On the Subduction Polarity Beneath the Semail Ophiolite

Abstract

The Semail ophiolite and the UAE-Oman mountain range offer a rare window into continental subduction and exhumation. Despite almost half a century of conflicting studies, the geometry and number of subductions that characterized the formation of the ophiolite and subsequent obduction remain debated. Competing tectonic models range from a single NE-directed subduction that initiated with ophiolite and sole formation at $\sim$96–95 Ma, to scenarios involving multiple metamorphic events linked to opposite subduction polarities - including prograde metamorphism at $\sim$110–130 Ma followed by retrograde metamorphism at $\sim$80 Ma–or models proposing the juxtaposition of two separate subduction zones. This study investigates the tectonic evolution of the Semail ophiolite, and the subduction polarity structurally beneath it using 3-D P- and S-wave tomographic models integrated with global tomographic datasets, plate reconstruction frameworks, and surface geology. The results reveal a northeast-dipping high-velocity anomaly extending 250 km beneath the metamorphic sole exposed in the northern mountain range, and 150 km beneath Jebel Akhdar, which I interpret as remnants of the Neo-Tethyan slab attached to the Arabian continental margin. These observations offer a plausible explanation for the contrasting exhumation conditions between the northern and southern segments of the mountain range. In the southern region, evidence of possible slab detachment is consistent with the exhumation of high-pressure rocks, such as those exposed in the Saih Hatat Dome. This study challenges earlier hypotheses of southwest-directed subduction and strongly supports a single northeast-dipping subduction system, providing new insights into continental subduction, obduction, exhumation, and the creation of orogenic belts.