Description: Reactions and partial melting of peraluminous rocks in the presence of H 2 O-CO 2 –salt fluids under parameters of granulite-facies metamorphism were modeled in experiments on interaction between orthopyroxene–cordierite–biotite–plagioclase–quartz metapelite with H 2 O, H 2 O-CO 2 , H 2 O-CO 2 -NaCl, and H 2 O-CO 2 -KCl fluids at 600 MPa and 850°C. Rock melting in the presence of H 2 O and equimolar H 2 O-CO 2 fluids generates peraluminous (A/CNK 1 〉 1.1) melts whose composition corresponds to magnesian calcic or calc–alkaline S-type granitoids. The melts are associated with peritectic phases: magnesian spinel and orthopyroxene containing up to 9 wt % Al 2 O 3 . In the presence of H 2 O-CO 2 -NaCl fluid, cordierite and orthopyroxene are replaced by the association of K-Na biotite, Na-bearing gedrite, spinel, and albite. The Na 2 O concentrations in the biotite and gedrite are functions of the NaCl concentrations in the starting fluid. Fluids of the composition H 2 O-CO 2 -KCl induce cordierite replacement by biotite with corundum and spinel and by these phases in association with potassium feldspar at X KCl = 0.02 in the fluid. When replaced by these phases, cordierite is excluded from the melting reactions, and the overall melting of the metapelite is controlled by peritectic reactions of biotite and orthopyroxene with plagioclase and quartz. These reactions produce such minerals atypical of metapelites as Ca-Na amphibole and clinopyroxene. The compositions of melts derived in the presence of salt-bearing fluids are shifted toward the region with A/CNK 〈 1.1, as is typical of so-called peraluminous granites of type I. An increase in the concentrations of salts in the fluids leads to depletion of the melts in Al 2 O 3 and CaO and enrichment in alkalis. These relations suggest that the protoliths of I-type peraluminous granites might have been metapelites that were melted when interacting with H 2 O-CO 2 -salt fluids. The compositions of the melts can evolve from those with A/CNK 〉 1.1 (typical of S-type granites) toward those with A/CNK = 1.0–1.1 in response to an increase in the concentrations of alkali salts in the fluids within a few mole percent. Our experiments demonstrate that the origin of new mineral assemblages in metapelite in equilibrium with H 2 O-CO 2 -salt fluids is controlled by the activities of alkaline components, while the H 2 O and CO 2 activities play subordinate roles. This conclusion is consistent with the results obtained by simulating metapelite mineral assemblages by Gibbs free energy minimization (using the PERPE_X software), as shown in log( \({a_{{H_2}O}}\) )–log( \({a_{N{a_2}O}}\) ) and log( \({a_{{H_2}O}}\) )–log( \({a_{{K_2}O}}\) ) diagrams.