| 阿拉善地区前寒武纪斜长角闪岩的岩石学、地球化学、形成环境和年代学 |
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| 引用本文： | 沈其韩,耿元生,王新社,吴春明.阿拉善地区前寒武纪斜长角闪岩的岩石学、地球化学、形成环境和年代学[J].岩石矿物学杂志,2005,24(1):21-31. |
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| 作者姓名： | 沈其韩 耿元生 王新社 吴春明 |
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| 作者单位： | 中国地质科学院,地质研究所,北京,100037 |
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| 基金项目： | 中国地质调查资助项目 ( 199913 0 0 0 0 0 6) |
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| 摘 要： | 阿拉善地区前寒武纪不同岩群、岩组和杂岩中的斜长角闪岩均呈层状产出 ,其原岩多为高铁拉斑玄武岩 ,普遍具有高钾高钛、稀土元素含量高、轻稀土元素富集的地球化学特征 ,与典型的大洋拉斑玄武岩、太古宙的TH1型和TH2 型拉斑玄武岩有较明显的区别。岩石组合特征和多种地球化学判别图解均表明 ,该区的斜长角闪岩主要形成于板内环境 ,属于板内裂陷或大陆边缘裂陷的大地构造环境。初步的同位素年代学研究表明 ,叠布斯格岩群中斜长角闪岩的原岩形成于新太古代 ,含黑云斜长角闪岩中的角闪石3 9Ar_40 Ar坪年龄和等时线年龄分别为 1918Ma和1919Ma ,说明其曾经历了古元古代角闪岩相变质作用的叠加。巴彦乌拉山岩组中斜长角闪岩形成于 2 2 71Ma～2 2 6 4Ma。波罗斯坦庙片麻杂岩中的斜长角闪岩已被 1818Ma和 1839Ma花岗片麻岩侵入 ,根据该杂岩体中斜长角闪岩与巴彦乌拉山岩组中同类岩石的地球化学特征 ,推断其形成于古元古代早期。阿拉善群德尔和通特组中的斜长角闪岩目前尚无确切的同位素年代学数据 ,但相同层位的石榴石二云母石英片岩中锆石离子探针定年已获得平均同位素年龄值为 136 3Ma ,推测它有可能形成于中元古代
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| 关 键 词： | 斜长角闪岩 地球化学 同位素年龄 板内裂陷或大陆边缘裂陷 阿拉善地区 |
Petrology, geochemistry, formation environment and ages of Precambrian amphibolites in Alxa region |
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| SHEN Qi-han,GENG Yuan-sheng,WANG Xin-she and WU Chun-ming.Petrology, geochemistry, formation environment and ages of Precambrian amphibolites in Alxa region[J].Acta Petrologica Et Mineralogica,2005,24(1):21-31. |
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| Authors: | SHEN Qi-han GENG Yuan-sheng WANG Xin-she and WU Chun-ming |
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| Abstract: | Petrology, geochemistry, formation environment and isotopic geochronology of Precambrian amphibolites in Alxa area are reported in this paper. Amphibolites in different group complexes, formation complexes and complex rock bodies all crop out in layers, and their protoliths are mainly ferrian tholeiite characterized geochemically by high potassium and titanium as well as rich REE and LREE. These characteristics are remarkably different from features of typical oceanic tholeiite, TH_1 and TH_2 tholeiite of Archean rock assemblages. Various geochemical diagrams indicate that amphibolites are mainly formed in an intraplate environment characterized by intraplate depression or epicontinental faulted depression. Isotopic geochronology shows that amphibolite in Diebusige group complex was formed in Neo_archean. ~(39)Ar_~(40)Ar age and isotopic age of hornblende from biotite_bearing amphibolite are 1?918 Ma and 1?919 Ma respectively, suggesting that they underwent metamorphism of amphibolite faces in Paleoproterozoic. Amphibolite in Bayanwulashan formation complex was formed between (2?271) Ma and 2?264 Ma. Amphibolite in Boluositanmiao gneiss complex was intruded by granitic gneiss of 1?818 Ma and 1?839 Ma. According to geochemical characteristics of amphibolite in the complex and the same sort of rocks in Bayanwulashan formation complex, it is concluded that it was formed in early Paleoproterozoic. Accurate isotopic chronological data of amphibolite from Delhetongte formation complex in Alxa Group are not available, but the average zircon ion probe age of garnet_muscovite_biotite_quartz_schist in the same layer is 1?363 Ma, which indicate that the amphibolite was probably formed in Meso_proterozoic. |
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| Keywords: | amphibolite geochemistry isotopic age intraplate depression or epicontinental faulted depression |
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