Finite-frequency P-wave tomography of the Western Canada Sedimentary Basin: Implications for the lithospheric evolution in Western Laurentia

Abstract

The lithosphere beneath the Western Canada Sedimentary Basin has potentially undergone Precambrian subduction and collisional orogenesis, resulting in a complex network of crustal domains. To improve the understanding of its evolutionary history, we combine data from the USArray and three regional networks to invert for P-wave velocities of the upper mantle using finite-frequency tomography. Our model reveals distinct, vertically continuous high (>1%) velocity perturbations at depths above 200km beneath the Precambrian Buffalo Head Terrane, Hearne craton and Medicine Hat Block, which sharply contrasts with those beneath the Canadian Rockies (<−1%) at comparable depths. The P velocity increases from −0.5% above 70km depth to 1.5% at 330km depth beneath southern Alberta, which provides compelling evidence for a deep, structurally complex Hearne craton. In comparison, the lithosphere is substantially thinner beneath the adjacent Buffalo Head Terrane (160km) and Medicine Hat Block (200km). These findings are consistent with earlier theories of tectonic assembly in this region, which featured distinct Archean and Proterozoic plate convergences between the Hearne craton and its neighboring domains. The highly variable, bimodally distributed craton thicknesses may also reflect different lithospheric destruction processes beneath the western margin of Laurentia.