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

Abstract 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...

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Bibliographic Details
Published in:Antarctic Science
Main Authors: Marschalek, James W., Thomson, Stuart N., Hillenbrand, Claus-Dieter, Vermeesch, Pieter, Siddoway, Christine, Carter, Andrew, Nichols, Keir, Rood, Dylan H., Venturelli, Ryan A., Hammond, Samantha J., Wellner, Julia, van de Flierdt, Tina
Other Authors: Natural Environment Research Council, National Science Foundation
Format: Article in Journal/Newspaper
Language:English
Published: Cambridge University Press (CUP) 2024
Subjects:
Amundsen Sea
Antarctic
Antarctic Peninsula
Byrd
Marie Byrd Land
Pine Island Glacier
Thurston
Thurston Island
Thwaites Glacier
West Antarctic Ice Sheet
Antarc*
Antarctic Science
Ice Sheet
Sif Island
Online Access:http://dx.doi.org/10.1017/s0954102023000287
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102023000287
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Summary:Abstract 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 ɛ Nd , 87 Sr/ 86 Sr and ɛ Hf 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.

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