| 甘肃柳园地区早二叠世正长花岗斑岩脉锆石U-Pb年代学、岩石地球化学特征——对北山造山带晚古生代构造背景的指示 |
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| 引用本文： | 孙海瑞,吕志成,于晓飞,李永胜,杜泽忠,吕鑫,公凡影.甘肃柳园地区早二叠世正长花岗斑岩脉锆石U-Pb年代学、岩石地球化学特征——对北山造山带晚古生代构造背景的指示[J].吉林大学学报(地球科学版),2020,50(5):1433-1449. |
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| 作者姓名： | 孙海瑞 吕志成 于晓飞 李永胜 杜泽忠 吕鑫 公凡影 |
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| 作者单位： | 1. 中国地质调查局发展研究中心, 北京 100037;2. 自然资源部矿产勘查技术指导中心, 北京 100083 |
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| 基金项目： | 国家重点研发计划项目（2018YFC0603806，2018YFC0603704）；中国地质调查局项目（DD20160050）；中央高校基本科研业务费专项资金项目（310827171122） |
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| 摘 要： | 甘肃北山地区位于中亚造山带中段，是诠释中亚造山带构造演化的关键区域之一，长期以来受到地质学界的广泛关注。柳园地区位于甘肃北山南带，区内脉岩发育，这些岩脉的研究可以为阐释北山造山带晚古生代构造背景提供更多证据。基于此，本文选取位于甘肃柳园地区的正长花岗斑岩脉开展了系统的锆石U-Pb-Hf同位素和全岩主量、微量元素分析。LA-ICP-MS锆石U-Pb分析显示，岩脉侵位于早二叠世（（288.5±1.4）Ma）。全岩地球化学分析显示，正长花岗斑岩脉的SiO2和全碱质量分数较高，Fe、Mg、Ca、Al和P质量分数较低，Rb、Th、U和Pb相对富集，Ba、Nb、La、Ce、Sr和Ti等元素相对亏损，Eu负异常显著，具有较高的Rb/Sr值和较低的K/Rb值及锆石饱和温度（730~844℃，集中于740℃左右），显示该岩脉为高钾钙碱性高分异I型花岗岩，并具有俯冲带岩浆活动的地球化学特征。正长花岗斑岩脉具有较低的Zr/Hf值（18.42~28.01，平均值为22.37）和Th/U值（3.82~7.99，平均值为5.34），与平均地壳组分接近，锆石εHf（t）值为2.94~9.66，平均值为5.72，TDM2值为955~611 Ma，指示源区主体为新元古代地壳的部分熔融，并存在幔源物质加入。根据构造判别图解并结合前人关于二叠纪区域构造变形、盆地沉积物源、岩浆演化等方面的研究结果，笔者认为该正长花岗斑岩脉形成于俯冲作用过程中的局部伸展环境，并认为北山地区增生造山事件至少持续到早二叠世。
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| 关 键 词： | 正长花岗斑岩脉 高分异I型花岗岩 地球化学 早二叠世 北山 中亚造山带 |
| 收稿时间： | 2020-04-12 |
Late Paleozoic Tectonic Evolution of Beishan Orogenic Belt: Chronology and Geochemistry Constraints of Early Permian Syenogranitic Porphyry Dyke in Liuyuan Area,Gansu Province |
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| Sun Hairui,L&#,Zhicheng,Yu Xiaofei,Li Yongsheng,Du Zezhong,L&#,Xin,Gong Fanying.Late Paleozoic Tectonic Evolution of Beishan Orogenic Belt: Chronology and Geochemistry Constraints of Early Permian Syenogranitic Porphyry Dyke in Liuyuan Area,Gansu Province[J].Journal of Jilin Unviersity:Earth Science Edition,2020,50(5):1433-1449. |
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| Authors: | Sun Hairui L&# Zhicheng Yu Xiaofei Li Yongsheng Du Zezhong L&# Xin Gong Fanying |
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| Institution: | 1. Development and Research Center, China Geological Survey, Beijing 100037, China;2. Mineral Exploration Technical Guidance Center, Ministry of Natural Resources, Beijing 100083, China |
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| Abstract: | Beishan orogenic belt is located in the middle part of Central Asia orogenic belt (CAOB), and it is crucial to discuss the accretionary evolution of the CAOB. Liuyuan area is in the southern part of Beishan orogenic belt, where granitoid rocks and different types of dykes are widely distributed. To study these rocks and dykes can provide us with more important clues about the reconstruction of the geological evolution of this area. The LA-ICP-MS zircon U-Pb dating of the syenogranitic porphyry dyke in northeast Liuyuan area yields the weighted 206Pb/238U ages of (288.5±1.4) Ma, the Early Permian. The geochemical results show that the contents of SiO2 and total alkali of the syenogranitic porphyry are high,while the contents of Fe, Mg, Ca, Al and P are low. In addition, the porphyry is characterized by rich in Rb, Th, U and Pb but poor in Ba, Nb, La, Ce, Sr and Ti, with obvious Eu negative anomaly. The value of Rb/Sr is high, the value of K/Rb is low, and the saturation temperature of zircon is lower (730-844 ℃, concentrating around 740 ℃). Based on the above geochemical results and the comprehensive discriminant analysis, we believe that the porphyry belongs to high-K calc-alkaline and high fractionated I-type granites. Also, the syenogranitic porphyry presents a narrow range of Zr/Hf (18.42 to 28.01, average 22.37) and Th/U values (3.82 to 7.99, average 5.34) respectively, which is similar to those of crust sourced rocks. The syenogranitic porphyry show positive εHf (t) values, varying from 2.94 to 9.66, with average of 5.72, and relatively young TDM2 ages, ranging from 955 to 611 Ma. Considering the occurrences of the coeval mafic igneous rocks in this region, we believe that the porphyry magma should be mainly derived from the partial melting of the crust-derived metamorphic igneous rocks with some contribution of mantle materials. The tectonic discriminant analysis shows that the Early Permian syenogranitic porphyry was formed in a subduction environment. Based on the previous studies on the regional tectonic deformation, basin sediment source, and the magma evolution from Permian to Triassic, it is concluded that the accretionary orogenic events in the southern part of Beishan orogenic belt lasted at least until the Early Permian, which provided important constraints on the reconstruction of the tectonic evolution of the Late Paleozoic Beishan orogenic belt. |
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| Keywords: | syenogranitic porphyry dyke high fractionated I-type granite geochemistry Early Permian Beishan area Central Asia orogenic belt |
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