Abstract:

The augen gneiss in the Gyirong Area of south Tibet belongs to the Greater Himalayan Crystalline Complex. It consists of quartz, plagioclase, Kfeldspar, biotite and minor muscovite. Zircons of the augen gneiss have corerim structures with inherited cores and magmatic rims indicated by concentric oscillatory zoning. The zircon rims gave a weighted mean age of 4989±44 Ma, hinting that the protoliths of the gneiss was early Paleozoic granite. The εHf ranges between -136 and -46 with a weighted mean value of -83±095. It implies that the source of granite came from crust, possibly resulted from partial melting of the crust in the northernmost margin of the India Craton. The zircon SHRIMP UPb ages,  combined with the published geochronological data, demonstrate that the Himalaya is a composite orogenic belt, which underwent an early Paleozoic orogenesis. The early Paleozoic Himalaya was an Andeantype orogen after the Gondwana assemblying, which resulted from the subduction of the protoTethys ocean beneath the India Plate, rather than a PanAfrican orogen that was formed by the continentcontinent collision during the Gondwana assembly.

Key words:  Greater Himalayan Crystalline Complex, augengneiss, SHRIMP UPb dating, Hf isotope, early Paleozoic orogenesis