Back-Arc Spreading and Proper Motion

Back-arc spreading was one of the big auxiliary surprises of second-generation plate tectonics. Tectonicists had visualized convergence of plates as resulting from converging convection cells with consequent compressive structures. As the geometric implications of plate tectonics began to be elaborated, the idea of convection cells tied to plate geometries evaporated. The documentation of back-arc spreading provided additional support for the decoupling of convection and plate kinematics. However, the mechanism for the origin of back-arc spreading has remained uncertain, although the ideas of Moberly were introduced shortly after spreading was demonstrated.