Nubia-Arabia separation: Clues from oceanic spreading fabric in the Red Sea

Abstract

The breakup of the Arabian-Nubian (Ar-Nu) shield created the Red Sea rift, a young continental rift transitioning to an ocean basin. Different Ar-Nu plate reconstruction models have emerged, which complicate interpreting the shield geology, reconstructing motions of other plates and leave open the question of how much oceanic crust underlies parts of the sea. Uncertainty of plate reconstructions also affects how we interpret the dynamics of rifting in this basin from geophysical data. Helping to address this issue, gravity anomalies reveal an oceanic segmentation fabric that constrains the opening direction since ∼ 10 Ma or half the total Ar-Nu movement. We derive an Euler plate reconstruction pole from that fabric and apply it to restore the configuration of Ar-Nu shield structures at ∼ 10 Ma. With the Ar and Nu structures brought closer together, the reconstruction supports a new association of those structures across the Red Sea. That association in turn constrains the pre-breakup relative positions of the Ar-Nu shield fragments in a NW-SE sense (i.e., rift obliquity). It allows us to prioritise earlier-published total opening Euler poles that also bring these structures together. In particular, one of them was derived using the known Dead Sea Transform (DST) and Suez Rift motions, which constrain total Ar-Nu separation magnitude and direction. New Moho depth estimates further allow an assessment of how much distributed extension has left coastal units displaced relative to plate interiors. Applying the total-opening pole, and allowing for those coastal displacements, the pre-breakup shield terranes of the two sides are brought together but with significant gaps remaining between the two sides. The results support the views that the northern Red Sea is underlain largely by stretched continental crust and that the central Red Sea is underlain by both continental and oceanic crust.