1] schistosity defined by the orientation of biotite in the matrix and quartz, ilmenite and graphite inclusions in garnet can be observed, although it was strongly modified during progressive metamorphism.
These facts suggest that growing processes for sector-zoning garnet can be interpreted as a non-equilibrium stage of progressive metamorphism, followed by the growing of sigmoidal-zoned garnet at the last stage of this event.
The reactions encountered in progressive metamorphism
generate H2O and CO2 that will tend to change the fluid composition, representing a problem for the first mechanism to evolve.
Then, a progressive metamorphism
in these rocks is marked by the passing of greenschist facies mineralogy [actinolite + chlorite + quartz + plagioclase (albite) + epidote minerals [+ or -] muscovite [+ or -] calcite] to epidote-amphibolite facies mineralogy [hornblende + epidote minerals + quartz + albite [+ or -] garnet], and finally to amphibolite facies mineralogy [hornblende + garnet + plagioclase [+ or -] quartz].