李敏, 任邦方, 段霄龙, 田健, 段连峰, 牛文超. 内蒙古北山造山带小红山地区三叠纪花岗岩成因—来自锆石U-Pb年龄和Hf同位素的约束[J]. 地质通报, 2020, 39(9): 1422-1435.
    引用本文: 李敏, 任邦方, 段霄龙, 田健, 段连峰, 牛文超. 内蒙古北山造山带小红山地区三叠纪花岗岩成因—来自锆石U-Pb年龄和Hf同位素的约束[J]. 地质通报, 2020, 39(9): 1422-1435.
    LI Min, REN Bangfang, DUAN Xiaolong, TIAN Jian, DUAN Lianfeng, NIU Wenchao. Petrogenesis of Triassic granites in Xiaohongshan area, Beishan orogenic belt: Constraints from zircon U-Pb ages and Hf isotopes[J]. Geological Bulletin of China, 2020, 39(9): 1422-1435.
    Citation: LI Min, REN Bangfang, DUAN Xiaolong, TIAN Jian, DUAN Lianfeng, NIU Wenchao. Petrogenesis of Triassic granites in Xiaohongshan area, Beishan orogenic belt: Constraints from zircon U-Pb ages and Hf isotopes[J]. Geological Bulletin of China, 2020, 39(9): 1422-1435.

    内蒙古北山造山带小红山地区三叠纪花岗岩成因—来自锆石U-Pb年龄和Hf同位素的约束

    Petrogenesis of Triassic granites in Xiaohongshan area, Beishan orogenic belt: Constraints from zircon U-Pb ages and Hf isotopes

    • 摘要: 对北山造山带小红山地区三叠纪花岗斑岩锆石U-Pb年龄、锆石Hf同位素和全岩地球化学组成进行了研究。LA-MC-ICP-MS锆石U-Pb测年结果显示,2个花岗斑岩样品的锆石206Pb/238U年龄为211.8±1.6 Ma和205.9±1.7 Ma,显示花岗斑岩的侵位时代为晚三叠世晚期。花岗斑岩具有高硅、富碱、准铝,贫钙、镁、铁的特征,属于高钾钙碱性至钾玄岩系列,分异程度较高,属高分异Ⅰ型花岗岩,富集Rb、Th、U、La、Ce等大离子亲石元素,亏损Nb、P、Ti等高场强元素和Ba、Sr,表现出低Sr,高Yb和Y的特点,并具有明显的负Eu异常。εHft)值较高(-1.43~9.93),Hf同位素地壳模式年龄TDMC为610~1335 Ma,指示花岗斑岩均源于具有幔源烙印的新生地壳并混有重熔的古老地壳。结合最近获得的数据及区域地质资料,提出在后造山伸展体制下,基性岩浆底侵带来的热导致新元古代—古生代新生地壳的部分熔融,并遭受了下元古界古老地壳重熔的岩浆混染,形成的岩浆经过分离结晶作用,最终在中上地壳侵位形成了晚三叠世花岗斑岩。

       

      Abstract: In this paper, zircon U-Pb ages, Hf isotopes and whole rock geochemical compositions of Triassic granite-porphyry in Xiaohongshan area of Beishan orogenic belt were systematically studied.Zircon LA-MC-ICP-MS U-Pb dating results show that the two ages of granite-porphyry are 211.8±1.6 Ma(the confidence value is 95%, n=24, MSDW=2.4)and 205.9±1.7 Ma(the confidence value is 95%, n=23, MSDW=2.9)respectively, which intruded at the late stage of Late Triassic.The granite-porphyry in the study area is characterized by high silicon, rich alkali, quasi-aluminum, and poor calcium, magnesium, and iron.It belongs to the series of high potassium calc-alkaline to potassic basanite with high degree of differentiation.It belongs to highly differentiated Ⅰ-type granite.It is enriched in Rb, Th, U, La, Ce and other large ion lithophile elements and depleted in Nb, P, Ti, Ba and Sr. It is characterized by low Sr, high Yb and Y with obvious negative europium anomaly.The εHf(t)values range from -1.43 to 9.93, which are relatively high, and the Hf isotopic crustal model ages range from 610 Ma to 1335 Ma, indicating that the granite-porphyry was derived from the juvenile crust with mantle imprint mixed with remelting old crust. According to the data obtained in this paper and other regional geological data acquired recently, it is proposed that, under the post-orogenic extension system, the heat brought by the underplating of basic magma caused the partial melting of the juvenile crust from Neoproterozoic to Paleozoic, and suffered magma contamination of the remelting of the old crust of Lower Proterozoic.In addition, the magma was finally emplaced in the middle and upper crust after fractional crystallization, forming the the Late Triassic granite-porphyry in the study area.

       

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