Abstract: Geochemistry of tonalitic gneisses in Banqiaogou area of Pingshan county shows high Si，A1，Na and low K．strong differentiation in its REE pattern，with higher(La／Yb)N，and distinct negative anolnalies of Nb，Ta，Ti and P，which are nearly the same as those of TTG in Archean．CL and BSE images of zircons in the tonalitic gneiss display dense regular zones and high Th／U，indicating the features of magmatic zircons，and narrow metamorphic rims with high brightness．SHRIMP dating shows that the age of the magmatic emplacement and metamorphism of these TTG gneisses are 2 536±9．8 Ma and 1 802±43Ma，respectively．The conclusion is that the West block was subducted under the East block．The subduction was responsible for the intrusion of TIG ,and finally leading to the amalgamation of Wutai block with Taihangshan block．Another independent tectonothermal event within the continent occurred at C．1.8Ga ago．