STRESS DISTRIBUTIONS ASSOCIATED WITH COMPENSATED PLATEAU UPLIFT STRUCTURES WITH APPLICATION TO THE CONTINENTAL SPLITTING MECHANISM

Regions of plateau uplift such as western USA and East Africa are known to be in isostatic equilibrium as a result of hot, low density regions in the underlying upper mantle. The combined effect of the excess topography and upthrust of the low density region below it causes deviatoric stresses to occur in the intervening region. These stresses have been investigated by finite element analysis. Assuming a purely elastic model, the horizontal deviatoric tension is about 20 MPa (200 bar) in the crust beneath a compensated plateau uplift of 2 km, with stress differences in the mantle dying off towards the base of the low density region. If the lithosphere is more realistically modelled by an upper elastic layer above a viscoelastic region, then the equilibrium deviatoric stresses are much larger in the elastic part of the crust, reaching about 100 MPa (1 kbar) if the elastic layer is 10 km thick. A small finite strength in the viscoelastic region has little effect on the equilibrium stresses. The value of the viscosity does not much affect the equilibrium. Such a stress system may explain the Occurrence of graben formation, dyke intrusion, and possibly continental splitting, within the setting of a hot upper mantle with associated domal uplift. Copyright © 1979, Wiley Blackwell. All rights reserved