Creation and Preservation of Cratonic Lithosphere

Abstract

Cratons are areas of continental lithosphère that exhibit long-term stability against deformation. Seismic evidence suggests that cratonic lithosphère may have formed via thrust stacking of proto-cratonic lithosphère. We conducted numerical simulations and scaling analysis to test this hypothesis, as well as to elucidate mechanisms for stabilization. We found that formation of cratonic lithosphère via thrust stacking is most viable for buoyant and viscous lithosphère that is thin and/or possesses low effective friction coefficients. These conditions lead to low integrated yield strength within proto-cratonic lithosphère that allows it to fail in response to convection-generated stresses. Specifically, formation via thrust stacking is viable for lithosphère with chemical to thermal buoyancy ratios of B = 0.75-1.5, viscosity contrasts between the lithosphère and convective mantle of Δη > 102, and friction coefficients of μ = 0.05-0.1. Preservation depends on the balance between the chemical lithosphère 's integrated yield and convection-generated stresses. The physical process of thrust stacking generates a thickened cratonic root. This provides a higher integrated yield stress within cratons, which is more conducive to stability subsequent to formation. Increased friction coefficient values, due to dehydration, can also provide higher integrated yield stresses within cratons. To provide long-term stability, integrated yield stresses must be great enough to offset future mantle convection-generated stresses, which can increase with time as the mantle viscosity increases due to cooling. Thin or rehydrated cratonic lithosphère may not provide stability against the increasing convective stresses, thus providing an explanation as to why some cratons are not long-lived. Show more