Geochronological, petrological, mineralogical and geochemical studies of the Xuanwoling mafic-ultramafic intrusion in Beishan area, Xinjiang.
新疆北山地区旋窝岭镁铁-超镁铁岩体的年代学、岩石矿物学和地球化学研究

The Xuanwoling mafic-ultramafic complex is located in the Beishan area, Xinjiang. It intruded into meta-sandstones of the Hongliuyuan Formation of the Lower-Carboniferous, and was dated 260.7±2.0Ma of zircon U-Pb age by SIMS. The intrusion consists of peridotite, troctolite, olivine gabbro and gabbro, which are fresh and display typical olivine peritectic and gabbro textures. Plagioclase occurs in all rock types and orthopyroxene only presents in olivine gabbro and gabbro. The Xuanwoling intrusion is characterized by Fo (80~85) and NiO (0.1%~0.2%) of olivines, augite and diopside dominating clinopyroxenes, and orthopyroxene is classified as bronzite. These mafic minerals plus plagioclases show good correlations with their whole rock compositions, suggesting their parental magmas were mainly controlled by the fractional crystallization. The Xuanwoling rocks are characterized by high MgO contents (9.5%~21.8%), flat REE pattern and positive Eu anomaly, and negative Nb, Zr and Hf anomalies in spider diagram. Therefore, the Xuanwoling mafic-ultramafic intrusion was most likely evolved from the high-Mg basaltic magmas which generated by the high degree partial melting of the lithospheric mantle during the formation of the Beishan rift, and has promising future for Ni-Cu sulfide ore exploration.