Abstract:

It is found that the zircon SHRIMP U-Pb ages of the Permian mafic granulite and its host rockdioritein Chaihulanzi of Chifeng area are 262.3±3.1 Ma and 256.6±6.5 Ma respectively, and that the zircon SHRIMP U-Pb ages of the Triassic mafic granulite and its host rockdioritein Henanyingzi of Ningcheng area are 229.7±2.6 Ma and 221±3 Ma respectively. Other forms of magmation in this period were also discovered in these areas, including Permian accretion edges around the Archaeozoic zircon and Permian dioriteveins. Comparative study suggests that the Permian magmation possessed the characteristics of the initial stage of a continental rift with relatively low content of highfieldstrength elements, and that the increased Triassic highfieldstrength elements indicate a higher degree of mantle partial melting. Those granulites in combination recorded important information about the transformation of North China Craton from stable to active in its early stage. Isotopegeological study indicates that such transformation began with the crustmantle interaction. The Permian magmation here was related to the global tectonic evolution and bimodal volcanic activity in Hinggan Mongolia Orogen at that period. The Triassic magmation here was related to intracontinental extension under the setting of underplating.

Key words: north margin of North China Craton; , Phanerozoic, mafic granulite, isotope geology, crustmantle interaction