Mantle xenoliths provide effective records of the metasomatic processes that affect continental lithosphere evolution, such as interaction with subducted components or modification via small-degree melts. Correlations between major/trace element geochemistry with stable and radiogenic isotope compositions can help constrain the source and timing of this metasomatism. We report new δ18O, δ44/40Ca, and δD values for twelve kimberlite-hosted mantle xenoliths from the Slave Craton (NWT, Canada), which show varying degrees of metasomatism. The δ18O values of olivine (δ18Ool = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ18O values (δ18Ocpx = +5.31 ± 0.10‰; δ18Ogrt = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ44/40Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ44/40Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ18O and high δ44/40Ca values. In general, Δ18Ocpx-ol and Δ18Ogrt-ol (ranging from −0.19‰ to +0.19‰ and from −0.56‰ to +0.35‰, respectively) are lower than expected equilibrium values at mantle temperatures. Strong negative correlations are found between δ18Ogrt and Δ18Ogrt-ol and garnet major and trace element composition (Na2O, H2O, La/YbN). Furthermore, phlogopite-bearing kelyphitic rims have δD values (avg. = −126 ± 13‰; 1σ) lower than typical mantle values. Whole rock Sm-Nd model ages and oxygen isotope diffusion modeling suggest that metasomatism occurred during the Mesozoic, shortly before kimberlite entrainment, consistent with indications from diamond-forming fluids from the Slave craton. The combined low δ18O, δD, and high δ44/40Ca signature of the mantle peridotite xenoliths, along with the age constraints, suggest the metasomatic fluid/melt is sourced from a recycled oceanic crust component related to Mesozoic subduction in western North America.

中文翻译：

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使用 Ca-、O- 和 H-同位素追踪次大陆岩石圈地幔的俯冲相关交代作用


地幔异石提供了影响大陆岩石圈演化的交代过程的有效记录，例如与俯冲成分的相互作用或通过小度熔化进行的修饰。主/痕量元素地球化学与稳定和放射性同位素组成之间的相关性有助于限制这种交代的来源和时间。我们报告了来自奴隶克拉通（加拿大西北地区）的 12 个金伯利岩承载的地幔异石的新 δ18O、δ44/40Ca 和 δD 值，它们显示出不同程度的交代作用。橄榄石的 δ18O 值 （δ18Ool = +5.33 ± 0.13‰; 1σ; n = 12） 与平均地幔值重叠。斜辉石和石榴石 δ18O 值 （δ18Ocpx = +5.31 ± 0.10‰;δ18Ogrt = +5.37 ± 0.23‰; 1σ）低于大多数地幔橄榄岩中报告的数值，并且分别与斜辉石 δ44/40Ca（平均值 = +1.00 ± 0.10‰;1σ）和石榴石 δ44/40Ca（平均值 = +1.18 ± 0.19‰; 1σ）密切相关，从典型的地幔值延伸到低 δ18O 和高 δ44/40Ca 值。一般来说，Δ18Ocpx-ol 和 Δ18Ogrt-ol（范围分别为 -0.19‰ 至 +0.19‰ 和 -0.56‰ 至 +0.35‰）在地幔温度下低于预期平衡值。δ18Ogrt 和 Δ18Ogrt-ol 与石榴石主要元素和微量元素组成 （Na2O、H2O、La/YbN） 之间存在很强的负相关关系。此外，含金云母的钙镁石边缘的 δD 值（平均 = −126 ± 13‰;1σ）低于典型的地幔值。全岩 Sm-Nd 模型年龄和氧同位素扩散模型表明，交代作用发生在中生代，在金伯利岩夹带之前不久，这与奴隶克拉通的金刚石形成流体的指示一致。 地幔橄榄岩异岩的低 δ18O、δD 和高 δ44/40Ca 特征的组合，以及年龄限制，表明交代流体/熔体来自与北美西部中生代俯冲相关的回收海洋地壳成分。