Conclusions
The absence of deformation in these samples of the Lago della Vecchia area permits the preservation of pre-eclogitic microstructures and assemblages, even where the Alpine metamorphic overprint is penetrative (i.e. the Eclogite Micaschists Complex).
The eclogite-facies re-equilibration is also testified by assemblages that resemble those of other area of the Eclogitic Micaschists Complex.
Coronitic microstructures reflect the stages of the prograde biotite break-down thorough a series of continuous reactions that progressively change the biotite composition, producing garnet coronas. Igneous primary plagioclase breakdown occurs during the burial stages and allows stabilization of Ca-phases as epidote and grossular-rich garnet coronas. Plagioclase break-down is also associated with the growth of hydrous minerals such as phengitic mica and epidote that imply a contribution of H2O and K2O to the reactions.
H2O may have an important role on the diffusive mass transfer, enhancing metamorphic reactions and providing chemical feeds to all reactions observed in the coronitic metagranite of the Lago della Vecchia: e.g. plagioclaseI cores, plagioclaseI rims, biotiteI rims, white micaI rims.
Deformation is absent within the studied samples of coronitic metagranite of the Lago della Vecchia but it is evident that the transformations are much more evolved within deformed volumes of metagranite than in the undeformed ones as shown in other field-based studies (Spalla et al, 2004) or at laboratory scale (Holyhoke and Tullis, 2006). Within the Lago della Vecchia metagranite deformation enhanced reaction kinetics in the progress of metamorphic transformations, as previously suggested by Hobbs et al. (2010) although the role of fluids during pre-burial and burial stages is still not understood.