Fig. 4: Thermodynamic-geochemical modeling of isobaric melting at 11 kbar.
a Simplified T-XH2O pseudosection for median enriched Archean basalt27 at 11 kbar, with contours delineating the proportions of garnet (purple-colored field and purple lines) and melt fraction (light-yellow dashed lines). The two bolded, dashed lines with arrows represent melting cases with bulk H2O contents of 1.5 wt.% (case A) and 3 wt.% (case B), respectively. b, c Mineral and melt proportions versus temperature for case A and case B, respectively, with the phase proportions at 20% and 30% partial melting highlighted along the white dashed lines. d, e Compositional comparisons (λ1 versus λ2, Sr versus Y) between modeling melts and TTGs, incorporating not just the 1.5 and 3.0 wt.% bulk H2O cases but also those with different H2O contents. Colors represent varying bulk H2O contents, and the numbers around the nodes correspond to the degree of partial melting. The calculated melt fractions are from 5 to 50% at 5% intervals. At a fixed pressure, the change in the composition of the modeling melt caused by the variation in bulk H2O content (from 1 to 4 wt.%) is minor.
