MANTLE AVALANCHES AND THE DYNAMIC TOPOGRAPHY OF CONTINENTS

The dynamic topography of continents associated with mantle avalanche events are discussed. Our flow simulations involve two-dimensional axi symmetric multi-phase mantle models which incorporate compressibility and a realistic, factor of similar to 40, increase in viscosity with d epth. The surface kinematic boundary conditions involve a mix of free and rigid (i.e., no-slip) constraints, with the latter intended to mim ic the influence of a spherical continental cap. We find that avalanch e events support regional vertical deflections of up to similar to 2.5 km. The horizontal length scale of the dynamic topography is similar to 2500 km and non-negligible deflections can persist on the order of 100-200 Ma. We also find that convergence rates in regions surrounding the continents are variable but can reach rates of the order of 3 cm/ a. Finally, we speculate that an avalanche event may have been respons ible for the development of the large-scale intracontinental basin sys tem in the western interior of North America from the Early Devonian t o Late Carboniferous [1].