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首页> 外文期刊>Journal of Asian earth sciences >Do Hf isotopes in magmatic zircons represent those of their host rocks?
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Do Hf isotopes in magmatic zircons represent those of their host rocks?

机译：岩浆锆石中的Hf同位素代表它们的宿主岩石吗？

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摘要

Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from similar to 630 degrees C to similar to 900 degrees C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.
机译：锆石中的Lu-Hf同位素系统是研究岩浆岩成因和地壳演化的有力且广泛使用的地球化学示踪剂，前提是锆石Hf同位素可以代表其母体整个岩石的初始Hf同位素。但是，这种假设可能并不总是正确的。大陆壳的不平衡部分熔融将优先融化具有高时间积分Lu / Hf比的非锆石矿物，并产生具有比其岩浆源更放射源的Hf同位素组成的部分熔融。锆石样品的溶解实验（使用热板，炸弹和烧结程序）证明了这种不平衡作用，其中部分溶解比完全溶解的样品具有可变的和更多的放射性Hf同位素组成。来自中国南部新元古代九陵岩床的一个案例研究表明，大约一半的调查样品显示锆石和大块岩石之间具有解耦的H同位素。这种解耦可能反映了复杂而漫长的岩浆过程，例如地壳同化，岩浆混合和不平衡融化，这与钛锆石温度计从大约630摄氏度到大约900摄氏度的宽温度谱一致。我们认为，岩浆锆石可能仅记录结晶过程中其周围熔体的Hf同位素组成，并且不确定其Hf同位素组成是否可以代表整体岩浆的主要Hf同位素组成。在这方面，使用锆石Hf同位素组成追踪地壳演化可能是有偏见的，因为其中大多数可能最初来自不平衡部分熔融。

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  • 来源
    《Journal of Asian earth sciences》 |2018年第1期|202-212|共11页
  • 作者

    Wang Di; Wang Xiao-Lei; Cai Yue; Goldstein Steven L.; Yang Tao;

  • 作者单位

    Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210046, Jiangsu, Peoples R China;

    Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210046, Jiangsu, Peoples R China;

    Columbia Univ, Dept Earth & Environm Sci, Lamont Doherty Earth Observ, Palisades, NY 10964 USA;

    Columbia Univ, Dept Earth & Environm Sci, Lamont Doherty Earth Observ, Palisades, NY 10964 USA;

    Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210046, Jiangsu, Peoples R China;

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  • 正文语种 eng
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  • 关键词

    Hf isotopes; Dissolution experiments; Disequilibrium melting; Decoupling; Zircon;

    机译：f同位素;溶解实验;不平衡熔融;解偶联;锆石;

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