甘肃北山北带明水西新井埃达克岩质石英闪长岩地球化学特征及地质意义

Geochemical Characteristics of Xinjing Adakitic Quartz-diorite Complex from the Beishan Area,Gansu Provine and Its Geological Significance

明水西新井石英闪长岩位于甘肃北山晚古生代白山岩浆弧带上。通过对其岩石化学组成的研究表明,主量元素SiO_2、Al_2O_3和MgO的含量分别为59.13%~67.90%、14.90%~16.42%和1.96%~3.12%,微量元素Y、Yb和Sr的含量分别为11×10^(-6)~22.8×10^(-6)、1.19×10^(-6)~2.33×10^(-6)和364×10^(-6)~871×10^(-6),LREE为富集型和Eu为正异常,这些特征反映石英闪长岩为埃达克质岩。是俯冲到深处具MORB性质的板片在一定的物理化学条件下部分熔融后直接侵位于近地表而形成的。本区埃达克岩与金矿化存在密切的时空关系。

The Xinjing quartz-diorite,lies in the Beishan area,Gansu Province,is occurred in the Paleozoic Beishan island arc belt.The results of petrochemistry show that,the contents of SiO_2,Al_2O_3 and MgO are（59.13%~67.90%）,（14.90%~16.42%）and（1.96%~3.12%）,respectively,while the values of trace elements（such as Y,Yb and Sr）are（11×10^（-6）~22.8×10^（-6））,（1.19×10^（-6）~2.33×10^（-6））and（364×10^（-6）~871×10^（-6））,and these rocks show positive Eu anomalies,indicating that the plagiogranite porphyry shows characteristics of adakitic rocks.These adakitic rocks were formed by the partial melting of subducting slab with MORB features under some physical and chemical conditions,and then they were directly emplaced to the near surface.Thus,these adakitic rocks have close spatial temporal relationship with gold mineralization in this studying area.