Geological insights from the newly discovered granite of Sif Island between Thwaites and Pine Island glaciers

• Published in: Antarctic Science
• Main Authors: Marschalek, J.W., Thomson, S.N., Hillenbrand, C.-D., Vermeesch, P., Siddoway, C., Carter, Andrew, Nichols, K., Rood, D.H., Venturelli, R.A., Hammond, S.J., Wellner, J., van de Flierdt, T.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2024
• Subjects: School of Natural Sciences; Amundsen Sea; Antarc*; Antarctic; Antarctic Peninsula; Antarctic Science; Ice Sheet; Marie Byrd Land; Pine Island Glacier; Sif Island; Thurston Island; Thwaites Glacier
• Online Access: https://eprints.bbk.ac.uk/id/eprint/53259/; https://eprints.bbk.ac.uk/id/eprint/53259/1/53259.pdf; https://doi.org/10.1017/S0954102023000287

Large-scale geological structures have controlled the long-term development of the bed and thus the flow of the West Antarctic Ice Sheet (WAIS). However, complete ice cover has obscured the age and exact positions of faults and geological boundaries beneath Thwaites Glacier and Pine Island Glacier, two major WAIS outlets in the Amundsen Sea sector. Here, we characterize the only rock outcrop between these two glaciers, which was exposed by the retreat of slow-flowing coastal ice in the early 2010s to form the new Sif Island. The island comprises granite, zircon U-Pb dated to ~177–174 Ma and characterized by initial ɛNd, 87Sr/86Sr and ɛHf isotope compositions of -2.3, 0.7061 and -1.3, respectively. These characteristics resemble Thurston Island/Antarctic Peninsula crustal block rocks, strongly suggesting that the Sif Island granite belongs to this province and placing the crustal block's boundary with the Marie Byrd Land province under Thwaites Glacier or its eastern shear margin. Low-temperature thermochronological data reveal that the granite underwent rapid cooling following emplacement, rapidly cooled again at ~100–90 Ma and then remained close to the Earth's surface until present. These data help date vertical displacement across the major tectonic structure beneath Pine Island Glacier to the Late Cretaceous.