Using tephrochronology to date temperate ice: correlation between ice tephras on Livingston Island and eruptive units on Deception Island volcano (South Shetland Islands, Antarctica)

Tephra layers are interstratified in the ice caps of the South Shetland Isl ands. Although previously poorly investigated, they are potential targets f or the application of tephrochronology and, hence, may provide temporal con straints on glaciological models for the region. Several tephra layers crop out in the coastal ice-cliffs and ablation ramps of Livingston Island. Usi ng stratigraphical position, granulometry and bulk sample geochemistry, the tephra layers can be divided into three groups (TPH1, TPH2 and TPH3, from top to base). The source for all of the tephras is unequivocally identified as Deception Island, a large active volcano in Bransfield Strait, situated about 35 km south of Livingston Island. TPH1 (a single layer) is strongly correlated compositionally with tephra erupted in 1970 from centres close t o Telefon Bay. This is the first time it has been possible to correlate a d istal tephra with a pyroclastic unit in the source volcano in the Antarctic Peninsula region. TPH2 (usually two layers, sometimes only one) was probab ly erupted from a tuff cone centre within the Crater Lake cluster of vents. From historical accounts, it is deduced that the numerous co-eruptive Crat er Lake vents were active prior to 1829 and, from their relatively fresh ap pearance, an eighteen-century age for the eruptions is possible. TPH3 compr ises at least four discrete tephra layers with a much wider compositional r ange than either TPH1 or TPH2. It may have been erupted during successive m onths or years. Compositional comparisons of TPH3 with possible source vent s on Deception Island are ambiguous, but there is a reasonably good similar ity with tephras erupted at Wensleydale Beacon and/or Vapour Col. However, it is also conceivable that the source(s) for TPH3 are no longer preserved on Deception Island. The age of the TPH3 eruptions is unknown but it must b e prior to 1829 and is unlikely to be more than a few centuries.