Recent discussion about the North-South bias of the major rift-valleys

The formation of the major rift-valleys is proposed to have been triggered off by the E—W oriented tensional “wave” caused by the slow rotation of the equatorial bulge passing as a stretching hoop through the Earth (Paleozoic—Mesozoic). This ‘wave’ follows the wandering of the polar axis through a great circle (e.g. Creer et al., 1969). The polar wandering is regarded as the readjustment of the Earth's rotational instability caused by the growth of a “weight” fixed on the surface of the Earth and endeavouring to increase its moment of inertia until the weight rotates on the new equator (Gold, 1950). This weight, which must topple the Earth through its fixed spacial axis of rotation, may be slowly developing Pangea. The “wave” of E—W tension is imposed on zones already under E—W tension, e.g., crests of N—S running welts, alias “craton ridges”. The intruding asthenosphere expands the crests and fractures them along tensional rift-valleys. These rifts may develop as spreading centers by gliding of the plates over a lubricating basalt magma.

The idea proposed by R. Schweickert (pers. commun., 1979) that the lithosphere is decoupled from the asthenosphere to an extent that the shell may rotate as a separate unit (as a means to explain how fixed plumes move in unison under the “roll” of the lithosphere) is dismissed. The subducted slabs act as braking flaps and cannot overcome the friction against the asthenosphere. The “roll” would be too young (50 m.y.), because the polar wandering according to Creer is much older.