Experimental tests of simple models for the dynamics of diffuse oceanic plate boundaries

Diffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here we build on our prior work in which we use analytical and numerical models to investigate the dynamics of diffuse oceanic plate boundaries assuming that the vertically averaged rheology of deforming oceanic lithosphere is characterized by a power-law rheology, that is, is an element of alpha tau(n) where 1 = 3. Here we use laboratory experiments to test the general validity of this conclusion. In these analogue experiments, deforming oceanic lithosphere is modelled alternately with a Newtonian fluid (n = 1) and a power-law fluid (n approximate to 6-10). The experimental results are consistent with the analytical and numerical models. In particular, the experimental results confirm that for a given applied force the pole of rotation is more strongly confined to the laboratory analogue of a diffuse oceanic plate boundary for a power-law fluid than it is for a Newtonian fluid. For forces applied far enough from the centre of the analogue diffuse plate boundary, however, results for Newtonian and power-law fluids are similar.