Structural setting and multiphase volcanism in the Shaban Deep, Northern Red Sea

Abstract

Shaban Deep (ShD) is one of several axial depressions discovered in the northern Red Sea, some considered sites of incipient seafloor spreading. Understanding the evolutionary history and salt tectonics of ShD is essential for constraining the rift-to-drift transition. This study integrates 2D seismic reflection profiles, gravity, magnetic, and bathymetric data to investigate the regional structural framework, salt tectonics, and volcanism in ShD. The seismic data clearly image the post-evaporite (Plio-Quaternary) strata, while reflections within the igneous basement are variable. Faults are at least partly inferred from progressively steepening reflectors, indicative of growth stratigraphy. Two main extensional fault systems, trending NW-SE and NE-SW, have been identified around an elongate NW-SE neo-volcanic axial ridge. The dominant NE-SW faults, perpendicular to the Red Sea rift axis, form several basement-controlled arcuate half-grabens. The structural framework varies across ShD. In the southeastern region, major NE-SW extensional faults dip to the NW and are interpreted as listric faults that experienced several reactivation phases between the Late Miocene and Quaternary. In contrast, the primary faults in the northwestern ShD likely developed after the deposition of Plio-Quaternary sediments and exhibit steeper dip angles. Despite the lack of strong evidence for the presence of salt diapirs near ShD, likely due to the formation of a volcanic caldera, significant seafloor bending and deformed evaporites on the easternmost area suggest salt movement, which likely began during the Late Miocene. Seismic interpretation, supported by previous geochemical studies, indicates that the axial volcanic ridge formed through multiphase volcanism, as evidenced by chemically heterogeneous basaltic lavas. This ridge is surrounded by a caldera measuring 5.7 × 8.5 km.