###### Abstract  
Dynamic metasomatism experiments were performed by reacting a lamproite melt with garnet peridotite by drawing melt through the peridotite into a vitreous carbon melt trap, ensuring the flow of melt through the peridotite and facilitating analysis of the melt. Pressure (2-3 GPa) and temperature (1050-1125 \({}^{\circ}\)C) conditions were chosen where the lamproite was molten but the peridotite was not. Phologoptic was formed and garnet and orthopyroxene reacted out, resulting in phylogenite wechrite (2 GPa) and phylogenite harzburtige (3 GPa). Phologopites in the peridotite have higher Mg/(Mg + Fe) and Cr\({}_{2}\)O\({}_{3}\) and lower TiO\({}_{2}\) than in the lamproite due to buffering by peridotite minerals, with Cr\({}_{2}\)O\({}_{3}\) from the elimination of garnet. Compositional trends in phlogopites in the peridotite are similar to those in natural garnet peridotite xenoliths in kimberlites. Changes in melt composition resulting from the reaction show decreased TiO\({}_{2}\) and increased Cr\({}_{2}\)O\({}_{3}\) and Mg/(Mg + Fe). The loss of phlogoptic components during migration through the peridotite results in low K\({}_{2}\)O/Na\({}_{2}\)O and K/Al in melts, indicating that chemical characteristics of lamproites are lost through reaction with peridotite so that emerging melts would be less extreme in composition. This indicates that lamproites are unlikely to be derived from a source rich in peridotite, and more likely originate in a source dominated by phlogopite-rich hydrous pyroxenites. Phlogopites from an experiment in which lamproite and peridotite were intimately mixed before the experiment did not produce the same phlogopite compositions, showing that care must be taken in the design of reaction experiments. reaction experiments; mantle metasomatism; peridotite; lamproite; phlogopite Article  
Dynamic Metasomatism Experiments Investigating the Interaction between Migrating Potassium Melt and Garnet Peridotite  
105 October 2021  
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to the conclusion that the melts were rich in potassium, with most favouring a lamproitic or orangeitic composition [10; 11]. The origin of orangeites (formerly Group II kimberlites; [12]) is the subject of renewed debate as these are more potassic than kimberlites, occur in the same craton as most MARID xenoliths, and are suggested by some to be the carbonate-rich equivalent of lamproites [13]. Interactions of more than one type of potassic melt with peridotite may thus be relevant to the formation of hydrous minerals during re-enrichment. We refer to the process of re-enrichment by reaction with passing melts as dynamic metasomatism, deliberately choosing the qualifier \"dynamic\" to emphasize that reactions are not static, but involve the flow of melt through the peridotite, with reaction products incorporating chemical components from both the melt and the host rock. In the case of crystallization in channels, dynamic metasomatism also occurs at the initial margins of veins and dykes, as seen, for example, in Ligurian periodites [14], whereas later crystallization in the centre of veins may simply correspond to igneous fractionation from a moving melt. The process of dynamic metasomatism has almost universally been studied in natural rocks but has received little attention in high-pressure experiments. Odling [15; 16] tested reactions between depleted periodtites and fluids and kimberlitic melts, finding mica and amphibole to be products of reaction with kimberlitic melt [16], whereas abundant alkali amphibole and less phlogopite were produced from reactions with a water-rich COH fluid [15]. These experiments used long capsules and a temperature gradient to drive melt migration. Here, we investigate reactions between peridotite and a lamproitic melt--another commonly invoked metasomatic agent--using a melt trap to draw the melt through the peridotite.