began at ca. 440–450 Ma with the attainment of the peak condition at ca. 430 Ma, overprinted by the second one at ca. 240–250 Ma with following decompression and exhumation stage at ca. 230 Ma. The other pelitic gneiss and mafic granulite detected only younger single event. Pelitic gneisses in the Kham Duc Complex recorded medium pressure metamorphism occurred at ca. 240 Ma without any traces of early metamorphic event.