Fast REE re-distribution in mantle clinopyroxene via reactive melt infiltration

Abstract

Melt-mineral interactions may strongly affect the mineralogy and chemistry of the upper mantle. Although the grain-scale processes governing the interaction have been theoretically investigated, the efficiency of melt-rock reaction in re-distributing trace elements in mantle clinopyroxene still remains to be experimentally evaluated. We performed high pressure reaction experiments at 1–2 GPa, 1200–1350 °C, on homogeneous mixtures of LREE-depleted clinopyroxene, San Carlos olivine and an Enriched-MORB glass. Melt-peridotite reaction leads to textural replacement of mantle clinopyroxene by dissolution and precipitation as a function of temperature and run duration. Experimental results indicate that rapid modification of the REE signature of mantle clinopyroxene occurs not only via dissolution and precipitation but even via trace element diffusion within unreacted crystal relicts. The extent of reacted melt crystallisation influences the REE fractionation in modified clinopyroxene. Aided by a high reaction rate, local chemical equilibrium between clinopyroxene and melt can be approached even at the time scale of the experiments. Results from this study demonstrate that infiltration of REE-enriched melt within a mantle peridotite is capable of completely resetting the pristine trace element budget of mantle clinopyroxene.