Fe-Mn interdiffusion in aluminosilicate garnets

Precise determination of cation diffusivity in garnet can provide critical information for quantitatively understanding the timescales and thermodynamics of various geological processes, but very few studies have been performed for Fe-Mn interdiffusion. In this study, Fe-Mn interdiffusion rates in natural single crystals of Mn-bearing garnet with 750 ppm H2O are determined at 6 GPa and 1273-1573 K in a Kawai-type multi-anvil apparatus. Diffusion profiles were acquired by electron microprobe and fitted using Boltzmann-Matano equation. The experimental results show that the Fe-Mn interdiffusion coefficient (DFe-Mn) slightly decreases with increasing XFe. The experimentally determined DFe-Mn in Mn-bearing garnet can be fitted by the Arrhenius equation: DFe ⠁Mn m2/s � � 1/4 D0XFen exp o ⠁E ⠃/RT thorn , where E ⠃ 1/4 o 1 ⠁ XFe thorn E ⠃Mn thorn XFeE ⠃Fe, D0 = 8:06 thorn 9:87 ⠁6:04 ⠄ 10 ⠁9 m2/s, E ⠃Mn 1/4 248 ⠅ 27 kJ/mol, E ⠃Fe 1/4 226 ⠅ 59 kJ/mol, n = ⠁1.36 +/- 0.51. The comparing the present results with previous experimental data suggest that water can greatly enhance the DFe-Mn in garnet. Our results indicate that the time required for homogenization of the compositional zoning of a garnet is much shorter than previously thought.@2023 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study determines the Fe-Mn interdiffusion rates in natural Mn-bearing garnet crystals with 750 ppm H2O using an experimental approach. The results show that the Fe-Mn interdiffusion coefficient slightly decreases with increasing Fe content, and water significantly enhances the Fe-Mn interdiffusion in garnet. These findings suggest that the time required for homogenization of the compositional zoning of a garnet is much shorter than previously thought.