Zircon crystallization in low-Zr mafic magmas: Possible or impossible?

Zircon is a ubiquitous accessory phase that carries important isotopic and geochemical information. Experimental work indicates that zircon solubility in silicate melts increases exponentially with decreasing silica; accordingly, crystallizing mafic magmas would only precipitate zircon from the last drops of residual melts, likely of granophyric composition. However, this view is inconsistent with the abundance of syn-magmatic zircons in many mafic rocks, in which zircon often occupies textural positions compatible with early crystallization. Given that factors other than temperature and magma composition negligibly affect the solubility of zircon, its precipitation from mafic magmas must involve the formation of small zircon-saturated transient zones. Here we explored that possibility using 2D finite elements to model the crystallization of MORB melts confined in pores. We found that zircon-saturated volumes may form locally at the growing mineral-melt interfaces if the growth rate of a low KdZr mineral (