The Geo/Thermochronology of Dismal Island (Marguerite Bay, Antarctic Peninsula)

Abstract

Dismal Island is located at the entrance of Marguerite Bay between Adelaide Island to the northeast and Alexander Island to the southwest within the Antarctic Peninsula (AP). Its unique position between Alexander and Adelaide islands provides the opportunity to perform testing and link these regions through Cenozoic magmatism and tectonics due to the subduction of the Pacific plate beneath the AP along the northern margin. Dismal Island was visited in February 2021 within the framework of the sixth Turkish Antarctic Expedition (TAE-VI). Thirteen samples were collected for petrography, geochronology, and low-temperature thermochronology (LTT). Of the samples, 3 were dated using laser ablation-inductively coupled plasma-mass spectrometer zircon U-Pb geochronology, 2 were dated using apatite fission-track (AFT) analysis, and 1 was dated using apatite uranium-thorium-helium (U-Th/He) (AHe) thermochronology. The island comprises massif quartz-diorite, tonalite, mafic, and felsic dikes, indicating a hybrid magma source. The 3 zircon U-Pb ages yielded a crystallization age of 47-48 for the magmatic body. The AFT ages yielded a cooling age of 41 Ma, suggesting either a shallow emplacement at a depth of similar to 4 km or an uplift/exhumation during middle-late Eocene boundary. In contrast, the AHe age of 1 sample was 20.1 +/- 1.1 Ma, together with a fast-cooling profile during the same period, which indicated an early Miocene uplift in the region. Similar early-middle Eocene crystallization ages within similar rock outcrops were determined on Adelaide and Alexander islands, Adelaide Island Intrusive Suite. The AFT ages obtained in this study (similar to 41 Ma), close to formation age, were also found on Adelaide and Alexander islands. The (LTT) literature of the region shows that the LTT ages get younger to the north along the AP, reflecting the northward migration of the ridge-trench collision and opening of the slab window along the western coast of the AP. The AHe age and the fast-cooling profile suggested that the ridge-subduction between the Tula and Adelaide fracture zones to the north of Dismal Island reached the region during Aquitanian-Burdigalian.