The petrogenesis and geodynamic significances of HREE depleted granitoids during Yanshan period in the Dabie Mountains.

The petrological and geochemical characteristics of Yanshanian granitoids i n the Dabie Mountains (mainly in Zhangjiazui area) suggest that there are t wo kinds of rocks among Yanshanian granitoids in the Dabie Mountains. One k ind is clearly depleted in HREE and Y (Sr/Y greater than or equal to 40.0, La/Yb greater than or equal to 40.0. Yb less than or equal to1.90 mug/g, Y less than or equal to 18.0 mug/g, Sr greater than or equal to 400 mug/g, Rb /Sr less than or equal to0.20, Rb/Ba less than or equal to 0.08), and the o ther kind shows no HREE and Y-depletion (Sr/Y < 40.0, La/Yb < 40.0, Rb/Sr > 0.20, Rb/Ba>0.08), including some A-type and I-type granites. In addition, the granitoids with the HREE and Y-depletion are further divided into two groups: Na-rich and K-rich granitoids, the former one is similar to adakiti c rocks and the latter one resembles high Ba-Sr granites. The HREE and Y-de pleted granites in the Dabie Mountains were most probably produced by parti al melting of lower mafic rocks in the thickened crust (>40km) due to the u nderplating mafic magmas heating the lower crust. Generation of magma with HREE and Y depletion in the Dabie Mountains also likely resulted in delamin ation of some materials in the lower crust.