MANTLE FLOW MECHANISMS FOR THE LARGE-SCALE SUBSIDENCE OF CONTINENTAL INTERIORS

Evidence in the geological record shows that continental interiors per iodically undergo enigmatic episodes of large-scale subsidence. We pro pose that mantle now associated with the descent of cold plumes and sl abs, and their interaction with the endothermic phase change at 660 la n depth, may provide a plausible mechanism for these epeirogenic event s. Simulations of mantle convection that incorporate the thermodynamic effects of the phase change and both depth- and temperature-dependent viscosity are used to model the descent of plumes and slabs through t he 660 km boundary. We find that the plume-stab flow scenarios are cap able of supporting topographic deflections of amplitudes of similar to 1 km and horizontal wavelengths of similar to 1000 km that persist ov er time scales of 100-150 m.y.