The anatectic effect on the zircon Hf isotope composition of migmatites and associated granites
The anatectic effect on the zircon Hf isotope composition of migmatites and associated granites
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深熔岩对混合岩及伴生花岗岩锆石Hf同位素组成的影响
DOI：
10.1016/j.lithos.2015.09.026
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发表时间：
2015-12
期刊：
影响因子：
3.5
通讯作者：
Yong-Fei Zheng
中科院分区：
文献类型：
--
作者：
Yi-Xiang Chen;Peng Gao;Yong-Fei Zheng
锆石Hf同位素组成被广泛用于追踪陆壳的生长和演化。然而，岩浆锆石的Hf同位素组成是否能如实反映其源区，特别是S型花岗岩的Hf同位素组成，一直存在争议。为了深入了解这一问题，我们重新查阅了苏鲁造山带和华夏地体中已发表的混合岩锆石及其伴生花岗岩的Lu-Hf同位素数据。结果表明，新生长的锆石微区的176Hf/177Hf比残存的锆石微区高出10ε以上。这表明在地壳深熔和随后的岩浆活动中，非锆石Hf对深熔熔体有相当大的贡献。此外，这种更具放射性成因的Hf同位素特征在岩浆过程中不会被抹去，例如熔体上升和侵位过程中的晶体分馏。源岩中Hf同位素相对于矿物Lu/Hf比值的平衡表明，含Hf的主要矿物通过将含Hf的主要矿物溶解到深熔熔体中而参与深熔反应。混合岩和花岗岩中一些深熔和岩浆锆石区域的Hf同位素显着变化，不仅表明了源区的不均一性，而且还表明了非锆石Hf贡献的多变性。因此，深熔和岩浆锆石的Hf同位素组成在很大程度上是由深熔反应产生的非锆石Hf和原岩锆石溶解到深熔熔体中产生的锆石Hf之间的质量平衡决定的。它们主要受控于地壳深熔的温压条件和机制，以及熔体演化过程中的岩浆作用。本研究突出了非锆石Hf对深熔和岩浆锆石区域的重要贡献。在这一点上，混合岩和花岗岩中新生长的锆石结构域的176Hf/177Hf比值大幅上升，不能反映其源岩的Hf同位素组成。在将相对贫化的Hf同位素组成与岩石成因解释中的源岩性质和陆壳生长联系起来时，必须牢记这一偏差。非锆石Hf的贡献也能较好地解释S型花岗岩中锆石经常表现出的Hf同位素组成的变化。
Zircon Hf isotope composition is widely used to trace the growth and evolution of continental crust. However, it is controversial whether the Hf isotope composition of magmatic zircons can faithfully reflect that of their sources, especially for S-type granites. In order to provide an insight into this issue, we have revisited the published Lu–Hf isotope data of zircons from well-studied migmatites and associated granites in the Sulu orogen and the Cathaysian terrane, respectively. The results show greatly elevated176Hf/177Hf ratios (by more than 10ε units) for newly grown zircon domains compared to the relict zircon domains. This indicates considerable contributions from non-zircon Hf to anatectic melts during crustal anatexis and subsequent magmatism. Furthermore, this more radiogenic Hf isotope signature was not erased during magmatic processes such as crystal fractionation during melt ascent and emplacement. The budget of Hf isotopes in source rocks with respect to mineral Lu/Hf ratios suggests the involvement of Hf-bearing major minerals in anatectic reactions by dissolving Hf-bearing major minerals into the anatectic melts. The significant Hf isotope variations in some anatectic and magmatic zircon domains from the migmatites and granites suggest not only the source heterogeneity but also the variable non-zircon Hf contributions. As such, the Hf isotope compositions of anatectic and magmatic zircons are substantially dictated by the mass balance between the non-zircon Hf from anatectic reactions and the zircon-Hf from the dissolution of protolith zircons into the anatectic melts. They are primarily controlled by P-T conditions and mechanism of crustal anatexis, and the magmatic processes during melt evolution. The present study highlights the important contribution of non-zircon Hf to the anatectic and magmatic zircon domains. In this regard, the greatly elevated176Hf/177Hf ratios for newly grown zircon domains in the migmatites and granites cannot reflect the Hf isotope compositions of their source rocks. Such a deviation must be kept in mind when linking relatively depleted Hf isotope compositions to the nature of source rocks in petrogenetic interpretation and to the growth of continental crust. The contribution of non-zircon Hf can also better account for the variable Hf isotope compositions often shown by zircons from S-type granites.
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影响因子：
3.5
作者：
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通讯作者：
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影响因子：
5.8
作者：
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作者：
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