西昆仑东部晚三叠世高镁闪长岩的成因及其地质意义
Petrogenesis of Triassic high-Mg diorites in western Kunlun orogen and its tectonic implication
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文摘
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三叠纪是西昆仑造山带地质演化的重要时期,本文首次发现的两个晚三叠世高镁闪长岩岩体对于讨论该造山带中晚三叠世构造-岩浆活动和古特提斯洋构造演化有重要意义。本文对西昆仑东部阿克萨依闪长岩(AKSY)和俘虏沟石英闪长岩(FLYT)进行了岩石学、元素和同位素地球化学及同位素年代学综合研究。阿克萨依和俘虏沟石英闪长岩的锆石U-Pb年龄分别为(216.7±1.8) Ma和(213.7±2.0) Ma,为晚三叠世岩浆活动的产物。这两个岩体有较高的MgO含量(分别为4.66%~5.01%和3.37%~3.52%)和Mg#值(分别为59.6~60.3和50.2~51.5),显示出与赞岐岩相似的地球化学特征,暗示它们是地幔部分熔融的产物。阿克萨依闪长岩和俘虏沟石英闪长岩又都明显富集Rb、Ba、Th、U等大离子亲石元素(LILE),亏损Nb、Ta、Ti、Zr等高场强元素,表明它们的形成过程中有陆壳物质加入。元素和同位素地球化学特征显示,阿克萨依闪长岩和俘虏沟石英闪长岩都是由俯冲流体交代的富集岩石圈地幔部分熔融形成,地幔源区的富集程度、部分熔融程度和熔融深度不同导致两者地球化学特征存在明显差异。鉴于这两个由交代地幔部分熔融形成的闪长岩出露于麻扎-康西瓦缝合带的南侧,以及西昆仑造山带中晚三叠世花岗岩主要分布在缝合带南侧的甜水海地体中,本文认为西昆仑古特提斯洋可能曾向南俯冲于甜水海地体之下。 |
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其他语种文摘
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This paper presents the first detailed LA-ICP-MS zircon U-Pb chronology, major and trace element analysis, and Sr-Nd-Hf isotope geochemical analysis of Late Triassic high-Mg diorites (AKSY and FLYT) in the eastern part of the western Kunlun orogen. LA-ICP-MS zircon U-Pb dating shows that the AKSY pluton was emplaced at (216.7±1.8) Ma, and the FLYT pluton was emplaced at (213.7±2.0) Ma. The AKSY diorite have SiO_2 contents of 55.93% to 57.9% and MgO contents of 4.66% to 5.01%, with high Na_2O/K_2O ratios (1.75–2.49), a high Mg# value (59.6–60.3), initial ~(87)Sr/~(86)Sr ratios of 0.7073–0.7074, e_(Nd)(t) values of –1.7 to –2.2, and ε_(Hf)(t) (in-situ zircon) values of 4.3–6.9. They are enriched in large ion lithophile elements (LILE) (i.e., Rb, Ba, Th, and U) and depleted in high field strength elements (i.e., Nb, Ta, Ti, and Zr); they also have relatively low Sr/Y and La/Yb ratios. Compare with the AKSY diorites, the FLYT quartz diorites have higher SiO_2 (58.43%~59.79%), K_2O (2.26%~2.57%), LILE, and light rare-earth element contents, and lower MgO (3.37%–3.52%) contents and Mg# (50.2–51.5) values, with a more enriched isotope composition ((~(87)Sr/~(86)Sr)i = 0.7079–0.7080, e_(Nd)(t) = –5.4, and ε_(Hf)(t) = –2.1 to –4.6). All of these elemental and isotopic geochemical feature indicate that the AKSY diorites and the FLYT quartz diorites were both derived from partial melting of mantle wedge peridotite, which was fluxed by fluids or melts liberated from the subducting slab, and the differences in the degree of mantle enrichment, degree of partial melting, and depth of the partial melting result in the different elemental and isotope geochemical characteristics of the two plutons. The two diorites and most of the Triassic granitoids in the western Kunlun orogen are widespread south of the Mazha-Kangxiwa suture, indicating that the Paleo-Tethys Ocean may have undergone southward subduction beneath the Tianshuihai terrane. |
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来源
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地球化学
,2018,47(4):363-379 【核心库】
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DOI
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10.19700/j.0379-1726.2018.04.005
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关键词
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西昆仑造山带
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古特提斯洋
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晚三叠世
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高镁闪长岩
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地址
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1.
中国科学院广州地球化学研究所, 中国科学院矿物学与成矿学重点实验室, 广东, 广州, 510640
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中国科学院大学, 北京, 100049
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中海油能源发展股份有限公司工程技术分公司, 天津, 300452
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国家305项目办公室, 新疆, 乌鲁木齐, 830000
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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0379-1726 |
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学科
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地质学 |
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基金
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新疆维吾尔自治区重大科技专项
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国家“十二五”科技支撑计划项目
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中国科学院广州地球化学研究所一三五项目
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文献收藏号
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CSCD:6291284
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