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首页> 外文期刊>Contributions to Mineralogy and Petrology >Small-scale Hf isotopic variability in the Peninsula pluton (South Africa): the processes that control inheritance of source ~(176)Hf/~(177)Hf diversity in S-type granites
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Small-scale Hf isotopic variability in the Peninsula pluton (South Africa): the processes that control inheritance of source ~(176)Hf/~(177)Hf diversity in S-type granites

机译：半岛岩体（南非）中的小规模H同位素变化：控制S型花岗岩中源〜（176）Hf /〜（177）Hf多样性遗传的过程

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摘要

The ~(176)Hf/~(177)Hf composition of inherited and magmatic zircon in the 538 Ma S-type Peninsula pluton (South Africa) has been determined at different scales. In the smallest rock samples investigated (<0.5 dm~3), as well as within individual thin sections, magmatic zircon crystals exhibit the same wide range in ε_(Hf(538))as the pluton (8ε units). In addition, across a significant range of bulk-rock compositions, both the range and average of the magmatic zircon Hf isotopic composition do not vary significantly with compositional parameters that are expected to scale with the proportion of mantle-derived magma addition (e.g., Mg# and Ca). At all scales, the ε_(Hf) variability in the magmatic zircon fraction matches well with that portrayed by the time-evolved inherited zircon population [i.e., with the ε_(Hf(538)) range of the inherited zircon cores]. This evidence suggests that the ε_(Hf) heterogeneity of magmatic zircon is directly inherited from the source. However, the analysis of zircon core-rim pairs reveals that the ~(176)Hf/~(177)Hf composition of the inherited crystals does not directly transfer to their magmatic overgrowths. Small-scale modeling of zircon dissolution and re-precipitation in a static magma generates sub-mm melt domains having variable Zr content and Hf isotope composition. The composition of these domains is controlled by the size and isotope composition of the nearest dissolving zircon crystals and the cooling rate of the magma. These results suggest that in magma systems with a substantial inherited zircon load, zircon crystals within the same rock should record variable ~(176)Hf/~(177)Hf in the magmatic zircon fraction.
机译：538 Ma S型半岛岩体（南非）中继承和岩浆锆石的〜（176）Hf /〜（177）Hf组成已按不同比例确定。在研究的最小岩石样品中（<0.5 dm〜3），以及在单个薄片内，岩浆锆石晶体的ε_（Hf（538））范围与range子（8ε单位）相同。另外，在很大范围的块岩成分中，岩浆锆石Hf同位素组成的范围和平均值均不会随预期随地幔来源的岩浆添加比例（例如镁）成比例的成分参数而显着变化。 ＃和Ca）。在所有尺度上，岩浆锆石组分中的ε_（Hf）变异性都与时间演化的继承锆石种群所描绘的[[，即，继承的锆石岩心的ε_（Hf（538））范围]匹配得很好。该证据表明岩浆锆石的ε_（Hf）异质性直接从源头继承。然而，对锆石核心-边缘对的分析显示，所继承晶体的〜（176）Hf /〜（177）Hf组成并未直接转移至其岩浆过度生长。锆石在静态岩浆中的溶解和再沉淀的小规模模型产生具有可变Zr含量和Hf同位素组成的亚毫米熔体域。这些畴的组成受最近溶解的锆石晶体的大小和同位素组成以及岩浆的冷却速率控制。这些结果表明，在具有大量继承的锆石负荷的岩浆系统中，同一岩石中的锆石晶体应在岩浆锆石中记录变量〜（176）Hf /〜（177）Hf。

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