Heterogeneous Nucleation as a Mechanism for Igneous Cumulate Formation without Buoyancy

Lydéric France

Journal of Petrology, Volume 67, Issue 9, September 2026, egag073

Voir en ligne : https://doi.org/10.1093/petrology/egag073

Cumulate rocks are generally interpreted as the products of crystal-melt segregation driven by buoyancy-related processes such as crystal settling, mush compaction, or melt percolation. Yet, the potential role of crystal nucleation processes in generating early crystal-melt heterogeneities remains largely unexplored. Here, I show that heterogeneous nucleation may constitute an efficient mechanism for crystal-melt segregation during the early stages of magma solidification. To isolate this effect, a simplified numerical model of magma solidification is coupled with a thermodynamic differentiation model of a mid-ocean ridge basalt magma using Rhyolite-MELTS and temperature- and composition-dependent partition coefficients. The results indicate that heterogeneous nucleation promotes crystal clustering and generates melt-rich and melt-poor domains within the solidifying magma. Even in the absence of buoyancy-driven processes, melt-poor domains may acquire bulk compositions depleted in incompatible elements and thus display rare earth element patterns characteristic of igneous cumulates. These results suggest that heterogeneous nucleation may represent an efficient, buoyancy-independent mechanism for crystal-melt segregation and may partly control the early architecture of crystal mushes and their subsequent differentiation.