Imaging the internal structure of cratons can unravel fundamental notions about the tectonic processes that operated on a younger hotter Earth. In eastern Canada, the surface geology spans almost 3 Ga of Earth’s history, making it a natural laboratory, ideal to study the change in tectonic processes through time.
In this study, we image the crustal and lithospheric structure of the North American craton and its margins in eastern Canada, using earthquake data recorded at a newly deployed network of broadband seismographs (QM-III), in conjunction with existing networks (POLARIS, CNSN, USArray). The QM-III stations are located along a profile across the eastern Canadian Shield, from the southern tip of Hudson Bay to the Atlantic Ocean coast and have been recording since 2012. The surface geology consists of rocks that range in age from over 2.5 Ga in the northwest of our study area to 300 Ma in the southeast.
We use receiver function analysis (H-k stacking and transdimensional Bayesian inversion) to examine the Vp/Vs ratio, Moho depth and crustal shear wave velocity structure beneath each station, and surface wave phase velocity analysis to investigate variations in lithospheric structure beneath the region.
Receiver function analysis shows a thinner more felsic and homogeneous crust beneath the Archean terranes as opposed to a thicker, more mafic and more complex crust beneath Proterozoic regions, indicating a change in tectonic processes at the end of the Archean. Preliminary surface wave dispersion analysis also indicates intriguing differences between the lithospheric structure of older and younger terranes.
