Geochronology and Petrogenesis for the Protolith of Biotite Plagioclase Gneiss at Lianghe, Western Yunnan

In this paper, we report an integrated study of U-Pb age and Hf isotope compositions of zircons from biotite plagioclase gneiss at Lianghe in western Yunnan. The zircons preserved inherited core and rim texture. Igneous zircon grains and rims yielded a weighted mean Pb-206/U-238 age of 120.4 +/- 1.7 Ma, their ern. (120 Ma) values were mainly negative ranging from -13.9 to -10.7, with Hf model ages between 1.9 Ga and 2.0 Ga, some zircons had positive epsilon(Hf) (120 Ma) values ranging from 0.2 to 2.1. The inherited cores showed the wide variations in the U-Pb age of 375-1315 Ma. One of them showed the epsilon(Hf)(506 Ma) value of -4.2, it was similar to the gray gneiss of old crust, which epsilon(Hf)(500 Ma) values were negative ranging from -4.5 to -3.3. Combining geological feature and geochemical data, we concluded that the protolith of biotite plagioclase gneiss was old crust-derived tonalitic magma during the early Cretaceous.