Element Partitioning and Li‐O Isotope Fractionation Between Silicate Minerals and Crustal‐Derived Carbonatites and Their Implications

Abstract

AbstractIn order to investigate element partitioning and Li‐O isotope fractionation between silicate minerals and carbonatite melts at variable levels from mantle to crust, we document elemental and Li‐O isotopic data for major minerals from crust‐derived carbonatites at Eppawala, Sri Lanka. Partition coefficients (D) of elements between olivine or clinopyroxene and carbonatite melts are consequently estimated. The estimated D values indicate that Li, Zn, Co, Cr, Mn, and Ni behave compatibly in olivine, while P and Sc are slightly compatible, and V and Al are mildly incompatible. Partition coefficients of elements between clinopyroxene and carbonatite melts are defined here, including highly compatible Li, Sc, Ti, V, Al, and Na, moderately compatible Zn, Co, Cr, and Ga, and incompatible Mn, Ni, P, and Cu. They are systematically higher than literature values obtained from mantle conditions, but their relative compatibilities at different systems are consistent. This indicates that element partitioning between silicates and carbonatite melts is highly temperature‐ and pressure‐dependent and can be used to evaluate geochemical proxies of carbonatite metasomatism, and evolution and mineralization of carbonatite melts. Profile analyses on olivine grains reveal that Fe‐loving elements in olivine could well preserve features of crystal growth and modal metasomatic interaction, while Li and O isotope fractionations are strongly controlled by element diffusion and Li isotopes are robust indicators of cryptic metasomatic interaction.