Two main groups of mineral assemblages can be distinguished in the calc-silicate rocks of the Alboran metamorphic basement (Holes 976B and 976E) on the basis of the presence of garnet or scapolite. Garnet-bearing rocks display a sequence of up to seven textural and compositional zones with different high-variance mineral assemblages. These zones are interpreted to have formed because of diffusional processes (mainly transfer of CaO) between adjacent impure calcite-bearing marble and aluminum-rich metapelites. The most representative assemblage, in the contact between two reaction zones, is formed by grossular-rich garnet + clinopyroxene + amphibole + plagioclase and was probably stable at T ~ 650°C, P = 7.4-8.2 kbar and XCO2 = 0.11-0.16, as suggested by phase-relationship analysis. Secondary actinolitic amphibole probably developed in decreasing P and increasing XCO2 conditions. The other type of calc-silicate rocks, scapolite-bearing rocks, grew at similar or slightly lower temperature and an undetermined pressure.
These metamorphic conditions compare well with those deduced by Soto et al. (Chap. 19, this volume) for the high-grade metapelites intercalated with the calc-silicate rocks and also with the P-T conditions deduced for metapelites in different units of the Alpujárride Complex from the Betic chain (see Monié et al., 1994; and Sánchez- Gómez et al., Chap. 23, this volume, for a review). Therefore, this paper demonstrates that phase-relationship analysis of reaction zones formed along metapelite-marble contacts can be a powerful tool contributing to understanding the metamorphic evolution of the Alboran Basement.