| 内蒙古北山哈珠东山泥盆系雀儿山群火山岩锆石U-Pb年龄、Hf同位素特征及其地质意义 |
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| 引用本文： | 任邦方,任云伟,牛文超,段连峰,孙立新,李敏,田健,段霄龙,张永清.内蒙古北山哈珠东山泥盆系雀儿山群火山岩锆石U-Pb年龄、Hf同位素特征及其地质意义[J].地球科学,2019,44(1):298-311. |
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| 作者姓名： | 任邦方 任云伟 牛文超 段连峰 孙立新 李敏 田健 段霄龙 张永清 |
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| 作者单位： | 1.中国地质调查局天津地质调查中心, 天津 300170 |
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| 基金项目： | 中国地质调查局项目DD20179382中国地质调查局项目12120114064601中国地质调查局项目DD20160039国家自然科学基金项目41572172中国地质调查局项目DD20160039-17 |
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| 摘 要： | 北山地区是研究古亚洲洋最终闭合过程的热点地区之一.前人对红石山-百合山-蓬勃山蛇绿混杂岩带的研究多集中在其俯冲作用的时限、极性及相关的石炭纪火山岩的源区及构造属性上，而对该蛇绿混杂岩带北侧出露的泥盆纪火山岩的构造背景和岩浆演化过程研究较为薄弱.对哈珠东山地区泥盆系雀儿山群哈珠组火山岩开展了岩石学、地球化学、锆石U-Pb年代学及Hf同位素研究，结果表明:哈珠东山地区雀儿山群哈珠组火山岩形成于中泥盆世晚期（386.9±1.7 Ma），属低钾拉斑-钙碱性系列，具富钠、低钾特征，微量元素亏损Nb、Ta、P、Ti等高场强元素，推测其形成于洋壳俯冲的岛弧环境，可能为古亚洲洋向南持续俯冲的产物.流纹岩锆石Hf同位素组成较为均一，εHf（t）值为+4.4~+15.0，二阶段Hf模式年龄为424~1 109 Ma，表明流纹岩源于早古生代-中新元古代新生年轻地壳的重熔.而安山岩岩浆源区为俯冲消减板片流体交代的地幔楔，岩浆上升中经历了一定的分离结晶作用和上地壳物质的同化混染.综合前人区域研究成果，红石山-百合山-蓬勃山洋的发育应形成于晚泥盆世之后雀儿山弧后盆地的扩张环境.
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| 关 键 词： | 北山造山带 雀儿山群 锆石U-Pb年龄 地球化学 Hf同位素特征 哈珠东山 |
| 收稿时间： | 2018-06-04 |
Zircon U-Pb Ages and Hf Isotope Characteristics of the Volcanic Rocks from Queershan Group in the Hazhudongshan Area of Beishan,Inner Mongolia and Their Geological Significance |
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| Abstract: | The Beishan orogenic belt has always been one of study hotspots on the time of closure of the Paleoasian Ocean. Previous studies on the Hongshishan-Baiheshan-Pengboshan ophiolite mélange belt are more focused on a direct constraint on the time of the oceanic subduction, subduction polarity, and the origin and structural attributes of Carboniferous volcanic rocks, resulting in a lack of understanding of the tectonic setting and magmatic evolution of the Devonian volcanic rocks. In this paper, we present new detailed petrologic, geochemical, U-Pb ages and Hf isotope analyses on the Devonian volcanic rocks from the Hazhu formation of the Queershan Group in the Hazhudongshan area of Beishan. Combining with the previous works in this region, our study reveals that the volcanic rocks from the Hazhu Formation of the Queershan Group from Hazhudongshan formed in the Middle Devonian (386.9±1.7 Ma), which is characterized by enriched Na and low K of the low potassium tholeiite to calc-alkaline series. In the aspect of trace elements, these rocks are depleted in high field strength elements of Nb, Ta, P and Ti. These rocks were probably formed in the island arc environment, representing products of the southward subduction of the Paleoasian Ocean. The εHf(t) values of the rhyolite sample are uniform, ranging from 4.4 to 15, with the two-stage Hf model ages between 424 Ma and 1 109 Ma. Thus, the rhyolite of Queershan Group should be derived from partial melting of Early Paleozoic and Meso-Neoproterozoic juvenile crust. However, the magma of andesite of Queershan Group is derived from depleted mantel wedge metasomatized by fluid from subducted plate. Meanwhile the product created by the rising magma has experienced a certain fractional crystallization and assimilation and contamination of upper crustal material. According to previous regional geological studies, the Hongshishan-Baiheshan-Pengboshan ocean should be formed in the extension setting of a Queershan back-arc basin after the Late Devonian. |
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