TAGGING GLACIAL EROSION AND TILL PRODUCTION FOR DRIFT PROSPECTING

Among challenges of mineral exploration in glaciated terrain are the characterization of glaciological processes that control till production, transportation, and deposition in regions glaciated by ice with varying thermal regimes. The basal thermal regime of ice caps and sheets control rates and styles of glacial erosion and therefore till production. In a selected region of northern Baffin Island we classified regions of past cold-based (ice frozen to substrate) or warm-based (sliding on and within bed) glacier cover based on sedimentology (clast angularity, matrix characteristics), clast provenance (abundance of exotic lithologies), and geomorphology (e.g. lateral meltwater channels). Tills from 19 sites were analysed for cosmogenic 10Be and 26Al to test the hypothesis that areas of cold-based (less erosive) ice should retain pre-glacial concentrations of the terrestrial in situ cosmogenic nuclides (TCN). In all sites the TCN concentrations reflected the degree of glacial erosion, with more than two orders of magnitude difference in concentrations between the end-member classes (normalized to sea level and adjusted for small amounts of post-glacial TCN production). A clear relationship between 26Al/10Be and classified thermal regime support these findings by showing that the cold-based regions experienced pre-glacial exposure interrupted by a long period(s) of burial, presumably by ice, whereas the warm-based zones had simple exposure histories with no evidence of burial. Three sites had features of both cold-based and warm based conditions, and the TCN concentrations and 26Al/10Be indicate an intermediate history of exposure and shorter burial than pure cold-based end member sites. UMISM, a finite element thermomechanical ice sheet model predicts the same basal conditions and is used in conjunction with the TCN to help resolve paleo-glacier dynamics and till provenance. The measurement of minimum ice burial durations of ~3 Myr, suggesting that recently deglaciated surfaces near modern ice caps may have been covered since the Pliocene, is a remarkable account of the impact of the current climate change on Baffin Island ice caps.