Based on the hypothesis that the chimpanzee-human-last-common-ancestor (CHLCA) split resulted from geographical isolation on the Danakil micro-continent (where species endemic to the Pliocene Afar region, such as Hippopotamus afarensis^[1], Hipparion afarense^[1] and Kolpochoerus afarensis^[1] would be results of speciation from geographical isolation as well), then Danakil would have separated from Ethiopia around the time when new species appear in the fossil record, with Ardipithecus Kadabba dating to 5.8 Ma.

Tentatively, a time-window for the Danakil-Ethiopia rift could be 6–10 Ma.

The tectonic history of Danakil

The Suph rift (what today is the Red Sea), Central Indian rift, and Turkana rift, extended towards a tectonic focal point north of the Afar region, the direction where there was least resistance, resulting from a simultaneous crustal rupture.

As the rifts progressed, the focal point moved south, causing the Central Indian Rift to change its angle (at the point in time ω), as well as a change in angle in the Turkana rift as it extended into the Ethiopian rift, intersecting with the Red Sea rift in the position where the Afar region is today.

The Red Sea rift reached the Danakil block before the Ethiopian rift, while it was still attached to Ethiopia (and so, before there even was a Danakil block). The Ethiopian rift cut through the Ethiopian continent slightly to the west of the southward progression of the Red Sea, separating a chunk of the continent. The Afar region, as the intersection and tectonic focal point of three separate crustal rifts, and the continuation of the Turkana rift, expanded in a west-east direction more than the Red Sea and Gulf of Aden, causing Danakil to move (relative the Turkana rift) in the direction of the Arabian continent, and rotate counter-clockwise.

For comparison, the separation of Madagascar was caused by a triple junction from the three rifts that initiated the opening of the Indian Ocean^[2], and progressed along a similar sequence of events as the separation of Danakil, with all rifts intersecting at a tectonic focal point south of Madagascar.

References

1. Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia
2. On the Origin of Continents and Oceans- A Paradigm Shift in Understanding