Hydrogen is a rapidly diffusing monovalent cation in nominally anhydrous minerals (NAMs, such as olivine, orthopyroxene, and clinopyroxene), which is potentially re-equilibrated during silicate melt-rock and aqueous fluid-rock interactions in massif and abyssal peridotites. We apply a 3D numerical diffusion modeling technique to provide first-order timescales of complete hydrogen re-equilibration in olivine, clinopyroxene, and orthopyroxene over the temperature range 600–1200 °C. Model crystals are 1–3 mm along the c-axis and utilize H+ diffusion coefficients appropriate for Fe-bearing systems. Two sets of models were run with different boundary compositions: (1) “low-H models” are constrained by mineral-melt equilibrium partitioning with a basaltic melt that has 0.75 wt% H2O, and (2) “high-H models,” which utilize the upper end of the estimated range of mantle water solubility for each phase. Both sets of models yield re-equilibration timescales that are identical and are fast for all phases at a given temperature. These timescales have strong log-linear trends as a function of temperature (R2 from 0.97 to 0.99) that can be used to calculate the expected re-equilibration time at a given temperature and grain size. At the high end of the model temperatures (1000–1200 °C), H+ completely re-equilibrates in olivine, orthopyroxene, and clinopyroxene within minutes to hours, consistent with previous studies. These short timescales indicate that xenolith NAM mantle water contents are likely to be overprinted prior to eruption. The models also resolve the decoupled water-trace element relationship in Southwest Indian Ridge peridotites, in which peridotite REE abundances are reproduced by partial melting models whereas the relatively high NAM H2O contents require later re-equilibration with melt.At temperatures of 600–800 °C, which correspond to conditions of hydrothermal alteration of pyroxene to amphibole and talc, H+ re-equilibration typically occurs over a range of timescales spanning days to years. These durations are well within existing estimates for the duration of fluid flow in oceanic hydrothermal systems, suggesting that peridotite NAM water contents are susceptible to diffusive overprinting during higher temperature hydrothermal alteration. Thus, diffusion during aqueous fluid-rock interactions may also explain NAM H2O contents that are too high to reflect residues of melting. These relatively short timescales at low temperatures suggest that the origin of water contents measured in peridotite NAMs requires additional constraints on sample petrogenesis, including petro-graphic and trace element analyses. Our 3D model results also hint that H+ may diffuse appreciably during peridotite serpentinization, but diffusion coefficients at low temperature are unconstrained and additional experimental investigations are needed.

中文翻译：

---

水相流体-岩石和硅酸盐熔体-岩石相互作用可能重新平衡橄榄岩名义上无水矿物中的氢

氢是名义上无水矿物（NAM，如橄榄石，邻比邻苯和斜向比邻苯）中快速扩散的单价阳离子，在地层和深渊橄榄岩中的硅酸盐熔体-岩石和含水流体-岩石相互作用期间，氢可能会重新平衡。我们应用3D数值扩散建模技术，在600-1200°C的温度范围内，提供橄榄石，斜辉石和邻辉石中氢完全重新平衡的一阶时间尺度。模型晶体沿c轴为1-3 mm，并利用适用于含铁系统的H +扩散系数。两组模型具有不同的边界成分：（1）“低-H模型”受矿物熔体平衡分配的约束，其中玄武岩熔体的H2O含量为0.75 wt％，（2）“高-H模型” ”，利用每个阶段的地幔水溶性估算范围的上限。两组模型都产生相同的重新平衡时间尺度，并且在给定温度下对于所有相都是快速的。这些时标具有随温度变化的强对数线性趋势（R2从0.97至0.99），可用于计算在给定温度和晶粒尺寸下的预期重新平衡时间。与以前的研究一致，在模型温度的上限（1000–1200°C）下，H +在几分钟至几小时内即可完全重新平衡于橄榄石，邻苯二茂铁和clinopyroxene中。这些短的时间尺度表明，在喷发之前，异种石的NAM地幔水含量可能会被套印。这些模型还解决了西南印度洋橄榄岩橄榄岩中水元素与微量元素的解耦关系，其中通过部分熔融模型再现橄榄岩的REE丰度，而相对较高的NAM H2O含量则需要随后与熔体重新平衡。在600-800°C的温度下，这对应于辉石将水热转变为闪石和滑石的条件，H +重新平衡通常发生在几天到几年的时间范围内。这些持续时间完全在海洋热液系统中流体流动持续时间的现有估计范围内，这表明橄榄岩NAM的水含量在高温热液蚀变过程中易受扩散套印的影响。因此，在水-岩石相互作用中的扩散也可能解释了NAM H2O含量太高而无法反映熔融残留物。这些在低温下相对较短的时间尺度表明，在橄榄岩NAM中测得的水的来源要求对样品的成岩作用有更多的限制，包括岩相图和痕量元素分析。我们的3D模型结果还暗示，在橄榄岩蛇纹石化过程中，H +可能会扩散，但是低温下的扩散系数不受限制，还需要进行其他实验研究。