| 西南极利文斯顿岛火山岩多种成因过程的地球化学证据 |
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| 引用本文： | 郑祥身.西南极利文斯顿岛火山岩多种成因过程的地球化学证据[J].极地研究,1996,8(3):4-15. |
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| 作者姓名： | 郑祥身 |
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| 作者单位： | 中国科学院地质研究所,巴塞罗那大学地质系,英国南极局自然环境研究理事会 |
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| 基金项目： | 国家自然科学基金委员会资助,国家“八五”科技攻关课题资助,西班牙CICYT资助 |
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| 摘 要： | 利文斯顿岛火山岩是南极南设得兰岩浆弧的一部分。对岩石的Ｓｒ、Ｎｄ、Ｐｂ同位素组成以及８７Ｓｒ／８６Ｓｒ与１／Ｓｒ、Ｒｂ、Ｋ和ＳｉＯ２关系的研究表明,利文斯顿岛火山岩具有不同的源区特征。百耳斯半岛和史莱夫角的火山岩、西多斯角的粗玄岩和第三纪的英云闪长岩显示出同成因的特点,和依诺特角第四纪橄榄玄武岩一样,它们均具有原生地幔的同位素组分,源区岩浆可能直接来自上地幔。汉那角和中利文斯顿岛火山岩岩浆则受到地壳成分的混染。不相容元素对Ｌａ／Ｓｍ－Ｌａ和Ｃｅ／Ｙｂ－Ｃｅ的研究进一步显示出,上述不同产地的岩石分别为不同源岩浆不同程度部分熔融的产物。结合岩相学和岩石化学特征的研究,提出百耳斯半岛和史莱夫角的火山岩以及西多斯角的粗玄岩是上地幔发生部分熔融所生成的玄武岩岩浆从深部岩浆囊沿构造薄弱带直接喷出形成的。古生代基底岩系的存在对中利文斯顿岛和汉那角火山岩的成因过程有重要的影响,即来自深部岩浆囊的原始岩浆在上地壳中的浅部岩浆囊受到了壳源物质混染。更新世－现代火山岩的源区岩浆直接自上地幔部分熔融生成,火山作用与晚新生代时该区的拉张构造有关。
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| 关 键 词： | Sr、Nd、Pb同位素 火山岩 岩浆成因 利文斯顿岛 南极 |
MULTIPLE MAGMA GENERATION PROCESSES OF THE VOLCANIC ROCKS FROM LIVINGSTON ISLAND,WEST ANTARCTICA: GEOCHEMICAL EVIDENCES |
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| Zheng Xiangshen.MULTIPLE MAGMA GENERATION PROCESSES OF THE VOLCANIC ROCKS FROM LIVINGSTON ISLAND,WEST ANTARCTICA: GEOCHEMICAL EVIDENCES[J].Chinese Journal of Polar Research,1996,8(3):4-15. |
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| Authors: | Zheng Xiangshen |
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| Abstract: | Meso Cenozoic volcanic rocks widely distributed on Livingston Island are part of the South Shetland magmatic arc.Early to Late Cretaceous volcanism is particularly well represented,but the magmatism also includes Early Tertiary plutonic tonalite and Holocene volcanic rocks. Eight representative lava and dolerite,as well as tonalite samples were analyzed for Sr,Nd,Pb isotope study.The isotopic composition and other geochemical characteristics of rocks,such as the relationship of 87 Sr/ 86 Sr vs 1/Sr,Rb,K and SiO 2,combining with the published and new petrographical and petrochemical data,indicate that the magmatic rocks outcropped on different locations in Livingston Island should be from different magma resources with distinguishable isotope features.Therefore multiple magma generation processes of the volcanism in Livingston Island have been suggested. The Late Cretaceous volcanic rocks from Byers Peninsula and Cape Shirreff,the dolerite at Siddons Point,and the Tertiary tonalite at Barnard Point are all charactered of relatively low 87 Sr/ 86 Sr ratios(≤0.7040) and positive ε Nd ,showing a syngenetic mantlederived magma feature.By contrast,rocks from the central Livingston Island and Hannah Point have significantly higher 87 Sr/ 86 Sr ratios(≥0.7050),implying a possible contamination process.All of the rocks analyzed are distributed within the mantle array in Sr Nd isotopic space, but data for the low Sr ratio group cluster close to primitive mantle values,whereas the high Sr ratio group did not.The primitive compositions of the Quaternary olivine basalt suggests direct derivation from a deep level,primary magma. Studies on the La/Sm La and Ce/Yb Ce pairs of incompatible elements further provide that the formation of above rocks was due to different magma resources by different partial melting degrees.The primary magma of the volcanic rocks from Byers Peninsula,Cape Shirreff,and Siddons Point would be generated by partial melting of upper mantle material in a deeper magma chamber and was directly erupted onto surface.Conversely,the rocks in central Livingston and Hannah Point might be undergone contamination process when the derived magma had to stay in a shallow chamber.The possible crustal source("contamination")could be the Early Triassic Miers Bluff Formation,the basement of Livingston Island,which is a sequence of continental derived metasedimentary rocks deposited in a submarine fan environment.The Pliocene to Recent volcanism is closely related to the extension of Bransfield Strait and the primary magma was directly derived from the upper mantle by partial melting. |
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| Keywords: | s Sr Nd Pb isotope volcanic rocks magma generation processes Livingston Island Antarctica |
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