Rutile_zircon_melt assemblages, key to understand processes in mafic layered intrusions: examples from the Bushveld Complex, South Africa

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This study focus on the systematic investigation of rutile, zircon, and associated melt inclusions in rocks of the Rustenburg Layered Suite (RLS) of the Bushveld Complex, and a related satellite intrusion (Uitkomst magma conduit) with the aim to understand the systematics of the formation and composition of these assemblages in (ultra)mafic rocks, and to obtain new information about processes during magma chamber evolution. This comprises information about the source(s) and composition(s) of the parental magma(s), and physical-chemical conditions (P-T-X-t-cooling rates) during crystallisation from the earliest cumulus crystallisation (reflected by rutile-melt inclusions in chromite), to the very late intra-cumulus melt stage (reflected by rutile-zircon pairs and related melt inclusions in zircon). In addition, zircon and rutile from contact metamorphic rocks will be studied, in order to gain information about fluid induced HFSE-mobilization and -homogenization due to Bushveld heating, and about a possible uptake of these elements into the RLS. In this respect zircon and rutile will be investigated for their textural context, zoning patterns, trace element compositions, mineral inclusions, and U-Pb-Hf-O isotopes. Melt inclusions in zircon, and rutile-bearing melt inclusions in chromite will additionally be studied in order to quantify melt fractionation during RLS crystallisation, and to estimate partitioning coefficients between zircon, rutile and melt.