| 内蒙古哈珠地区石炭纪白山组火山岩:北山北部晚古生代活动陆缘岩浆作用的产物 |
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| 引用本文： | 任云伟,任邦方,牛文超,孙立新,李敏,张阔,张家辉,段连峰.内蒙古哈珠地区石炭纪白山组火山岩:北山北部晚古生代活动陆缘岩浆作用的产物[J].地球科学,2019,44(1):312-327. |
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| 作者姓名： | 任云伟 任邦方 牛文超 孙立新 李敏 张阔 张家辉 段连峰 |
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| 作者单位： | 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： | 中国地质调查局地质调查项目DD20160039 |
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| 摘 要： | 北山北部晚古生代岩浆事件的性质对该地区这一时期的构造演化研究具有重要意义.对内蒙古北山哈珠地区石炭纪白山组火山岩进行了系统的年代学、地球化学、Lu-Hf同位素测试，结果显示:白山组主要由玄武安山质、安山质、英安质、流纹质火山岩组成，LA-ICP-MS锆石U-Pb测年获得安山岩、英安岩、流纹岩的成岩年龄分别为325.6±1.4 Ma、313.5±3.4 Ma、314.7±1.7 Ma，时代为早石炭世晚期-晚石炭世.火山岩空间分布上表现出明显的"组成极性"，区域上由北至南从中性火山岩（钙碱性系列）→酸性火山岩（高钾钙碱性系列）演化，K2O含量与K2O/Na2O比值也呈相应的增加趋势，其中玄武安山岩、安山岩具有高Al2O3、低TiO2以及低的Ni、Cr含量，所有样品普遍亏损Nb、Ta、P、Ti等高场强元素，呈轻稀土富集、重稀土亏损的右倾稀土元素配分模式，以上特征指示白山组火山岩形成于洋壳向南俯冲过程中的活动大陆边缘背景下.另外，白山组中安山岩具有高的εHf（t）值（+7.0~+14.1）和年轻的平均地壳模式年龄TDMC（437~891 Ma），接近上地幔的Rb/Sr比值（0.01~0.15），Nb/Ta比值（12.59~18.80）处于地壳平均值和地幔平均值之间；流纹岩具有相对较低的εHf（t）值（4.3~8.2）和偏老的平均地壳模式年龄TDMC（804~1 054 Ma），Rb/Sr比值（0.80~1.73）远大于地壳平均值，Nb/Ta比值（10.66~13.08）接近地壳平均值反映岩浆源区向洋侧以新生地壳和地幔物质为主，向内陆一侧逐渐演化为更多陆壳（较老地壳）物质的加入.综合以上分析并结合前人资料，北山哈珠地区晚古生代石炭纪白山组火山岩是红石山洋向南侧马鬃山-旱山地块俯冲过程中活动陆缘岩浆作用的产物.
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| 关 键 词： | 北山造山带 白山组 地球化学 锆石U-Pb年龄 岩石成因 哈珠地区 |
| 收稿时间： | 2018-04-27 |
Carboniferous Volcanics from the Baishan Formation in the Hazhu Area,Inner Mongolia: Implications for the Late Paleozoic Active Continental Margin Magmatism in the Northern Beishan |
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| Abstract: | The character of Late Paleozoic magmatic events has great significance for the study of tectonic evolution in the northern Beishan. A systematic study of geochemistry, geochronology and Lu-Hf isotopes is made on Baishan Formation volcanic rocks in the Beishan Hazhu area of Inner Mongolia. The results show that Baishan Formation volcanic rocks are composed of basaltic andesite, andesite, dacitic and rhyolitic volcanic rocks. The diagenetic ages of andesite, dacite and rhyolite from the LA-ICP-MS zircon U-Pb dating are 325.6±1.4 Ma, 313.5±3.4 Ma and 314.7±1.7 Ma respectively, all which belong to the later period of Early Carboniferous epoch-medium period of Late Carboniferous epoch. Geochemical studies show that the Baishan Formation volcanic rocks are characterized by apparent "component polarity feature" in spatial distribution, displaying regional north-to-south evolution from intermediate volcanic rocks (calc-alkaline series) to acid volcanic rocks (high-K calc-alkaline series), with the increased content of K2O and ratio of K2O/Na2O, in which basaltic andesite and andesite belong to higher content of Al2O3, lower content of TiO2 and lower content of Ni and Cr. Additionally, microelements of all volcanic samples generally show depletion of high field strength elements such as Nb, Ta, P, Ti and apparent right-leaning distribution patterns of the REE with depletion in LREE and enrichment in HREE. The above characteristics suggest that the Baishan Formation volcanic rocks are formed from active continental margin arc in the process of southern subduction oceanic crust. Additionally, andesite in the Baishan Formation is characterized by higher value of εHf(t) (7.0-14.1)and the young average crustal model age TDMC (437-891 Ma), Rb/Sr ratio (0.01-0.15) near the upper mantle and Nb/Ta ration (12.59-18.80) between mean values of crust and mantle; rhyolite is characterized by later value of εHf(t) (4.3-8.2) and the older average crustal model age TDMC (804-1 054 Ma), Rb/Sr ratio (0.80-1.73) that is much larger than the mean values of crust and Nb/Ta ration (10.66-13.08) near the mean values of crust, which all indicate that magma source region was mainly new crust and mantle material near the ocean side and it was evolved gradually into the increasing of more continental crust (older crust) material close to the inland side. Based on the above analysis and combined with the previous data, it is concluded that Beishan Hazhu area Late Paleozoic Carboniferous Baishan Formation volcanic rocks were formed in the subduction process of Hong Shishan Ocean into the south side of micro plot of Mazong Mountain-Han Mountain, and it had been resulted from magmatism of the active continental margin. |
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