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引用本文:郭喜运,孙华山,董挨管,任建勋,徐瑞英,高博. 内蒙古锡林浩特北早二叠世花岗岩类定年及成因[J]. 中国地质, 2019, 46(6): 1396-1409.
GUO Xiyun,SUN Huashan,DONG Aiguan,REN Jianxun,Xu Ruiying,GAO Bo. The genesis and dating of the Early Permian granitic rock in the north of Xilin Hot, Inner Mongolia[J]. Geology in China, 2019, 46(6): 1396-1409(in Chinese with English abstract).
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内蒙古锡林浩特北早二叠世花岗岩类定年及成因
郭喜运1,2, 孙华山2, 董挨管3, 任建勋3, 徐瑞英1, 高博3
1.山西省矿山调查测量队, 山西 太原 030024;2.中国地质大学 (武汉) 资源学院, 湖北 武汉 430074;3.山西省地质调查院, 山西 太原 030006
摘要:
内蒙古锡林浩特北部朝克乌拉山附近分布有早二叠世花岗岩类,可作为兴蒙造山带东部构造-岩浆活动的研究载体。本文通过对花岗岩类进行岩相学、岩石地球化学、锆石U-Pb年代学的研究,讨论其岩石成因、构造环境。早二叠世侵入岩岩性主要为正长花岗岩、二长花岗岩、正长斑岩。地球化学上,岩石具有高硅、富碱、贫钙、贫镁的特点,属于偏铝—过铝质碱性花岗岩。轻重稀土元素存在一定程度的分馏,总体表现出轻稀土相对富集、重稀土相对亏损,具有明显的负Eu异常,Rb、Th、K、La、Ce、Nd、Zr、Hf、Sm元素明显富集,Ba、Ta、Nb、Sr、P、Ti元素显著亏损。岩石的锆石饱和温度为802℃,具有低Sr高Yb特征,指示岩体形成于高温低压环境,结合岩石地球化学表明岩体属于铝质A型花岗岩,其源岩与岛弧岩浆作用有关。锆石U-Pb测年结果为(275.6±1.3)Ma(正长花岗岩)、(274.2±1.4)Ma(正长斑岩),表明岩体形成时代为早二叠世晚期。结合区域上阿木山组中安山岩夹层的锆石U-Pb年龄,古生物、花岗岩证据表明晚石炭世至早二叠世晚期,贺根山洋闭合并完成了板块碰撞挤压到碰撞伸展的转换。
关键词:  地质意义  A型花岗岩  锆石U-Pb年龄  地球化学  贺根山
DOI:10.12029/gc20190611
分类号:P595;P597+.3
基金项目:中国地质调查局项目(1212011220447)资助。
The genesis and dating of the Early Permian granitic rock in the north of Xilin Hot, Inner Mongolia
GUO Xiyun1,2, SUN Huashan2, DONG Aiguan3, REN Jianxun3, Xu Ruiying1, GAO Bo3
1.Shanxi Party of Mine Survey and Measurement, Taiyuan 030024, Shanxi, China;2.Faculty of Resource Department, China University of Geosciences, Wuhan 430074, Hubei, China;3.Shanxi Institute of Geology Survey, Taiyuan 030006, Shanxi, China
Abstract:
The Permian granitic rock near the Chaokewula Mountain in the north of Xilin Hot area are very important for the study of the structural and magmatic acitivities in eastern Xing'an-Mongolian orogenic belt. The purpose of this study is to discuss the petrogenesis and tectonic setting based on detailed investigation of petrography, litho-geochemical characteristics and zircon U-Pb chronology of the granitic rock. The rocks are mainly composed of syenogranite, monzonitic granite and orthophyre. Geochemically, the granites are characterized by rich silicon and alkalis as well as depletion of calcium and magnesium, thus belonging to aluminous-peraluminous alkali granite. The rare earth elements demonstrate a slightly high degree of fractionation, and are characterized by richness of LREE and poorness of HREE. The rocks exhibit significant negative Eu anomalies. Trace element analyses show that the rocks are enriched in Rb, Th, K, La, Ce, Nd, Zr, Hf and Sm and depleted in Ba, Ta, Nb, Sr, P and Ti. The zircon saturation temperature of rock is 802℃, with geochemical characteristics of low Sr and high Yb, showing that the rocks were formed in an environment of high temperature and low pressure. Combined with the geological and geochemical data, the authors hold that the rocks belong to aluminous A-type granite, and the sources of rocks were formed in an island-arc environment. The zircon U-Pb age of syenogranite is (275.6±1.3) Ma, and the zircon U-Pb age of orthophyre is (274.2±1.4) Ma, respectively. These results indicate that the rock body was formed in late period of early Permian. With a set of volcanic rocks of Amushan Formation as the research object, the authors obtained the zircon U-Pb age of andesite. Combined with the palaeontology, granitoids and chronological evidence, the authors consider that the Hegenshan Ocean was closed and completed the transformation from collision to post-collision during the period from late Carboniferous to late Early Permian.
Key words:  geological significance  A-type granite  zircon U-Pb age  geochemistry  Hegenshan orogenic belt