Three field photos of the study area.
One of the sampled eskers in the Canadian Northwest Territories: (a) overview aerial photo (the esker is indicated by “SCR”); (b) field photo of the esker showing the boulders and sand making it up; (c) pit from which zircon sample was collected. Credit: Bilak et al. [2022], Figure 3(a-c)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Geochemistry, Geophysics, Geosystems

The Acasta Gneiss Complex is a small region of bedrock in the Northwest Territories, Canada, that contains the oldest rocks currently known on Earth (4.02 billion years old). The study of this area is crucial to understanding how terrestrial crust first formed on our planet. Despite its significance, the region is poorly mapped with the exception of the initial discovery site due to its remoteness and widespread glacial-sedimentary cover.

In a new study, Bilak et al. [2022] adapted a strategy from diamond exploration and sampled regional-bedrock derived sediments from eskers (deposits formed by subglacial streams under the North American ice-sheet during glacial times). They then extracted and dated zircon crystals from these sediments to estimate relative proportions of diversely-aged bedrock in the area. The zircon-age distribution indicate that the majority of unmapped bedrock is roughly 3.37 billion years old; however, small vestiges of bedrock as old as 3.95 billion years old remain to be discovered in the unmapped area east of the region. This study provides guidance for future mapping projects and sampling campaigns in the region. 

Citation: Bilak, G. S., Niemetz, K., Reimink, J. R., Reyes, A. V., Chacko, T., DuFrane, S. A., et al. (2022). Evaluating the age distribution of exposed crust in the Acasta Gneiss Complex using detrital zircons in Pleistocene eskers. Geochemistry, Geophysics, Geosystems, 23, e2022GC010380.

—Peter van der Beek, Editor, Geochemistry, Geophysics, Geosystems

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