## 4 Discussion
### Melt Compositions before and after Reaction with Peridotite  
The time-series experiments G138 (24 h), G131 (58 h) and G137 (132 h) had similar proportions of lamproite, peridotite and carbon traps in the starting materials and the melt compositions in the traps are broadly similar but show some significant inhomogeneities between melt pools. [PERSON] and [PERSON] [20] noted that the SiO\({}_{2}\) content of melt in the extraction trap decreased in experiments with long durations, whereas the Al\({}_{2}\)O\({}_{3}\) content increased. This could be the result of initial high-SiO\({}_{2}\) melt entering the trap first, followed by equilibration with a later melt from the rest of the run charge. This may indicate that the equilibrium concentrations of mobile elements such as alkalis or Ti should lie at the high end of the compositional variations displayed by the individual melt trap analyses (Figure 6). Ti, Na, K and Ba contents in melts in the melt trap increase with experimental duration, probably due to more extensive reaction during migration through the peridotite. In the shortest run of the time series, Opx has higher Al\({}_{2}\)O\({}_{3}\) and Cr\({}_{2}\)O\({}_{3}\) and lower FeO contents close to the carbon trap, which may be caused by the reaction with the percolating melt not having progressed as far as in the longer duration experiments.  
The main differences in melt compositions at either side of the peridotite section are that the melt in the melt traps, which is modified by reaction with peridotite, has higher Mg#, Al\({}_{2}\)O\({}_{3}\), Cr\({}_{2}\)O\({}_{3}\) and Na\({}_{2}\)O but lower K\({}_{2}\)O and BaO. These reacted melts have less variable compositions than residual melts in the former lamproite section: this may be a function of quench modification in the larger areas of the latter, whereas melts quench well to glass in the melt trap. The higher and consistent Mg# is a result of buffering by the peridotite minerals, which are volumetrically dominant in the experiments. Peridotite minerals with Mg# \(\approx\)90 seek to impose an equilibrium Mg# of 70-73 on coexisting melts: the Mg# of the lamproite flowing in is slightly lower than this and is reduced further by the formation of high-Mg# phlogopite. The peridotite, therefore, removes Fe from the melt, forming the thin Fe-rich rims seen in BSE images (Figure 2) and the resultant melt in the melt trap has a higher and consistent Mg# (Figure 6b). If the melt/rock ratio were lower (corresponding to lower temperatures close to the lamproite solidus), this process would induce freezing of the melt and thus stoppage of the metasomatic process [44]. The lower contents of K\({}_{2}\)O and BaO in the melt are due to the formation of metasomatic phlogopite, whereas the increase in Al\({}_{2}\)O\({}_{3}\) and Cr\({}_{2}\)O\({}_{3}\) is caused by the removal of garnet through reaction with the melt.  
No phosphorus-bearing mineral was found in the experiments, but the concentration of ca. 0.6 wt% in melts in the extraction traps indicates dilution by a factor of two compared to the original leucite lamproite. This degree of dilution of phosphorus may mean that the contribution of peridotite to the melt is relatively high.