New radiometric dating of the dykes from the Hurd Peninsula, Livingston Island, South Shetland Islands

Fifteen new K-Ar ages in the range of 79-31 Ma are partially confirmed by three 40Ar/39Ar plateaus and isochron data of 64.9 +/- 0.4, 55.5 +/- 0.1 and 52.8 +/- 0.6 Ma. The new geochronological data reveal a much more detailed picture of the subduction imprint in the Hurd Peninsula. Using cutting relationships, the dyke emplacement history is divided into four episodes. The Late Cretaceous-Paleocene dykes in the range of 80-60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of subduction of the proto-Pacific oceanic crust. The Early Eocene dykes (56-52 Ma) fill the gap in volcanic activity 70-50 Ma ago. They are the only magmatic event manifested at this time in the region. The 45-42 Ma dykes may be related to the intrusion of the Barnard Point tonalite. Three samples of Oligocene age appear to represent the last igneous activities on the Hurd Peninsula prior to the opening of the Bransfield Strait. (C) 2002 Elsevier Science Ltd. All rights reserved.