甘肃高台-临泽地区109-2隐伏岩体岩石地球化学特征

对高台-临泽地区109-2隐伏岩体岩相学研究,岩体组成以二辉橄榄岩相为主,具有橄榄石堆晶结构,橄榄石主要为贵橄榄石,阳起石化、绿泥石化、碳酸岩化与金川岩体非常相似。与金川地质背景对比显示它们属于同一个三级构造单元(龙首山隆起带),围岩地层相近。微量、稀土数据证明金川岩体岩浆源区富集程度或受地壳混染程度较109-2岩体强,分异结晶过程存在差异,109-2岩体Cr有明显的亏损现象,Ni/Cu比值明显较金川超镁铁质岩体(Ni/Cu≈2)高。109-2岩体所在地区可能是一个新的岩浆能量聚集地带,值得进一步探矿工作。

LITHOGEOCHEMICAL CHARACTERISTICS OF 109-2 HIDDEN ULTRAMAFIC INTRUSIONS AT GAOTAI-LINZE, GANSU PROVINCE

Petrographic study of 109-2 hidden ultramafic intrusions at Gaotai-Linze, Gansu province suggests that the intrusive is mainly composed of lherzolite with olivine-cumulate texture, in which the olivines are mainly chrysolites, and alterations such as development of actinolite, chlorite and carbonates are similar to those in Jinchuan intrusives. A comparison in geological setting between 109-2 and Jinchuan intrusives indicates that they occur in the same tectonic unit of Longshou uplift belt, as they show similar features of surrounding rocks. Geochemical data prove that the magmatic source area is more concentrated for Jinchuan intrusives than for 109-2 intrusives, or that crustal contamination is more intense for Jinchuan intrusives than for 109-2 intrusives, indicating difference in degree of differential crystallization for them. The 109-2 intrusives are distinctly depleted in Cr content and the ratio of Ni/Cu is higher in 109-2 intrusives than in Jinchuan intrusives, clearly suggesting difference in REE distribution pattern between 109-2 and Jinchuan intrusives. The area of 109-2 intrusives is probably a new belt for concentration of magmatic energy, which deserves more attention for further prospecting.