| 内蒙古大青山逆冲推覆体系中生代逆冲构造活动的40Ar-39Ar定年 |
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| 引用本文： | 张进江,戚国伟,郭磊,刘江.内蒙古大青山逆冲推覆体系中生代逆冲构造活动的40Ar-39Ar定年[J].岩石学报,2009,25(3):609-620. |
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| 作者姓名： | 张进江 戚国伟 郭磊 刘江 |
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| 作者单位： | 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;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;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;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 |
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| 基金项目： | 国家自然科学基金项目（90714006）及全国优秀博士学位论文活动者专项资金（200022） |
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| 摘 要： | 内蒙古大青山呼和浩特段北侧发育3条走向北东东、指向北西的逆冲断层，并与被其分割的3个逆冲席体及一个原地系构成大青山逆冲推覆体系。逆冲断层上盘底部发育较深层次的糜棱岩,下盘顶部多发育低温的千糜岩。本研究在构造地质调查基础上，结合宏-微观岩石矿物学分析，采用40Ar-39Ar定年对该逆冲体系的活动时间进行约束。逆冲断层带内3个千糜岩绢云母40Ar-39Ar年龄范围为120~119Ma，另一样品给出了120Ma的概率统计峰值年龄。千糜岩为低温同变形变质产物，细粒绢云母为同变形新生矿物，其40Ar-39Ar年龄可代表变形年龄。侵位在断层内弱变形的花岗闪长岩为同构造晚期侵位，角闪石40Ar-39Ar年龄限定其冷却时间下限为121Ma，概率统计峰值年龄为119Ma。逆冲断层上盘底部发育较高温的糜棱岩，而低温千糜岩的形成时间应属于变形后期。因此，120Ma至119Ma期间，大青山逆冲推覆体系的逆冲作用应已是处于变形晚期。
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| 关 键 词： | 大青山逆冲推覆体系 逆冲作用 千糜岩 40Ar-39Ar定年 |
| 收稿时间： | 2008/11/19 0:00:00 |
| 修稿时间： | 1/9/2009 12:00:00 AM |
40Ar-39Ar dating of the Mesozoic thrusting in Daqingshan thrust-nappe system, Inner Mongolia, China |
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| ZHANG JinJiang,QI GuoWei,GUO Lei and LIU Jiang.40Ar-39Ar dating of the Mesozoic thrusting in Daqingshan thrust-nappe system, Inner Mongolia, China[J].Acta Petrologica Sinica,2009,25(3):609-620. |
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| Authors: | ZHANG JinJiang QI GuoWei GUO Lei and LIU Jiang |
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| Institution: | The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China;The Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China |
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| Abstract: | The northern Daqingshan orogen in Hohhot area is tectonically characterized by a northwest-directed thrust-nappe system, the Daqingshan thrust-nappe system, which consists of three east-northeast trending thrusts, three nappes and an autochthon. Higher-grade mylonite was formed at the bases of the hanging walls of the thrusts, while lower-grade phyllonite was produced on the top of the footwalls. Based on structural geological investigation and integrating macro-/micro-analyses of petrology and mineralogy, this study adopts 40Ar-39Ar dating method to constrain the deformation time of the Daqingshan thrust-nappe system. Three sericite samples of phyllonite give a 40Ar-39Ar age range of 120~119Ma and the other sample presents a peak age of 120Ma in the age-probability spectrum. Phyllonite was formed by a deformation at low temperatures and the fine-graded sericite in it was new-born syn-deformational mineral, therefore the sericite 40Ar-39Ar age can represent the deformation time very well. A weak-deformed granodiorite dike intruding the thrust indicates an emplacement in a late deformational stage, and its hornblende 40Ar-39Ar dating presents a lower-limitation age of 121Ma for the cooling of and the statistical peak age is also 119Ma. The lower-temperature phyllonite should be formed in a late stage of the deformation because higher-temperature mylonite developed at the bases of the nappes. Therefore, the thrusting of the Daqingshan thrust-nappe system must have been in its late deformational stage during the time form 120 to 119Ma. |
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| Keywords: | Daqingshan thrust-nappe system Thrusting Phyllonite 40Ar-39Ar dating |
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