Crustal structure of the northern Yukon and Mackenzie Delta, northwestern Canada

Abstract

Travel time inversion and amplitude forward modeling have been applied to two seismic refraction profiles from the northern Yukon‐Mackenzie Delta region of northwestern Canada. The two‐dimensional crustal P wave velocity models feature a near‐surface layer which is 1–7 km thick and has an average velocity of 4 km/s; this overlies three crustal units, each having an average thickness of 11–15 km and with average velocities of 5.9, 6.1, and 7.1 km/s. The Moho is at ∼37 km with little relief and overlies an upper mantle with a poorly constrained velocity. Tectonically, the study area lies between cratonic and Cordilleran North America and adjacent Mesozoic polar continental margin. The velocity models clearly illustrate a domainal crustal structure in the study area. A cratonic domain is characterized by a middle and lower crust with homogeneous velocities of 6.6–6.8 km/s. The other domain (“Yukon domain”) is characterized by midcrustal velocities near 6 km/s and a lower crustal layer with velocities near 7.1 km/s. The transition zone between these domains is well‐defined and is interpreted as a Proterozoic paleocontinental margin, supporting previous interpretations based on geological trends and potential field data. Lateral homogeneity of the crustal velocity structure within Yukon domain supports interpretations that Arctic Alaska was not emplaced into its present position on strike‐slip faults. Local variations in lower crustal thickness, together with clear wide‐angle Moho reflections, suggest a lower crustal and Moho signature possibly related to rifting, crustal extension, and magmatic intrusion and underplating during the Jura‐Cretaceous development of the Arctic Ocean and polar continental margin.