| 内蒙古狼山地区石炭纪-三叠纪岩浆作用及其构造意义 |
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| 引用本文： | 田健,辛后田,滕学建,刘洋,郭硕,滕飞,何鹏,王文龙.内蒙古狼山地区石炭纪-三叠纪岩浆作用及其构造意义[J].地球科学,2019,44(1):206-219. |
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| 作者姓名： | 田健 辛后田 滕学建 刘洋 郭硕 滕飞 何鹏 王文龙 |
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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矿产调查项目DD20160039 |
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| 摘 要： | 华北地块北缘广泛发育石炭纪-三叠纪岩浆岩，岩浆岩的时空展布及反映的构造背景对研究古亚洲洋的俯冲增生作用具有重要的意义.然而，目前的研究集中在华北地块北缘中东部，该期岩浆活动的向西延伸有待深入研究.通过对狼山地区近年来获得的晚古生代-早中生代岩浆岩岩石学、地球化学、锆石U-Pb年龄及Hf同位素数据的综合分析，结果表明该区经历了早石炭世-晚二叠世、中-晚三叠世两期构造岩浆作用.其中，早石炭世-晚二叠世岩浆活动时限在338~251 Ma，岩性主要为辉长岩、角闪辉长岩、闪长岩、石英闪长岩、花岗闪长岩及二长花岗岩，辉长岩类的微量元素蛛网图及稀土元素配分型式与岛弧火山岩的曲线类似，花岗岩类具高Sr（>250×10-6，平均值为425×10-6）低Y（6.89×10-6~24.30×10-6）的特点.中-晚三叠世岩浆活动时限在245~228 Ma，岩性主要为正长花岗岩，花岗岩具高K2O/Na2O（1.48~1.58）、低Sr（154×10-6~49×10-6）低Yb（1.01×10-6~1.38×10-6）的特点，稀土配分曲线表现为轻稀土略富集、Eu负异常中等-强（Eu*=0.54~0.23）、重稀土平坦的近似海鸥型，总体反映了后造山花岗岩的地球化学特征.结合构造判别图解及区域地质资料，结果表明狼山地区早石炭世-晚二叠世为俯冲挤压的构造背景，中-晚三叠世则进入了后造山伸展的构造阶段.狼山地区晚古生代-早中生代发育的两期构造岩浆作用与华北陆块北缘中东部（330~265 Ma及250~200 Ma）类似，古亚洲洋的向南俯冲形成了华北陆块北缘近东西向延伸的晚古生代岩浆岩带，华北陆块与其北缘增生造山带拼贴作用的时限为二叠纪末-三叠纪初.
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| 关 键 词： | 构造岩浆作用 晚古生代 三叠纪 华北陆块北缘 狼山地区 地球化学 |
| 收稿时间： | 2018-04-30 |
Tectonic Significance of Carboniferous-Triassic Magmatism in Langshan Area,Inner Mongolia |
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| Abstract: | The Carboniferous-Triassic magmatites are widely developed in the northern margin of the North China Block. It is an effective way to study subduction and accretion of the Paleo-Asian Ocean via magmatic rocks. However, the existing research focuses on the middle-eastern part of the northern margin of the North China Block, and the westward extension of magmatic activity needs further study. Through comprehensive analysis for the Late Paleozoic-Early Mesozoic magmatic rocks, we propose the Langshan area has experienced the obvious tectonic magmatism of the Early Carboniferous-Late Permian and Middle-Late Triassic. The Early Carboniferous-Late Permian magmatism was in 338-251 Ma, resulting in large scale regional exposure of gabbro+hornblende gabbro+diorite+quartz diorite+granodiorite+monzonitic granite rock assemblage.The trace elements and REEs characteristics of the gabbrides display affinity to arc signature, and the granitoids show characteristics of high Sr (>250×10-6, average 425×10-6), and low Y (6.89×10-6-24.30×10-6). The Middle-Late Triassic magmatism was in 245-228 Ma, resulting in large scale regional exposure of monzonitic granite+Syenite, whole rock geochemical data reveal that the granitoids are characterized by high K2O/Na2O (1.48-1.58), low Sr (154×10-6-49×10-6), low Yb (1.01×10-6-1.38×10-6) and the approximate seagull type of chondrite-normalized REE patterns, which reflects the geochemical characteristics of post-orogenic extension. Combining discrimination diagrams and regional geological data, the Langshan area was under the tectonic setting of continental margin arc during Early Carboniferous-Late Permian and post-orogenic during Middle-Late Triassic. The tectonic magmatism of Late Paleozoic-Early Mesozoic magmatic is similar between Langshan area and middle-eastern part of northern margin of NCC. Thus, the southern subduction of the Paleo-Asian Ocean formed the Late Paleozoic magmatic belt extending from east to west, and the collaged time for NCC and accretion orogenic belt was restricted to Latest Permian-Earliest Triassic. |
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