Zircon Cameca U-Pb dating and its significance for granulite-facies gneisses from the western Awulale Mountain, West Tianshan, China.

Petrographic and geochemical characteristics of low-pressure granulite-facies gneisses from the western Awulale Mountains (in the western Tianshan Mountains) indicate that the protolith was a graywacke, which is featured by proximity of its origin and rapid deposition. In the chondrite-normalized diagram, the distribution patterns of rocks show steep LREE-type (light rare earth elements) and flat HREE-type, which suggests negative Eu anomaly and Nb, Ta, Ti, Ba, P and Sr depletions. The Cameca ion probe zircon U-Pb dating gave an upper interception age of 1609Ma±40Ma and a lower interception age of 764Ma±72Ma, representing the ages of magma crystallization and Pb-loss thermal event, respectively. The latter thermal event may represent the low-pressure metamorphic age. The outcrop of granulite-facies gneisses suggests that the Yili block may be underlain by Middle Proterozoic crystalline basement. The ~764 Ma thermal event probably records the break-up of the Rodinia supercontinent.