Archean mantle fluids preserved in fibrous diamonds from Wawa, Superior craton
Archean mantle fluids preserved in fibrous diamonds from Wawa, Superior craton
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苏必利尔克拉通瓦瓦纤维状钻石中保存的太古代地幔流体
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发表时间：
2012
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通讯作者：
J. Ryder
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作者：
Evan M. Smith;M. Kopylova;G. Nowell;D. Pearson;J. Ryder
我们分析了第一个样品的新太古代地幔流体捕获的包裹体中的纤维状金刚石从2.701-2.697 Ga瓦瓦变砾岩（加拿大）。富钾、钠、氯的含碳酸盐盐流体包裹体与中生代纤维状金刚石的包裹体有很强的相似性。这种相似性的主要和微量元素，挥发性成分和氮的特性意味着均匀延伸的一些地幔过程，包括形成流体丰富的纤维金刚石，回到新太古代。低初始Sr同位素比值（87 Sr/ 86 Sr i = 0.700-0.702）的钻石在2.7 Ga的太古代亏损地幔或散装硅酸盐地球的估计误差范围内，与非富集，对流地幔/I组金伯利岩样的流体源。Eu异常出现在新太古代和古生代含盐纤维金刚石流体中，而不出现在碳酸盐岩或碳酸盐岩流体中。这种限制表明，富Cl流体的相互作用可能会导致地幔岩中的Eu异常，因此，不应该自动分配到俯冲起源时，成岩史涉及盐水流体被怀疑。
We analyzed the first samples of Neoarchean mantle fluid captured as inclusions in fibrous diamonds from the 2.701–2.697 Ga Wawa metaconglomerate (Canada). The K-, Na-, and Cl-rich carbonate-bearing saline fluid inclusions bear a strong resemblance to those of Phanerozoic fibrous diamonds. This similarity in major and trace elements, volatile components, and nitrogen characteristics implies the uniformitarian extension of some mantle processes, including the formation of fluid-rich fibrous diamonds, back to the Neoarchean. Low initial Sr isotope ratios ( 87 Sr/ 86 Sr i = 0.700–0.702) for the diamonds at 2.7 Ga are within error of estimates of Archean depleted mantle or bulk silicate Earth at 2.7 Ga, consistent with a non-enriched, convecting mantle/group I kimberlite-like source of the fluid. Eu anomalies occur in both Neoarchean and Phanerozoic saline fibrous diamond fluid, but not in silicic or carbonatitic fluid varieties. This restriction suggests that interaction with Cl-rich fluid may lead to Eu anomalies in mantle rocks, which therefore should not be automatically assigned to a subduction origin when a petrogenetic history involving saline fluids is suspected.