新疆东天山奥姆尔塔格岩体地球化学特征及锆石定年

GEOCHEMICAL CHARACTERISTICS AND ZIRCON U-Pb DATING OF THE OMLTAG MASSIF IN THE EASTERN TIANSHAN,XINJIANG

奥姆尔塔格岩体作为哈尔里克造山带的一部分,通过该岩体7件岩石化学全分析和1件锆石U-Pb年代学样品分析,可以制约哈尔里克造山带晚石炭纪构造属性。奥姆尔塔格岩体以二长花岗岩为主,w(SiO2)62.51%~75.65%,w(K2O)(1.52%~5.86%),富w(CaO)(1.07%~4.08%)、贫w(Al2O3)(11.83%~17.7%),w(TiO2)0.08%~0.49%,FeO^T值为0.98%~4.19%,Mg^#值为33.02~43.32,铝饱和指数值(A/CNK)0.90~1.01,里特曼指数(σ)1.14~2.74,属中—高钾、富碱、准铝质—弱过铝质岩石。岩石ΣREE较低(92.76~131.04×10^-6),富集Rb,Ba等大离子亲石元素和活泼的不相容元素(Th,U),相对亏损Nb,Ta,Sr,Ti等高场强元素,与典型岛弧型岩浆岩相似。La/Ta值20.33~143.68,La/Sm值2.59~7.42,SiO2与Fe2O3,CaO,P2O5,TiO2具负相关性,显示奥姆尔塔格属于成熟度较高的花岗岩,其母岩浆可能为闪长质,受到了地壳物质不同程度混染,经历了较高程度的结晶分离,为壳幔混合成因。锆石U-Pb年龄为311.7±2.2Ma(晚石炭世)。奥姆尔塔格岩体岩浆形成于碰撞前的岛弧环境,为哈尔里克造山带碰撞挤压-伸展转换阶段的产物。

7geochemical samples and one zircon U-Pb geochronologic sample are analyzed in order to constrain the late Carboniferous structural attributes of the Harlik orogenic belt.Omltag rock mass is mainly composed of mainly monzogranite.Geochemical analysis shows that its w(SiO2)content=62.51%-75.65%,w(K2O)=1.52%-5.86%,w(CaO)=1.07%-4.08%,poor in w(Al2O3)(11.83%-17.7%),w(TiO2)=0.08%-0.49%,w(FeO^T)=0.98%-4.19%,Mg^#=33.02-43.32,aluminium saturation index value(A/CNK)=0.90-1.01,Ritman index(σ)=1.14-2.74,characteristic of a high potassium,alkali rich,quasi aluminum and weakly peraluminous rock.TheΣREE in the rock is low(92.76-131.04×10^-6),but rich in Rb,Ba and other large ion lithophilic elements and active incompatible elements(Th,U),relatively deplete in high field strength elements such as Nb,Ta,Sr and Ti,which are similar to typical island arc magmatic rocks.La/Ta values are 20.33-143.68,and La/Sm values are 2.59-7.42,and SiO2is negatively correlated with Fe2O3,CaO,P2O5,and TiO2,indicating that Omltag rock mass belongs to the high maturity granite.Its parent magma may be diorite,which is mixed with crustal materials to varying degrees and experienced a high degree of crystal separation,and is of crust-mantle mixing origin.The zircon U-Pb dating of the rock mass yields a 311.7±2.2Ma age(late Carboniferous).It is considered that the Omltag rock mass magma is formed in the island arc environment before the collision and is the product of the collision compression-extension transition of the Hallik orogenic belt.