Precambrian Basement Beneath the King George Island (Antarctica Peninsula) Revealed by Zircon Xenocrysts from Eocene to Miocene Volcanic Rocks

Our knowledge of the Precambrian geological records of deep crust beneath the Antarctic Peninsula is still sparse. The King George Island located to the northwestern part of the South Shetland Islands (Antarctic Peninsula) was mainly covered by Cenozoic volcanic and intrusive rocks. We derive new petrology, geochronological (LA-ICP-MS zircon U-Pb dates), and geochemical data from King George Island volcanic rocks. The accidental discovery of xenocrystic zircons in these volcanic rocks offers valuable insights into the information of the deep crust in the region. The zircon ages indicate the presence of Proterozoic to Cambrian basement in the King George Island. Among them, 58 zircons with 90–110% concordance yield concordant ages from 101 ± 1.7 Ma to 2756 ± 26 Ma, and form major age peaks at ca. 1.8–1.6 Ga, ca. 1.2–0.75 Ga, and ca. 0.55–0.5 Ga. These xenocryst populations show similar age ranges and zircon εHf(t) values to the basement of the South America (Patagonia) continental block. This may suggest that Proterozoic to Cambrian Patagonia crustal fragments extended into the King George Island, South Shetland Islands (Antarctic Peninsula). Accordingly, we consider the paleogeographic position of the South Shetland Islands was probably at the southwestern end of South America, forming the southwestern margin of Gondwana during Early Mesozoic.