Strong lateral strength contrasts in the mantle lithosphere of continents: A case study from the hot SW Canadian Cordillera

Abstract

This study aims at quantifying the 3-D variability in lithosphere strength of the south-eastern Canadian Cordillera and adjacent craton to the east. Strength is calculated in a forward manner, starting from rheological laws of brittle and ductile deformation. The work flow calculates a temperature model based on a multi-layer compositional model and subsequently estimates the strength distribution from both the compositional and temperature models. The temperature modeling involves numerical inversion and cubic spline algorithms which enable to impose boundary conditions that account better for strong lateral variations in lithosphere thickness and lateral heat flow. This addresses the lithosphere structure between the Canadian Cordillera and craton. The Canadian Cordillera is marked by a hot and thin lithosphere of ~60 km thickness that stands in contrast to a cold and thick craton of ~170 km thickness to the east, which consequently results in pronounced changes in bulk lithosphere strength. The high surface heat flow of the Cordillera interior and its contrast with the Foreland Basin can be reproduced by temperature models that combine elevated mantle heat flow due to the thin lithosphere and higher crustal heat production from magmatic intrusions. A series of rheological models, which examines the role of different temperature input models, composition and strain rate, shows that the first-order strength pattern is persistent. For the hot Canadian Cordillera, strength resides for >80% in the upper crust and with integrated lithosphere strength of 2.0–3.5⋅106 MPa⋅m. For the cold craton, the upper mantle provides >75% of the integrated strength with values of 4.0–8.0⋅106 MPa⋅m for the crust and 20–65⋅106 MPa⋅m for the lithosphere. Effective elastic thickness is estimated between 5 and 15 km for the Cordillera and 40–80 km for the craton. This illustrates the Cordillera to craton transition as a prominent rheological feature for upper mantle flow dynamics and spatial seismicity trends.