Abstract

Lead isotope analysis of individual feldspar grains and 40Ar/39Ar analysis of individual hornblende grains from three samples taken from Baffin Island ice-proximal till deposits are consistent with a provenance recording a two-stage geologic history including formation of continental crust in the Late Archean and partial isotopic resetting and (or) reequilibration during major Paleoproterozoic regional metamorphism and magmatism. Significantly, although the populations are small, and the two-stage Archean–Paleoproterozoic history of their sources are similar, the Pb isotope compositions of samples from Baffin Island do not match the results from Heinrich layer H2 in core HU87-033-009 from northeast of the Hudson Strait in the Labrador Sea. Specifically, in H2 samples from HU87-033-009, the 207pb/204pb is high for a given value of 206Pb/204Pb. Additionally, the range in 206Pb/204Pb is greater in HU87-033-009 samples, and there are two distinct trajectories of 208Pb/204Pb. The steeper of the 208Pb/204Pb versus 206Pb/204Pb trends is not seen in the studied Baffin Island glacial sediment samples. Samples of feldspar grains from Heinrich layers H1, H2, H4, and H5 from core V28-82 in the eastern North Atlantic have a 207Pb/204Pb versus 206Pb/204Pb relation similar to that of Baffin Island till samples, but there is also a high 208Pb/204Pb that we have not captured in this suite of glacial sediment samples. Our results highlight the strength of a combined radiogenic isotope approach to characterizing the geological history of sediment sources and provide a first step in assessing the variability in isotope character in this region of dynamic glacial events during the late Quaternary Period.

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