赵守仁, 岳鋆璋, 吴喆. 西藏麻米地区晚侏罗世—早白垩世侵入岩锆石U-Pb年龄、地球化学特征及其对班-怒特提斯洋俯冲过程的制约[J]. 地质通报, 2022, 41(8): 1342-1357. DOI: 10.12097/j.issn.1671-2552.2022.08.003
    引用本文: 赵守仁, 岳鋆璋, 吴喆. 西藏麻米地区晚侏罗世—早白垩世侵入岩锆石U-Pb年龄、地球化学特征及其对班-怒特提斯洋俯冲过程的制约[J]. 地质通报, 2022, 41(8): 1342-1357. DOI: 10.12097/j.issn.1671-2552.2022.08.003
    ZHAO Shouren, YUE Yunzhang, WU Zhe. Zircon U-Pb ages, geochemical characteristics and constraints on the Bangong-Nujiang Tethys Ocean subduction of Late Jurassic-Early Cretaceous intrusive rocks from Mami area, Tibet[J]. Geological Bulletin of China, 2022, 41(8): 1342-1357. DOI: 10.12097/j.issn.1671-2552.2022.08.003
    Citation: ZHAO Shouren, YUE Yunzhang, WU Zhe. Zircon U-Pb ages, geochemical characteristics and constraints on the Bangong-Nujiang Tethys Ocean subduction of Late Jurassic-Early Cretaceous intrusive rocks from Mami area, Tibet[J]. Geological Bulletin of China, 2022, 41(8): 1342-1357. DOI: 10.12097/j.issn.1671-2552.2022.08.003

    西藏麻米地区晚侏罗世—早白垩世侵入岩锆石U-Pb年龄、地球化学特征及其对班-怒特提斯洋俯冲过程的制约

    Zircon U-Pb ages, geochemical characteristics and constraints on the Bangong-Nujiang Tethys Ocean subduction of Late Jurassic-Early Cretaceous intrusive rocks from Mami area, Tibet

    • 摘要: 班公湖-怒江缝合带南、北两侧分布的大量中生代火成岩对约束班公湖-怒江特提斯洋演化过程具有重要意义。通过班公湖-怒江缝合带南侧麻米乡一带酸性侵入岩的锆石U-Pb年龄及地球化学特征研究,获得花岗斑岩206Pb/238U年龄加权平均值为146~145 Ma,花岗闪长岩为140 Ma,代表这套侵入岩的形成时代为晚侏罗世末期—早白垩世早期。花岗斑岩与花岗闪长岩均显示出较高的SiO2(69.12%~76.54%)和Al2O3(12.44%~14.93%)含量及较低的MgO含量(0.19%~0.89%),属弱过铝质—强过铝质钙碱性花岗岩;同时富集大离子亲石元素Rb、K,亏损高场强元素Nb、Ta、Ti等;稀土元素总量较低(∑REE=129 ×10-6~201×10-6),分馏程度较高(LREE/HREE=2.06~9.18),呈现出轻稀土元素富集、重稀土元素亏损的特征,并具有负Eu异常,接近活动大陆边缘酸性岩浆岩的稀土元素配分模式。综合分析,麻米晚侏罗世—早白垩世酸性侵入岩主要来源于古老地壳物质的部分熔融,岩浆演化过程经历了分离结晶作用。这套侵入岩表现出火山弧型性质,形成于俯冲的构造背景。结合前人研究与区域资料,认为班公湖-怒江洋晚侏罗世—早白垩世存在南向俯冲,形成了区域上的措勤-申扎构造岩浆弧,进一步证实班公湖-怒江特提斯洋在晚侏罗世—早白垩世发生了双向俯冲,为特提斯的构造演化提供了新的岩石学证据。

       

      Abstract: Large-scale Mesozoic igneous rocks distributed on the north and south sides of the Bangong - Nujiang suture zone are important in constraining the evolution of the Tethyan Ocean.This paper reports the zircon U-Pb age, major and trace geochemical characteristics of the felsic intrusive rocks in the Mami area, south of the Bangong-Nujiang suture zone.The 206Pb/238U weighted average ages of 146~145 Ma for the granitic porphyry and 140 Ma for the granitic amphibolite indicate that the intrusive rocks were emplaced during the Late Jurassic to Early Cretaceous.Both granitic porphyry and granodiorite show high content of SiO2(64.67%~77.45%), Al2O3 (12.59%~16.24%)and low MgO(0.19%~0.89%), which are weakly - strongly peraluminous calc-alkaline granite.These rocks are also enriched in large-ion lithophile elements(LILE)of Rb, K, and depletion in high field strength elements(HFSE)of Nb, Ta, Ti.The total amount of rare earth elements(REE)is low(∑REE=129 ×10-6~201×10-6), and the fractionation degree is high(LREE/HREE= 2.06~9.18).The REE patterns show enrichment in light rare earth elements(LREEs)with negative Eu anomalies, which consistent with the REE distribution patterns of felsic magmatic rocks formed on the active continental margin.Comprehensive analysis shows that the Late Jurassic-Early Cretaceous felsic intrusive rocks in Mami mainly originated from the partial melting of ancient crustal materialand and underwent fractional crystallization during the magmatic evolutionary process.Theses intrusive rocks show the characteristics of volcanic arc-type, suggesting that they formed in the background of ocean subduction.Previous studies, in combination with regional data, show that Bangong - Nujiang Ocean underwent southward subduction during the Late Jurassic to Early Cretaceous, forming the Cuoqin-Shenzha tectonic-magmatic arc.It further confirmed the bidirectional subduction of the Bangong - Nujiang Tethyan Ocean during the Late Jurassic - Early Cretaceous period, which provides new lithological evidence for the tectonic evolution of the Tethyan Ocean.

       

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