Xe_s-Xe_n spectra and age of zircons from high-grade metamorphic rocks in the Napier Complex, East Antarctica

Studies have been made on the Xe_s-Xe_n age spectra and fission xenon release kinetics of four zircon samples from the Napier complex in East Antarctica. Theoretical concepts on the method indicate that an ideal age spectrum on heating should take the form of rising steps passing into a horizontal plateau corresponding to the actual age of the specimen. For three of the zircon speciments, plateau in the range from 700 to 1400°C was obtained, which accounted for from ~70% to ~30% of the total radiogenic xenon. At 1420-1800°C, 20-60% of the total xenon is released, which gives ages lower than the plateau value. There is a correlation between the shape of the mass spectrum and the turning points on the xenon release curves because the gas is released from various phases in the zircon grains or from grains that differ in geochemical history. -from Journal summary