EXPERIMENTAL CHARACTERIZATION OF MGO DIFFUSION DURING OLIVINE DISSOLUTION IN A HYDROUS BASALTIC MELT

Olivine dissolution in silicate melts and glasses has been documented in numerous experimental works. Most of our knowledge is based on published diffusion data that are generally applicable to dry systems¹. However, these data may not be entirely appropriate to use for H₂O-bearing magmas, and yet such diffusivities have not been characterized before. In this project, we conducted piston-cylinder experiments at 1125-1550°C and 1.0 GPa to quantify olivine dissolution induced by MgO-diffusion into a hydrous basaltic melt. We measured concentration profiles via electron microprobe analysis to determine the MgO wt. % and olivine dissolution distance (µm) in each of our experimental glasses. We performed FTIR analysis on some samples to constrain the H₂O concentration in the glasses. We estimated the diffusion coefficient of MgO (D_MgO) by using semi-infinite solution approaches and forward modeling. D_MgO showed Arrhenian relation with temperature and enhancement of diffusivity in the presence of H₂O—that is, D_MgO increases with increasing temperature and increasing H₂O content. This study provides a new data set of MgO diffusivities in hydrous settings. These data may have significant applications when used in models that seek to understand time scales and derive thermal histories recorded by arc basalt systems.

¹Chen, Y. and Zhang, Y. (2008) Geochim Cosmochim Acta 72, 4756-4777.