Las texturas de reacción en gneises calcosilicatados como indicadores de la trayectoria retrógada P-T-XCO2: el ejemplo del domo gneísico del Tormes, NO Salamanca

• Autores: Javier Escuder Viruete
• Localización: Cadernos do Laboratorio Xeolóxico de Laxe: Revista de xeoloxía galega e do hercínico peninsular, ISSN 0213-4497, Nº 20, 1995, págs. 19-26
• Idioma: español
• Títulos paralelos:
  • Reaction textures in calc-silicate gneisses from the Tormes gneiss complex: implications for the retrogade P-T-XCO2 path
• Enlaces
  • Texto completo
• Resumen

  • Calc-silicate gneisses from the Lower Unit of the Tormes Gneiss Complex, NW Salamanca, exhibit a sequence of reaction textures that have been used to elucidate their retrograde P-T-XCO2 path. The highest temperature recorded in the calc-silicates is represented by the wollastonite- and scapolite- (meionite-rich) bearing assemblages which yield at least 750º C at 6 kbar based on experimental results. The calc-silicates have partially re-equilibrated at lower temperatures (down to 450º C) as evidenced by the successive reactions: (1) Wo + Scp + Cal → Grt + CO2; (2) Wo + CO2 → Cal + Qtz; (3) Scp → Pl + Cal + Qtz; (4) Grt + CO2 + H2O → Ep/Clz + Cal + Qtz ± Pl; y (5) Cpx + CO2 + H2O → Tr + Cal + Qtz. The cooling down to lower temperatures of 450º C (at P <3 kbar), in the andalusite stability field, is also suggested by the secondary andalusite replacement of previous fibrolitic sillimanite in adjacent metapelites. In this paper, mineral devolatilization equilibria are used to constrain the composition of both syn- and post-peak-D2 fluids in the deepest exposed levels of the metamorphic complex. The results indicate that during the transitional granulite facies metamorphism, large-scale CO2 advection did not occur.