黔南罗甸酸性岩脉年代学、地球化学及其对火成岩省岩浆活动的响应  

Geochronology and geochemistry of Luodian acidic dykes in the Southern Guizhou Province and its response to magmatism of igneous province

作　　者：周琨 田亚洲[1,2] 杨经绥 杨华燊 田云雷[1,2] 武勇 钱丰 许秋媛 ZHOU Kun;TIAN Yazhou;YANG Jingsui;YANG Huashen;TIAN Yunlei;WU Yong;QIAN Feng;XU Qiuyuan(College of Resources and Environmental Engineering,Guizhou University,Guiyang 550025,Guizhou,China;Key Laboratory of Karst Georesources and Environment,Ministry of Education,Guizhou University,Guiyang 500025,Guizhou,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,Jiangsu,China;Center for Advanced Research on Mantle(CARMA),Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;CNNC Key Laboratory of Uranium Resources Exploration and Evaluation Technology,Beijing Research Institute of Uranium Geology,Beijing 100029,China)

机构地区：[1]贵州大学资源与环境工程学院,贵州贵阳550025 [2]贵州大学喀斯特地质资源与环境教育部重点实验室,贵州贵阳550025 [3]南京大学地球科学与工程学院,江苏南京210023 [4]中国地质科学院地质研究所自然资源部深地动力学重点实验室地幔研究中心,北京100037 [5]中核集团核工业北京地质研究院铀资源勘查与评价技术重点实验室,北京100029

出　　处：《中国地质》2021年第3期854-871,共18页Geology in China

基　　金：国家自然科学基金项目(41663005);贵州大学人才引进项目(702400163301);贵州省人才基地项目(RCJD2018-12)联合资助。

摘　　要：黔南罗甸地区位于峨眉山大火成岩省分布区外带,区内出露众多与峨眉山玄武岩同期的辉绿岩墙。酸性岩脉为石英二长斑岩,侵入于辉绿岩中,对该岩脉的研究有助于丰富峨眉山大火成岩省岩石组合规律及岩浆活动的认识。本文对罗甸酸性岩脉进行了岩石学、SIMS年代学和地球化学研究。岩石主量元素平均含量SiO_(2) 66.83%,CaO 1.76%,Al_(2)O_(3) 14.74%,MgO 0.76%,TFe_(2)O_(3) 4.49%,K_(2)O 3.67%,Na_(2)O 5.24%,A/CNK平均为0.93,显示高硅富碱、准铝质的特征。(La/Yb)_N=7.71~10.60,轻重稀土元素分馏强烈,稀土元素球粒陨石标准化配分曲线呈右倾型,具有OIB特征。δEu值平均为0.91,富集Rb、Ba、Th、K、Nd等元素,强烈亏损Nb、Ta、P、Ti等元素。石英二长斑岩(^(87)Sr/^(86)Sr)i和ε_(Nd)(t)值分别为0.704247~0.705292、1.08~1.54,与辉绿岩相似。研究表明,石英二长斑岩是由地幔柱部分熔融产生的玄武质岩浆经历分离结晶的产物,并混染了少量上地壳物质。锆石SIMS U-Pb年代学研究显示石英二长斑岩年龄为(259±2)Ma,与峨眉山大火成岩省岩浆作用时间一致。样品中存在大量继承锆石,可能为扬子地块不同阶段构造活动的响应。Luodian,located in the southern Guizhou Province,belongs to the outer zone of Emeishan Large Igneous Province.Numerous diabase of the same period as the Emeishan Large Igneous Province are exposed in the area.The acidic dykes are quartz monzonite porphyry,and invade into diabase.The study of acidic dykes is conducive to enriching the understanding of the law of lithology combination and magmatism in Emeishan Large Igneous Province.Petrology,SIMS chronological and geochemical studies of the acidic rock in Luodian were performed.Average content of major oxides are SiO_(2) 66.83%,Cao 1.76%,Al_(2)O_(3) 14.74%,MgO 0.76%,TFe_(2)O_(3) 4.49%,K_(2)O 3.67%,Na_(2)O 5.24%,and average value of A/CNK is 0.93,displaying the features of high silicon,rich alkali and quasi-aluminous.(La/Yb)Nratios of 7.71 to 10.60 displays apparent differentiation between LREE and HREE with an averageδEu of 0.91.The chondrite-normalized curve of REE is right inclined,showing ocean island basalts(OIB)signature.The dykes are enriched in elements such as Rb,Ba,Th,K and Nd,and depleted in elements such as Nb,Ta,P and Ti.The values of(^(87)Sr/^(86)Sr)i(0.704247-0.705292)andεNd(t)(1.08-1.54)are similar to those of diabase.It is suggested that the acidic rock is originated from fractional crystallization of basaltic magma produced by partial melting of mantle plume,and contaminated with a small amount of upper crust material.The acidic rock was dated at(259±2)Ma by SIMS,which is consistent with the magmatism age of the Emeishan Large Igneous Province.The large number of inherited zircons in the samples were found,might be the response to tectonic activity at different stages in the Yangtze block.

关 键 词：石英二长斑岩 岩石地球化学 SIMS年代学 峨眉山大火成岩省 黔南 地质调查工程 

分 类 号：P597[天文地球—地球化学] P588.121[天文地球—地质学]