| 内蒙古白乃庙白银都西群的形成环境及其构造意义 |
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| 引用本文： | 张臣,吴泰然.内蒙古白乃庙白银都西群的形成环境及其构造意义[J].高校地质学报,1999,5(2):175-182. |
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| 作者姓名： | 张臣 吴泰然 |
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| 作者单位： | 北京大学地质学系 |
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| 摘 要： | 白乃庙地区的白银都西群主要为一套中－高级变质岩系，具有以长英质变粒岩类、云母质片岩类和角闪质岩石为主的岩石组合特征。白银都西群长英质岩类主要原岩为长石石英砂岩和泥质岩石，属于在不稳定陆壳上形成的过渡型陆屑建造，原岩形成环境相当于一种非稳定陆壳基底上的盆地环境；白银都西群中角闪质岩石原岩为基性火山岩，岩石化学成分具大陆拉斑玄武岩特征，原岩来自幔源，但含有较多陆壳组分，其形成环境相当于大陆边缘。白银都西群沉积和岩浆建造特征表明，其形成环境是拉张条件下古大陆边缘裂陷槽环境，具火山型被动大陆边缘建造特征，代表中晚元古代陆缘拉张解体早期阶段形成的拉张型过渡壳。
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| 关 键 词： | 内蒙古 白银都西群 中元古代 形成环境 变质岩 |
| 收稿时间： | 1999-06-20 |
| 修稿时间： | 1999-06-20 |
ROCK ASSEMBLAGE OF BAIYINDUXI GROUP AND ITS TECTONIC INTERPRETATION IN BOIN SUM REGION, INNER MONGOLIA |
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| Zhang Chen,Wu Tairan.ROCK ASSEMBLAGE OF BAIYINDUXI GROUP AND ITS TECTONIC INTERPRETATION IN BOIN SUM REGION, INNER MONGOLIA[J].Geological Journal of China Universities,1999,5(2):175-182. |
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| Authors: | Zhang Chen Wu Tairan |
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| Institution: | Department of Geology, Peking University 1008711 |
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| Abstract: | There is a suite of middle- high grade metamorphic rocks in Boin Sum region, Inner Mongolia which was named as Baiyinduxi Group. The rock assemblage of the group consists of leptynite, mica shist and amphibolite. There are different opnuons in tectonic interpretation among the geologists, who work over there. A representative one considers that the Baiyinduxi Group was the product of island arc or other active continental margin. Based on the field and experimental works, we have gotten some new idea. The original rocks of leptynite are considered to be feldspar-quartz sandstone and mudstone. The important characteristics of these rocks are low maturity in fabric, high maturity in composition and well- developed rhythm. It implies that the original rocks would be formed in an instable basin on the continental crust. The original rocks of amphibolite in Baiyinduxi Group are considered to be basic volcanic rocks. The chemical composition of amphiblitic rocks is：SiO2, 49.93:Ca , 8.91:MgO, 4.24:Na20+K20, 4.69 in average and FeO>Fe2O3:Na20> K2O, LREE/HREE =4.8. In chemical composition they are similar to continental tholeiite. These basic volcanic rocks have εNd(t)= -1.1～+1.4. It means that the magmas of basic volcanic rocks come from mantle and are mixed with continental materials. However, the contents of trace elements are higher than those of volcanic rocks in active magin. Its tectonic environment would be continental margin. According to the characteristics of the rock assemblage, like relatively large amount of quartz fragment, low maturity in fabric, high maturity in composition, well- developed rhythm and other chemical characteristics, Baiyinduxi Group would precipitate in all environment of volcanic passive continental margin. It indicates that the tectonic environment in Boin Sum region was extentional transitional type of continental crust in Middle- Neo Proterozoic rather than an island arc assemblage that was recognized before Rifting was the most important event of North China Platform Based on the new data described in this paper, it may be suggested that the north margin of North China Plate underwent a large scale rifting or down- warping in Middle Neo Proterozoic and a volcanic passive margin was
formed. Baiyinduxi Group might be the product of that event. At the end of Neo-Proterozoic, the violent tectonic movement ended the evolution history of passive continental margin and began an active margin regime. |
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| Keywords: | Inner Mongolia Baiyinduxi Group Middle Proterozoic extentional transition crust |
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