Extended Data Fig. 6: Further T–H2O diagrams and isopleth diagrams for the median sodic TTG.
From: Earth’s early continental crust formed from wet and oxidizing arc magmas
a and b correspond to the T–H2O diagrams calculated at 0.2 and 0.5 GPa, respectively, assuming initial ΔFMQ = 0 at 800 °C, whereas c and d are the corresponding isopleth diagrams. In c and d, paths A′ and A″ correspond to zircon crystallization in initially H2O-undersaturated magmas with lower H2O content and predict a negative correlation between fO2 and H2O, which is not observed. By contrast, paths B′ and B″ correspond to zircon crystallization in H2O-saturated magmas at 0.2 and 0.5 GPa, respectively, and can explain the observed magmatic H2O content of about 6 wt% and about 10 wt% in most Archaean granitoids.
