The Wilson Cycle Revisited

Abstract

The purpose of this section is to show that plate evolution is a dynamic, non-conservative process. Therefore, plate deformation should occur not only at the boundaries of plates, but also in their interior. We will focus on the aspects of the Wilson cycle (Dewey and Burke 1974; Kearey and Vine 1996) where soft plate tectonics allows a different view from the standard theory. We can envisage that some processes which are known in the geological record can nevertheless be better approached in the context of dynamic systems than in the context of the various branches of linear basic sciences, namely mechanics. We also consider that plate tectonics is mainly a very efficient kinematic description but much of the underlying dynamics are just beginning to be sorted out now. Steady plate tectonic regimes are much easier to explain than the mandatory changes in regime recorded in tectonic history. We will pay special attention to modern analogues of transition situations where the plate tectonic setting is changing either in space or in time. Plate changes in time include (Davies 1999): steady growth or shrinkage of plates, changes in plate velocity, sudden or gradual formation of new plate margins, such as formation of new spreading centres, and finally, their propagation and jumping and formation of new subduction zones. The last case represents a major turning point in the Wilson cycle. All these changes are difficult to deal with in terms of the classical plate tectonics paradigm, and in fact have remained obscure until recently. Therefore, although many of the dynamic processes have been described in the classical literature of plate tectonics, because there is ample evidence that they operate in the geological record, there is still a lack of detailed and quantified studies that must explain these processes. Much work remains undone and we will try to show, in a non-linear approach to plate tectonics, that these processes must be considered inevitable rather than being anomalies that remain unexplained in a linear approach and only assume the steady state of plate kinematics.