西藏措勤地区则弄群火山岩源区------地球化学及Sr-Nd同位素制约
Volcanic rock provenance of Zenong Group in Coqen area of Tibet: geochemistry and Sr-Nd isotopic constraint
查看参考文献35篇
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文摘
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西藏中冈底斯带出露大面积早白垩世则弄群火山岩. 措勤地区则弄群火山岩具有较高的SiO_2含量(61.91% ~74.28%),轻稀土元素相对富集,富集大离子亲石元素Rb、Ba、Th、U,亏损高场强元素Nb、Ta等,并具Sr负异常,同时具有高的初始Sr同位素(0.707 89~0.710 17)和低的Nd的同位素(-3.4~-9.3)特征,与壳源岩浆的地球化学特征类似. 在εNd(t)-(~(87)Sr/~(86)Sr)i图解上,措勤地区则弄群火山岩所有样品均投于第四象限,而且都分布在上地壳与雅鲁藏布江MORB型亏损地幔混合线附近. 微量元素构造环境判别图解显示,则弄群火山岩形成于岛弧环境. 综合已有研究成果以及最新1:25万区域地质调查资料,认为措勤地区则弄群长英质火山岩很可能是幔源基性岩浆的热量促使地壳物质脱水发生重熔的产物,其形成的大地构造背景很可能与班公湖-怒江特提斯洋南向的俯冲作用有关 |
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其他语种文摘
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Magmatic rocks of Early Cretaceous Zenong Group are extensively developed in the Gangdise belt o Tibet, and the genesis of these rocks has given rise to much controversy. In view of this, the authors sample and analyzed systematically felsic volcanic rocks of Zenong Group in Coqen area of Gangdise orogenic belt. Th results show that magmatic rocks of Zenong Group are characterized by high SiO_2content, relative enrichment o LREE and evident enrichment of LILE, Rb, Ba, Th and U, depletion of suchHFS elements as Nb and Ta, an the appearance of Sr negative anomalies, with isotopic features of high Sr (0.707 89~0.710 17) and low N (-3.4~-9.3). They are aluminum-oversaturated (A/CNK=1.09~1.17) and geochemically similar to th crustal magma. In the diagram of ε Nd(t)-(~(87)Sr/~(86)Sr)i, all the samples fall in the No.4 quadrant and are distributed around the mixture line of the upper crust and the Yarlung Zangbo River MORB-type depleted crust suggesting the existence of fairly abundant upper crust matters and the participation of small amounts of mant materials. Moreover, magmatic rocks of Zenong Group are extensively distributed almost in the whole region The diagram of La/Sm-La indicates that the felsic magmatic rocks of Zenong Group are probably different parti melting products from the same magma source. The felsic magmatic rocks are greatly enriched in LREE an have a spidergram very similar to that of the upper continental crust. The tectonic-setting discrimination diagra of trace elements implies that magmatic rocks of Zenong Group were formed in a island-arc tectonic setting Based on previous research results and the latest 1:250 000 regional geological survey, the authors hold that th felsic magmatic rocks of Zenong Group might be products of the dehydration and remelting of the crustal mater als caused mainly by the heat of the mantle basic magma with the participation of some mantle materials. Th tectonic setting of the magmatic rocks of Zenong Group was probably associated with the southward subductio of the Bangong Lake-Nujiang River Tethys oceanic crust |
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来源
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岩石矿物学杂志
,2010,29(4):367-376 【核心库】
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关键词
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地球化学
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Sr-Nd同位素
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岩石成因
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措勤则弄群火山岩
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冈底斯带
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地址
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中国地质调查局成都地质调查中心, 四川, 成都, 610081
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中国地质调查局成都地质调查中心, 中国科学院广州地球化学研究所同位素年代学和地球化学实验室, 四川, 成都, 610081
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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1000-6524 |
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学科
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地质学 |
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基金
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国土资源大调查资助项目"雅鲁藏布江成矿带基础地质综合研究
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文献收藏号
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CSCD:3908774
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