High-pressure granulite from Western Kunlun, northwestern China: Its metamorphic evolution, zircon SHRIMP U-Pb ages and tectonic implication

摘要

High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were obtained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic condition of these high-pressure granulites is about 760—820℃, 1.0—1.2 GPa and the retrograde metamorphic condition is about 620—720℃, 0.7—0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T path which suggests that the Western Kunlun underwent initial crustal thickening, subsequent exhumation and cooling. The SHRIMP zircon U-Pb dating gives two groups of ages for high-pressure granulites. One is 177 ± 6 Ma which is obtained from the rim of the zircon. We consider this age should be the metamorphic age. And the other is 456 ± 30 Ma which is obtained from the core of the zircon and should be the protolith age. The formation of these high-pressure granulites in western Kunlun is closely correlated with the evolution of the Paleo-Tethys and has important implications for the research on Tethys and Paleo-Asian tectonic zone.