Reddish Metagranites from the Gennargentu Igneous Complex (Sardinia, Italy): Insight into Metasomatism Induced by Magma Mingling

Abstract

the recrystallization of quartz and plagioclase to higher calcium concentrations. The progressive increase in the MgO/(MgO þFeO) of chlorite closer to the contact indicates that this phase also recrystallized.The iron released during chlorite recrystallization was buffered by hematite formation in the pores of metasomatic K-feldspar. The Gennargentu metagranites provide evidence that metasomatic fluids can play a major role in driving metamorphic reactions in contact aureoles. For instance, the expected increase of Ca in plagioclase owing to thermal equilibration was not achieved in the high-T zone of the aureole because of fluid-assisted removal of cations. We conclude that caution should be taken when interpreting the processes that underpin contact metamorphism in terms of thermally driven, ionic diffusion alone, because the role of fluids may be significant, if not overwhelming, in the domains closest to the magmatic source.