A RE-OS ISOTOPE STUDY OF ULTRAMAFIC XENOLITHS FROM THE MATSOKU KIMBERLITE

Abstract

Ultramafic xenoliths erupted within the Matsoku kimberlite pipe display a range of petrographic features that have been interpreted as the products of melt injection or infiltration and metasomatic processes. We have analysed Re and Os concentrations and the Os isotope composition of these samples with the aim of investigating how such processes affect the Re—Os system. In particular, we have focused on the relationships between: (1) veins, dykes and sheets, that are thought to record melt injection or infiltration processes; (2) the coarse peridotite wallrocks to the veins, dykes and sheets, which usually do not show modal metasomatism but have been affected by low-volume melt infiltration; and (3) common coarse peridoties which show little, if any, evidence of modal metasomatism or melt infiltration.