Phosphorus zoning reveals dendritic architecture of olivine

The texture and composition of igneous minerals are unique recorders of the temperature, pressure, and composition of magma reservoirs, conduits, and lava flows. Decoding this information is predicated on the idea that magmatic crystals grow in a concentric pattern, and that any deviation from this model (such as anhedral crystal morphologies and complex chemical zoning) is the consequence of extrinsic processes such as magma mixing, dissolution, or deformation. Our analysis of the spatial distribution patterns of slowly diffusing impurities (phosphorus, aluminum) in volcanic, plutonic, and experimental olivine crystals reveals, however, that the crystallization record is not a straightforward time progression from crystal core to rim. We propose here an internal dendrite hypothesis that unites diverse manifestations of thermodynamic disequilibrium crystallization, and may be fundamental to interpreting chemical stratigraphy, subgrain domain structures, and the formation of melt inclusions within olivine.