Contrasting Archaean crustal records in western part of the Napier Complex, East Antarctica: New constraints from SHRIMP geochronology

Abstract

U–Pb zircon geochronology of 6 samples collected from Fyfe Hills (2 felsic orthogneisses and 1 quartzo-feldspathic gneiss) and Mt. Cronus (1 quartzo-feldspathic gneiss and 2 quartzites) in the western part of the Napier Complex, East Antarctica, revealed an Archaean–Proterozoic history ranging from 3128 to 1824Ma. The absence of ancient evidence >3800–3600Ma indicates that these ages were not always dominant in these two areas. The 3128–2580Ma protolith ages are similar to those of other areas (e.g., Mt. Riiser-Larsen, Tonagh Island), while the magmatic protolith age of 2741Ma obtained for the Fyfe Hills orthogneiss is a new component of the Archaean magmatic protolith in the Napier Complex. Metamorphic overgrowth or recrystallized zircons yielded systematic disconformable ages for both Fyfe Hills (>2518Ma) and Mt. Cronus (~2490Ma). The presence of 2580Ma inherited zircons provides important constraints that place the ultrahigh temperature metamorphic peak later than 2580Ma. The post metamorphic ages suggest local fluid infiltration or local deformation event(s).