内蒙古赤峰五十家子岩体成因及其对岩石圈伸展减薄的指示
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国家重点研发计划“深地资源勘查开采”重点专项(2017YFC0601305,2017YFC0602403)、国家自然科学基金项目(41602098)及中国地质调查局项目(DD20160072)联合资助。


Petrogenesis and its implications for the lithospheric thinning of the Wushijiazi pluton in Chifeng, Inner Mongolia
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    摘要:

    研究目的】内蒙古赤峰五十家子岩体位于大兴安岭南段成矿带的西南部,对其进行系统的年代学和地球化学研究有助于丰富对区域构造-岩浆演化和成矿规律的认识。【研究方法】本文基于岩石学与地球化学研究工作,采用LA-ICP-MS锆石U-Pb测年、主微量元素分析和锆石Lu-Hf同位素测试等方法分析了岩体成因。【研究结果】LAICP-MS锆石U-Pb测年结果表明,五十家子岩体中的斑状含黑云母二长花岗岩、斑状含黑云母正长花岗岩和斑状黑云母正长花岗岩分别形成于(150.3±1.3) Ma,(145.9±1.8) Ma和(137.1±2.2) Ma,属晚侏罗世至早白垩世的产物。地球化学组成上,该花岗岩体具有富硅、富碱、低铝、低钙的特点,属于碱性、准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果显示斑状含黑云母正长花岗岩具有正的εHft)值(+7.5~+14.3)和年轻的二阶段模式年龄(tDM2=285~718Ma),与大兴安岭南段晚中生代花岗岩εHft)值相近,表明其源区物质中年轻下地壳的贡献占主导地位,斑状含黑云母二长花岗岩中暗色包体的发育指示其可能经历了岩浆混合作用。【结论】根据本文研究结果,结合区域地质背景,五十家子岩体可能形成于晚中生代岩石圈伸展减薄环境下,软流圈上涌导致年轻下地壳发生部分熔融形成初始岩浆,并与幔源岩浆混合,后经高程度分异演化并于浅部侵位,最终固结形成了五十家子花岗岩体。五十家子岩体具有显著的高分异和深源浅侵位特征,与区域内锡多金属成矿作用有密切的成因联系。
    创新点:采用LA-ICP-MS锆石U-Pb测年方法获取五十家子岩体3个岩相的形成时间,依据岩相学特征、成岩时间、地球化学特征、锆石Hf同位素特征及区域地质背景综合分析岩体成因。

    Abstract:

    This paper is the result of geological survey engineering.
    [Objective]The Wushijiazi pluton in Chifeng area, Inner Mongolia, is located in the southwestern part of the metallogenic belt of the southern Great Xing'an Range. A systematic geochronological and geochemical study can provide insights into understanding of regional tectonic-magmatic evolution and metallogenic regularity.
    [Methods]Based on the petrological and geochemistry study, this paper uses LA-ICP-MS zircon U-Pb dating, major and trace element analysis and Zircon Hf isotopic analysis methods to analyze the genesis of the pluton.
    [Results]LA-ICP-MS zircon U-Pb dating results show that the porphyritic biotite-bearing monzogranite, porphyritic biotite-bearing syenogranite and porphyritic biotite syenogranite in the Wushijiazi pluton were formed at (150.3±1.3) Ma, (145.9±1.8) Ma and (137.1±2.2) Ma, respectively, which are the magmatic products during the Late Jurassic to Early Cretaceous. The pluton is geochemically characterized by high contents of silica and alkalis, but low contents of aluminium and calcium, belonging to alkaline and quasi aluminous-weakly peraluminous A-type granites. Zircon Hf isotopic analysis displays that the porphyritic biotite-bearing syenogranite has positive εHf(t) values (+7.5-+14.3) and juvenile two-stage (tDM2) Hf model ages (tDM2=285-718 Ma), which was consistent with those of Late Mesozoic granites in the southern of Great Xingan Range. Therefore, it is suggested that the contribution of the juvenile lower crust is dominant in the source region. The occurrence of mafic microgranular enclaves in porphyritic biotite-bearing monzogranite indicates magma critical role of mantle-crust interaction.
    [Conclusions]Combined with regional geological background, our study suggests that the asthenosphere upwelling resulted in partial melting of the juvenile lower crust and formed the primitive magma mush under the late Mesozoic lithospheric extension and thinning environment, and then the magma mush mixed with the mantle-derived magma. The highly fractionated mixed magma was emplaced in the shallow level, and finally formed the Wushijiazi granitic pluton. Wushijiazi pluton is characterized by the high degree of differentiation, as well as deep-source but shallow-emplacement, which is closely related to the tin-polymetallic mineralization in this area.
    Highlights: The formation time of the three lithofacies of the Wujiazi pluton was obtained by LA-ICP-MS zircon U-Pb dating method, and the genesis of the pluton was comprehensively deciphered according to the petrographic characteristics, diagenetic time, geochemical characteristics, zircon Hf isotope characteristics and regional geological background.

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尚永明,李小伟,祝新友,邹滔,黄行凯,程细音,王力,王树星. 内蒙古赤峰五十家子岩体成因及其对岩石圈伸展减薄的指示[J]. 中国地质, 2022, 49(4): 1323-1345.
SHANG Yongming, LI Xiaowei, ZHU Xinyou, ZOU Tao, HUANG Xingkai, CHENG Xiyin, WANG Li, WANG Shuxing. Petrogenesis and its implications for the lithospheric thinning of the Wushijiazi pluton in Chifeng, Inner Mongolia[J]. Geology in China, 2022, 49(4): 1323-1345(in Chinese with English abstract).

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  • 收稿日期:2019-03-21
  • 最后修改日期:2019-12-11
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  • 在线发布日期: 2022-09-09
  • 出版日期: 2022-08-20
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