Article

West Antarctic subglacial geology distinguished by Pb isotopes and Rb–Sr ages in ice-rafted feldspars

Thomas Arney, Claus-Dieter Hillenbrand, Thomas M. Belgrano, J. Andy Milton, Christine S. Siddoway, Gavin L. Foster, Paul A. Wilson, Julia S. Wellner, and Steven M. Bohaty

Earth and Planetary Science Letters vol. 693 () : 120298 DOI: 10.1016/j.epsl.2026.120298

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Abstract

Provenance data from sediment delivered to the marine environment by icebergs can trace past ice sheet dynamics and help constrain the ice sheet models used in sea level projections. This approach requires an interpretative framework, but in Antarctica, blanketing ice sheets hinder knowledge of upstream geology. Here, we tackle this problem by presenting a coupled laser ablation–based Pb isotope and Rb–Sr age study of ice-rafted feldspar grains from shelf sediments along West Antarctica’s Pacific margin. We identify five distinct clusters in Pb isotope composition, each associated with Rb–Sr age clusters interpreted as West Antarctic magmatic episodes. One cluster suggests granitoids recently identified in geophysical data from the Thwaites Glacier bed may be Ross orogen plutons in a rifted block of Transantarctic Mountains crust. A Middle Jurassic cluster fringing the Thurston Island crustal block reflects Chon Aike magmatism, and a cluster restricted to western Marie Byrd Land points to extensive subglacial exposure of Carboniferous anatectic granites in the Ford Ranges. These Pb isotope groups can be used as tracers to infer past ice extent and erosional dynamics of glaciers in the Amundsen Sea Embayment, including the Thwaites and Pine Island glaciers. Our approach provides a powerful and high-throughput tool for studying detrital provenance in West Antarctica and could be generalized for use in other inverse provenance studies around Antarctica and beyond.

Highlights

  • Coupled in situ feldspar Pb–Pb and Rb–Sr in ice-rafted marine surface sediments.
  • Machine learning used to cluster Pb isotopes and reveal geographical patterns.
  • Each Pb cluster has a distinct Rb–Sr age, validating the clustering method.
  • Unique Pb–Pb, Rb–Sr signals for Thwaites Glacier and Thurston Island debris.

The interior of West Antarctica is covered by ice thousands of metres thick, and its geology is therefore much less well-constrained than most other areas, hindering our understanding of the tectonic evolution of the region.

Material eroded from the bedrock beneath the large glaciers which cover Antarctica is transported to the coast and then by icebergs to depositional sites on the continental shelf. This provides physical material from under the ice, and therefore constitutes an excellent opportunity to study the geology of subglacial terrains.

Using laser ablation mass spectrometry, we measured Pb, Rb, and Sr isotopes in ice-rafted feldspar grains from marine sediments around the West Antarctic margin. We then applied clustering algorithms to the Pb isotope data to identify distinct groups of grains, and constructed Rb–Sr isochrons for each group to arrive at a magmatic age for each group. The resulting multi-proxy fingerprints provide an insight into the geology and tectonic history of the West Antarctic interior.

By helping to characterise the geology of the West Antarctic interior, our results also provide a foundation for future studies of ice sheet history in the region because if IRD can be matched back to a known source, researchers can infer erosion in that area and a transport pathway to the depositional site. This can be used to constrain ice sheet models, which are used in projections of sea level rise.