大兴安岭中段塔尔气地区流纹岩年龄、地球化学特征及其地质意义  

Geochronological and geochemical characteristics of the rhyolites in Taerqi of middle Da Hinggan Mountains and their geological significance

作　　者：李杰[1] 吕新彪[1,2] 陈超[3] 衮民汕 杨永胜[3] 徐益群[1] 王琳[3] 张帅[1] 

机构地区：[1]中国地质大学(武汉)资源学院,湖北武汉430074 [2]中国地质大学成矿过程与矿产资源国家重点实验室,湖北武汉430074 [3]中国地质大学(武汉)地质调查研究院,湖北武汉430074

出　　处：《地质通报》2016年第6期906-918,共13页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:NMKD2014-23)

摘　　要：塔尔气地区位于大兴安岭主脊中段,晚中生代广泛发育一套玄武岩、安山岩、英安岩、流纹岩及相应火山碎屑岩的岩石组合。以流纹岩为研究对象,进行了LA-ICP-MS锆石U-Pb年龄、岩石地球化学研究。测年结果显示,流纹岩形成于132±2Ma（MSWD=1.5,2σ）,属早白垩世中期。岩石地球化学特征表明,流纹岩属于典型的弱过铝质高钾钙碱系列岩石,具有高硅（71.6%~77%）、富碱（Na_2O＋K_2O=7.94%~9.64%）且富钾（K_2O=4.5%~5.46%）的特征;轻、重稀土元素分馏明显,具中等Eu负异常（δEu=0.22~0.7）,亏损高场强元素Nb、Ta、P、Ti,相对富Th、U、Zr、Hf,富集大离子亲石元素K、Rb,相对贫Ba、Sr,显示A型流纹岩特征。岩浆源区与硬质砂岩相似,具有较高的锆饱和温度,可能为地壳部分熔融的产物,形成于后碰撞伸展的大地构造环境。Taerqi area is located in the middle main ridge of Da Hinggan Mountains, where there is developed a suite of late Mesozoic volcanic rocks, which include basalt, andesite, dacite, rhyolite and tuff. In this paper, detailed LA-ICP-MS zircon U-Pb geochronological and element geochemical studies were carried out for the rhyolites. The zircon U-Pb dating yielded a weighted average age of 132 ± 2Ma（MSWD=1.5,2σ）, indicating that the rhyolites were formed at the middle stage of the early Cretaceous. Rock geochemical characteristics show that the rocks are peraluminous cal-alkaline rhyolites, which are characterized by high SiO 2 （71.6%~77%）, high potassium and alkali content （K2O=4.5%~5.46%, Na2O＋K2O=7.94%~9.64%）. Trace elements have a similar variation trend that systematic enrichment of LILE and depletion of HFSE as well as LREE fractionation are more obvious than that of HREE, and also show significant weak anomaly of Eu （δEu=0.22~0.7）. In addition, there exist the depletion of Sr, Ba, P, Ti, Nb, Ta and enrichment of Rb, K, Th, U, Zr, Hf. The rocks belong genetically to A type with a high zirconium saturation temperature （TZr=842°C） ,＆amp;nbsp;and the magma source was probably similar to the metagrewacks. Accordingly, it is inferred that the A-type rhyolites were products of partial melting of the crust and formed in a post-collision environment and an extensional tectonic setting.

关 键 词：大兴安岭中段 塔尔气地区 锆石U-PB年龄 A型流纹岩 后碰撞 

分 类 号：P588.141[天文地球—岩石学] P591[天文地球—地质学]