龙岗火山区早更新世玄武质熔岩成因及其构造意义——来自Rb-Sr同位素定年、元素地球化学及Pb同位素证据  

Genesis and Tectonic Significance of Early Pleistocene Basaltic Lava in Longgang Volcanic Area:Evidence from Rb-Sr Isotopic Dating,Element Geochemistry and Pb Isotope

作　　者：徐智涛 孙立影 李忠伟[2] 李萌萌 刘宏岩[2] 马飞 Xu Zhitao;Sun Liying;Li Zhongwei;Li Mengmeng;Liu Hongyan;Ma Fei(Institute of Volcanology,China Earthquake Administration,Changchun 130117,China;Jilin Earthquake Agency,Changchun 130117,China)

机构地区：[1]中国地震局火山研究所,长春130117 [2]吉林省地震局,长春130117

出　　处：《吉林大学学报（地球科学版）》2023年第3期887-903,共17页Journal of Jilin University：Earth Science Edition

基　　金：中国工程院院地合作项目(JL2021-03-1);吉林长白山火山国家野外科学观测研究站基金(NORSCBS22-05);吉林省地震局青年科技发展基金(JZQ-202213)。

摘　　要：龙岗火山区位于吉林省东部辉南县与靖宇县境内,是我国东北部陆缘第四纪陆相火山岩区的重要组成部分。为了深入探讨研究区玄武质熔岩成因及其构造意义,在野外地质调查基础上,开展了岩体的Rb-Sr同位素测年、元素地球化学和全岩Pb同位素测定。结果表明:1)粗面玄武质熔岩中7件全岩、斜长石和角闪石Rb-Sr等时线年龄为(1.81±0.34)Ma(MSWD=0.17,n=7);2)粗面玄武质熔岩中w(Na_(2)O+K_(2)O)值范围为6.44%~6.65%,具有偏高的A/CNK(1.24~1.27)和Mg^(#)(39.09~39.81)值,与原始地幔相比,明显富集Li、Cs、Be、Rb、Ba、Sr等大离子亲石元素(LILE),富集轻稀土元素(LREE),弱富集Nb、Ta、Zr、Hf、U、Th等高场强元素(HFSE),亏损重稀土元素(HREE),具有弱的Eu异常(δEu=0.95~1.07)和弱Pb元素富集,与长白山玄武质岩石具有相似的元素地球化学特征;3)岩石中的(^(87)Sr/^(86)Sr)_(i)值为0.705 074~0.705 206,全岩中^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb和^(208)Pb/^(204)Pb值分别为17.984~18.329、15.490~15.523和38.315~38.400。新近研究成果及区域构造演化现有认识综合表明,该期次玄武质熔岩成岩石时代为早更新世卡拉布里亚阶(Calabrian)阶段,成岩岩浆主要由幔源岩浆作用形成,并有少量年轻大陆下地壳成分加入,显示出洋岛玄武岩(OIB)或板内交代玄武岩的属性特征。此外,火山区粗面玄武质熔岩的形成及其伴随的火山活动发生于约1.81 Ma的拉张性构造环境中,可能与太平洋板块俯冲欧亚东北部陆块之后的回撤有关。Longgang volcanic area is located in Huinan and Jingyu County,Eastern Jilin Province,and is an important part of the Quaternary continental volcanic rock area on the continental margin of Northeast China.In order to further explore the genesis and tectonic significance of basaltic lava in the study area,based on field geological investigation,Rb-Sr isotopic dating,element geochemistry and whole rock Pb isotopic analysis were carried out.The experimental results show that:1)The Rb-Sr isochron age of whole rocks,plagioclase and amphibole from seven trachybasalt lava samples is(1.81±0.34)Ma(MSWD=0.17,n=7).2)The values of Na_(2)O+K_(2)O in trachybasaltic lavas range from 6.44%to 6.65%,with high A/CNK(1.24-1.27)and Mg^(#)(39.09-39.81)values.Compared with the primitive mantle,the trachybasaltic lavas significantly enriched in Rb,Ba,Sr and other large ion lithophile elements(LILE),enriched in light rare earth elements(LREE),weakly enriched high field strength elements(HFSE)such as Nb,Ta,Zr,Hf,U and Th,depleted heavy rare earth elements(HREE),with weak Eu anomalies(δEu=0.95-1.07)and weakly enriched in Pb.3)The(^(87)Sr/^(86)Sr)i values in the studied rocks range from 0.705074 to 0.705206,and the ratios of ^(206)Pb/^(204)Pb,^(207)Pb/^(204)Pb and ^(208)Pb/^(204)Pb in the whole rocks are 17.984-18.329,15.490-15.523 and 38.315-38.400,respectively.Combined with the recent research results and the existing understanding of regional tectonic evolution,it shows that the diagenetic age of basaltic lava is the Calabrian stage of the Early Pleistocene.The diagenetic magma is mainly formed by mantle-derived magma,with a small amount of young lower crust components added,showing the attributes of oceanic island basalts(OIB)or intraplate metasomatic basalt.In addition,the formation of trachybasaltic lava and its associated volcanic activity occurred in an extensional tectonic environment at about 1.81 Ma,which may be related to the roll-back after the subduction of the Pacific plate under the northeastern Eurasia continent.

关 键 词：Rb-Sr测年 元素地球化学 PB同位素 玄武质熔岩 龙岗火山区 吉林省 

分 类 号：P59[天文地球—地球化学]