Abstract Hydrogen concentration profiles through olivine and pyroxene in peridotite xenoliths carried in rift basalts from northern Tanzania (Lashaine, Eledoi, and Kisite localities) show bell-shaped distributions, indicating that diffusive hydrogen loss has occurred in all minerals. Homogeneous major element concentrations and equilibration of hydrogen between the cores of olivine and coexisting pyroxene suggest that hydrogen loss resulted from diffusive degassing during host magma emplacement. For these samples, hydrogen diffusivities in olivine and coexisting pyroxene must be within the same order of magnitude, similar to experimentally determined diffusivities, but in contrast to previous observations made on xenolithic peridotites. We demonstrate here, for the first time using natural samples, that significant differences in activation energy is likely the primary parameter that causes the discrepancy between hydrogen diffusion in olivine and pyroxene observed in different suites of mantle xenoliths. Because hydrogen diffuses faster in olivine than in pyroxene as temperature increases, hydrogen loss in the Tanzanian mantle xenoliths must have occurred at relatively low temperatures (∼750 to ∼900 °C), whereas hydrogen loss observed in previous xenolith studies likely occurred at higher temperatures (∼950 to >1200 °C). Thus, the diffusive loss of hydrogen in the Tanzanian mantle xenoliths may have occurred at shallow depths or at the Earth’s surface.

中文翻译：

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调和捕虏体侵位过程中地幔橄榄石和辉石脱水率之间的差异

摘要 来自坦桑尼亚北部（Lashaine、Eledoi 和 Kisite 地区）的裂谷玄武岩中橄榄石和辉石的氢浓度分布显示出钟形分布，表明所有矿物都发生了扩散性氢损失。橄榄石和共存辉石核心之间的均匀主要元素浓度和氢平衡表明，氢损失是由宿主岩浆侵位过程中的扩散脱气造成的。对于这些样品，橄榄石和共存辉石中的氢扩散率必须在同一数量级内，与实验确定的扩散率相似，但与先前对捕虏橄榄岩的观察结果形成对比。我们在这里首次使用自然样本进行演示，活化能的显着差异可能是导致在不同地幔包体中观察到的橄榄石和辉石中氢扩散差异的主要参数。由于随着温度升高，氢在橄榄石中的扩散速度比在辉石中的扩散速度快，坦桑尼亚地幔包体中的氢损失一定发生在相对较低的温度（~750 至 900 °C），而在先前的包体研究中观察到的氢损失可能发生在较高温度下（～950 至 >1200 °C）。因此，坦桑尼亚地幔包体中氢的扩散损失可能发生在浅层或地球表面。由于随着温度升高，氢在橄榄石中的扩散速度比在辉石中的扩散速度快，坦桑尼亚地幔包体中的氢损失一定发生在相对较低的温度（~750 至 900 °C），而在先前的包体研究中观察到的氢损失可能发生在较高温度下（～950 至 >1200 °C）。因此，坦桑尼亚地幔包体中氢的扩散损失可能发生在浅层或地球表面。由于随着温度升高，氢在橄榄石中的扩散速度比在辉石中的扩散速度快，坦桑尼亚地幔包体中的氢损失一定发生在相对较低的温度（~750 至 900 °C），而在先前的包体研究中观察到的氢损失可能发生在较高温度下（～950 至 >1200 °C）。因此，坦桑尼亚地幔包体中氢的扩散损失可能发生在浅层或地球表面。