SHRIMP U-Pb zircon geochronology of granulites at Rimana(Southern Tibet) in the central segment of Himalayan Orogen

High-pressure mafic granulites, occurring as lenses within gneisses and quartzite in the central segment of the Himalayan orogen, were dated using SHRIMP U-Pb technique. 13 analyses out of a total of 15 are plotted along a concordia line and yield a mean 206Pb/238U age of 17.6 0.3 Ma. This age indicates adiabatic decompression and a metamorphic event associated with rapid uplift of granulites in a tectonic environment resulted from the collision between India and Eurasia, synchronous with large-scale thrusting, extension, detachment as well as emplacement of leu-cogranite. One analysis gives a 206Pb/238U age of 29.5 0.4 Ma that is interpreted to represent the timing of the final closure of the Neo-Tethys. Another age is 1991 26 Ma that represents the age of the protolith of the granulites. In sum-mary, dating results show that granulites in this area under-went multiphase metamorphism and complex geological evolution.