1. College of Earth Sciences，Jilin University，Changchun 130061，China; 2. International Center for Geoscience Research and Education in Northeast Asia，Jilin University，Changchun 130026，China; 3. Bureau of Geology and Mineral Resources of Shandong Province，Ji'nan 250013，China

The systematically petrographical，geochemical and Sr- - Nd isotopic research of the Middle Triassic Xiachangzhuang magnetite amphibolites (242 Ma) show that they are mainly composed of hornblende (40% ～ 45%)，magnetite (35% ～ 45%)，plagioclase (10% ～ 15%) and clinopyroxene (1% ～ 3%)． The magnetite amphibolites have low contents of SiO 2 (24. 25% ～ 38. 40%)，K 2 O (0. 02% ～ 1. 09%)，Na 2 O (0. 16% ～ 1. 68%)，and high concentrations of MgO (6. 86% ～11. 81%)，Fe 2 O T 3 (21. 69% ～36. 62%)，TiO 2 (7. 37% ～ 13. 46%)． They are enriched in light rare earth elements (LREEs) and depleted in high field strength elements (HREEs) (∑LREE/∑HREE =7. 09 ～ 8. 97) with high (La/Yb) N values (10. 67 ～ 16. 62) and weak negative Eu anomaly (δEu =0. 83 ～1. 01)． Additonally，they are enrichment of LILEs (Rb，Ba and Sr)，nondepletion of HFSEs (Nb，Ta，Zr and Hf)，and show normal Pb and Ti anomalies． The whole- rock 87 Sr/ 86 Sr initial ratios range from 0. 702 645 to 0. 706 534，corresponding to ε Nd (t) and model ages (T DM1 ) ranging from －7. 51 to －12. 59 and 237 4 to 2 413 Ma，respectively． The above results suggest that the protolith of the Xiachangzhuang magnetite amphibolites may be hornblende gabbros derived dominantly from partial melting of enriched lithospheric mantle of North China Block． The forming age of the Middle Triassic Xiachangzhuang magnetite amphibolites is similar to the peak period age of the Dabie - -Sulu UHP metamorphism，which suggests that they might form in a transformation tectonic setting changing from ocean- continent subduction to the continent- continent collision in Early Mesozoic．