## 2 Materials and Methods
### Starting Materials and Analytical Methods  
The alkaline melt is a natural lamproite from Gaussberg, eastern Antarctica, chosen because of its suitable composition and because phase relations at these pressures are known from previous studies [24; 28]. The peridotite is a natural garnet lherzolite from Jagersfontein, South Africa, which has was also used previously in experiments, commonly as mineral separates. Compositions of the rocks and the constituent minerals of the peridotite are given in Table 2.  
The melt trap consisted of 60-80 \(\upmu\)m grains of vitreous carbon (Deutsche Carbone AG, Frankfurt) and was used in preference to diamond aggregates for the melt trap since it simplifies polishing of experimental charges and quenched melts. Trace element analysis shows that the only major contaminant in the vitreous carbon is Zr (1340 ppm) with minimal amounts of Ba (18 ppm) and Rb (4.7 ppm).  
The lamproite is a glassy pillow rim sample (4891-3) of the Gaussberg lamproite with a composition close to the range given by Sheraton and Cundari ([29] Table 2). The sample was crushed and ground under acetone in an agate mortar; the resulting grain size was mostly 20-30 \(\upmu\)m with a maximum of 50 \(\upmu\)m. Previous experiments [24] show that at 2 GPa and 1125 \({}^{\circ}\)C the lamproite should be completely molten, whilst at 2 GPa and 1050 \({}^{\circ}\)C and at 3 GPa and 1100 \({}^{\circ}\)C phlogopite coexists with a large amount of melt, ensuring adequate reaction with the peridotite.  
The modal mineral composition of the J4 garnet lherzolite was estimated by XRD analysis to be 65% olivine, 15% orthopyroxene, 10% clinopyroxene and 15% garnet. The resulting calculated bulk composition of the rock and the mineral analyses are given in Table 2.  
Electron microprobe analyses of run products were obtained at Heidelberg (Cameca SX-51, Cameca, Paris, France), Utrecht (JEOL JXA 8600 Superprobe, JEOL, Tokyo, Japan) and Macquarie (Cameca SX100, Cameca, Paris, France) Universities using standard analytical procedures (15 kV, 10-20 nA) calibrated on a variety of natural and synthetic mineral standards. For phlogopites and quenched melts, the beam was defocused to 10-15 \(\upmu\)m whereas for all other minerals a focused beam (1-2 \(\upmu\)m) was used.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Starting Material**} & \multicolumn{5}{c}{**65\%**} & **15\%** & **10\%** & **10\%** & **Average** \\ \cline{2-7}  & **Gaussberg** & **J4** & **J4** & **J4** & **J4** & **J4** & **Garnet** \\ \cline{2-7}  & **Lamproite** & **Peridotite** & **Olivine** & **Opx** & **Cpx** & **Grt** & **Lherzolite** \\ \hline SiO\({}_{2}\) & 51.1 & 44.88 & 40.8 & 57.58 & 55.14 & 42.1 & 45.98 \\ TiO\({}_{2}\) & 3.3 & 0.18 & 0.03 & 0.23 & 0.49 & 0.78 & 0.09 \\ Al\({}_{2}\)O\({}_{3}\) & 10.28 & 2.56 & 0.04 & 0.98 & 2.89 & 20.93 & 1.57 \\ MgO & 7.08 & 40.89 & 48.98 & 33.94 & 18.11 & 21.51 & 43.46 \\ FeO & 6.08 & 8.56 & 9.94 & 6.08 & 4.05 & 7.81 & 6.91 \\ CaO & 4.03 & 2.19 & 0.07 & 1.02 & 15.65 & 4.25 & 1.16 \\ Na\({}_{2}\)O & 1.8 & 0.3 & 0.03 & 0.32 & 2.25 & 0.11 & 0.16 \\ K\({}_{2}\)O & 12.46 & 0.01 & 0.01 & 0.01 & 0.03 & 0.01 & 0.12 \\ Cr\({}_{2}\)O\({}_{3}\) & 0.03 & 0.34 & 0.03 & 0.21 & 0.82 & 2.02 & 0.32 \\ MnO & 0.08 & 0.13 & 0.11 & 0.12 & 0.13 & 0.28 & 0.11 \\ NiO & 0.01 & 0.23 & 0.36 & & & & 0.29 \\ BaO & 0.55 & & & & & & \\ P\({}_{2}\)O\({}_{5}\) & 1.37 & & & & & & \\ H\({}_{2}\)O & 1.17 & & & & & & \\ Sum & 99.34 & 100.27 & 100.4 & 100.49 & 99.56 & 99.8 & 100.17 \\ Mg\# & 67.49 & 89.49 & 89.78 & 90.87 & 88.85 & 83.08 & 91.81 \\ \hline \end{tabular}
\end{table}
Table 2: Compositions of starting materials: lamproite and peridotite and its constituent minerals.