SHRIMP U-Pb zircon geochronology of granulites at Rimana(Southern Tibet)in the central segment of Himalayan Orogen
Abstract 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 ± 0.3Ma. 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 leucogranite.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 summary,dating results show that granulites in this area underwent multiphase metamorphism and complex geological evolution.
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