Variations in effective elastic thickness of the North American lithosphere

Abstract

THE isostatic response of the lithosphere to loading can often be successfully represented by a model in which the weight of topographic features on the Earth's surface is supported in part by stresses within a flexed elastic plate overlying an inviscid asthenos-phere, and in part by the buoyancy forces associated with the deflection of density interfaces accompanying flexure^1,2. Previous estimates^3–10 of the apparent thickness of the elastic plate in North America, based on the shapes of sedimentary basins or the deformation accompanying slip on faults, range from a few to more than a hundred kilometres—or equivalently, flexural rigidities ranging from about 10²¹ to 10²⁵ N m⁻¹. Here we use a technique for estimating flexural rigidity that is not limited to sedimentary basins to map variations in the effective elastic thickness of the North American lithosphere. The effective elastic thickness ranges from a minimum of ∼4 km in the Basin and Range Province to >100 km in the Precambrian core of the continent, supporting the idea that flexural rigidity increases with time since the last thermal event¹¹.