CRUSTAL STRUCTURE OF THE NORTHERN YUKON AND MACKENZIE DELTA, NORTHWESTERN CANADA

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 an d has an average velocity of 4 km/s; this overlies three crustal units , each having an average thickness of 11-15 lan and with average veloc ities of 5.9, 6.1, and 7.1 km/s. The Moho is at similar to 37 km with little relief and overlies an upper mantle with a poorly constrained v elocity. Tectonically, the study area lies between cratonic and Cordil leran North America and adjacent Mesozoic polar continental margin. Th e velocity models clearly illustrate a domainal crustal structure in t he 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 transit ion zone between these domains is well-defined and is interpreted as a Proterozoic paleocontinental margin, supporting previous interpretati ons based on geological trends and potential field data. Lateral homog eneity of the crustal velocity structure within Yukon domain supports interpretations that Arctic Alaska was not emplaced into its present p osition on strike-slip faults. Local variations in lower crustal thick ness, together with clear wide-angle Moho reflections, suggest a lower crustal and Moho signature possibly related to rifting, crustal exten sion, and magmatic intrusion and underplating during the Jura-Cretaceo us development of the Arctic Ocean and polar continental margin.