Transition from continental rifting to oceanic spreading in the northern Red Sea area

Abstract

Lithosphere extension, which plays an essential role in plate tectonics, occurs both in continents (as rift systems) and oceans (spreading along mid-oceanic ridges). The northern Red Sea area is a unique natural geodynamic laboratory, where the ongoing transition from continental rifting to oceanic spreading can be observed. Here, we analyze travel time data from a merged catalogue provided by the Egyptian and Saudi Arabian seismic networks to build a three-dimensional model of seismic velocities in the crust and uppermost mantle beneath the northern Red Sea and surroundings. The derived structures clearly reveal a high-velocity anomaly coinciding with the Red Sea basin and a narrow low-velocity anomaly centered along the rift axis. We interpret these structures as a transition of lithospheric extension from continental rifting to oceanic spreading. The transitional lithosphere is manifested by a dominantly positive seismic anomaly indicating the presence of a 50–70-km-thick and 200–300-km-wide cold lithosphere. Along the forming oceanic ridge axis, an elongated low-velocity anomaly marks a narrow localized nascent spreading zone that disrupts the transitional lithosphere. Along the eastern margins of the Red Sea, several low-velocity anomalies may represent crustal zone of massive Cenozoic basaltic magmatism.

Lithospheric Structure of the Red Sea Based on 3D Density Modeling: A Contrasting Rift Architecture

“…Taking this into account, together with the very good agreement of Model 1 to the recent tomography model of El Khrepy et al. (2021) (Figure 10), we suggest that the limited oceanic crust option is more realistic for the northern Red Sea. Although segmentation trails were inferred from the vertical gravity gradient data to support an extended oceanic crust distribution in this area (Augustin et al., 2021), previous gravity interpretations are also in disagreement regarding such lithospheric setting (e.g., Almalki et al., 2016; Saada et al., 2021; Saleh et al., 2006).…”

“…In the northern Red Sea, the recent tomographic model of El Khrepy et al. (2021) shows high‐velocity anomalies coinciding with the Red Sea basin and a narrow low‐velocity anomaly centered beneath the rift axis, interpreted as a transition of the lithospheric extension from continental rifting to oceanic spreading. In the central southern regions of the basin, the diluted seismic network in the western flanks hampers the accuracy of seismic tomography models.…”

“…These observations also provide information regarding lithospheric thickness, suggesting an LAB (Lithosphere Asthenosphere Boundary) depth of ∼90-110 km beneath the Arabian shield (Hansen et al, 2007;Park et al, 2008), although a recent seismic tomography suggests the lithosphere might be thinner in the western parts of the shield (Yao et al, 2017). In the northern Red Sea, the recent tomographic model of El Khrepy et al (2021) shows high-velocity anomalies coinciding with the Red Sea basin and a narrow low-velocity anomaly centered beneath the rift axis, interpreted as a transition of the lithospheric extension from continental rifting to oceanic spreading. In the central southern regions of the basin, the diluted seismic network in the western flanks hampers the accuracy of seismic tomography models.…”

“…The lack of modern active seismic data, ocean bottom seismometers and seismic networks on the western flanks limit the knowledge regarding the deep lithospheric configuration. Nevertheless, seismic tomography and receiver function studies have shed light on the lithospheric structure underneath the northern Red Sea and the Arabian shoulders (e.g., El Khrepy et al., 2021; Hansen et al., 2007; Mai et al., 2019; Yao et al., 2017). For instance, the source of the Cenozoic volcanism in Arabia has been attributed to a lateral heat flow from the Afar plume area, rather than from distinct deep mantle sources underneath the volcanic fields (Faccenna et al., 2013; Mai et al., 2019).…”

“…However, these models relied on limited data that could not image the deep lithospheric structures. A recent seismic velocity model for the northern Red Sea revealed a narrow low‐velocity anomaly along the rift axis, which was interpreted as an evidence for a transition from continental rifting to oceanic spreading (El Khrepy et al., 2021). However, the lithospheric structure along the central‐southern Red Sea is still unknown.…”