Cretaceous magmatism in the Antarctic Peninsula and its tectonic implications

• Published in: Journal of the Geological Society
• Main Authors: Bastias, Joaquin, Spikings, Richard, Riley, Teal, Chew, David, Grunow, Anne, Ulianov, Alexey, Chiaradia, Massimo, Burton-Johnson, Alex
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Geological Society of London 2023
• Subjects: Antarctic; The Antarctic; Antarctic Peninsula; Weddell Sea; Weddell; Alexander Island; Graham Land; Palmer Land; Antarc*; South Atlantic Ocean
• Online Access: http://nora.nerc.ac.uk/id/eprint/532407/; https://nora.nerc.ac.uk/id/eprint/532407/1/jgs2022-067.pdf; https://www.lyellcollection.org/doi/10.1144/jgs2022-067

Periods of cessation, resumption and enhanced arc activity are recorded in the Cretaceous igneous rocks of the Antarctic Peninsula. We present new geochronological (LA-ICP-MS zircon U-Pb) analyses of 36 intrusive and volcanic Cretaceous rocks, along with LA-ICP-MS apatite U-Pb analyses (a medium-temperature thermochronometer) of 28 Triassic–Cretaceous igneous rocks of the Antarctic Peninsula. These are complemented by new zircon Hf isotope data along with whole-rock geochemistry and isotope (Nd, Sr and Pb) data. Our results indicate that the Cretaceous igneous rocks of the Antarctic Peninsula have geochemical signatures consistent with a continental arc setting and were formed during the interval ∼140–79 Ma, while the main peak of magmatism occurred during ∼118–110 Ma. Trends in εHft (zircon) combined with elevated heat flow that remagnetised rocks and reset apatite U-Pb ages suggests that Cretaceous magmatism formed within a prevailing extensional setting that was punctuated by periods of compression. A noteworthy compressive period probably occurred during ∼147–128 Ma, triggered by the westward migration of South America during opening of the South Atlantic Ocean. Cretaceous arc rocks that crystallised during ∼140–100 Ma define a belt that extends from southeastern Palmer Land to the west coast of Graham Land. This geographic distribution could be explained by (i) a flat slab with east-dipping subduction of the Phoenix Plate, or (ii) west-dipping subduction of the lithosphere of the Weddell Sea, or (iii) an allochthonous origin for the rocks of Alexander Island. A better understanding of the geological history of the pre-Cretaceous rocks of Alexander Island and the inaccessible area of the southern Weddell Sea is required.