We found unexpected complexities resulting from the miscible displacement of a non-Newtonian fluid for both convergent and divergent flow as observed by displacing a miscible shear-thinning fluid (xanthan gum) in a radial Hele-Shaw cell. Such complex patterns have not been described before for either Newtonian or non- Newtonian fluids. A more viscous fluid was injected into the cell to displace a less viscous fluid (divergent flow) then withdrawn at the injection site (convergent flow). A variegated mixing fringe between the fluids developed during the injection phase, though this should have been a stable piston-like displacement. In addition to producing a large volume of blended fluid, the fringe altered the development of viscous fingers during the withdrawal phase. The dynamics of the interface during withdrawal was characterized by a concentric, superimposed fingering geometry, a result of the concentration gradient developed in the fringe. This poorly defined multifaceted interface was markedly different than what is seen in Newtonian displacements with similar viscosity contrast carried out with glycerol. The observed complexities of miscible displacement in shear-thinning fluids have implications for subsurface engineering applications such as oil recovery and groundwater remediation.