Unmasking xenolithic eclogites: Progressive metasomatism of a key Roberts Victor sample

Most eclogite xenoliths from the Roberts Victor kimberlite in South Africa have been altered by melts and fluids along the carbonatitic–kimberlitic spectrum. This study aims to delineate a progressive metasomatic process observed in one specific sample (RV07-17) through the use of petrography, major and trace element compositions, and isotopic analysis of strontium and oxygen. The research recognizes several metasomatic stages, identifying four distinct zones based on garnet compositions. Transitioning from Zone 1 to Zone 4 reveals a decrease in microstructural equilibrium and an increase in secondary minerals and fluid inclusions, along with higher pyrope content and magnesium enrichment in clinopyroxene. The garnets display varied Rare Earth Element (REE) patterns, with notable changes in light and middle REE concentrations. Additionally, isotopic analyses indicate a rise in 87Sr/86Sr ratios alongside increasing strontium concentration, while 18O values in garnet decrease. This indicates that the fluids involved in metasomatism were more carbonatitic than kimberlitic. The findings suggest significant alteration of the original compositional data in the xenolith, obscuring its protolith origin.