Nature and Thermal State of the Cordilleran Lithosphere in Northwestern Canada From a Compilation of Broadband Seismic Studies

Date: 4/26/2019

Time: 04:45 PM

Room: Cascade II

Various geophysical and geological data indicate that the lithosphere in the northern Canadian Cordillera (NCC) is thin and hot due to its position in a former arc and back arc setting. However, models of the origin and nature of the lithospheric mantle and persistence of the heat source beneath the NCC are debated and direct constraints on lithospheric mantle structure are sparse. The deployment of various broadband seismic networks in the area, including the USArray Transportable Array, is now affording a new opportunity to study the structure of the Cordilleran crust and mantle. In this work we co-examine recent seismic structural models that constrain various components of the NCC lithosphere at different resolution, including receiver functions, teleseismic shear-wave splitting, surface-wave tomography, and teleseismic body-wave tomography. These models indicate that: the Moho has low topography and lies at ~30-35 km depth; the seismic lithosphere-asthenosphere boundary is located at ~50-60 km; and the Cordillera-Craton (CC) boundary at lithospheric depth extends beneath the Cordillera. Toward the south of the NCC, we also identify a structure dipping toward the NCC that is anchored west of the Cordilleran Deformation Front. We examine end-member tectonic models that explain these observations: 1) the thin lithosphere is long-lived; or 2) the lower lithosphere was recently removed and is being rejuvenated. In the long-lived model, steady-state thermal calculations indicate that the Moho is ~950ºC; in the lithosphere removal model, time-dependent thermal calculations suggest that an event occurring 10-20 My ago can reproduce the thermal and structural constraints. Finally, we discuss the tectonic and geophysical consequences of both end-member models combined with geologic evidence and favor models where the lithosphere of the NCC is either exotic or the result of progressive thickening and cooling since the Miocene.

Presenting Author: Pascal Audet

Authors