Characterization of diverse origins for orthopyroxene in ultramafic rocks

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Some upper mantle peridotites have recently been found to be strongly enriched in orthopyroxene due to interaction of silica-rich melt with surrounding mantle. Additionally, some eclogite xenoliths from Archaean Cratons have lost a silica-rich melt fraction. Recent findings on Kaapvaal Craton peridotite xenoliths point towards different orthopyroxene trace element compositions in peridotite which previously experienced high degree partial melting and orthopyroxene crystallization due to reaction with silica-rich metasomatic melts. This project will examine naturally occurring peridotitic orthopyroxene from different petrogenetic settings. Differences in the trace element composition of orthopyroxene with different petrogenetic histories (e.g. residues after melt depletion, reaction of peridotite with subduction-related melt or cumulate crystallization) will help understanding the process of silica enrichment of the upper mantle. Additionally, preliminary high pressure and high temperature experiments will be conducted analysing the behaviour of trace elements in orthopyroxene during partial melting and melt/rock interactions.