腾冲早白垩世花岗岩的高分异成因及其构造意义
Early-Cretaceous highly fractionated granites from the Tengchong terrane:Petrogenesis and tectonic implication
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文摘
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腾冲地块东缘发育大量早白垩世花岗岩,这些花岗岩普遍具有高硅(69.2% ~ 77.4%)、富钾(K_2O/Na_2O >1.1)、弱过铝-强过铝质(A/CNK = 1.03 ~ 1.23)及不同程度Eu的负异常(δEu = 0.13 ~ 0.69)的特征,被认为是S型花岗岩或者是高分异的I型花岗岩。厘清这些花岗岩的成因对于理解腾冲地块早白垩世岩浆活动、构造演化及其与西藏拉萨和羌塘等陆块的构造对应关系具有重要意义。本文选择了腾冲地块中3个典型的早白垩世岩体(明光、勐连、小棠-芒东)中的二长花岗岩、白云母花岗岩及正长花岗岩重点进行了高精度SIMS氧同位素研究,结合SIMS U-Pb年代学、全岩主微量元素、Sr-Nd同位素分析探讨了这些花岗岩的成因及构造意义。锆石SIMS U-Pb定年结果表明3个岩体花岗岩的侵位年龄为112 ~ 122Ma,SIMS氧同位素分析结果表明这些花岗岩都具有一致的低δ~(18)O值(6.5‰ ~ 7.0‰)。全岩Sr-Nd同位素结果表明它们具有一致的富集同位素特征,(~(87)Sr/~(86)Sr)_i变化于0.7062 ~ 0.7213,ε_(Nd)(t)变化于- 9.1 ~ - 4.7。以上全岩和锆石的地球化学分析结果表明这些花岗岩的源区主要为古老的镁铁质下地壳,属于高分异I型花岗岩,并非前人认为的S型花岗岩。结合前人研究,本文认为这些高分异I型花岗岩可能形成于拉萨-腾冲与羌塘-保山地块碰撞后,中特提斯洋板块发生回转或板片断离的构造背景下,跟拉萨地块北缘岩浆岩带同期构造背景一致,是其东南向延伸。 |
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其他语种文摘
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Abundant Early Cretaceous granites were developed in the eastern margin of the Tengchong terrane.These granites are high SiO_2(69.2% ~ 77.4%),K-rich(K_2O/Na_2O >1.1),slightly peraluminous to strongly peraluminous(A/CNK = 1.03 ~ 1.23)and display significantly negative Eu anomalies(δEu = 0.13 ~ 0.69),which were thought to be S-type or highly fractionated I-type.Clarifying the origin of these granites is of great significance for understanding the Early Cretaceous magmatism and tectonic evolution of the Tengchong terrane and its correspondence with the Lhasa and Qiangtang terranes in Tibet.In this study,three Early Cretaceous granitic plutons(Mingguang,Menglian,Xiaotang-Mangdong)from the Tengchong terrane were selected for SIMS zircon oxygen isotope analyses.Combined with SIMS zircon U-Pb,and whole-rock major and trace element and Sr-Nd isotope data,the petrogenesis and tectonic significance of these granites were discussed.SIMS zircon U-Pb dating of six granite samples from different plutons indicate that these granites were emplaced coevally during 112 ~ 122Ma.They have uniformly low zircon δ~(18)O values of 6.5‰ ~ 7.0‰.Wholerock isotopic compositions show enriched ~(87)Sr/~(86)Sr(i)(0.7062 ~ 0.7213)and ε_(Nd)(t)(- 9.1 ~ - 4.7).These results,especially zircon oxygen isotopes,provided robust evidence that the granites are highly fractionated I-type,not S-type as previously thought.Our data,in combination with published geochronological and geochemical data,show that these highly fractionated I-type granites were formed by slab rollback and subsequent breakoff of the subducting Bangong-Nujiang ocean lithosphere during the Tengchong(Lhasa)- Baoshan(Qiangtang)collision.This geodynamic scenario is similar to that for north margin of the Lhasa Terrane at that time,indicating southeast extension of the Lasha Terrane to the Tengchong terrane. |
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来源
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岩石学报
,2021,37(4):1177-1195 【核心库】
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DOI
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10.18654/1000-0569/2021.04.13
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关键词
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腾冲地块
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氧同位素
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高分异I型花岗岩
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班公湖-怒江洋
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地址
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1.
中国科学院广州地球化学研究所, 同位素国家重点实验室, 广州, 510640
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中国科学院深地科学卓越创新中心, 中国科学院深地科学卓越创新中心, 广州, 510640
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中国科学院大学, 北京, 100049
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南方海洋科学与工程广东省实验室, 南方海洋科学与工程广东省实验室, 珠海, 519000
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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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1000-0569 |
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学科
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地质学 |
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基金
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国家重点研发计划项目
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第二次青藏高原科学考察项目
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文献收藏号
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CSCD:6972516
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