Geochemistry of metapelitic rocks from the Garmichay Area, East Azerbaijan, NW Iran; protolith nature and whole rock control on metamorphic mineral assemblages

Abstract

The protoliths of metamorphosed argillaceous rocks from the Garmichay area in the East Azerbaijan province of NW Iran were clay-rich sediments of reworked nature, originating most likely from an andesite to andesite-basalt source and deposited in an active continental margin tectonic setting. The protoliths of the Garmichay metapelites experienced low to moderate chemical weathering. Andalusite, cordierite, biotite, and muscovite are produced due to metamorphism under low-pressure and medium-temperature conditions. Cordierite throughout the whole assemblages is altered to the pseudomorphs pinite. Some rock samples contain both andalusite and altered cordierite as porphyroblasts, whereas others contain only andalusite or altered cordierite. Pressure and temperature estimates indicate that pressure for metamorphism was in the range 1-2.5 kbar with temperature between 500-600°C. Major oxides abundance show similar values in all analyzed samples, while concentration of some minor elements, especially zinc, show meaningful differences in rocks with different metamorphic mineral assemblages. The variations in the abundance of these minor elements may have played important role in the control of the mineral assemblages present.