Hydrogen diffusion mechanism in the mantle deduced from H-D interdiffusion in wadsleyite
Hydrogen diffusion mechanism in the mantle deduced from H-D interdiffusion in wadsleyite
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DOI：
10.1016/j.epsl.2021.116815
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发表时间：
2021-05
影响因子：
5.3
通讯作者：
Wei Sun;T. Yoshino;N. Sakamoto;H. Yurimoto
中科院分区：
文献类型：
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作者：
Wei Sun;T. Yoshino;N. Sakamoto;H. Yurimoto
经典观点解释了名义上无水矿物 (NAM) 中的氘核扩散速度略慢于质子扩散速度（克努森极限为 2），而在此我们根据使用一对瓦兹利石单晶在 16 GPa 和 900-1300 下进行的 HD 相互扩散偶实验，报道了 Mg 2 SiO 4 瓦兹利石中氘核的扩散速度比质子快约 3∼ 7 倍 K.我们的结果表明氢在瓦兹利石中的扩散受到多种扩散机制的影响，其中，沿着间隙缺陷迁移的质子（氘核）对于分离晶体网络中的氢同位素特别有效，这可能是由于量子筛分效应。由此产生的扩散驱动的 H/D 分馏可以解释地幔捕虏体中 NAM 贫氘的常见现象，表明捕虏体中的 MORB 包裹体比捕虏体 NAM 更能可靠地指示地幔的氢同位素组成。
Classical view has interpreted deuterons in nominally anhydrous minerals (NAMs) diffuse slightly slower than protons by the Knudsen limit of 2, whereas here we report deuteron diffusion is about 3∼ 7 times faster than proton one in Mg 2 SiO 4 wadsleyite based on the HD interdiffusion couple experiments using a pair of wadsleyite single crystal at 16 GPa and 900-1300 K. Our results indicate hydrogen diffusion in wadsleyite is affected by multiple diffusion mechanisms, of which, proton (deuteron) migrating along interstitial defects is particularly efficient to separate hydrogen isotopes in crystalline network probably owing to a quantum sieving effect. The resulting diffusion-driven H/D fractionation can explain common observations of deuterium depletion of NAMs in mantle xenoliths, suggesting that MORB inclusions hosted in xenoliths are more reliable for indicating the hydrogen isotope composition of the mantle rather than the xenolithic NAMs.