In Permian and Triassic times (300-200 Ma) long thin rifts were established across Africa that show both sinistral and dextral strike-slip movement. This was the first sign of Gondwana becoming unstable as a large continental entity. An Euler pole for this movement is 90 degrees distant from the rifts, NW of Africa in present-day coordinates. If we inscribe Euler small circles about the equator to this pole on the global reference frame, some intersting observations emerge (see animation).

In Early Jurassic times the Bouvet matle plume appears on this Euler equator. Northwest of it, West Gondwana continues its slow movement to the northeast while, southeast of it, East Gondwana starts to separate towards the southeast. The direction of separation changes at about 155 Ma and then, at about 130 Ma, the process of fragment dispersal accelerates as both East and West Gondwana develop the proto-oceans that become the present-day margins. Remarkably, the Euler equator remains the line of separation between the East and West Gondwana fragments with only Madagascar and Patagonia (Hoorn) showing any tendency to move with the 'other' part of Gondwana.

The Bouvet plume head and the triple junction in the ocean south of Africa remain firmly fixed to each other. Various traces of the mid-ocean ridge system are shown in colour for different times. Note that the track of Africa involves the Agulhas fault zone moving tangetially and monotonously along the Euler equator line (dashed outlines of the coast of South Africa shown at interval intervals of 20 myr).

Three phases of rifting are indicated within Africa. The Karoo (Permian-Triassic) rifts are shown in brown, the Early Cretaceous rifts in green and the current East Africa rift system in Yellow.

Is there something fundamental about our Euler equator in the global scheme of continental movements?

date: 2021-04-21