CRUSTAL STRUCTURE OF THE EASTERNMOST CANADIAN SHIELD: EVIDENCE FROM RECEIVER FUNCTION ANALYSIS IN NORTHERN QUÉBEC AND LABRADOR

Eastern Canada preserves 4 billion years of geological history, including the Archean eastern Superior and North Atlantic cratons, the Paleoproterozoic Trans-Hudson, New Quebec and Makkovik orogens, and the Mesoproterozoic Grenville orogen. To understand the processes that have affected this complex portion of the North American continent, we use receiver function analysis to model crustal structure at 9 seismograph stations distributed across northern Québec and Labrador. The stations sample the edges of the eastern Superior craton, its neighbouring Paleoproterozoic orogens, and the remaining fragment of the North Atlantic craton preserved in Canada. We model 1D profiles of shear wave velocity structure using receiver function waveforms inverted jointly with dispersion curves based on a global compilation. The dispersion curves reduce the problems of non-uniqueness inherent to receiver function analysis.

Across this vast and remote region, we observe significant variations in crustal thickness, Moho sharpness and shear wave velocity structure. Many of the stations also exhibit back-azimuthal variations consistent with dipping and/or anisotropic structures. The thickest crust (44-55 km) is associated with Paleoproterozoic orogenic belts, whereas stations situated within Archean domains exhibit a shallower Moho (33-38 km). Bulk crustal Vp/Vs ratios do not show an obvious correlation with surface geological age, unlike in other parts of the Canadian Shield; however, this may be at least in part due to the complexity of the crustal structure.

We integrate the new crustal models with information from previous studies in the region based on both receiver function and active-source data, and discuss the implications for the assembly and evolution of the eastern Canadian Shield.