Experimental study of the joins forsterite–diopside–leucite– and forsterite–leucite–åkermanite up to 2.3 GPa [P(H2O) = P(Total)] and variable temperatures: Its petrological significance

We conducted a series of melting experiments in the join forsterite–diopside–leucite under 0.1 and 2.3 GPa and in the join forsterite–leucite–åkermanite under 2.3 GPa to understand paragenetic relationships amongst different types of lamproitic and lamprophyric magmas with K-rich mafic and ultramafic volcanic (kamafugitic) rocks. Both the joins were studied in the presence of excess water. The experimental results of the join forsterite–diopside–leucite at 0.1 GPa show that the five-phase point of forsterite (Fo)ss + diopside (Di)ss + leucite (Lc)ss + liquid (Liq) + vapour (V) (equivalent to ugandite lava) occurs at Fo2Di50Lc48 at 880 ± 5 °C. Phlogopite appears as the last phase at 830 ± 15 °C. The final crystalline assemblage of forsteritess + diopsidess + leucitess + phlogopite is similar to the phenocryst assemblage of missourite lava. Present study suggests that an olivine leucitite (ugandite) can be derived from an olivine italite, a slightly potassic peridotite and a leucitite magma.A study of the join Fo–Di–Lc [P(H2O) = P(Total)] at 2.3 GPa shows that liquid compositions penetrate the primary phase volumes of forsteritess, phlogopitess, kalsilitess, K-feldsparss and diopsidess. It has the following three five-phase points: 1) one occurring at Fo9Di49Lc42 and 1005 ± 5 °C, where liquid and vapour coexists with forsteritess, phlogopitess and diopsidess (phlogopite-bearing madupite), 2) the second one at Fo4Di50Lc46 and 990 ± 10 °C, where diopsidess, K-feldsparss and phlogopitess coexist with liquid and vapour (pyroxene-bearing minette), and 3) the third one at Fo3Di21Lc76 and 775 ± 5 °C, where phlogopitess, kalsilitess and K-feldsparss are in equilibrium with liquid plus vapour (kalsilite-bearing minette).The experimental results of the join Fo–Lc–åkermanite (Ak) show that the join 40 penetrates the primary phase volumes of forsteritess, phlogopitess, kalsilite, K-feldsparss, diopsidess and merwinitess. The data indicate the presence of four five-phase points: 1) one occurring at Fo7Lc42Ak51 and 1165 ± 5 °C, where phlogopitess, forsteritess, diopsidess coexists with liquid and vapour (olivine-bearing madupite), 2) the second one at Fo3Lc49Ak48 and 1140 ± 10 °C, where a liquid is in equilibrium with phlogopitess, K-feldsparss, diopsidess and vapour (pyroxene-bearing minette), 3) the third one at Fo18Lc21Ak61 and 1255 ± 10 °C, where merwinitess, forsteritess and diopsidess are in equilibrium with liquid and vapour (merwinite-bearing wherlite), and 4) the fourth one at Fo5Lc73.5Ak21.5 and 770 ± 5 °C, where kalsilitess, phlogopitess and K-feldspar coexist with liquid and vapour (kalsilite-bearing minette). The present data suggest that high pressure heteromorphic equivalent of a katungite magma is represented by a kalsilite-bearing minette, a pyroxene-bearing minette, or an olivine-bearing madupite.