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

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.