侯云东, 蒋子文, 刘新社, 罗静兰, 范立勇, 胡新友, 杜一凡. 2023: 鄂尔多斯盆地西南部早中生代侵入岩脉的形成时代及成因. 地质通报, 42(7): 1098-1117. DOI: 10.12097/j.issn.1671-2552.2023.07.004
    引用本文: 侯云东, 蒋子文, 刘新社, 罗静兰, 范立勇, 胡新友, 杜一凡. 2023: 鄂尔多斯盆地西南部早中生代侵入岩脉的形成时代及成因. 地质通报, 42(7): 1098-1117. DOI: 10.12097/j.issn.1671-2552.2023.07.004
    HOU Yundong, JIANG Ziwen, LIU Xinshe, LUO Jinglan, FAN Liyong, HU Xinyou, DU Yifan. 2023: Age and petrogenetic implication of the Early Mesozoic dykes in the southwestern Ordos Basin. Geological Bulletin of China, 42(7): 1098-1117. DOI: 10.12097/j.issn.1671-2552.2023.07.004
    Citation: HOU Yundong, JIANG Ziwen, LIU Xinshe, LUO Jinglan, FAN Liyong, HU Xinyou, DU Yifan. 2023: Age and petrogenetic implication of the Early Mesozoic dykes in the southwestern Ordos Basin. Geological Bulletin of China, 42(7): 1098-1117. DOI: 10.12097/j.issn.1671-2552.2023.07.004

    鄂尔多斯盆地西南部早中生代侵入岩脉的形成时代及成因

    Age and petrogenetic implication of the Early Mesozoic dykes in the southwestern Ordos Basin

    • 摘要: 鄂尔多斯盆地西南部龙门地区早中生代侵入岩是盆地内少有的岩浆活动记录, 为探讨盆地早中生代形成构造背景提供了理想的研究对象。对鄂尔多斯盆地龙门地区早中生代侵入岩开展岩相学、岩石地球化学及年代学研究。结果表明, 侵入岩为钙碱性-高钾钙碱性闪长玢岩和二长玢岩, 二者均呈低Mg#、Cr、Ni和Co含量, 富集REE和LILE, 贫HFSE, 亏损Nb、Ta、Ti和P的特征, 锆石εHf(t)=-33.89~-9.73, tDM2=1564~2780 Ma, 主要为古元古代和部分新太古代陆壳物质部分熔融的产物。二长玢岩的轻、重稀土元素分馏略低于闪长玢岩, 具有更低的Yb、Y和高的Sr、Sr/Y值, 指示其为压力较高条件下盆地基底较深陆壳物质部分熔融的产物; 闪长玢岩则为较低压力下的较浅基底陆壳物质熔融的产物。两类岩石均获得242 Ma的形成年龄, 与盆地以南秦岭造山带早中生代洋盆俯冲闭合、陆-陆碰撞挤压初期的岩浆活动一致, 表明秦岭造山带早中生代以来的构造岩浆活动影响到鄂尔多斯盆地西南部地区, 盆地内早中生代侵入岩的出现是秦岭勉略洋盆向北俯冲汇聚挤压环境背景下, 鄂尔多斯盆地基底不同深度陆壳物质部分熔融侵入的结果。2类岩石的形成年龄与盆地南缘秦岭造山带中生代构造转折时期相对应, 即从晚三叠世长7段沉积开始, 鄂尔多斯盆地由之前的挤压环境开始向伸展环境转变。

       

      Abstract: The Early Mesozoic dykes in Longmen area, the southwestern Ordos Basin are infrequent records of magmatism, which provides an ideal object for discussing the tectonic setting of the Early Mesozoic in the Ordos Basin.Petrography, petrogeochemistry and zircon U-Pb dating as well as Lu-Hf isotope for the Early Mesozoic dykes in the Longmen area of the southwestern Ordos Basin are studied.The result shows that these dykes are calc-alkaline to high poassium calc-alkaline dioritic porphyrite and monzonitic porphyrite characterized by low Mg#, Cr, Ni and Co contents.They are relatively rich in REE and LILE, poor in HFSE and depleted in Nb, Ta, Ti and P.However, the LREE/HREE ratios of monzonitic porphyrite are slightly lower and with much lower Yb, Y and higher Sr, Sr/Y ratios than those of the dioritic porphyrite, indicating that the former was formed by partial melting of deeper crustal materials under relatively high pressure, while the later was the product of melting of shallow crust material under lower pressure.Both of the dioritic and monzonitic porphyrite yield 242 Ma, consisting with those magmatism during the initial compression after the Early Mesozoic ocean basin closure in the Qinling orogenic belt.Their zircon εHf(t)=-33.89~-9.73, tDM2=1564~2780 Ma, which implies that the tectonic and magmatic activity occurred in Qinling orogenic belt since the Early Mesozoic has affected the southwestern Ordos Basin.All suggested that these dykes are resulted from the partial melting of Neoarchean and Paleoproterozoic basement of the Ordos Basin at different depths under the background of northward subduction of the Mianlue ocean basin in Qinling orogenic belt, which were roughly corresponding to the early Mesozoic tectonic transition from compression to extension in the Qinling orogenic belt.Consequently, the Ordos Basin has entered into a tectonic setting from the compression to the extension at the initiation of Chang 7 Member deposition during the Late Triassic.

       

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