An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts

Abstract

The central portions of garnet porphyroblasts from Harpswell Neck, Maine, exhibit small discrete regions of high Mn content, dispersed in three dimensions. Orientation contrast imaging (OCI) and quantitative crystallographic orientation measurements from electron backscatter diffraction (EBSD) patterns show that most garnet porphyroblasts contain no variations in crystallographic orientation. It is difficult to reconcile these data with a model in which each high-Mn region represents a discrete garnet nucleus.