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

新疆北山地区的旋窝岭岩体侵位于下石炭统红柳园组变质砂岩中,辉长岩的锆石SIMSU-Pb定年结果为260.7±2.0Ma,晚于区域上其它岩体的成岩年龄。该岩体由橄榄岩、橄长岩、橄榄辉长岩和辉长岩组成,岩石较新鲜,具有典型的包橄结构和辉长结构,各岩性中均可见斜长石,而斜方辉石仅在辉长岩中出现。橄榄石的Fo值在80～85之间,NiO含量介于0.1%～0.2%之间;单斜辉石主要为普通辉石和透辉石,斜方辉石为古铜辉石。这些镁铁质矿物和斜长石成分与全岩的地球化学特征具有很好的相关性,说明该岩体母岩浆的演化过程主要受控于结晶分异作用。全岩的MgO含量在9.5%～21.8%之间,具有平坦的稀土配分型式和正Eu异常以及微量元素Nb、Zr、Hf的负异常等。因此,旋窝岭岩体可能是在北山裂谷形成过程中由于岩石圈地幔高程度部分熔融形成的高镁玄武质岩浆分异演化的产物,具有一定的铜镍硫化物矿床的成矿潜力。

Geochronological, petrological, mineralogical and geochemical studies of the Xuanwoling mafic-ultramafic intrusion in Beishan area, Xinjiang.

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.