柴达木盆地北缘锡铁山铅锌矿区辉长岩锆石U-Pb年代、岩石地球化学和Hf同位素特征  

Zircon U-Pb age,petrochemistry and Hf isotope characteristics of gabbro in Xitieshan Pb-Zn mining area in northern margin of Qaidam Basin

作　　者：廖宇斌[1] 李碧乐[1] 孙永刚[1] 杨佰慧 高歌悦 刘国文 LIAO Yu-bin;LI Bi-le;SUN Yong-gang;YANG Bai-hui;GAO Ge-yue;LIU Guo-wen(College of Earth Sciences,Jilin University,Changchun 130061,China)

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《世界地质》2020年第3期495-508,共14页World Geology

基　　金：中国地质调查局整装勘查项目(121201004000150017)。

摘　　要：为确定锡铁山矿区辉长岩的形成时代、原岩性质和岩石成因,笔者对其进行锆石U-Pb年代学、岩石地球化学及Hf同位素的研究。结果表明:辉长岩LA-ICP-MS锆石U-Pb年龄为(514.7±1.1)Ma,属于中寒武世;岩石中SiO2含量为47.88%~49.87%,MgO为4.66%~5.21%,TiO2为0.47%~0.51%,P2O5为0.04%~0.05%,K2O为0.34%~0.56%,Na2O为2.67%~3.24%,Mg#为61.67~65.84,为高铝的钙碱性系列岩石;具有略右倾的稀土配分曲线模式,显示明显的正Eu异常(δEu=1.74~1.92);岩石的锆石Hf同位素εHf(t)为4.1~7.67,单阶段模式年龄(TDM1)为950~812 Ma,表明岩浆源区为亏损地幔。岩石富集大离子亲石元素K、Ba、Sr和不相容元素U,亏损高场强元素Nb、Zr和P和Ti,显示为典型的岛弧岩浆岩特征。综合研究认为,锡铁山辉长岩形成在柴达木洋向北俯冲于祁连山地块之下的岛弧环境,进一步证实柴北缘在中寒武世发生了洋壳俯冲作用。In order to confirm the formation age,protolith characters and petrogenesis,the LA-ICP-MS zircon U-Pb dating,petrochemistry and Hf isotope analysis are carried out for the gabbro in the Xitieshan mining area.The results show that the gabbro has the zircons with weighted mean age of (514.7±1.1) Ma,implying that the gabbro emplaced in Middle Cambrian.Geochemical data indicate that the gabbro has such major element contents as Si O2:47.88%~49.87%,Mg O:4.66%~5.21%,Ti O2:0.47%~0.51%,P2O5:0.04%~0.05%,K2O:0.34%~0.56%,Na2O:2.67%~3.24%,Na2O>K2O and Mg#:61.67~65.84,which show the characters of high aluminum calc-alkaline rocks.Slightly right-leaning REE distribution patterns and obvious positive Eu anomaly (δEu=1.74~1.92) are also indicated.TheεHf(t) values of the gabbro range from 4.1 to 7.67and single-stage Hf model ages (TDM1) range from 950 Ma to 812 Ma,suggesting that the magma originated from depleted mantle.The rock is enriched in LILE (e.g.,K,Ba,Sr) and incompatible elements U,but depleted in HFSE (e.g.,Nb,Zr,P and Ti),showing the typical island-arc magmatic rock characteristics.The gabbro in Xi-tieshan area was formed in the island-arc setting where the northern margin of Qaidam oceanic crust subducted beneath the southern Qilian block.It further confirms that oceanic crust subduction occurred in the northern margin of Qaidam Basin during the Middle Cambrian.

关 键 词：岩石地球化学 锆石U-PB测年 Hf同位素 辉长岩 锡铁山铅锌矿区 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]