青海南山奥陶纪岩浆弧:来自茶卡北山闪长岩锆石U-Pb年代学、元素地球化学和Hf同位素的证据  

Ordovician Magmatic Arc in the Nanshan Area,Qinghai Province:Evidence from Zircon U-Pb Chronology,Element Geochemistry and Hf Isotope Compositions of the Diorites in the Chakaibeishan Area

作　　者：李五福[1,2] 潘彤 王秉璋 张新远[1,2] 郑英 王春涛[1,2] 李善平 韩杰[1,2] LI Wufu;PAN Tong;WANG Bingzhang;ZHANG Xinyuan;ZHENG Ying;WANG Chuntao;LI Shanping;HAN Jie(Qinghai Institute of Geological Survey,Xining 810012,Qinghai,China;Qinghai Provincial Key Laboratory of Geological Process and Mineral Resources for Northern Qinghai-Tibet Plateau,Xining 810012,Qinghai,China;Bureau of Geology and Mineral Exploration and Development of Qinghai Province,Xining 810001,Qinghai,China)

机构地区：[1]青海省地质调查院,青海西宁810012 [2]青海省青藏高原北部地质过程与矿产资源重点实验室,青海西宁810012 [3]青海省地质矿产勘查开发局,青海西宁810001

出　　处：《大地构造与成矿学》2022年第4期788-802,共15页Geotectonica et Metallogenia

基　　金：第二次青藏高原综合科学考察研究(STEP)项目(2019QZKK0702);青海省地质调查局地质调查项目(2020021022jc013);中国地质调查局地质调查项目(1212011221151)联合资助。

摘　　要：青海南山构造带发育NW-SE向展布的早古生代侵入岩,对其开展研究对了解青海南山构造带早古生代阶段地质属性与地质过程具有重要意义。本文对茶卡北山恰让地区闪长岩进行了详细的岩石学、地球化学和LA-ICP-MS锆石U-Pb年代学研究。结果表明,恰让闪长岩形成于晚奥陶世(446~447 Ma)。岩石具中等含量的硅(SiO_(2)=49.68%~62.52%)、富钠(Na_(2)O=2.48%~3.13%、K_(2)O/Na_(2)O=0.37~1.30,平均0.79)、高镁(MgO=4.45%~6.84%、Mg^(#)值为62~68)、高Cr(158×10^(-6)~384×10^(-6))和Ni(74.7×10^(-6)~136×10^(-6))特征。岩石的稀土元素总量较低,稀土元素配分曲线显示富集轻稀土元素,略亏损重稀土元素,具有轻微的Eu负异常(δEu=0.76~0.82)。微量元素蛛网图显示富集大离子亲石元素(LILE)K、Cs、Sr、Rb,相对亏损高场强元素(HFSE)Nb、Ta、P、Ti等元素。锆石ε_(Hf)(t)值较低为-7.8~-2.6。结合区域地质背景资料,我们认为恰让闪长岩岩体形成于岛弧背景,可能是南祁连洋向北俯冲背景下俯冲沉积物熔体与地幔楔橄榄岩反应的产物。The Early Paleozoic intrusive rocks in the NW-SE trending Qinghai Nanshan tectonic belt are of great significance for the understanding of the geological properties and geological processes of the tectonic belt.This paper presents petrological,geochemical,and LA-ICP-MS zircon U-Pb chronological and Hf isotope results of the Qiarang diorites.The results show that the Qiarang diorites were generated in the Late Ordovician(446 to 447 Ma).These diorites are characterized by low and variable silicon(SiO_(2):49.68%to 62.52%),high sodium(Na_(2)O:2.48%to 3.13%,K_(2)O/Na_(2)O:0.37 to 1.30,with an average of 0.79)and magnesium(MgO:4.45%to 6.84%,Mg^(#):62 to 68)and high Cr(158×10^(-6)to 384×10^(-6))and Ni(74.7×10^(-6)to 136×10^(-6)).They have relatively low total amount of rare earth elements,relatively enriched in light rare earth elements and depleted in heavy rare earth elements with weak Eu negative anomalies(δEu:0.76 to 0.82).They also show enrichment of large-ion lithophile elements(LILE)(K,Cs,Sr and Rb),and relatively depletion of high field strength elements(HFSE)Nb,Ta,P,Ti and other elements.They have negative and slightly variableε_(Hf)(t)values(-7.8 to-2.6).Combined with the regional geological background,we suggest that the Qiarang diorites were formed in an arc setting,and were generated by the interaction between subducted oceanic sediment-derived melts and mantle wedge peridotites during the northward subduction of the Southern Qilian Ocean.

关 键 词：青海南山 恰让闪长岩 锆石U-Pb定年 地球化学 构造环境 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]