| 阿尔金造山带南缘晚奥陶世赞岐质闪长岩的发现及其地质意义 |
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| 引用本文： | 曾忠诚,洪增林,边小卫,陈宁,张若愚,李琦.阿尔金造山带南缘晚奥陶世赞岐质闪长岩的发现及其地质意义[J].地学前缘,2022,29(4):345-357. |
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| 作者姓名： | 曾忠诚 洪增林 边小卫 陈宁 张若愚 李琦 |
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| 作者单位： | 1.陕西省矿产地质调查中心, 陕西 西安 7100682.西北工业大学, 陕西 西安 7100723.陕西省地质调查院, 陕西 西安 7100544.自然资源部矿山地质灾害成灾机理与防控重点实验室, 陕西 西安 710054 |
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| 基金项目： | 科学技术部第二次青藏高原综合科学考察研究项目(2019QZKK0802);中国地质调查局地质调查项目(12120114081901) |
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| 摘 要： | 本文以阿尔金造山带南缘出露的高镁赞岐质闪长岩为研究对象,通过系统的野外地质工作、显微岩相学、年代学和全岩地球化学分析,探讨其成因类型和源区性质,限定了阿尔金造山带构造演化格架。闪长岩LA-ICP-MS锆石U-Pb测年结果表明其形成年龄为(445±3) Ma,属晚奥陶世。地球化学数据显示:闪长岩Al2O3含量为15.11%~16.19%,且具有高MgO(3.93%~5.29%)和K2O(1.68%~2.67%)含量的特征,属于高镁钙碱性准铝质岩石;闪长岩具有较高的Cr(29.3×10-6~140×10-6)、Ni(27.1×10-6~43.5×10-6)、Ba(606×10-6~936×10-6)、Sr(513×10-6~734×10-6)和Y(26.4×10-6~31.1×10-6)含量,与典型的高镁赞岐岩类地球化学特征一致;稀土配分图和微量元素蛛网图显示闪长岩样品富集轻稀土元素和大离子亲石元素(如Rb和K),而亏损高场强元素(如Nb、Ti和Zr),表现出与俯冲带环境岩浆岩相似的性质;高Ti/Zr比值(48~60)与Mg#(46.74~53.06)、高Cr(29.3×10-6~140×10-6)与高Ni(27.1×10-6~43.5×10-6)含量等暗示闪长岩岩浆源区来自遭受俯冲组分交代过的富集岩石圈地幔。岩石成因分析表明,阿尔金造山带南缘晚奥陶世高镁赞岐质闪长岩是后碰撞构造环境下俯冲板片断离诱发地幔楔发生减压熔融而形成,代表了早古生代最强烈的区域性幔源基性岩浆侵入事件。
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| 关 键 词： | 南阿尔金造山带 晚奥陶世 高镁赞岐岩质闪长岩 后碰撞构造环境 幔源基性岩浆 |
| 收稿时间： | 2020-11-02 |
Discovery of Late Ordovician sanukitoid-like diorite in southern Altyn orogeny and its geological significance |
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| ZENG Zhongcheng,HONG Zenglin,BIAN Xiaowei,CHEN Ning,ZHANG Ruoyu,LI Qi.Discovery of Late Ordovician sanukitoid-like diorite in southern Altyn orogeny and its geological significance[J].Earth Science Frontiers,2022,29(4):345-357. |
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| Authors: | ZENG Zhongcheng HONG Zenglin BIAN Xiaowei CHEN Ning ZHANG Ruoyu LI Qi |
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| Institution: | 1. Shaanxi Mineral Resources and Geological Survey, Xi’an 710068, China2. Northwestern Polytechnical University, Xi’an 710072, China3. Shaanxi Institute of Geological Survey, Xi’an 710054, China4. Key Laboratory of Mine Geological Hazards Mechanism and Control, Ministry of Natural Resources, Xi’an 710054, China |
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| Abstract: | In this study, we report the occurrence of Late Ordovician sanukitoid-like diorites of the southern Altyn orogeny, and discuss, on the basis of detailed field work, their petrography, geochronology, whole-rock geochemistry, petrogenesis, mantle source as well as constraint on the tectonic evolution framework of the orogeny. LA-ICP-MS zircon U-Pb dating yielded weighted 206Pb/237U age of 445±3 Ma, which is interpreted as the formation age of diorite. Geochemically, the diorites had low Al2O3 (15.11%-16.19%) and high MgO (3.93%-5.29%) and K2O (1.68%-2.67%) contents belonging to high Mg, calc-alkaline and metaluminous series. In addition, the diorites possess high Cr (29.3×10-6 -140×10-6), Ni (27.1×10-6-43.5×10-6), Ba (606×10-6-936×10-6), Sr (513×10-6-734×10-6) and Y (26.4×10-6-31.1×10-6) contents, consistent with global high-Mg sanukitoid. They were enriched in REE and LILE (Rb, K), but depleted in HFSE (Nb, Ti, Zr), consistent with arc magma of the subduction zone. Moreover, the diorites could be generated from enriched lithospheric mantle metasomatized by subduction components, on account of high Ti/Zr ratio (48-60) and Mg# value (46.74-53.06), as well as high Cr (29.3×10-6-140×10-6) and Ni (7.1×10-6-43.5×10-6) contents. Thus we propose that the Late Ordovician high-Mg sanukitoid-like diorites are the product of decompression melting of mantle wedge during the slab break-off process in a post-collision tectonic setting, and represent the most intensive Paleozoic mantle-derived mafic intrusion in the southern Altyn orogeny. |
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| Keywords: | southern Altyn orogeny Late Ordovician high-Mg sanukitoid-like diorite post-collisional tectonic setting mantle-derived mafic magma |
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