## 4 Discussion  
### Reaction Experiment Design  
Reaction experiments have been used increasingly over the last ten years to study hybridization reactions between melts and rocks they pass through, mostly peridotites. One of two methods are usually used: either (i) two rocks (or powdered rocks) are placed in capsules as separate blocks or cylinders with a sharp boundary between them similar to the layered configuration used here (\"reaction experiments\" using the terminology of [PERSON] and [PERSON] [30]; or (ii) the two powdered rocks are intimately mixed in different proportions (\"mixed experiments\" in [30]). Layered experiments have been used to assess hybridization by a variety of melts from clastic sedimentary or carbonate-rich through basalt to granite [22; 23; 31; 32; 33; 34; 35; 36; 37]. A similar array of melts has been studied with the mixing of the two reactant rocks [38; 39; 40; 41], but few studies have used both methods to compare them. Of these, the experiments of [30] compared mineral compositions using the two methods, concluding that they were the same and that the homogenized mixtures were, therefore, useful to study minerals in thin reaction layers in layered experiments where the formation of new minerals had created a barrier to melt flow. Experiment G141 was conducted with a homogenized mixture of lamproite and garnet lherzolite in the same ratio as the layered experiment (Table 1) in order to compare results to those from experiments with the layered run charges. This experiment was also run at the same pressure and temperature as the time series experiments. In Figure 7, the compositions of the phlogopites from this experiment are compared to those in layered experiment G131, which had the most similar experiment duration (58 vs. 72 h). Figure 7 shows that the phlogopites from the experiment with the homogenised starting materials are distinct from those in both the peridotite layer and the lamproite residue from Experiment G131: they have low TiO\({}_{2}\) resembling those in the peridotite layer, but high SiO\({}_{2}\) characteristic of those in the lamproite residue. The difference to earlier experimental studies in which similar mineral compositions were found in layered and mixed experiments lies in the inclusion of the carbon melt trap, which has effectively removed the melt components from the reacting system, creating a \"flow-through\" scenario: the phlogopites in the peridotite layer mimick the reaction products from a flowing melt that is no longer present in the system. The use of melt traps has had a chequered history since its introduction to separate fluids and melts from rock matrices to optimize chemical analysis [20; 42; 43]. Tests have shown that the melt compositions in traps may correspond to  
Figure 7: Comparison of phlogopite compositions in layered experiment G131 (green squares) to those in homogenized experiment G141 (both experiments were conducted at 3 GPa, 1100 \({}^{\circ}\)C). This shows that minerals from experiments in which lamproite and peridotite are mixed before the experiment (G141) are not equivalent to reaction products in the peridotite section of layered runs. lower pressures than the nominal experimental pressure due to the initial pore space in the traps [19], but that this can be circumvented by ensuring that the volume of the pore space in the trap is exceeded by the volume of melt, facilitating continued chemical communication and thus equilibrium [44]. However, the extraction traps in our experiments were included to serve as a suction pump to assure sufficient reaction of the lamproite melt during complete passage through the peridotite section, rather than to assess equilibrium melt compositions. Nevertheless, the melt compositions in the melt traps may approach equilibrium, as the volume of the pore space is estimated to be only 1-1.5% of the original volume of lamproite melt in the whole experiment.