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The geo/thermo-chronology of Dismal Island (Marguerite Bay, Antarctic Peninsula)

   Karaoglan, Fatih; Karatas, Burcu; Ozdemir, Yavuz; Gulyuz, Erhan; Vassilev, Oleg; Selbesoglu, Mahmut Oğuz; Gildir, Semih

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. It’s unique position between Alexander and Adelaide islands allows us to test and link these regions regarding Cenozoic magmatism and tectonics due to subduction of the Pacific plate beneath the AP along the northern margin.

Dismal Island was visited in February 2021 in the frame of Turkish Antarctic Expedition VI (TAE-6). Thirteen samples were collected for petrography, geochronology, and low-temperature thermochronology (LTT). Three samples were dated by LA-ICP-MS zircon U-Pb, two samples were dated by apatite Fission Track, and one sample was dated by apatite U-Th/He method.

The island comprises massif quartz-diorite, tonalite, mafic, and felsic dikes, indicating a hybrid magma source. Three zircon U-Pb ages yield a 47-48 Ma crystallization age for the magmatic body. The apatite Fission Track (AFT) ages yield a 41 Ma cooling age suggesting either a shallow emplacement at a depth of ~4 km or an uplift/exhumation during middle-late Eocene boundary. In contrast, one sample's apatite U-Th/He (AHe) age of 20.1±1.1 Ma, together with a fast cooling profile during the same period, indicates an early Miocene uplift in the region.

Similar early-middle Eocene crystallization ages within the similar rock outcrops were outcropped in the Adelaide and Alexander islands, Adelaide Island Intrusive Suite (AIIS). The AFT ages obtained in this study (~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 getting 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 suggest that the ridge-subduction between the Tula and Adelaide fracture zones to the north of Dismal Island reached the region during Aquitanian-Burdigalian.

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