对冈底斯带中段仁堆地区二云母花岗岩进行LA-ICP-MS锆石U-Pb定年,主量和微量元素地球化学分析表明,二云母花岗岩的结晶年龄为226.3±0.98Ma.二云母花岗岩为高钾钙碱性强过铝质花岗岩,SiO2含量为72.83%~74.99%,K2O/Na2O为1.58~2.37,Alk为7.37%~8.72%,A/CNK为1.21~1.39(>1.1),刚玉标准分子ω(C-norm)大于1%.稀土元素总量为61.71×10-6~175.16× 10-6,其中,轻稀土元素总量为53.93×10-6~165.49×10-6,重稀土元素总量为7.588×10-6~13.880×10-6,轻、重稀土元素分馏明显, (La/Yb)N介于10.49~42.170之间.在稀土元素配分模式图上,表现为轻稀土元素富集的右倾型,有明显的负Eu异常,δEu介于0.264~0.57之间;在微量元素蛛网图上,表现出Ba、Nb、Sr、Ti、P亏损和Rb、K、U富集的特征.二云母花岗岩是增厚的冈底斯地壳在印支晚期应力松弛阶段,由于构造减压诱发部分熔融形成的.%This paper reports LA-ICP-MS zircon U-Pb ages and whole rock major and trace element analyses of two-mica granite in the middle part of the Gangdise terrane, Tibet. Magma zircons from the two-mica granite yielded a weighted 206Pb/238U mean age of 226.3 ± 0.98Ma. The two-mica granite is of strongly peraluminous high-K calc-alkaline series, with SiO 2 values from 72.83%to 74.99%, K2O/Na2O values from 1.58 to 2.37, total alkali content from 7.37%to 8.72%, A/CNK ratios from 1.21 to 1.39(>1.1), andω(C-norm) higher than 1%. The ∑REE values vary from 61.71 × 10-6 to 175.16 × 10-6, LREE from 53.93 × 10-6 to 165.49 × 10-6, HREE from 7.588×10-6 to 13.880×10-6, REE patterns are inclined toward the HREE side with intensive enrichment of LREE, and (La/Yb)N values are from 10.49 to 42.17. Eu anomalies are strong, with Eu/Eu?values varying from 0.264 to 0.57. In the primitive mantel-normalized spidergrams of trace elements, the depletion of Ba, Nb, Sr, Ti and enrichment of Rb, K, U are obvious. It is sug-gested that the magma for the two-mica granite was dominantly derived from partial melting of argillaceous rocks in the crust, in-duced by dehydration of mica minerals.
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