西天山阿吾拉勒西段石炭纪花岗岩与暗色包体岩石成因及地质意义  

Petrogenesis and Tectonic Implications of Carboniferous Granites and Its Dark Enclaves in the Western Awulale Mountain,Western Tianshan

作　　者：李丽娟 张涛 李强 贠杰 何立 程学芹 赵力颖 LI Lijuan;ZHANG Tao;LI Qiang;YUN Jie;HE Li;CHENG Xueqin;ZHAO Liying(Henan Geology Mineral College,Zhengzhou 451464,Henan,China;Regional Geological Survey Institute of Hebei Province/Geotourism Research Center of Hebei Province,Langfang 065000,Hebei,China)

机构地区：[1]河南地矿职业学院,河南郑州451464 [2]河北省区域地质调查院∕河北省地学旅游研究中心,河北廊坊065000

出　　处：《西北地质》2024年第3期73-90,共18页Northwestern Geology

基　　金：国家自然科学基金项目(41502061);中国地质调查局项目(1212011220649)联合资助。

摘　　要：西天山出露的古生代岩浆岩的岩石成因及动力学背景对于恢复区域构造演化历史具有重要意义。笔者选取阿吾拉勒西段巩乃斯种羊场北西地区的花岗岩及其中暗色包体进行了岩石学研究、锆石U-Pb年代学和岩石地球化学分析。研究表明暗色包体为细粒闪长岩,闪长质包体K_(2)O=0.93~2.50,K_(2)O/Na_(2)O=0.20~0.21,A/CNK=0.83~0.87,里特曼指数σ=2.33~3.02,为准铝质钙碱性岩石系列。寄主花岗岩K_(2)O=2.92~3.48,含量较高,K_(2)O/Na_(2)O=0.60~0.79,里特曼指数σ=1.87~2.17,A/CNK=1.01~1.04,为弱过铝质钙碱性系列岩石,属I型花岗岩。二者均富集大离子亲石元素Rb、Ba、Pb等,亏损高场强元素Nb、Ta、Ti,稀土总量较低,轻稀土元素相对富集,重稀土元素相对亏损。闪长质包体无显著Eu、Sr异常,而花岗岩具明显的负Eu异常,且Sr、P、Ti元素强烈亏损。锆石U-Pb测年结果显示花岗岩成岩年龄为(320.0±2.7)Ma,属晚石炭世早期;闪长质包体成岩时代为(344.5±1.4)Ma,属早石炭世中期。闪长质包体类型为捕掳体,是寄主花岗质岩浆上位过程中捕获的围岩。岩石地球化学和年代学特征揭示二者有不同的成因,闪长质包体为早期北天山洋南向俯冲过程中形成的,而花岗岩侵位于后碰撞伸展环境,是由于软流圈上涌加热导致基性下地壳部分熔融而成。综合区域地质资料分析,早晚石炭世之交很可能是西天山区域构造体制转换的重要阶段,即由碰撞挤压环境转化为伸展拉张环境。The petrogenesis and dynamic background of the magmatic rocks in the West Tianshan Mountains are of great significance to reveal the tectonic evolution history of the restoration area.In this paper,the granite and its dark enclaves in the northwestern area of Kunes Zhongyangchang in the western Awulale Mountain were selected for petrology and zircon U-Pb chronology and petrogeochemical analysis.The results show that the dark enclaves are fine-grained diorite,with K_(2)O=0.93~2.50,K_(2)O/Na_(2)O=0.20~0.21,A/CNK=0.83~0.87 andσ=2.33~3.02,which are quasi-aluminous calc-alkaline rock series.Host granites belong to I type granites with K_(2)O=2.92~3.48,K_(2)O/Na_(2)O=0.60~0.79,Ritman indexσ=1.87~2.17,and A/CNK=1.01~1.04,which are weakly peraluminous calc-alkaline rock series.Both of them are enriched in large ion lithophile elements(LILE,e.g.Rb、Ba、Pb)and depleted in high field strength elements(HSFE,e.g.Nb,Ta,Ti),The total amount of rare earth elements is low,accompanied by the relative enrichment of light rare earth elements,and the relative loss of heavy rare earth element.The diorite enclaves have no significant Eu and Sr anomalies,while the granites have obvious negative Eu anomalies and strong loss of Sr,P and Ti elements.Zircon U-Pb dating shows that the formation age of granite is(320.0±2.7)Ma,belonging to the early Late Carboniferous.The diagenetic age of the diorite enclaves is(344.5±1.4)Ma,belonging to the Early Carboniferous.The type of diorite enclaves is xeno-lith,which were captured during the rising of the host granitic magma.The geochemical and chronological char-acteristics of the rocks reveal that they have different petrogenesis.The dioritic enclaves were formed during the northern Tianshan Ocean subduction southward,and the granite intrusion was located in the post-collision exten-sion environment,which was formed due to the upwelling of the asthenosphere,leading to the partial melting of the lower crust.Based on regional geological data,it is likely that the early Carboniferous to late Carb

关 键 词：西天山 花岗岩 包体 锆石U-PB 岩石成因 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]