| 阿拉善地块东部早古生代(约420 Ma)变质事件的发现及其地质意义:来自独居石与锆石U-Pb定年的新证据 |
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| 引用本文： | 刘平华,邹雷,田忠华,冀磊,施建荣.阿拉善地块东部早古生代(约420 Ma)变质事件的发现及其地质意义:来自独居石与锆石U-Pb定年的新证据[J].地球科学,2019,44(7):2441-2460. |
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| 作者姓名： | 刘平华 邹雷 田忠华 冀磊 施建荣 |
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| 作者单位： | 1.中国地质科学院地质研究所, 北京, 100037 |
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| 基金项目： | 国家重点研发计划重点专项项目2017YFC0601301中国地质调查局地质大调查项目DD20160121国家自然科学基金项目41602199中国地质调查局地质大调查项目DD20190003国家自然科学基金项目41672191中国地质科学院地质研究所基本科研业务经费J1514 |
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| 摘 要： | 前寒武纪变沉积岩系是阿拉善地块重要组成部分，准确测定其原岩成岩时代和变质时代，对于进一步认识阿拉善地块起源、形成、演化与亲缘性具有十分重要的科学意义.本文对阿拉善地块东部阿拉坦敖包地区德尔和通特组含蓝晶石石榴云母石英片岩开展了系统的野外地质调查、岩相学观察和同位素年代学研究.碎屑锆石U-Pb定年和野外地质调查表明，阿拉坦敖包地区德尔和通特组和祖宗毛道组碎屑锆石年龄介于3 306~1 146 Ma，并以出现中元古代锆石年龄（1 800~1 100 Ma）高频区为特征，最小一组碎屑锆石年龄约为1 123 Ma，结合区域上它们被约900 Ma花岗质片麻岩侵入的野外关系，阿拉坦敖包地区德尔和通特组与祖宗毛道组变沉积岩系的沉积时代被限定在1 123~900 Ma之间，为一套中元古代晚期?新元古代早期陆缘沉积建造，具有亲华北板块的特点.此外，变质独居石和变质锆石U-Pb定年和微量元素分析表明，阿拉坦敖包地区德尔和通特组含蓝晶石泥质片岩中发育大量变质独居石，它们具有典型变质独居石的稀土元素配分模式（轻稀土元素强烈富集而重稀土元素强烈亏损），其加权平均年龄为419±3 Ma（MSWD=7.1，n=40），类似地，一个锆石变质边也记录了406±7 Ma的206Pb/238U年龄.这些变质年龄被解释为阿拉善地块东部阿拉坦敖包地区德尔和通特组含蓝晶石石榴云母石英片岩遭受早古生代末角闪岩相变质?变形作用的时代，可能是阿拉善地块与周缘微陆块早古生代末碰撞造山作用的响应.
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| 关 键 词： | 阿拉善地块东部 含蓝晶石榴云母石英片岩 早古生代变质事件 独居石与锆石U-Pb定年 岩石学 |
| 收稿时间： | 2019-02-27 |
Discovery and Geological Significance of an Early Paleozoic (Ca. 420 Ma) Metamorphic Event from the Eastern Alxa Block: New Evidence from Monazite and Zircon LA-ICP-MS U-Pb Dating |
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| Abstract: | Precambrian meta-sedimentary rock is an important part of the Alxa Block, and accurate determination of the depositional and metamorphic timing of the meta-sedimentary rock is of great scientific significance for further understanding the origin, formation, evolution and affinity of the Alxa Block. This paper presents a detailed study on the field geological investigation, petrological observation, and zircon and monazite U-Pb dating of kyanite-bearing garnet mica quartz schists of the Deerhetongte Formation in the Alatanaobao area. The results of detrital zircon U-Pb dating and field geological investigation show that the crystallization age of detrital zircons of the Deerhetongte and Zuzongmaodao formations in Alatanaobao area ranges from 3 306 Ma to 1 146 Ma, and is characterized by the occurrence of high-frequency regions of Mesoproterozoic zircon age (1 800-1 100 Ma). The crystallization age of the youngest detrital zircons is circa 1 123 Ma, and the meta-sedimentary rocks are intruded by circa 900 Ma granitic gneisses. Thus, the depositional timing of the meta-sedimentary rocks of the the Deerhetongte and Zuzongmaodao formations in the Alatanaobao area is limited to 1 123~900 Ma, and it is a set of Late Mesoproterozoic-Early Neoproterozoic continental margin sedimentary rocks. In addition, the results of U-Pb dating and trace element analysis of metamorphic monazites and zircons indicate that a large number of metamorphic monazites are identified in the kyanite-bearing garnet mica quartz schists of the Deerhetongte Formation. They have typical REE distribution patterns of metamorphic monazites (strong enrichment of light REEs and strong depletion of heavy REEs). These monazites record a weighted average age of 419± 3 Ma (MSWD=7.1, n=40). Similarly, a zircon metamorphic rim also records 206Pb/238U age of 406±7 Ma. The metamorphic ages are interpreted as the timing of the late Early Paleozoic amphibolite-facies metamorphism-deformation of the kyanite-bearing garnet-mica quartz schist of the Deerhetongte Formation, probably in response to the late Early Paleozoic collision orogeny between the Alxa Block and the surrounding micro-continental blocks. |
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