Comparison of melting relationships of some plutonic and volcanic peralkaline undersaturated rocks

From previous studies and from results of melting and crystallization sequences determined for four plutonic rocks and for four glass-bearing volcanic rocks all with peralkaline chemistry, the degree of peralkalinity, ZrO₂, TiO₂, F and Cl contents of the plutonic and holocrystalline volcanic rocks can be correlated with their melting intervals. This correlation does not hold for the glassy volcanic rocks. Analyses of whole rock and coexisting glasses suggest that rapidly chilled peralkaline volcanics may behave differently from holocrystalline peralkaline rocks due to different cooling rates causing variations in the distribution of volatiles such as Cl, between liquid and solid phases of the crystallizing melt.