Polar wander and global tectonics

Evidence suggests that irregularly-distributed degassing of the Earth has produced lateral physico-chemical variations in the mantle and the crust which in turn have instigated changes in the planet's moments of inertia. Intermittent events of spatial reorientation of the globe (polar wander) and a mixture of continual and episodic changes of planetary spin rate have ensued. Thus, the developing lithosphere has time and again been subjected to stepwise latitude-dependant torsion (wrenching) producing fold belts along time-equivalent equators, with a second set of tectonomagmatic rift belts evolving in palaeomeridional settings. Due to Earth's rotational slowing through time, the rift belts - oriented orthogonal to, and breaking away from, their corresponding palaeoequators - were of much greater significance in the Precambrian than during the Phanerozoic. However, in the course of time the global tectonic pattern has changed in concurrence with events of polar wander - the equatorial bulge and associated fold belt have now and then shifted their position across the globe. The relatively fast-spinning Archaean Earth had approximately its present spatial setting, but at around the Archaean-Proterozoic boundary a major event of polar wander took place, heralding a significant change in Earth history. Inertia-driven continental rotations, producing the presently-observed discrepancies in palaeomagnetic polar wander paths, basically dates from the time of the Alpine climax.