内蒙古哈马尔乌拉花岗斑岩的锆石U-Pb定年及其岩石地球化学特征

哈马尔乌拉花岗斑岩出露于大兴安岭中段东坡，形成于早白垩世（K1），锆石U-Pb等时线测年分析结果表明，206Pb/238U表面年龄加权平均值为124.9±2.5 Ma.该花岗斑岩的化学成分显示高SiO2（71.262%~77.61%），平均值为74.48%；富碱（K2O+Na2O为6.32%~8.77%），平均值为7.46%；高K2O/Na2O比值（1.1~2.2）；富铝，贫钙、铁、镁，岩石属高钾钙碱性系列.微量元素Sr、Rb、Th、Ce富集，Zr、Hf、Sm、Y、Yb相对亏损.稀土分配曲线呈右倾型，轻稀土较富集，且分馏较好；重稀土相对亏损，分馏较差.具明显的铕负异常.结合形成的构造背景分析，该岩体属于晚造山期花岗岩类.

ZIRCON U-Pb AGES AND GEOCHEMICAL CHARACTERISTICS OF THE HAMAERWULA PLUTON IN INNER MONGOLIA

The Hamaerwula granite-porphyry,outcropping in the eastern slope of the middle section of Daxinganling Mountains,was formed in Early Cretaceous.The U-Pb isochron dating of zircon shows that the weighted average of apparent age is 124.9±2.5 Ma,representing the intrusion era of Hamaerwula pluton.The chemical composition of the rock reveals high SiO2(71.262%-77.61%,averagely 74.48%),rich alkali(6.32%-8.77% of K2O+Na2O,averagely 7.46%),high K2O/Na2O ratio(1.1-2.2),rich Al and scarce Ca,Fe and Mg,belonging to high-K calc-alkaline series.The trace elements show enrichment in Sr,Rb,Th and Ce and relative deficiency of Zr,Hf,Sm,Y and Yb.The rare earth elements distribution curves tend right.The light rare earth elements are concentrated with well fractionation and obvious Eu negative anomaly.The heavy rare earth elements are relatively deficient with poor fractionation.Combining with structure formation background,it is considered that the Hamaerwula granite-porphyry is granitoid pluton of late orogenic epoch.