A pressure-temperature path was established for the Bossòst dome which can be used as a guide for the Aston and Hospitalet domes (Figure 14, Mezger et al. 2004). However, lacking additional mineral compositional data and whole rock geochemistry to calculate pseudosections, a quantitative P-T path can not yet be established. Nevertheless, the similarities between both regions outlined above allow for qualitative comparison. The crucial assemblages are 5a-c, with coexisting cordierite, staurolite, biotite and muscovite, which are considered metastable and the result of polymetamorphism (Holdaway et al. 1982; Garcia-Casco & Torres-Roldán 1999; Pattison et al. 1999). For the Bossòst dome this is supported by geochemical data (Mezger et al. 2004), and need yet to be done for the Aston-Hospitalet domes.
Figure 14. Reconstructed P-T path
Reconstructed P-T path for the Bossòst dome using petrogenetic grids and pseudosections calculated with THERMOCALC. A similar path may be envisioned for the Aston and Hospitalet domes.
Consumption of andalusite by cordierite (reaction 7) is a retrograde reaction with a negative slope. The location of that reaction is dependent on the Mg/Fe ratio of biotite and the graphite content (Pattison et al. 2002). For the Bossòst dome it could be shown that it lies close to the sillimanite-andalusite equilibrium.