Multiple post–peak metamorphic fluid infiltrations in southern Perlebandet, Sør Rondane Mountains, East Antarctica

Abstract

This paper reports multiple fluid infiltration events during retrograde metamorphism in the Sør Rondane Mountains, East Antarctica. Pelitic gneisses from southern part of Perlebandet have cordierite–biotite intergrowth rimming garnet, implying that garnet breakdown occurred by fluid infiltration. Using the Raman peak of CO2 in cordierite and Cl–bearing composition in biotite, this study revealed that the cordierite–biotite intergrowth was formed in equilibrium with one–phase CO2–Cl–H2O fluid. The intergrowth texture is cut by thin selvages composed of Cl–bearing biotite, suggesting Cl–bearing fluid infiltration. Since andalusite is exclusively observed in the selvage, near isobaric cooling path is presumed for the pressure–temperature (P–T ) path of these post–peak fluid–related reactions. The inconsistence with counter–clockwise P–T path reported from northern Perlebandet is probably due to the granodiorite/leucocratic granite bodies beneath the studied metamorphic rocks. In order to understand the tectonic evolution at the final stage of Gondwana amalgamation, therefore, effect of hidden igneous rocks needs to be taken into consideration.