Chemistry and formation mechanism of garnet in the metapelites amd metabasites from the Gol-e-Gohar metamorphic complex, Kerman province

The recorded textural evidences of garnets included in the metapelites and metabasites from the Gol-e-Gohar complex in southeastern Sanandaj-Sirjan zone highlight evidences of syn-S1 growth, after S1 schistosity, syn-S2 and after S2 schistosity, and the presence of two generations of garnet (GrtIa, GrtIb) in metapelites suggest dehydration continuous reaction GrtIa+Bt = GrtIb+Qz. Combinational profiles of garnet crystals in the metapelites and metabasites show the decrease of spessartine and XFe proportions and increase of pyrope and almandine from the center to the rim. All garnets belong to the pyralspite series (Spessartine-Almandine-Pyrope) and are almandine-rich. The increase in Mn in the garnet core is indicative of differentiation and crystalline growth associated with metamorphic processes. On the other hand, the lack of clear zoning of Ca and Al from the center to the rim of garnets and the minor changes of Fe element from the center to the rim could be an indicative of a closed system and Fe2+/Fe3+ non-oxidation during metamorphism indicating growth of garnets occurred due to crystalline growth and differentiation of elements during metamorphism. Also, increasing Mg and Fe from the center to the garnet rim along with increasing Ca contents in hornblendes and decreasing Ca and An contents in plagioclase from their centers to the margins suggest that the garnets probably formed by reaction between hornblende and plagioclase as the reaction Hornblende + Anorthite = Garnet + Quartz + H2O. The rapid growth of garnet and hornblende porphyroblasts removed H2O from the fluids and resulted in a gradual increase in the CO2 contents of the fluids. Sporadic calcites in the matrix may have been formed by these CO2-rich fluids.