Sm-Nd Isotope Mapping of the Ottawa-Bonnechere Graben within the Grenville Province
The Ottawa-Bonnechere Graben (OBG) and the Grenville Province (GP) are major crustal features that intersect along the border of Ontario and Quebec. The OBG was formed during a rifting event approximately 600 million years ago, creating a complex, seismically active normal fault system. The OBG can be found cross-cutting the GP, which is the youngest component of the Canadian Shield. The GP formed during a major mountain building event known as the Grenville orogeny caused by a continental collision approximately 1100 million years ago. While these geological features have been studied extensively as separate entities, the possibility of these structures interacting is high. One issue is the Chalk River nuclear waste facility, which is in the area and could be threatened by seismic activity. The region could provide valuable insight into how the formation of the OBG has altered the structure of the GP.
This study examined the relationship between the OBG and the GP using Samarium-Neodymium isotope dating to determine crustal formation ages. Rock samples collected southeast of Algonquin Park were analyzed. The resulting ages could be separated based on the structural divisions of the GP which were used to map faulted blocks of crust. Samples furthest northeast were found to be influenced by the OBG, with multiple blocks of downfaulted crust, while samples further southwest were unaffected. This research is crucial to finding the extent at which the OBG has altered the Earth’s crust on a local scale and how likely the area is to experience earthquakes.