Geological Insights from the Newly Discovered Granite of Sif Island between Thwaites and Pine Island Glaciers

Marschalek, James W.; Thomson, Stuart N.; Hillenbrand, Claus-Dieter ORCID:; Vermeesch, Pieter; Siddoway, Christine; Carter, Andrew; Nichols, Keir; Rood, Dylan H.; Venturelli, Ryan A.; Hammond, Samantha J.; Wellner, Julia; van de Flierdt, Tina. 2024 Geological Insights from the Newly Discovered Granite of Sif Island between Thwaites and Pine Island Glaciers. Antarctic Science, 36 (2). 51-74.

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© The Author(s), 2024. Published by Cambridge University Press on behalf of Antarctic Science Ltd. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://, which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
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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.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 0954-1020
Additional Keywords: Pine Island Bay; West Antarctica; Thermochronology; Geochemistry; Zircon U-Pb Geochronology; Zircon Hf isotopes
Date made live: 23 Feb 2024 14:54 +0 (UTC)

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