High εNd（t）-εHf（t） granites are robust evidence for crustal growth. In this paper we report results of petrologic, geochronological and geochemical investigations on the Huashiban granites from the Ailaoshan tectonic zone in western Yunnan （SW China）. Zircon grains separated from the two samples （10HH-119A and 10HH-120A） yield the weighted mean 206pb/238u ages of 229.9 ± 2.0 Ma and 229.3 ± 2.3 Ma, respectively, interpreted as the crystallization ages of the granites. Based on our results, in combination with the existing U-Pb geochronological data for the Ailaoshan metamorphic rocks, we propose that the Ai- laoshan Group might be a rock complex composed of the Mesoproterozoic, Neoproterozoic, Hercynian, Indosinian and Hima- layan components, rather than a part of the crystalline basement of the Yangtze block. The zircon grains show highly depleted Lu-Hf isotope compositions, with positive eHf（t） values ranging from 8.4 to 13.1. The Huashiban granites have high SiO2 （72.66 wt%-73.70 wt%）, low Mg# （0.28-0.34） with A/CNK=1.01-1.05, and can be classified as peralumious high-K calc-alkaline I-type granites. A synthesis of these data indicates that the Ailaoshan tectonic zone had evolved into a post-collisional setting by the Late-Triassic （229 Ma）. Genesis of the Huashiban high εNd（t）-εHf（t） granites involved into two processes： （1） underplating of the sub-arc mantle into the lower crust, and （2） remelting of the juvenile crustal materials in re- sponse to the upwelling of the asthenospheric mantle in the post-collisional setting.
LIU HuiChuanWANG YueJunFAN WeiMingZI JianWeiCAI YongFengYANG GuangLin
