Abstract

‘The compositional zoning exhibited by many metamorphic minerals serves as a time-resolved record of processes occurring during mineral growth and diffusive relaxation. In garnet derived from a global suite of subduction zones, oscillatory elemental zoning—rhythmic cycles of peaks and troughs in concentration—is commonly observed. This zoning may therefore reflect a fundamental dynamic or petrogenetic process operating during garnet crystallization in the subducting slab.

‘In this talk I will explore the origins of these geochemical patterns. In particular, I will present data that elucidates the potential for fluid buffering during mineral growth and discuss the record of mass transfer and equilibration preserved in garnet. Our findings suggest multiple mechanisms of chemical/mass transfer operate at the grain and rock scale during subduction, but are unable to account for the elemental oscillations, which may instead form in response to externally triggered changes in solubility or fluid pressure.’