The System Diopside-Nepheline-Akermanite-Leucite and Its Bearing on the Genesis of Alkali-Rich Mafic and Ultramafic Volcanic Rocks

The join Ne-Ak-Lc within the system, diopside (Di)- nepheline (Ne)- akermanite (Ak)- leucite (Lc), has been studied at 1 atm. The results show that it is pseudoternary with a four-phase point at $$Ne_{34.5}Ak_{20.5}Lc_{45}$$ and 1,170° ± 5° C where nepheline solid solution ($$Ne_{ss}$$) + melilite (Mel) + leucite solid solution ($$Lc_{ss}$$) coexist with liquid. Forsterite solid solution ($$Fo_{ss}$$), as a subliquidus phase, has a reaction relationship with liquid. A pseudobinary join $$(Di_{38}Ak_{3}Ne_{59})_{100-x} - Lc_{x}$$, investigated to determine the temperature of six phase assemblages within the Di-Ne-Ak-Lc system, cuts the primary phase volumes of $$Fo_{ss}$$ and $$Lc_{ss}$$ and has a pseudoeutectic at 39 wt% of Lc and 1,130° ± 5° C where $$Fo_{ss} + Lc_{ss}$$ + liquid coexist. An assemblage ($$Di_{ss} + Fo_{ss} + Mel + Ne_{ss} + Lc_{ss}$$ + liquid) occurs at 1,105° ± 10° C. Forsterite solid solution begins to react with liquid at this point and is eliminated completely at 1,075° ± 10° C. Stud...