The tectonic jigsaw puzzle of the Red Sea

What is it about?

Early reconstructions of Earth's tectonic plates were based on the similarities of the shapes of opposing coastlines and similarities of the geology on the adjacent continents. This is illustrated by Du Toit's map (Figure 1), where he joined sites of ancient granites and fauna across the South Atlantic. The tectonic plates, viewed in this way, are like jigsaw puzzle pieces, which we assemble by matching continental edges and patterns of terrains within the continents. Some researchers have similarly tried reconstructing the Red Sea like this, as the geology of the shield rocks is well exposed on both sides. However, new information has emerged from maps of Earth's gravity field derived by measuring the sea's topography very accurately with radar altimeters on satellites (water flows "downhill" to where the attraction is strongest, hence equilibrium water level reflecs the gravitational attraction). Such maps reveal almost straight structures crossing the sea caused by the topography of denser rocks underlying thick sediments. These structures were created as the Red Sea rift opened, suggesting the direction of that opening. In Figure 2, the Shagara Structures in Sudan are linked with the Bi'r Umq Suture in Arabia, whereas the Nakaseib is linked with the Fatma shear zone. These are different associations from those made previously from merely comparing the geology on land on both sides.

Featured Image

Photo by Hans-Peter Gauster on Unsplash

Photo by Hans-Peter Gauster on Unsplash

Why is it important?

The new reconstruction is consistent with plate-reconstructions based on the more recent marine magnetic anomalies and GPS, further supporting the view that the Red Sea opening has occurred about a single Euler pole of rotation. The connection between the shield structures and the offshore gravity structures also suggests that the shield structures controlled the geometry of rifting and subsequently also controlled the geometry of the new oceanic spreading ridge (i.e., its segmentation). This connection has been noted for very large transform faults but not, as far as we are aware, for such small "non-transform oceanic discontinuities".

Perspectives