南岭地区五团岩体锆石LA-ICP-MS U-Pb定年、地球化学特征及其地质构造意义  

Zircon LA-ICP-MS U-Pb Age,Geochemistry and Tectonic Significance of Wutuan Granite in Western Nanling

作　　者：黄子进 付建明[2,3] 路远发 周洁 卢友月[2,3] 程顺波[2,3] 

机构地区：[1]长江大学资源与环境学院,武汉430100 [2]中国地质调查局武汉地质调查中心,武汉430205 [3]中国地质调查局花岗岩成岩成矿地质研究中心,武汉430205

出　　处：《地质科技情报》2017年第6期83-93,共11页Geological Science and Technology Information

基　　金：中国地质调查局地质矿产调查评价专项项目"南岭成矿带资源远景调查评价"(12120114084501);"南岭成矿带中西段地质矿产调查"(121201009000150002)

摘　　要：五团岩体位于南岭地区西段,主要岩性为黑云母二长花岗岩。利用LA-ICP-MS微区原位测试技术,对五团岩体黑云母二长花岗岩进行了锆石U-Pb定年及CL显微结构分析。结果表明:2件锆石样品的^(206)Pb/^(238)U加权平均年龄分别为(211±0.95)Ma(MSWD=0.08)和(227±3.2)Ma(MSWD=1.9),结合前人获得的年龄数据,认为岩体形成于晚三叠世中期且具有多次侵位;岩石具高硅、富铝、高钾特征,w(SiO_2)70.54%~72.55%,平均71.67%;w(Al_2O_3)13.62%~14.55%,平均14.03%;w(K_2O)4.18%~5.28%,平均4.85%;全碱(Na_2O+K_2O)7.09%~7.89%,平均7.51%;K_2O/Na_2O比值1.44~4.51,平均2.02;总体属铁质、高钾钙碱性-钾玄岩系列过铝质花岗岩类;Ba、Nb、Sr、P、Ti表现为明显亏损,Rb、Th、U、K、La、Ce、Nd、Zr、Hf、Sm、Y、Yb、Lu等则相对富集,w(∑REE)62.07×10^(-6)~149.58×10^(-6),平均126.68×10^(-6),δEu值0.26~0.50,地球化学特征表明花岗岩为S型花岗岩,源岩主要为中、上地壳变质杂砂岩;花岗岩微量元素构造环境判别图解主要显示为后碰撞构造环境。基于岩石成因、构造环境判别以及区域构造演化过程,推断五团岩体形成于印支晚期后碰撞环境,是加厚地壳在碰撞应力减弱、深部压力降低等条件下部分熔融的产物。The Wutuan granitic pluton in western Nanling is mainly composed of biotite. We report the in- tegrated study of zircon U-Pb age and Cathodoluminescence images of zircon grains. The result reveals that the 206Pb/238U mean age of magmatic zircon is （211±1）Ma（MSWD=0. 08） and （227＋3）Ma（MSWD： 1.9）,indicating that the granites were formed in middle Late Triassic with multi-stage intrusion features. The rocks are silicon-high （SiO2 = 70. 54%- 72. 55%, 71. 67% on average）, aluminum-rich（Al2O3= 13.62%-14.55%, 14.03% on average） and alkali-moderate （Na2O＋K2O=7. 09%--7. 89%,7. 51% on average）, with K2O/Na2O ratios being 1.44-4.51 （2.02 on average）, and they thus belong to ferric, high-K calc-alkaline series and shoshonite series peraluminous granitoids. Ba, Nb, Sr, P and Ti are pro- nouncedly depleted, while Rb, Th, U, K, La, Ce, Nd, Zr, Hf, Sin, Y, Yb, and Lu are comparatively concentrated. The rocks have low ∑REE values of 62.07× 10 6-149.58× 10-6 （126.68× 10-6 on aver- age）, δEu values of 0.26-0.50 （ 0.40 on average）, （La/Yb）N values of 8.03-15.42 （10.15 on aver- age）. And Al2O3/TiO2 ratios of peraluminous granite samples are less than 100. All these data point to S- type granitoids and suggest that the granites might have come mainly from acid-rocks of the middle-upper crust. Trace element diagrams for discrimination of the structural environment show that the granites were formed in a post-collisional tectonic setting. According to the petrogenesis, the discrimination of structural environment and regional tectonic evolutional setting, it is infered that the formation mechanism of the Wutuan pluton should be as follows, the thickening of the crust in Indosinian movement caused the rise of the temperature of the crust, and later the weakening of the stress in the post-collisional tectonic setting caused the melting of the middle-upper crust, with the magma emplaced in a relatively open environment.

关 键 词：锆石LA-ICP-MSU-PB年龄 地球化学特征 印支期 五团岩体 南岭地区 

分 类 号：TP588.12[自动化与计算机技术]