The Lithosphere of the Mackenzie Mountains in northwest Canada

The Mackenzie Mountains are an enigmatic mountain range in northwestern Canada.  Earthquake focal mechanisms show the mountain range is actively building, even though it is 700 km from the nearest plate boundary, and there is little deformation closer to the plate boundary.  In this study, we present new results from the region, including joint local, Pn and teleseismic P tomography, crustal thickness from the Virtual Deep Seismic Sounding method and joint ambient noise/receiver function inversion, and temperatures inferred from earthquake-based and ambient noise-based Rayleigh wave phase velocities.  We find a thin lithosphere under the Mackenzies surrounded by a thick lithosphere, suggesting that mantle viscosity variations are contributing to the ongoing deformation.  However, we also find only a small increase in crustal thickness in the area which suggests the Mackenzies have not experienced significant contraction, despite several instances of uplift since about 100 Ma.  Velocity structure shows a plume-like low velocity structure ascending under the central Mackenzies.  The nature of the plume remains a mystery, as it is continuous from the mantle into the crust, but there is no evidence of magmatism at the surface.   It may be fluids, magma that hasn’t reached the surface, or a sub-solidus thermal anomaly.