Basement chronology of the Antarctic Peninsula: recurrent magmatism and anatexis in the Palaeozoic Gondwana Margin

Abstract

A revised pre-Jurassic chronology is presented for the Antarctic Peninsula on the basis of new U-Pb zircon dating, using both conventional (11 samples) and SHRIMP microprobe data (10 samples). The age range for plutonism and high-grade metamorphism is from 435 ±8 Ma (Silurian) to c. 206 Ma (approximately the Triassic-Jurassic boundary), with peaks of activity in Devonian, Carboniferous, Permian and mid-Triassic times, although some are represented by rocks with limited outcrops. The new data confirm the importance of Mid- and latest Triassic magmatic events, previously identified using Rb-Sr geochronology. The Adie Inlet gneiss, previously thought to be Neoproterozoic, is recognized as a Permian migmatite derived from paragneiss with a provenance dominated by Cambrian granitoids. Granite gneiss from NW Palmer Land, previously dated as Cambrian, is shown to be Triassic. Detrital zircons in metasedimentary rocks, and inherited zircons in granitoids, are dominated by Mesoproterozoic to Cambrian components, with sparse Palaeoproterozoic to Archaean grains, suggesting sources within Gondwana. At times these sources were nearby, as shown by an Archaean cobble-sized granite clast from a Permo-Triassic conglomerate; another clast in the same conglomerate, previously thought to be Devonian in age, has an Ordovician crystallization age.