Abstract:

The Pobei gabbroic intrusion is located in the Beishan rift zone of the northeastern margin of Tarim cratonThe Poyi and Poshi NiCu bearing ultramafic bodies are situated in the western portion of the Pobei intrusionIt is sharp contact between the Poshi ultramafic body and the Pobei gabbroHowever，both the Poshi ultramafic rocks and the Pobei gabbros have similar trace element and isotope compositions，indicating that they are comagmaticThe triangle plots of MnOTiO2P2O5 and ThHfTa show that the parental magmas of the Pobei and Poshi intrusions have features of island arc magmaIn contrast，the layered intrusions and maficultramafic dykes in the Bachu area of the Tarim large igneous province (TLIP) show that the intraplate volcanic featuresIn the trace element spider diagram，the Pobei gabbros and Poshi wehrlites are relatively  enriched in large ion lithophile elements (such as Rb，Sr，Ba) and depleted in high field strength element (such as Nb，Ta，Zr，Hf，HREEs)，and show extensive negative NbTa anomaliesThese geochemical features are similar to the typical island arc volcanics and Alaskantype intrusionsHowever，the layered intrusions and maficultramafic dykes in the Bachu area are similar to the ocean island basalt (OIB)These geochemical features indicate that the parental magmas of the Pobei gabbros and Poshi ultramafic rocks were derived from a metasomatized mantle modified by subduction events，rather than the Tarim mantleData of SrNd isotopes show that the magmas of the Pobei and Poshi intrusion underwent 3% to 10% contamination of the Proterozoic metamorphic rocks of the Tarim craton

Key words: the Beishan rift zone, the Poshi intrusion, the Tarim large igneous province, a metasomatized mantle