40Ar/39 Ar dating of Tephra in blue ice (Northern Victoria Land, Antarctica): Prospects and limitations

Tephra layers are commonly embedded within ice in Antarctica. They represent powerful qualitative and quantitative stratigraphic markers of ice ages and dynamics, as well as a chronometer for all palaeoclimatic and palaeoenvironmental information that ice might contain. The 40Ar/39Ar method was used to date tephra sampled in northern Victoria Land, in the productive Frontier Mountain meteorite trap and in nearby regions, in an attempt to constrain the age of the ice field. The first results were not conclusive because both laser total-fusion ages and laser step-heating ages varied widely, an indication of sample contamination and/or biased original samples due to the presence of parentless 40Ar. The youngest recorded ages for each layer can be considered an upper limit for the age of the tephra and its enclosing ice. They are of the order of 150-170 ka for Frontier Mountain, in good agreement with the limit indicated by meteorite terrestrial ages, and 60-80 ka for Lichen Hills and Oona Cliff.