Plate Tectonics - is it in need of reassessment?

The past 50 years has seen a profound shift in the modelling of the processes thought to have shaped the continental and oceanic crust of our planet. Plate Tectonics (PT) has provided the paradigm towards which a major part of empirical earth sciences has been directed and assessed. It now dominates views on what predated the present disposition of continents and oceans, how their current arrangement came about, and the processes that even today are continuing to reshape the Earth’s crust. Few research projects are formulated to investigate other theories and little appears to be published that challenges the validity of this now dominant model.

There are however, increasingly acknowledged problems with the PT model. This and the following few posts briefly summarise what appear to be some of PT’s more substantial areas of weakness. They will then go on to outline a new hypothetical model that seems to provide a more consistent explanation for what has and continues to shape the crust of our planet. They will argue that massive and periodic changes from a dominance of tension to a dominance of compression forces within the crust are required to at once explain: the vertical upheaval of thickening oceanic floor to form continental land masses; the vertical depression of eroded continents to form new ocean floors; the formation of mid-oceanic mountain chains often adjacent to mid-oceanic rifts and “spreading zones”; the existence of compressive related fracture faulting adjacent to mid-oceanic rifts where tension failures should dominate; the processes whereby mountains continue to be formed on continental land masses; and the process whereby plateau continue to rise and fall. Similar to the processes responsible for the periodic ice-ages and the glacials and inter-glacials experienced during an ice-ages, it will be suggested that these cycles of tension and compression, periods of continental wide lifting and sinking, ... have at least part of their origin in the immense changes in thermal regime accompanying the very long term cyclic occurrence of the ice-ages, and to a lesser degree the glacials and inter-glacials experienced during an ice age. Whether as a result of the changes in cosmic ray flux, thought to be responsible for the ice-ages, or the variations in the Earth’s orbit around the Sun and the relationships between its axis of spin and the orbital plane, the consequential alternations in levels of solar radiation reaching the crust, the changing dispositions of surface water and ice and their effects on solar reflection and the changes of the surface thermal insulation affecting the conduction and convection of geothermal energy, will be argued to combine so as to produce massive changes in the thermal regimes within the earth’s crust. Over ice-age periodicities, occurring at intervals of circa 120Ma and lasting 10'sMa, there will be massive changes in geothermal flux with accompanying changes in geothermal gradient. Changes in geothermal gradient are suggested to be accompanied by phase changes beneath the crust and as a result give rise to significant changes in the effective thickness of the earth's crust. These periodic changes in the thickness of crust will in turn result in buoyancy swings that could well be the cause of the vertical tectonics and the periods of observed epirogeny and mountain building. Restraint of the expansions wanting to take place when the crust warms will induce massive compressive forces, while during the cooling cycles these same restraints will act to induce a dominantly tension field. Add to these through crust processes the less extensive but nevertheless substantial fluctuations in near surface temperatures caused by the period glacials and inter-glacials during an ice-age, and it becomes possible to envisage the  various cycles of thermal loading acting like a form of pump driving the many processes currently explained by PT. But importantly, it will be demonstrated how this new model is capable of resolving many paradoxes of PT and in particular could help to explain the issue upon which PT is noticeably silent, namely, the processes that cause long term vertical movement of both continental and ocean crust (“plates”).        

 Much of the above post has been taken from the paper "On the Causes of Vertical Motions of Lithosphere", James G A Croll, Frontiers meeting, Geological Society of London, November, 2011.