南天山英买来花岗岩:磁铁矿系列还是钛铁矿系列?

位于南天山中段英买来岩体的主体由中粗粒似斑状黑云母钾长花岗岩组成,局部有粗粒似斑状二云母钾长花岗岩。二者全岩化学成分相似,但在矿物组成上表现出一定差异。前者不透明矿物为钛铁矿,而后者出现原生白云母,不透明矿物全部为磁铁矿。根据石原舜三(1977)的划分方案,黑云母钾长花岗岩全部符合钛铁矿系列特征,而二云母钾长花岗岩虽然表现出不透明矿物为磁铁矿、所含黑云母富镁等看似符合磁铁矿系列的特征,但所有的磁铁矿均和黑云母、钾长石共生,因此推测磁铁矿是由黑云母分解析出而成,并结合其同样具有全岩Fe3+/(Fe3++Fe2+)低、且出现钛铁矿系列的特征共生矿物白云母,亦判定其属于钛铁矿系列。另外,英买来岩体的矿物学和地球化学特征均符合S型花岗岩的特征,说明在本区钛铁矿系列和S型花岗岩相当。研究结果也表明南天山地区在早二叠世还没有完全进入板内演化阶段。

Yingmailai Granitic Intrusion in the Southern Tianshan:Magnetite-series or Ilmenite-series?

The Yingmailai granitic intrusion is located in the middle part of the southern Tianshan. It consists predominantly of biotite K-feldspar granite with minor two-mica K-feldspar granite. They have similar whole-rock geochemical characteristics, but distinct mineralogy. Opaque minerals in biotite K-feldspar granite are ilmenite, whereas they are magnetite in two-mica K-feldspar granite. According to Ishiharas classification(1977), biotite K-feldspar granite can undoubtedly be classified to ilmenite-series. Although some characteristics, e.g., presence of magnetite and Mg-rich biotite, suggest magnetite-series, it should be noted that the magnetite in two-mica K-feldspar granite is formed by post magmatism. In combination with low Fe~(3+)/(Fe~(3+)+Fe~(2+))ratio and presence of indicating mineral-muscovite, it can be inferred that it also belongs to ilmenite-series. In addition,the mineralogical and geochemical characteristics of the Yingmailai granitic intrusion indicate S-type granitoids,which suggests that ilmenite-series correspond to S-type granite in the southern Tianshan. This research also suggests that the southern Tianshan had not experienced within plate during Early Permian.