Hotspot paths below Arabia and the Horn of Africa: evidence and consequences

S. Vicente de Gouveia¹, J. Besse¹, D. Frizon de Lamotte², M. Greff-Lefftz¹, M. Lescanne³, F. Gueydan⁴ and F. Leparmentier⁵

¹Institut de Physique du Globe de Paris - Sorbonne Paris Cité, Université Paris Diderot, UMR CNRS 7154. 1 rue Jussieu, 75252 Paris 05, France, vicente@ipgp.fr ; besse@ipgp.fr ; greff@ipgp.fr

²Département Géosciences et Environnement, Université de Cergy-Pontoise, Cergy-Pontoise, France, Dominique.Frizon-de-Lamotte@u-cergy.fr

³Total EP, Pau, France, marc.lescanne@total.com

⁴Géosciences Montpellier, Université de Montpellier, CNRS UMR 5243, Montpellier, France, frederic.gueydan@umontpellier.fr

⁵Total EP, Paris La Défense, France, francois.leparmentier@total.com

This webpage is a summary of: Vicente de Gouveia, S., J. Besse, D. Frizon de Lamotte, M. Greff-Lefftz, M. Lescanne, F. Gueydan, and F. Leparmentier (2018), Evidence of hotspot paths below Arabia and the Horn of Africa and consequences on the Red Sea opening, Earth planet. Sci. Lett., 487, 210-220, doi:https://doi.org/10.1016/j.epsl.2018.01.030.

We investigate the history of three hotspots of the East African area widely described in the literature (Afar, East-Africa and Lake-Victoria) with the aim of retrieving their ancient traces, and linking their activity to the evolution of the Red Sea Rift system. Hotspot activity is episodic and irregular, as shown by the discontinuously spaced volcanic edifices on oceanic hotspot tracks, while the tracks themselves have a finite duration of tens to hundreds of millions of years. With the exception of continental flood basalts, knowledge of hotspot locations under the continental lithosphere remains poor, and their tracks are particularly difficult to know as the lithospheric thickness filters their surface effects. We defined from various lines of evidence present day hotspot coordinates. We then predicted past locations of our East African hotspots using a hotspot reference frame classically established on oceanic plates, which assumes that hotspots are approximately fixed and stable features over time in the mantle. Our preferred model is that of O’Neill et al. (2005) (for a summary, see de Gouveia et al., 2018).

Our starting point is to refine as much as possible the present location of:

The computed hotspot trajectories are shown on Figure 1 from the present to 110 Ma. The track expected for the Afar hotspot started from northeast of Arabia and continued along the eastern boundary of the plate close to the present Zagros Front (Figure 1). At 50 Ma it changed direction and moved toward the present Afar triple junction, where it is currently located (Figure 1). The track expected for the East-Africa hotspot followed exactly the incipient plate boundary between Africa and Arabia, i.e., the present Red Sea, from 90 Ma to 40 Ma. At 40 Ma. It underlies the site of the present Afar triple junction, and continued to its present location (Figure 1). The Lake-Victoria hotspot came from the middle part of the present Red Sea and travelled southward to its current location (Figure 1).

Figure 1: Geological context of the Arabian and African plates. The computed hotspot tracks were determined at 10 Ma time-intervals, according to O'Neill et al. (2005). Triangles with white dots – present day hotspot locations. Shaded area – minimum influence area of a hotspot with a diameter of 500 km. The Ethiopian-Yemen traps lie at the junction of the East-Africa and Lake-Victoria hotspot paths. Map presented as a Robinson projection.

We then searched for evidence of hotspot activity along the predicted paths. We particularly focused on:

1. heat-flow anomalies;
2. uplift due to plume buoyancy (Campbell, 2001);
3. geochemical signatures of alkali basalt volcanism, indicating plume-like magmas (Campbell, 2001).

We supposed that any hotspot effects would be seen within a circle of 500 km diameter at the surface, keeping in mind that this area could be wider if the plume head had spread beneath the continental lithosphere. We also assumed that all hotspot effects occurred above the hotspot’s expected location. We considered the advection of plumes to be of minor significance.

Evidence for long-lived hotspot activity along the predicted hotspots tracks may be summarized (Figure 1):

Along the Lake-Victoria hotspot track:

Along the Afar hotspot track:

Figure 2: (a) Map of Arabian plate heat flow. Diamonds – heat-flow data from Morgan et al. (1985) and Rolandone et al. (2013). Dots – heat-flow data estimated from borehole data (TOTAL database). Green triangles symbolise the Afar hotspot location over time, according to the hotspot reference frame of O'Neill et al. (2005). The green shaded area indicates the minimum influence area within which hotspot consequences should be found. (b) Heat-flow profile along ABB' which crosses the Afar hotspot path at ~45 Ma. The blue shaded area indicates high heat-flow values. Only data with an error of less than 20 mW/m² are plotted. The heat-flow map is presented as a cylindrical projection. Corresponding topographic profiles relative to the sea floor (solid line), and the thickness of the lithosphere (dashed line) were determined using Google Earth and the lithospheric model of Globig et al. (2016).

Along the East-Africa hotspot track:

East-Africa and Afar hotspot activity was found at least episodically back to 110 Ma and 90 Ma respectively. No activity was found for the Lake-Victoria hotspot prior to the Cenozoic. The results for the East-Africa hotspot track showed that the Afar hotspot cannot be the origin of the Ethiopian-Yemen traps at 30 Ma because it was located too far away. Conversely, our reconstruction shows that the East-Africa hotspot is the best candidate for explaining this volcanic activity. The existence of activity along the East-Africa track as far back as the Cretaceous suggests that this hotspot was episodically active long before the eruption of the Ethiopian-Yemen traps, and may indicate that continental flood basalts are related to an earlier-existing hotspot, and not necessarily to the birth of a new one. Finally, the coincidence between the Red Sea axis and the East-Africa hotspot path supports a causal relationship between thermal weakening along the hotspot path trajectory and the subsequent Red Sea rift system location.

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