Ar-40/Ar-39 and Pb-Pb study of individual hornblende and feldspar grains from southeastern Baffin Island glacial sediments: implications for the provenance of the Heinrich layers

摘要

Lead isotope analysis of individual feldspar grains and Ar-40/Ar-39 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 H-2 in core HU87-033-009 from northeast of the Hudson Strait in the Labrador Sea. Specifically, in H-2 samples from HU87-033-009, the Pb-207/Pb-204 is high for a given value of Pb-206/Pb-204. Additionally, the range in Pb-206/Pb-204 is greater in HU87-033-009 samples, and there are two distinct trajectories of Pb-208/Pb-204. The steeper of the Pb-208/Pb-204 versus Pb-206/Pb-204 trends is not seen in the studied Baffin Island glacial sediment samples. Samples of feldspar grains from Heinrich layers H-1, H-2, H-4, and H-5 from core V28-82 in the eastern North Atlantic have a Pb-207/Pb-204 versus Pb-206/Pb-204 relation similar to that of Baffin Island till samples, but there is also a high Pb-208/Pb-204 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. [References: 72]