Reaction texture and Fe-Mg zoning in granulite garnet from Søstrene Island, Antarctica: Modeling and constraint on the time scale of metamorphism during the Pan-African collisional event

Abstract

Garnets from the Søtrene island, Antarctica, show reaction textures corresponding to two metamorphic episodes, one at c. 1000 Ma (M1) and the other at c. 500 Ma (M2). The latter is associated with a Pan-African tectono-metamorphic event that has been interpreted to represent a continent-continent collision followed by extensional collapse. Reaction-diffusion modeling of the compositional zoning of garnet associated with the development of reaction texture during M2 yields a time scale of ∼ 5-16 Myr for the duration of the peak of this overprinting metamorphism at ∼ 730 ± 20°C. The associated velocity of the reaction front is ∼ ∼ 5.0-1.6 μm/Myr. The inferred duration of peak metamorphism during the Pan-African event seems to be in good agreement with the available U-Pb SHRIMP ages of zircon and monazite that may be interpreted to have formed at the beginning and end stages of crystallization of granite during the metamorphic peak.