7. Tectonic Plate movements driven by Circumferential forces
7.1 Regional metamorphism
In order to maintain the sustained unidirectional movement of Pangea northwards followed by the east and westward movements of crustal plates either side of the central part of the African plate, the applied forces have to be both substantial and have a stable permanent origin. It is this requirement that will cause the relative movement of the continental crust, with its variable underside topography, to be forced over the almost mountainous terrains of the oceanic crust. The resistance to motion will result in a plethora of metamorphic processes varying from high and low pressure water rejection, to high pressure/high temperature regional metamorphism that would change the crystal structure of the rocks involved. This is in addition to the pushing, tilting, deformation and uplift of sedimentary sequences from their original horizontal position thus forming the mountain ranges we are now familiar with. The forces associated with the above-mentioned processes would need to be evaluated in conjunction with laboratory simulations and reported field observations to determine the realistic value of the Circumferential Force F and the applied pressure loads at the particular locations. These processes are illustrated in Fig 29.
7.2 Tectonic Plate Movement sequence diagram
Fig 30 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.