西藏冈底斯带中段南木林县仁堆侵入体LA-ICP-MS锆石U-Pb年龄及岩石成因  

LA-ICP-MS zircon U-Pb ages and petrogenesis of Rindu intrusion near Namling, middle Gangdise magmatic belt

作　　者：卜涛[1,2] 魏启荣[2] 丁鹏飞[2] 王程[2] 刘小念[2] 张小强[2] 孙骥[2] 王敬元[2] 

机构地区：[1]国土资源部岩浆作用成矿与找矿重点实验室/中国地质调查局西安地质调查中心,陕西西安710054 [2]中国地质大学资源学院,湖北武汉430074

出　　处：《地质通报》2015年第12期2254-2265,共12页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:1212011086040;12120113046400)

摘　　要：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,Si O2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 weighted206Pb/238 U mean age of 226.3±0.98 Ma. The two-mica granite is of strongly peraluminous high-K calc-alkaline series, with Si O2 values from 72.83% to74.99%, K2O/Na2 O 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^-6to 175.16×10^-6, LREE from 53.93×10-6to 165.49×10-6,HREE from 7.588×10^-6to 13.880×10^-6, REE patterns are inclined toward the HREE side with intensive enrichment of LREE, and（La/Yb）Nvalues 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 suggested that the magma for the two-mica granite was dominantly derived from partial melting of argillaceous rocks in the crust, induced by dehydration of mica minerals.

关 键 词：LA-ICP-MS锆石U-PB定年 岩石地球化学 强过铝质花岗岩 印支期 冈底斯 西藏 

分 类 号：P595[天文地球—地球化学] P597.3[天文地球—地质学]