Knowledge of oxygen diffusion in garnet is crucial for a correct interpretation of oxygen isotope signatures in natural samples. A series of experiments was undertaken to determine the diffusivity of oxygen in garnet, which remains poorly constrained. The first suite included high-pressure (HP), nominally dry experiments performed in piston-cylinder apparatus at: (1) T = 1050–1600 °C and P = 1.5 GPa and (2) T = 1500 °C and P = 2.5 GPa using yttrium aluminum garnet (YAG; Y3Al5O12) cubes. Second, HP H2O-saturated experiments were conducted at T = 900 °C and P = 1.0–1.5 GPa, wherein YAG crystals were packed into a YAG + Corundum powder, along with 18O-enriched H2O. Third, 1 atm experiments with YAG cubes were performed in a gas-mixing furnace at T = 1500–1600 °C under Ar flux. Finally, an experiment at T = 900 °C and P = 1.0 GPa was done using a pyrope cube embedded into pyrope powder and 18O-enriched H2O. Experiments using grossular were not successful.for the fast pathway. We interpret the two pathways as representing diffusion following vacancy and inter-stitial mechanisms, respectively. Regardless, our new data suggest that the slow mechanism is prevalent in garnet with natural compositions, and thus is likely to control the retentivity of oxygen isotopic signatures in natural samples.The diffusivity of oxygen is similar to Fe-Mn diffusivity in garnet at 1000–1100 °C and Ca diffusivity at 850 °C. However, the activation energy for O diffusion is larger, leading to lower diffusivities at P-T conditions characterizing crustal metamorphism. Therefore, original O isotopic signatures can be retained in garnets showing major element zoning partially re-equilibrated by diffusion, with the uncertainty caveat of extrapolating the experimental data to lower temperature conditions.

中文翻译：

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石榴石中的氧扩散：变质过程时间尺度和原始 O 同位素特征保留的实验校准和影响

石榴石中氧扩散的知识对于正确解释天然样品中的氧同位素特征至关重要。进行了一系列实验来确定石榴石中氧的扩散率，但仍然受到很差的约束。第一组包括在活塞缸装置中进行的高压 (HP) 标称干燥实验：(1) T = 1050–1600 °C 和 P = 1.5 GPa 和 (2) T = 1500 °C 和 P = 2.5 GPa 使用钇铝石榴石 (YAG; Y3Al5O12) 立方体。其次，在 T = 900 °C 和 P = 1.0-1.5 GPa 条件下进行 HP H2O 饱和实验，其中 YAG 晶体与富含 18O 的 H2O 一起装入 YAG + 刚玉粉末中。第三，在 T = 1500–1600 °C 的气体混合炉中，在 Ar 通量下对 YAG 立方体进行 1 个大气压的实验。最后，在 T = 900 °C 和 P = 1 下进行实验。使用嵌入镁铝榴石粉末和富含 18O 的 H2O 中的镁铝榴石立方体完成 0 GPa。使用毛囊素的实验没有成功。对于快速途径。我们将这两种途径解释为分别代表空位和间隙机制后的扩散。无论如何，我们的新数据表明缓慢机制在天然成分的石榴石中普遍存在，因此很可能控制天然样品中氧同位素特征的保持性。氧的扩散率类似于 1000– 石榴石中的铁锰扩散率1100 °C 和 850 °C 时的 Ca 扩散率。然而，O 扩散的活化能较大，导致在表征地壳变质作用的 PT 条件下的扩散率较低。所以，