Abstract

It is well established that the cratonic lithospheric mantle formed as a residue of extensive mantle melting during the Archaean. However, an unexpected feature of peridotite xenoliths from the cratonic lithosphere is that they exhibit silica contents that extend both above and below that expected after simple peridotite melting, implying a role for open system processes. High-silica peridotites, rich in orthopyroxene, are commonly found in the Kaapvaal and Siberian cratons, whereas low-silica samples, such as those from parts of Greenland and Tanzania contain anomalously high olivine. Komatiites are produced by advanced peridotite melting and predominantly erupted during the Archean, observations that appear to compliment the highly refractory nature of Archean peridotites. However, a simple melt-residue relationship is undermined by observations that both komatiite and cratonic peridotite have depleted initial Hf-isotope compositions. Using insights from petrology, thermodynamic modelling, geochemistry and high pressure experiments, this talk will investigate the conditions of silica enrichment and discuss a potential role for komatiite-peridotite interaction.