Geomorphology of the Mabahiss Deep area, Northern Red Sea: New insights from high-resolution multibeam bathymetric mapping

The Red Sea is a unique place to study a young oceanic rift basin and the interplay between magma and tectonics at a young divergent plate boundary. The spreading rate of the Red Sea rift changes from ~17 mm/yr in the south to ~7 mm/yr in the north, and so does the morphology. The southern Red Sea is a continuous and well-developed oceanic rift, whereas the so-called deeps characterize the central portion with oceanic crust separated by shallower inter-trough zones, and the northern part contains more widely spaced deeps with extensive areas covered by sediments in between. While the central Red Sea morphology has been extensively studied, the structure of the northern Red Sea and its link to the central Red Sea are less clear. Indeed, the northern Red Sea rift, marked at its southern end by Mabahiss Deep, is offset by about 60 km to the central Red Sea axis by the still poorly understood Zabargad Fracture Zone.

Here we aim to improve the understanding of the volcano-tectonic setting of the Mabahiss Deep area with new high-resolution bathymetric data from multiple multibeam surveys with R/V Thuwal and R/V Pelagia. Our results show that the 15 km long, 9 km wide, and 2250 m deep Mabahiss Deep, and the 800 m high and 5 km wide central volcano, are the most prominent structures of the area. The deep is bordered by a series of Red Sea parallel normal faults on both sides, forming a graben-like structure and thus suggesting a rift-like morphology. The central volcano has a 2 km wide summit caldera containing several volcanic cones. Several normal faults cut its southern flank, and radial fractures are present on its summit. In the multibeam backscatter data, several recent lava flows (<10 kyrs) are visible on the northern and southern flanks of the volcano. Even if the ocean floor outside the deep is mainly covered by salt flows, limiting structural analysis of the surrounding areas, the Mabahiss Deep area and the central Red Sea have similar rift-like structures with stable axial MORB-volcanism, showing typical features found at other (ultra-)slow-spreading ridges, such as magma focusing on the segment centers. This suggests that although the Mabahiss Deep appears to be offset from the central Red Sea rift, the same processes are probably taking place in this area.

Our new high-resolution bathymetric mapping allows a more precise structural and geomorphological analysis of the Mabahiss Deep area that represents a starting point for understanding the overall structure of the poorly studied northern Red Sea.