NWT RESEARCH DATABASE

Tags: physical sciences, geology, sediment, acasta gneiss

Objective(s): To identify previously unmapped outcrops of ancient continental crust in the Acasta Gneiss Complex.

Project Description: For this research the Principal Investigator (PI) propses an innovative combination of quaternary geology, isotope geochemistry, and Precambrian geochronology that will identity previously unmapped outcrops of ancient continental crust in the Acasta Gneiss Complex (AGC). An age range and bedrock composition will be generated for the research area and used to help further the understanding of the processes involved during the formation of early continental crust. In the field the research team will be sampling eskers, sinuous deposits of sediment laid down by rivers that flowed beneath the ice during the retreat of the Laurentide ice sheet. These eskers are composed of sediments eroded subglacially from local/regional bedrock, and cut across bedrock terrane boundaries within the Acasta Gniess Complex. The PI will sample up-ice-flow and down-ice-flow of known bedrock contacts, including those that define mapped 3.8-4.0 Ga (a billion years) outcrops, to test the hypothesis that esker sediments preserve geochemical and geochronological signatures of local bedrock. Next, the PI will sample several esker transects in unmapped areas of the AGC. By exploiting the sediment left behind in these eskers, a large, unexplored area of the AGC can be efficiently sampled and geochemically analysed. Specifically the research team will be targeting the sand rich areas of the esker ridges for sampling. Samples will be obtained by hand using a spade. Samples will be individually bagged and labeled, and then placed in 22L buckets for transport to the University of Alberta. Roughly 10 kg of sand will be taken per transect, and 3-5 transects should be expected. In the lab, the PI will use laser-ablation inductively-coupled-plasma mass-spectrometry to date detrital zircons recovered from esker sediments, with clusters of ages 3.8-4.0 Ga indicating ancient continental crust outcrops in the up-ice-flow direction. The PI will also identify the unique geochemical signature of the source rocks contributing to the glacial sediments. Collectively, these techniques will allow the research team to identify ancient crustal relics and provide direct empirical evidence to form and support a model for the initial formation of continental crust. The PI will be presenting the findings to any interested local community members at the Yellowknife Geosciences Forum. At the forum, the PI will discuss the techniques and methods employed during the research, as well as any findings and conclusions. The samples I collect will also be shared with members of the Northwest Territories Geological Organization for use in Kimberlite exploration. Kimberlites are diamond bearing cylinders of rock brought up from the deep sub-surface and are of significant economic importance. This research will be presented at the annual Yellowknife Geoscience Forum in the Fall of 2017. Here the team will present the findings and conclusions to local community leaders, fellow northern researchers, the local industry representatives, as well as any government representatives in attendance. The research team will coordinate with the Aurora Research Institute in planning one or more visits to NWT communities to directly communicate the results of this study and other northern research themes, including visits to local schools to share unique research samples. The team will also be presenting the research to the University of Alberta northern research community at the annual Northern Research Day conference. The fieldwork for this study will be conducted from July 13, 2017 to July 22, 2017.