9. Momentum Considerations
9.1 The Momentum of the moving Continental Plate drives the Subduction Process
9.2 Topography and orogenic activity related to slab detachment
With reference to the subduction process as described in (fig 16) it is feasible to explain the South Alaskan sequence (fig 17) as being due to the continuous movement of the overriding Continental plate. This movement was responsible for the successive separate orogenic cycles resulting from oceanic lithosphere bending followed by slab detachment. This cyclical activity led to the formation of the St. Elias Range which in turn led to the formation of the Alexander and Yukon Terranes and the present-day Accretionary Wedge as the Continental Plate moved south.
9.3 Summary. Subduction is a consequence of Tectonic Plate movements
Present wisdom regarding the role of subduction with respect to tectonic plate movements needs to be re-examined as the absence of a slab and thus the absence of a slab-pull force does not impede the movement of the continental plate. It therefore follows that subduction cannot be considered as the major driving force of plate tectonics. As such, subduction of the oceanic plate must be considered as the consequence of continental plate movements rather than as the driving force of plate tectonics. Using the above hypothesis in which subduction and with or without Slab pull is not the driving force for tectonic processes it is not unrealistic to relate the tectonic forces to the unbalanced rotation of the Earth.
9.4 Tectonic Plate Movement sequence diagram
Fig 17 reinterprets the original Hess model of subduction by circulatory convection currents with one that shows tectonic plate movements as being a function of the centripetal and differential tensile forces associated with the constant rotational velocity of the Earth. Thus ‘Slab Pull’ on the oceanic crust is replaced by ‘Tensile Stress Pull’ on the continental crust as being the major force for moving continents together or apart. In this respect the variable omnidirectional convection current driving force is replaced by a permanent constant force related to the rotational speed of the Earth. Furthermore, ‘Seafloor Spreading’ as described by Hess is replaced by ‘Upper Mantle Stretching’ and magma intrusion onto the sea floor is considered as an inevitable consequence of the propagation of the rifting of the mantle. As such, magma intrusion has no contribution to the forces moving tectonic plates. This interpretation does not invalidate research work at the convergent and divergent margins as the mineralogical and geological outcomes will be the same. As the stress calculations are based on the Earth’s constant rotational velocity, the forces available for all tectonic processes are not subject to conjecture regarding both the source and direction of the omnidirectional convection currents. This approach allows for the mathematical analysis that is applicable to fixed rotating bodies to be modified and utilised for the study of tectonic, orogenic and metamorphic processes.