大兴安岭北段一脑丸地区花岗斑岩锆石U-Pb年代学及地球化学特征

大兴安岭北段一脑丸地区花岗斑岩锆石U-Pb年代学和地球化学特征研究结果表明该岩石的加权平均年龄为140.5±2.4 Ma,属早白垩世,同时含有较多中-晚三叠世的捕获锆石(223~232 Ma)。岩石的SiO_2含量为63.73%~64.35%,(K_2O+N_2O)为6.77%~7.31%,Al_2O_3含量为15.20%~15.40%,MgO含量和Mg#值分别为1.85%~2.01%和32~34,Fe_2O_3/FeO值为1.37~1.53,铝饱和指数(A/CNK值)为0.94~0.96之间,属于高钾钙碱性系列、准铝质I型花岗岩岩石。岩石的稀土总量相对较低(∑REE=110.37×10~(-6)~117.55×10~(-6)),轻重稀土元素分馏较高((La/Yb)N=22.39~31.72),Eu异常不明显(Eu/Eu*=0.91~1.07),富集轻稀土元素和Rb、K等大离子亲石元素,相对亏损重稀土元素和Nb、Ta、Ti、P等高场强元素,高Sr(515×10~(-6)~665×10~(-6)),低Y(6.73×10~(-6)~7.39×10~(-6)),具有埃达克岩性质。结合区域构造演化特征,认为该花岗斑岩起源于增厚下地壳部分熔融,应与蒙古—鄂霍茨克洋闭合后的陆陆碰撞造山作用有关。

Zircon U-Pb geochronology and geochemistry of granite porphyry in Yinaowan region of northern Great Xing'an Range

Zircon U-Pb geochronology and geochemical data for the granite porphyry in Yinaowan region of northern Great Xing'an Range has been studied, the results show that the weighted mean age of the rock was 140.5±2.4 Ma,belonging to Early Cretaceous, with captured zircons of Middle-Late Triassic(223~232 Ma) in the samples. Petrogeochemically, SiO2 contents is 63.73%~64.35%,(K2O+N2O)is 6.77%~7.31%,Al2O3 contents is 15.20%~15.40%,MgO and Mg# are of 1.85%~2.01% and 32~34, Fe2O3/FeO is 1.37~1.53, and aluminum saturation index(A/CNK)is 0.94~0.96,respectively, belonging to high-K calc-alkaline volcanic rock series, quasi-aluminous rock and I-type granite. The total amount of rare earths is relatively low (∑REE=110.37×10-6~117.55×10-6), fraction of light and heavy rare earth elements is high ((La/Yb)N=22.39~31.72), Eu anomaly is not obvious (Eu/Eu*=0.91~1.07). The samples are also enriched in light rare earth elements and large ion elements (Rb, K), depleted in heavy earth elements and high field strength elements (Nb, Ta, Ti, P). High Sr content (515×10-6~665×10-6) and low Y content (6.73×10-6~7.39×10-6) indicate the character of adakite. Combined with regional tectonic, it is suggested that the granite porphyry was originated from the partial melting of the thickened lower crust, and was related to continental collision orogeny after the closing of Mongolia-Okhotsk Ocean.