New M⁴⁰Ar/³⁹Ar and K/Ar Ages of Dikes in the South Shetland Islands (Antarctic Peninsula)

Eighteen plagioclase 40Ar/39Ar and 7 whole rock K/Ar ages suggest that dikes in the South Shetland Islands
(Antarctic Peninsula) are of Paleocene to Eocene age. The oldest dikes are exposed on Hurd Peninsula (Livingston Island)
and do not yield 40Ar/39Ar plateaux. Our best estimates suggest dike intrusion at about the Cretaceous/Paleogene boundary.
An older age limit for the dikes is established by Campanian nannofossil ages from their metasedimentary host. Dike
intrusion began earlier and lasted longer on Hurd Peninsula (Danian to Priabonian) than on King George Island (Thanetian
to Lutetian). Arc magmatism on King George Island, possibly accompanied also by hypabyssal intrusions, began in the
Cretaceous as indicated by ages from the stratiform volcanic sequence. The dikes on King George Island were emplaced
beginning in the late Paleocene and ending 47–45 Ma. The youngest arc-related dikes on Hurd Peninsula were emplaced
~37 Ma