Archaean crust in the Rayner Complex of east Antarctica: Oygarden Group of islands, Kemp Land

Abstract

Archaean zircon grains from the Oygarden Group of islands in Kemp Land, east Antarctica, record evidence for multiple episodes of recrystallisation, dissolution and growth from the Early to Middle Archaean to the Neoproterozoic. Zircon grains in layered felsic orthogneiss have an age of ∼3650 Ma, a minimum protolith age for this rock. These zircon grains were subsequently affected by a ∼3470 Ma Pb-loss event. Homogeneous felsic orthogneiss that cuts S₁, but contains an intense S₂ foliation, has disturbed ∼2780 Ma metamorphic zircon cores and rims that suggest a minimum age of ∼2780 Ma for the protolith to the orthogneiss. All zircon U-Pb data display considerable disturbance with further Pb-loss at ∼2400 Ma and ∼1600 Ma, and a major episode of isotopic resetting at ∼930 Ma. The highly disturbed data are related to complexly zoned zircon grains that developed through growth and modification during successive metamorphic events. Zircon cores with relic growth zoning patterns are inferred to have resulted from partial annealing or recrystallisation of older magmatic zircon. Highly luminescent zircon rims that embay cores along curved boundaries are interpreted to have formed through recrystallisation of zircon cores, and not new growth. The ages reported here confirm that central Kemp Land is composed of Archaean crust reworked during the Neoproterozoic Rayner Structural Episode.