Thermal resetting of the Early Cretaceous volcanic rocks of Low Island, South Shetland Islands, Antarctica

Abstract

The Albatross Hill Member is an Early Cretaceous volcanic and volcaniclastic succession, which overlays the sedimentary rocks of the Pencil Beach Member and together constrain the Cape Wallace Beds in Low Island, South Shetland Islands, Antarctica (63°15’S, 62°12’W). Along with other coeval volcanic units present in nearby Livingston Island, the Albatross Hill Member represents the first products of the magmatic arc after its resumption during the Cretaceous. The Albatross Hill Member is dominated by dacites with a widespread occurrence of secondary minerals, of which the latter occur partially replacing phenocrysts, filling veins and veinlets and, to a lesser degree, in the groundmass/matrix. 40Ar/39Ar analyses on plagioclase phenocrysts from two biotite dacites yield plateau ages between ∼111 and 109 Ma, which are ∼31 to 26 Myr younger than the 40Ar/39Ar groundmass plateau ages for the same samples. We suggest that this difference is associated with the presence of secondary minerals, which greatly affected the phenocrysts of the sequence and disturbed the 40Ar/39Ar analyses.