New ocean spreading beneath the Arabian Shield controlled by LAB-structure

Abstract

Formation of new oceans by continental break-up is traditionally understood as a continuous evolution from rifting to ocean spreading. Here we show that already the break-up phase may involve a jump of extensional axis, as earlier observed in e.g. the mature North Atlantic Ocean. The Red Sea is one of few locations on Earth where a new plate boundary presently forms. The new plate boundary is already active in the southern Red Sea oceanic spreading centre, but the north-central segment is still in a continental rifting stage, and the associated magmatism is offset by ca 300 km into Arabia.This situation is similar to the Baikal Rift Zone, where the rift-related magmatism in the north is offset by 200-300 km into the Sayan-Baikal Fold Belt, but not offset in the south. Our earlier numerical modelling has shown that the location of the magmatism may be controlled by thinning of the lithosphere from the Siberian Craton into the fold belt, whereas the rift location is controlled by pre-existing crustal scale weakness zones (Yang et al., 2018).Here, we propose a new geodynamic model for the evolution of the Red Sea region which is consistent with all geological and geophysical observations. We demonstrate that the north-central rift is a transient feature that will not develop into coincident ocean spreading. Instead, a new plate boundary forms across Arabia. Our numerical experiments predict that in 1–5 Myr the north-central extensional axis will jump ~300 km eastward into Arabia. The existing Ad Damm strike-slip fault, perpendicular to the central Red Sea rift axis, will evolve into a transform fault between the on-going ocean spreading in the southern Red Sea and the future spreading in north-central Arabia.We demonstrate that crustal-scale weakness zones can control lithosphere extension and lead to long-distance jumps of extensional axes in continental lithosphere not affected by hotspots. Therefore, our model also provides theoretical basis for understanding dynamics and mechanisms of the transition from rifting to continental break-up at passive continental margins not affected by hotspots.