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内蒙古正镶白旗中二叠世花岗岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及构造意义
投稿时间:2018-04-03  修订日期:2018-08-22  点此下载全文
引用本文:彭云彪,蒋孝君,剡鹏兵,戴明建,邢亚杰.2018.内蒙古正镶白旗中二叠世花岗岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及构造意义[J].地质论评,64(6):1379-1392
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作者单位E-mail
彭云彪 核工业二〇八大队包头014000 208y@bog.com.cn 
蒋孝君 核工业二〇八大队包头014000  
剡鹏兵 核工业二〇八大队包头014000  
戴明建 核工业二〇八大队包头014000  
邢亚杰 核工业二〇八大队包头014000  
基金项目:本文为中国核工业地质局项目(编号:201604)和中国地质调查局项目(编号:DD2016013624)的成果。
中文摘要:前呼和陶勒盖岩体位于白乃庙岛弧,岩性主要为黑云母花岗岩。岩石锆石具有明显的环带结构,Th/U比值介于0.37~0.69之间,为典型的岩浆成因。LA- ICP- MS锆石U- Pb同位素测年结果表明,其形成年龄为276.4±1.5Ma,为中二叠世。该岩体富硅(70.99%~71.78%),富碱(7.32%~8.08%),K2O/Na2 O值为0.73~0.95,Al2O3 含量为14.60%~14.73%。所有样品相对富集轻稀土而亏损重稀土,(La/Yb)N=11.89~13.59,铕具有微弱的负异常(δEu=0.69~0.76);大离子亲石元素K、Rb等明显富集;高场强元素Nb、Ta、P、Ti强烈亏损。根据数据处理分析及对比研究,认为该岩体属于分异的I型花岗岩类,其岩浆来源于地壳物质受俯冲板片脱水产生的流体影响而发生的低程度部分熔融,侵位于西伯利亚板块和华北板块北缘碰撞接近尾声的活动大陆边缘弧环境,所以研究区内两大古板块碰撞缝合结束时间应不早于276.4Ma。
中文关键词:花岗岩  年代学  地球化学  中二叠世  古亚洲洋  正镶白旗
 
LA- ICP- MS Zircon U- Pb Ages, Geochemical Characteristics of Middle Permian Qianhuhetaolegai Granite in Zhengxiangbai Banner, Inner Mongolia and Their Tectonic Significances
NameInstitution
PENG YunbiaoGeological Survey No. 208, China National Nuclear Corporation, Baotou, Inner Mongolia, 014000
JIANG XiaojunGeological Survey No. 208, China National Nuclear Corporation, Baotou, Inner Mongolia, 014000
YAN PengbingGeological Survey No. 208, China National Nuclear Corporation, Baotou, Inner Mongolia, 014000
DAI MingjianGeological Survey No. 208, China National Nuclear Corporation, Baotou, Inner Mongolia, 014000
XING YajieGeological Survey No. 208, China National Nuclear Corporation, Baotou, Inner Mongolia, 014000
Abstract:Objectives: There are abundant magmatic rocks in the south of the Central Asian orogenic belt, recording the Neoproterozoic to Permian subduction of the Paleo- Asian ocean. However, there is still no uniform understanding of the final closing time. Based on the study of Qianhuhetaolegai intrusion in the Bainaimiao island arc, this paper provides a further constraint for determining the time limit. Methods: Five fresh samples were collected for analyzing the whole- rock main and trace elements in Qianhuhetaolegai of Zhengxiangbai Banner. One sample was selected to carry out the zircon U- Pb dating study by LA- ICP- MS method. The determination of major elements, trace elements and rare earth elements in chemical analysis samples was completed in the laboratory of Beijing Yanduzhongshi Testing Technology Co., Ltd. The sample was pretreated by digestion method, and the content of trace rare earth elements in whole rock was determined by inductively coupled plasma mass spectrometer (ICP- MS) M90. The precise analysis of the main elements of rock was carried out by XRF fluorescence spectrometer melting method. The test was performed using LA- Q- ICP- MS. The laser ablation system was New Wave UP213 and ICP- MS was Bruker M90. The zircon dating area was selected according to zircon photomicrography, and the diameter of the ablation spot was selected to be 30 μm. The isotope ratio correction was performed using the Andersen method. The U- Pb age, Pb isotope ratio and trace element content in zircon dating were processed using the ICP- MS DataCal program, and the weighted mean age calculation and mapping were performed using the Isoplot program.Results: Based on the study of the field occurrence characteristics, microscopic characteristics, geochemistry characteristics and chronological characteristics of the intrusion, the lithology and rock types were identified in detail, its emplacement age was determined, and its origin and tectonic background were discussed. Zircons collected from the intrusion exhibit zone texture and have high Th/U ratios of 0.37 to 0.69, consistent with magmatic zircons. LA- ICP- MS zircon U- Pb dating revealed that the intrusion was emplaced in the middle Permian (276.4±1.5Ma). All the samples are enriched in SiO2 (70.99% to 71.78%), alkalis contents (7.32% to 8.08%), with high K2 O/Na2O ratios (0.73 to 0.95). They are enriched in LREEs relative to HREEs, with (La/Yb)N= 11.89 to 13.59 and slightly negative Eu anomalies of 0.69 to 0.76. All the samples are relatively enriched in LILEs (e.g., K and Rb) and depleted in HFSEs (e.g., Nb, Ta, P and Ti). Conclusions: The Qianhuhetaolegai biotite granite was emplaced in the middle Permian. The Elemental data suggest that the intrusion belongs to I- type granite and was derived by partial melting of crustal source induced by subducted slab- released fluids. Thus, the intrusion was likely emplaced in an active continental margin. We consider that the final collision between two paleo- plates in the study area should not be earlier than 276.4 Ma.
keywords:granites  LA- ICP- MS zircon U- Pb dating  geochemistry  Middle Permian  Paleo- Asian Ocean  Zhengxiangbai Banner, Inner Mongolia
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