Figure 7. A. PT paths followed by high-grade schist. PT plots of selected thermobarometric results per sample (thin lines) and approximate PT evolution during and after (thick arrow) D2 of the high-grade schist. Black squares represent simultaneous intersection between garnet-biotite thermometer (Hodges and Spear, 1982) and GASP barometer (Hodges and Crowley, 1985). P conditions for plagioclase included in garnet porphyroblasts (dark gray) and garnet-plagioclase rims in the matrix (light gray) are shown for reference. Thick lines represent key reactions in KFMASH system (Spear and Cheney, 1989). Invariant points [I1] and [I2] represent Pl-bearing (i.e., in KNASH system) and Pl-absent (i.e., in KASH system) invariant points, respectively, for the muscovite-melting reaction. Granite solidus is represented by reaction 1 (in the Qtz-Ab-Or-H2O system; Ms + Ab + Bt + Kfs + Qtz + H2O = L; which under [I1] is transformed to Kfs + Als + Bt + Qtz + H2O = L) and reaction 2 (in the Qtz-Or-H2O subystem; Ms + Bt + Kfs + Qtz + H2O = L; which under [I2] is transformed to Kfs + Als + Bt + Qtz + H2O = L). B. PT evolution of the pelitic and migmatite gneiss (thick arrow). The cooling path is indicated by the broken line. Dark gray area represents the deduced PT conditions for the first stages of melting (see text). Selected reactions in the KFMASH system are taken from Vielzeuf and Holloway (1988; XMg ~ 0.5); dashed lines represent reactions involving Al-rich micas (Al-rich biotite: Bt´, [Al]vi = 1.0; and Al-rich muscovite: Ms´, Si:Aliv > 3:1). Other melting reactions are from Vielzeuf and Clemens (1992). Data sources for granite solidi are summarized in Johannes and Holtz (1996). Reactions (right term points to the higher temperature side of the reaction) 1: Bt + Kfs + Qtz + H2O = L; 2: Ms + Kfs + Qtz + H2O = L which under [I1] is transformed to Als + Kfs + Qtz + H2O = L; 3: under [I3] is Ms´ + Qtz = Crd + Kfs + Als + H2O, between [I3] and [I4] is Ms´ + Qtz = Bt´ + Kfs + Als + H2O, and above [I4] is Ms´ + Qtz = L + Kfs + Als + Bt´; 4: L + Grt + Als + Qtz = Crd + Kfs; 5: Bt´ + Crd + Opx = L + Grt + Opx. Notice that the location of the divariant reactions Als + Grt + Qtz + H2O = Crd and Grt + Qtz + H2O = Opx + Crd (thick lines in the diagram) depends on the XMg contents of the phases. We have represented for comparison the location of both reactions for a fixed composition of XMg ~ 0.5 (from Vielzeuf and Holloway, 1988). Al-silicate triple point is from Berman (1988).

Figure 7. A. PT paths followed by high-grade schist. PT plots of selected thermobarometric results per sample (thin lines) and approximate PT evolution during and after (thick arrow) D₂ of the high-grade schist. Black squares represent simultaneous intersection between garnet-biotite thermometer (Hodges and Spear, 1982) and GASP barometer (Hodges and Crowley, 1985). P conditions for plagioclase included in garnet porphyroblasts (dark gray) and garnet-plagioclase rims in the matrix (light gray) are shown for reference. Thick lines represent key reactions in KFMASH system (Spear and Cheney, 1989). Invariant points [I1] and [I2] represent Pl-bearing (i.e., in KNASH system) and Pl-absent (i.e., in KASH system) invariant points, respectively, for the muscovite-melting reaction. Granite solidus is represented by reaction 1 (in the Qtz-Ab-Or-H₂O system; Ms + Ab + Bt + Kfs + Qtz + H₂O = L; which under [I1] is transformed to Kfs + Als + Bt + Qtz + H₂O = L) and reaction 2 (in the Qtz-Or-H₂O subystem; Ms + Bt + Kfs + Qtz + H₂O = L; which under [I2] is transformed to Kfs + Als + Bt + Qtz + H₂O = L). B. PT evolution of the pelitic and migmatite gneiss (thick arrow). The cooling path is indicated by the broken line. Dark gray area represents the deduced PT conditions for the first stages of melting (see text). Selected reactions in the KFMASH system are taken from Vielzeuf and Holloway (1988; X_Mg ~ 0.5); dashed lines represent reactions involving Al-rich micas (Al-rich biotite: Bt´, [Al]^vi= 1.0; and Al-rich muscovite: Ms´, Si:Al^iv> 3:1). Other melting reactions are from Vielzeuf and Clemens (1992). Data sources for granite solidi are summarized in Johannes and Holtz (1996). Reactions (right term points to the higher temperature side of the reaction) 1: Bt + Kfs + Qtz + H₂O = L; 2: Ms + Kfs + Qtz + H₂O = L which under [I1] is transformed to Als + Kfs + Qtz + H₂O = L; 3: under [I3] is Ms´ + Qtz = Crd + Kfs + Als + H₂O, between [I3] and [I4] is Ms´ + Qtz = Bt´ + Kfs + Als + H₂O, and above [I4] is Ms´ + Qtz = L + Kfs + Als + Bt´; 4: L + Grt + Als + Qtz = Crd + Kfs; 5: Bt´ + Crd + Opx = L + Grt + Opx. Notice that the location of the divariant reactions Als + Grt + Qtz + H₂O = Crd and Grt + Qtz + H₂O = Opx + Crd (thick lines in the diagram) depends on the X_Mg contents of the phases. We have represented for comparison the location of both reactions for a fixed composition of X_Mg~ 0.5 (from Vielzeuf and Holloway, 1988). Al-silicate triple point is from Berman (1988).