华北克拉通东南缘蚌埠隆起新太古代晚期片麻状二长花岗岩的年龄、成因及构造意义  

Age,genesis and tectonic significance of late Neoarchean gneissic monzogranitein Bengbu Uplift,southeastern margin of North China Craton

作　　者：李斌[1] 王朝[1] 管后春[1] 雷丁尔 Li Bin;Wang Chao;Guan Houchun;Lei Dinger(Geological Survey of Anhui Province(Anhui Institute of Geological Sciences),Hefei,Anhui 230001)

机构地区：[1]安徽省地质调查院(安徽省地质科学研究所),安徽合肥230001

出　　处：《资源环境与工程》2024年第4期373-380,392,共9页Resources Environment & Engineering

基　　金：1∶5万楚店集、高炉集、江集和望町集覆盖区综合地质调查(2016-g-3-32);蚌埠隆起区东段金成矿叠加条件研究(2023-k-15)。

摘　　要：华北克拉通东南缘前寒武纪下地壳经历幕式生长与多期改造,在新太古代晚期发生了大规模的构造热事件,并伴随新生陆壳增生。对华北克拉通东南缘蚌埠隆起新发现的片麻状二长花岗岩开展锆石U-Pb定年和岩石地球化学分析,探讨其成因及构造意义。结果表明,片麻状二长花岗岩的锆石发育明显的核幔结构和震荡生长环带,Th/U比值高,为岩浆成因锆石,其LA-ICP-MS U-Pb年龄为(2557±24)Ma,指示其形成时代为新太古代晚期;岩石具有高SiO_(2)(69.03%~70.05%)、高Al_(2)O_(3)(14.71%~15.63%)、低MgO(0.92%~1.43%)特征,K_(2)O/Na_(2)O比值为0.95~1.06,铝饱和指数为1.08~1.12,属于弱过铝质高钾钙碱性岩石;岩石富集Rb、K、Ba等大离子亲石元素,亏损Nb、Zr、P、Y等高场强元素,稀土元素含量较低(∑REE=81.25×10^(-6)~123.74×10^(-6)),轻重稀土元素强烈分异((La/Yb)N比值为52.71~72.13),显示Eu正异常(δEu=1.36~2.40),综合说明其属于中下地壳部分熔融形成的I型花岗岩。蚌埠隆起新太古代晚期片麻状二长花岗岩的发现,表明该地区在该时期发生过强烈的构造热事件,契合华北克拉通地壳生长和演化历史,佐证了2.5 Ga是华北克拉通陆壳生长重要阶段。The southeastern margin of North China Craton experienced episodic growth and underwent multiple reworking in the Precambrian crust.In the late Neoarchean,a significant tectono-thermal event occurred,resulting in the addition of new continental crust.Zircon U-Pb dating and geochemical analysis were carried out on the newly discovered gneissic monzogranite in Bengbu uplift,southeastern margin of North China Craton,and its genesis and tectonic significance were discussed.The results show that the zircons of the gneissic monzogranite have obvious core-mantle structure,with oscillatory growth zone and high Th/U ratio,which are characteristic of magmatic zircons.The LA-ICP-MS U-Pb age of the gneissic monzogranite is(2557±24)Ma,indicating that it was formed in the late Neoarchean.The rock has high SiO 2(69.03%-70.05%),high Al_(2)O_(3)(14.71%-15.63%),low MgO(0.92%-1.43%),with K_(2)O/Na_(2)O ratio of 0.95 to 1.06 and A/CNK ratio of 1.08 to 1.12,suggesting that they belong chemically to weak peraluminous,high fractionated high-K and calc-alkaline rocks.The rock shows enrichment in large ion lithophile elements like Rb,K,and Ba,while displaying depletion in high field strength elements such as Nb,Zr,P,and Y.The REE content is low(∑REE=81.25×10^(-6)-123.74×10^(-6)),with a significant segregation between light and heavy rare earth elements,and a(La/Yb)N ratio ranging from 52.71 to 72.13,showing a positive Eu anomaly(δEu=1.36-2.40).The above characteristics indicate that it belongs to the I-type granite formed by partial melting of the middle and lower crust.The discovery of late Neoarchean gneissic monzogranite indicates that there was a strong tectonic thermal event in the Bengbu uplift during this period,which is consistent with the crustal growth and evolution history of the North China Craton,and supports the idea that 2.5 Ga is an important stage of lithospheric growth in the southeastern North China Craton.

关 键 词：片麻状二长花岗岩 锆石U-PB年龄 新太古代 Ⅰ型花岗岩 蚌埠隆起 

分 类 号：P581[天文地球—岩石学] P619.222[天文地球—地质学]