中祁连西段晚奥陶世-中志留世镁铁质岩脉的成因与构造启示  

Petrogenesis and tectonic implications of Late Ordovician-Middle Silurian mafic dykes in the western Central Qilian Belt,NW China

作　　者：贾开军 王超[1] 孙晓奎 喻遵谱 李雪 马得青 刘良[1] JIA KaiJun;WANG Chao;SUN XiaoKui;YU ZunPu;LI Xue;MA DeQing;LIU Liang(State Key Laboratory of Continental Evolution and Early Life,Department of Geology,Northwest University,Xi'an 710069,China;Shaanxi Provincial Land Engineering Construction Group,Xi'an 710075,China;The Seventh Geological Team of Jiangxi Geological Bureau,Ganzhou 341000,China)

机构地区：[1]大陆演化与早期生命全国重点实验室,西北大学地质学系,西安710069 [2]陕西省土地工程建设集团,西安710075 [3]江西省地质局第七地质大队,赣州341000

出　　处：《岩石学报》2025年第4期1279-1296,共18页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42272054、42030307);大陆动力学国家重点实验室课题联合资助.

摘　　要：中基性岩脉不仅是地球深部过程的信息载体,也是解码地幔源区性质和地球动力学背景的重要指示标志。本文对中祁连构造带西段出露的柳树沟辉长岩、大青沟辉长岩脉、大青沟闪长玢岩脉和冬草沟辉长岩脉开展了岩石学、地球化学和锆石U-Pb年代学研究。年代学分析结果表明,柳树沟辉长岩和这些岩脉分别形成于465Ma、448Ma、449~450Ma、430Ma。地球化学分析结果表明,柳树沟辉长岩属于碱性系列,具有钾玄岩特征,其轻、重稀土分异较弱,Nb、Ta和Ti等高场强元素亏损程度较弱,具有较高的Sr(363×10^(-6)~422×10^(-6))和Nb(16.5×10^(-6)~16.7×10^(-6)),表现出富Nb玄武岩的特征。此外,柳树沟辉长岩的(87 Sr/86 Sr)i介于0.708992~0.709067之间、εNd(t)值为-6.59~-6.84,具有高的Nb/Ta(22~23)比值,表明其形成过程与富集地幔源区和碳酸盐熔体的相互作用有关。大青沟闪长玢岩脉属于高钾钙碱性系列,具有相对较高的SiO_(2)(51.00%~57.18%),Na_(2)O(3.11%~3.57%)、K 2O(1.92%~2.35%)和较低的MgO(4.22%~4.58%)、TiO_(2)(0.71%~1.02%),Mg#值介于50.8~57.9,轻重稀土分馏明显((La/Yb)N=10.7~15.1),富集Rb、Ba(588×10^(-6)~858×10^(-6))和Sr(625×10^(-6)~644×10^(-6)),表现出赞岐质高Mg闪长岩的特征。大青沟闪长玢岩脉的(87 Sr/86 Sr)i为0.708593,εNd(t)值为-5.08,同时具有较高的Th/Nb(0.75~1.64)、Sr/Y(26~35)、La/Yb(15~21)和Nb/Ta(15~18)比值,较高的Zr、Hf元素,且Dy/Yb比值较低(1.94~2.0),Y元素含量处于中等(18~25),代表了俯冲洋壳和沉积物熔流体与上覆岩石圈地幔交代的产物。冬草沟辉长岩脉和大青沟辉长岩脉均具有高Ba/La、Ba/Th比值和Ba、Sr值以及低的Th(0.8×10^(-6)~2.07×10^(-6)),表明在岩浆源区中来自板片流体的影响较大,俯冲沉积物熔体参与较少。这些中基性岩脉的源区差异主要反映了地幔源区俯冲组分的差别,不同类型的俯冲组分交代上覆地幔,最终形成了中祁连西段广泛分布�Mafic dyke is not only information carrier of the deep earth processes,but also important indicator for deciphering the nature of mantle source and geodynamic background.In this paper,we carried out petrological,geochemical and zircon U-Pb geochronological studies on the Liushugou gabbro,the Daqinggou gabbroic dyke and dioritic porphyrite dyke,and the Dongcaogou gabbroic dyke outcropped in the western Central Qilian Belt,NW China.Geochronological results show that the crystallization ages of the Liushugou gabbro and the studied dykes are at ca.465Ma,ca.448Ma,ca.449~450Ma and ca.430Ma,respectively.Geochemical analysis results indicate that the Liushugou gabbro(465Ma)is the alkaline series and exhibits the characteristic of shoshonite.It also shows weakly light and heavy rare earth element(HREE)fractionation,and small negative high field strength elements(HFSEs;such as Nb,Ta and Ti)anomalies in bulk-rock compositions.It has relatively high Sr(363×10^(-6)~422×10^(-6)),Nb(16.5×10^(-6)~16.7×10^(-6))contents and Nb/Ta ratio(22~23),with(87 Sr/86 Sr)i andεNd(t)values ranging from 0.708992 to 0.709067 and from-6.59 to-6.84,reflecting the characteristics of Nb-rich basalt formed in the source with interaction between the enriched mantle and carbonate melt.The Daqinggou dioritic porphyrite dykes(449~450Ma)belong to high-potassium calc-alkaline series,they have relatively high SiO_(2)(51.00%~57.18%),Na_(2)O(3.11%~3.57%)and K 2O(1.92%~2.35%)contents,and relatively low MgO(4.22%~4.58%)and TiO_(2)(0.71%~1.02%)contents.The Mg#values range from 50.8 to 57.9,and the fractionation of light and heavy rare earth elements is more obvious((La/Yb)N=10.7~15.1).The analyzed samples are enriched in Rb,Ba(588×10^(-6)~858×10^(-6))and Sr(625×10^(-6)~644×10^(-6)),showing the characteristics of sanukitoid high-Mg diorite.Furthermore,the isotopic analysis reveals they have an averaged(87 Sr/86 Sr)i value of 0.708593 andεNd(t)value of-5.08.The measured samples have relatively high Th/Nb(0.75~1.64),Sr/Y(26~35),La/Yb(15~21)and Nb/Ta(15~18

关 键 词：中基性岩脉 高Mg闪长岩 晚奥陶世 中志留世 中祁连西段 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]