## 4 Discussion
### Applications to Mantle Metasomatism
#### 4.3.2 Reactivity of Different Alkaline Melts with Peridotite  
There are a range of melts that may be involved in the metasomatic process when they infiltrate peridotites, and these melts should produce different mineralogical assemblages. Current summaries of metasomatic types in peridotites of the Kaapvaal C ration in South Africa recognize principally two types of phlogopite-bearing assemblages, known as MARID (mica-amphibole-rutile-ilmenite-diopside) and PIC (phlogopite-ilmenite-clinoproxene) [9; 53], although other minor types (e.g., IRPS; [51]) may have been neglected. Candidates for melt types for cratonic processes include kimberlite, orangeite (formerly Group II kimberlite), lamproite, as well as carbonate-rich melts such as carbonates and carbonated silicate melts with <30 wt% SiO\({}_{2}\) that are recognized as potential metasomatic agents from high-pressure experiments more than from natural rocks [56; 57].  
The formation of PIC and MARID xenolith suites has been assigned to interaction with kimberlites and orangeite melts, respectively [9]. However, orangeites and lamproites may be related, although the exact relationship is currently uncertain. Some refer to them as carbonate-rich lamproites [13; 58], a Kaapvaal equivalent of carbonate-poor lamproites elsewhere that have been shown to originate in reduced source regions where carbonate would not be stable [24; 59]. This mode of origin also occurs in eastern Zambia [60].  
Few studies that produced phlogopites from the reaction between melts and peridotite are available for comparison with our experimental results. Odling [16] reacted kimberlite melts (25 wt% SiO\({}_{2}\), 5.9 wt% CO\({}_{2}\), 6.5 wt% H\({}_{2}\)O) with harzburgeite in experiments with a temperature gradient, finding interstitial phlogopite and glass coexisting with olivine+Cpx+Sp at high temperatures, which transitioned to Ol+Cpx+Phl and were joined by orthopyroxene and finally K-richterite at a lower temperature. [PERSON] et al. [53] studied the interaction of a synthetic potassic carbonate (0% SiO\({}_{2}\), 35-44 wt% CO\({}_{2}\), 8.1-11.6 wt% H\({}_{2}\)O, 0-4.9 wt% Na\({}_{2}\)O) mixed at different proportions with peridotite, finding K-richterite in addition to phlogopite and carbonates, but only if Na\({}_{2}\)O-bearing carbonatite melts were used. Other experiments using dry carbonatite or carbonated silicate melts and peridotite did not produce phlogopite [37].  
[PERSON] et al. [53] confirmed the observation that Cr\({}_{2}\)O\({}_{3}\) in phlogopite is highest where garnet was consumed, implying a similar interpretation for the natural phlogopites of [4] but involving a carbonatite melt in contrast to our CO\({}_{2}\)-free lamproite melt. K-richterite was found as a product of reaction with kimberlite [16] and carbonatite [53] but not in our experiments with lamproitic melt, which is noteworthy since K-richterite occurs in lamproites but not in kimberlites or carbonates. The phlogopites in all three studies of reaction experiments are enriched in Cr\({}_{2}\)O\({}_{3}\) (Figure 8; [PERSON]'s single analysis had 1.51 wt%), whereas there is a small but distinct difference in TiO\({}_{2}\). Those in the current experiments have 1.07-1.26 wt % TiO\({}_{2}\) presumably due to the high TiO\({}_{2}\) in the lamproite, whereas those resulting from reaction with carbonatite have an average of 0.61 wt% and with kimberlite 0.21 wt%. This difference, together with any inclusions of Cr-spinel or especially carbonates, as in the experiments of [53], may prove critical in deciding which melt type drove the metasomatic reactions in natural rocks.