Influence of intracrystalline deformation on chemical diffusion in garnet around coesite inclusions

Coesite inclusions in garnets are emblematic observations, typical of Ultra-High-Pressure (UHP) rocks.  While small inclusions may fully preserve coesite, sufficiently large inclusions undergo partial transition of coesite to quartz. Here, we focus on samples from UHP rocks from Dora Maira Massif (Western Alps). Classical petrographic analysis indeed reveals the coexistence of quartz and coesite as well as deformation of the surrounding garnet (radial fractures). In addition, microprobe analysis further shows chemical zoning in garnet around partially transformed inclusions. This observation suggests a link between chemical zoning and deformation related to the phase transition. Such an observation provides a unique opportunity to investigate the relation between multi-component diffusion and garnet deformation using both microprobe analysis and quantitative modelling.