兴蒙造山带中段沙麦花岗岩成因分析

Analysis on genesis of Shamai granite in middle Xingmeng orogenic belt

对沙麦花岗岩岩体进行主量、微量、稀土元素和Nd-Sm同位素地球化学特征分析,主量元素显示为高钾钙碱性、过铝质,且P_2O_5随SiO_2含量增加而含量降低;微量元素显示大部分Y/Ho与Ⅰ型花岗岩演化趋势一致;稀土元素显示具有Eu负异常且Nb/Ta、K/Rb比值均小于相应的最高阀值,说明其经历了高度分离结晶作用。岩石Nd-Sm同位素特征显示大部分样品ε_(Nd)(t)>0,正值被认为成岩物质来自地幔,结合花岗岩浆的演化特征进行综合分析,判定沙麦花岗岩的成因类型为Ⅰ型花岗岩。

Studies were focused on the major, trace and rare earth element and Nd-Sm isotope geochemical characteristics of Shamai granite pluton. Major elements were characterized as high-k Calc-alkaline, peraluminous, negative relation between PzOs and SiO2 content with most trace elements show the same Y/Ho evolution trend as I-type Granites. Rare-earth element have a negative Eu anomaly and Nb/Ta, the K/Rb ratio is lower than the corresponding maximum thresholds, which suggest the granite experienced a high degree of fractional crystallization. Nd-Sm isotope characteristics shew that most samples eNd（t）〉0, which is considered the derived mantle diagenetic material. Combined with a comprehensive analysis granite evolution, granite genetic types of Shamai was judged as I- type granites.