吉林双阳石门水库早三叠世C型埃达克质岩的发现及其地质意义  

Discovery of Early Triassic C-type adakitic rocks in Shimen reservoir of Shuangyang,Jilin and its geological significance

作　　者：朱书宏[1] 袁鹏宇 孔凡乾 聂立军[1] 张海莹 李广铁 郭道鹏 ZHU Shuhong;YUAN Pengyu;KONG Fanqian;NIE Lijun;ZHANG Haiying;LI Guangtie;GUO Daopeng(Regional Geology and Mineral Resources Survey of Jilin Province,Changchun 130022,China)

机构地区：[1]吉林省区域地质矿产调查所,长春130022

出　　处：《世界地质》2022年第2期272-282,共11页World Geology

基　　金：吉林省地矿局地质勘查费(省财政拨款)项目(jdk[2018]ky001)。

摘　　要：吉林双阳地区石门水库花岗闪长岩多呈岩株产出,通过对该花岗闪长岩开展岩石学特征、锆石U-Pb测年及岩石地球化学特征的综合研究,旨在确定其形成年代并讨论了岩石类型及源区、岩浆活动和构造演化。锆石U-Pb测年结果表明石门水库花岗闪长岩形成于早三叠世(246.3±1.2)Ma。岩石地球化学分析结果表明该岩体具有富钠、贫钙镁的特点,A/CNK值为1.03~1.07,属于弱过铝质高钾钙碱性系列。富集大离子亲石元素Ba、Th、U和轻稀土元素La、Ce、Pr,具有弱的负Eu异常,轻稀土分馏明显,重稀土分馏不明显且明显亏损的特征。岩体较高的Al_(2)O_(3)含量(15.23%~15.95%)、Na_(2)O含量(4.45%~4.68%)、Sr含量(637.6×10^(-6)~717.7×10^(-6))和Sr/Y比值(61.18~98.32),较低的MgO含量(0.71%~0.76%)、Y(7.30×10^(-6)~10.60×10^(-6))、Yb(0.71×10^(-6)~1.09×10^(-6))含量,显示出埃达克质岩的地球化学特征,且根据较高的K_(2)O含量(2.88%~3.46%)和Rb/Sr比值(0.08~0.12)、较低的Mg#值(34.47~35.55)和Cr含量(4.86×10^(-6)~5.25×10^(-6)),进一步认定该岩体的成因为增厚下地壳部分熔融形成的C型埃达克质岩。结合区域构造演化背景,认为石门水库早三叠世花岗闪长岩是在华北板块与其北侧板块碰撞造山环境中由加厚下地壳部分熔融而形成。The Shimen reservoir granodiorite in Shuangyang area of Jilin mostly occurs as stocks.A comprehensive study of petrological characteristics,zircon U-Pb dating and rock geochemical characteristics of the granodiorite has been conducted,in order to determine the formation age,rock type,magma source,magmatic activity and tectonic evolution.Zircon U-Pb dating results show that the Shimen reservoir granodiorite was emplaced in the Early Triassic(246.3±1.2)Ma.Geochemical analysis results show that the granodiorite samples are rich in sodium and poor in calcium and magnesium,with an A/CNK value of 1.03~1.07,which belongs to the weak peraluminous,high potassium,calc-alkaline series.They have the characteristics of enrichment of large ion lithophile elements Ba,Th,U and light rare earth elements La,Ce,Pr,weak negative Eu anomalies,obvious light rare earth fractionation,insignificant heavy rare earth fractionation but obvious depletion.Their high Al_(2)O_(3)(15.23%~15.95%),Na_(2)O(4.45%~4.68%),Sr(637.60×10^(-6)~717.70×10^(-6))contents and Sr/Y ratio(61.18~98.32),as well as low MgO(0.71%~0.76%),Y(7.30×10^(-6)~10.60×10^(-6)),Yb(0.71×10^(-6)~1.09×10^(-6))contents,show the geochemical characteristics of adakitic rocks.Moreover,considering the high K_(2)O content(2.88%~3.46%)and Rb/Sr ratio(0.08~0.12),low Mg#value(34.47~35.55)and Cr content(4.86×10^(-6)~5.25×10^(-6)),it is further determined that the origin of the granodiorite is due to the partial melting of the thickened lower crust.Combined with the regional tectonic evolution,it is believed that the Shimen reservoir Early Triassic granodiorite was generated by the partial melting of the thickened lower crust in the orogenic environment caused by the collision between the North China plate and its northern plate.

关 键 词：C型埃达克质岩 早三叠世 加厚下地壳 吉林双阳 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]