Lead isotopic composition and genesis of Dalongshan and Chengshan igneous bodies

A detailed study of Pb isotopic compositions in potash feldspars from Dalongshan and Chengshan bodies taking consideration of their biotite chemical compositions, Sr isotopes, rare earth elements, petrochemistry and information on geophysics indicates that the igneous bodies are multi-staged composites and genetically they are related to Lu Zhong volcanic rock series as the products of magma activities during the late Yanshanian movement. Their initial magma substance was derived from the upper mantle through partial melting, but in the process of moving upward and emplacing, the magma was contaminated by the upper crustal materials in varying degrees. It is estimated that there are 61.6% of lead derived from the upper mantle and 38.4% from the upper crust. The average crustal age is about 26 x 108 a. There appears a tendency to enrich uranium during the evolution process of the crust in the region. Additionally, the emplacement of the igneous bodies were closely related to the development of deep fracture and the mantle uplifting