内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义

北京大学学报（自然科学版）

内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义

贺淑赛¹,李秋根^1,2,王宗起³,徐学义⁴,刘树文¹,陈隽璐⁴,李智佩⁴,胡兆初⁵

1. 造山带与地壳演化教育部重点实验室, 北京大学地球与空间科学学院, 北京 100871; 2. 大陆动力学国家重点实验室, 西北大学地质学系, 西安 710069; 3. 中国地质科学院矿产资源研究所, 北京 100037; 4. 西安地质矿产研究所, 西安 710054; 5. 地质过程与矿产资源国家重点实验室, 中国地质大学地球科学学院, 武汉 430074;

收稿日期:2013-10-08 出版日期:2015-01-20 发布日期:2015-01-20

Zircon U-Pb-Hf Isotopic Characteristics from Felsic Volcanic Rocks of Baoligaomiao Formation, the Middle Segment of Inner Mongolia: Implications for Geological Evolution

HE Shusai¹, LI Qiugen^1,2, WANG Zongqi³, XU Xueyi⁴, LIU Shuwen¹, CHEN Junlu⁴, LI Zhipei⁴, HU Zhaochu⁵

1. The Key Laboratory of Orogenic Belts and Crustal Evolution MOE, School of Earth and Space Sciences, Peking University, Beijing 100871; 2. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069; 3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037; 4. Xi’an Institute of Geology and Mineral Resources,Xi’an 710054; 5. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074;

Received:2013-10-08 Online:2015-01-20 Published:2015-01-20

摘要/Abstract

摘要： 锆石SHRIMP U-Pb定年结果显示: 内蒙古中部白音乌拉地区原宝力高庙组的流纹岩形成时代为300.0±2.9 Ma, 属晚石炭世; 青格勒宝拉格地区原宝力高庙组的凝灰岩结晶年龄为159.6±1.4 Ma, 并获得 3颗捕获锆石的年龄分别为291.8±3.4, 304.0±3.3和734.7±9.2 Ma, 应属于晚侏罗世满克头鄂博组。锆石LA-MC-ICP-MS Hf同位素分析显示: 流纹岩锆石ε_Hf(t) 值为+10.5~+12.9, T_DM^C值为493~645 Ma; 凝灰岩岩浆锆石ε_Hf(t)值为+10.1~+13.1, T_DM^C值为369~563 Ma。研究结果表明, 流纹岩源于晚古生代新生地壳的重熔并混入少量老地壳物质, 凝灰岩源于晚古生代地壳的熔融。Hf同位素特征显示晚古生代流纹岩和中生代凝灰岩源于相似的源区, 揭示了晚古生代的一次重要的增生事件, 并且在约160 Ma时期发生过地壳的再造。结合前人的研究成果表明, 兴蒙造山带在约300 Ma时处于古亚洲洋演化过程中岛弧向碰撞后伸展环境的转换时期, 在约160 Ma受到蒙古?鄂霍茨克构造域的影响。

关键词: 内蒙古, 宝力高庙组, 火山岩和火山碎屑岩, SHRIMP锆石U-Pb定年, Hf同位素, 地壳演化

Abstract: Zircon SHRIMP U-Pb ages and LA-MC-ICP-MS Lu-Hf isotopic compositions of a rhyolite sample and a tuff sample of Baoligaomiao Formation from Baiyinwula region and Qinggelebaolage region respectively in the middle Inner Mongolia were determined. Zircon U-Pb dating gives the eruption age of rhyolite from the Baiyinwula region as 300.0±2.9 Ma, indicating that the volcanic member of Baoligaomiao Formation formed during the Late Carboniferous. The Qinggelebaolage tuff, which was considered as a part of Baoligaomiao Formation, has a zircon SHRIMP U-Pb age of 159.6±1.4 Ma, belonging to Late Jurassic Manketouebo Formation, with three ages of captured zircons (291.8±3.4, 304.0±3.3 and 734.7±9.2 Ma, respectively). In-situ zircon LA-MC-ICP-MS Hf analyses show that magmatic zircons from Baiyinwula rhyolite and Qinggelebaolage tuff have ε_Hf(t) values of +10.5?+12.9 and +10.1?+13.1, with T_DM^C of 493?645 Ma and 369?563 Ma, respectively. Thus, the Baiyinwula rhyolite should be derived from partial melting of Late Paleozoic juvenile crust with involvement of ancient crustal materials whereas the Qinggelebaolage tuff should be generated by partial melting of Late Paleozoic crust. Integrating previous studies, the results review that the Mesozoic and Paleozoic volcanic rocks in the Uliastai continental margin might be derived from similar sources, revealing that there was an important crustal accretion event in Late Paleozoic. Moreover, two Paleozoic captured zircon grains in Qinggelebaolage tuff, which have U-Pb ages of ca. 300 Ma, are similar in Hf isotopic features to the magmatic zircons from both the Baiyinwula rhyolite and the Qinggelebaolage tuff, signifying significant crust reworking during formation of the Late Jurassic Qinggelebaolage tuff. These results, together with previous data from the literature, indicate that in the Inner Mongolia Orogenic Belt, a transition from island arc to post-collision extension related to evolution of Paleo-Asian Ocean occurred at ca. 300 Ma, whereas the influence of the Mongol-Okhotsk tectonic regime was responsible for the Mesozoic volcanism (ca. 160 Ma).

Key words: Inner Mongolia, Baoligaomiao Formation, volcanic/pyroclastic rocks, zircon SHRIMP U-Pb dating, Hf isotopes, crustal evolution

中图分类号:

P588
P597

贺淑赛,李秋根,王宗起,徐学义,刘树文,陈隽璐,李智佩,胡兆初. 内蒙古中部宝力高庙组长英质火山岩U-Pb-Hf同位素特征及其地质意义[J]. 北京大学学报（自然科学版）.

HE Shusai,LI Qiugen,WANG Zongqi,XU Xueyi,LIU Shuwen,CHEN Junlu,LI Zhipei,HU Zhaochu. Zircon U-Pb-Hf Isotopic Characteristics from Felsic Volcanic Rocks of Baoligaomiao Formation, the Middle Segment of Inner Mongolia: Implications for Geological Evolution[J]. Acta Scientiarum Naturalium Universitatis Pekinensis.

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https://xbna.pku.edu.cn/CN/Y2015/V51/I1/50

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