The initial foundering of lithosphere into the upper mantle, known as subduction initiation, is one of the key, most intriguing, and least understood processes of the solid Earth’s cycle. Despite being a relatively ephemeral phenomenon only lasting a few million years, subduction initiation is paramount to understand the driving forces of plate tectonics. The study of subduction initiation processes has mainly focused on supra-subduction zone ophiolites, which are emerged relics of oceanic lithosphere originally formed above a nascent subduction zone. Geological evidence from these ophiolites strongly suggest that subduction initiation causes extreme thinning of the rocks located above the incipient subduction zone; yet, the origin and main features of this process cannot be investigated directly in modern active systems. The main objective of this project is to investigate the tectonic processes triggered by a nascent subduction zone to fully untangle the complex and still poorly understood process of subduction initiation. The proposed research will analyse for the first time the deformation in the mantle section of one of the best preserved and most complete ophiolites of the world (the Semail ophiolite of Oman) to ultimately unveil the mechanism(s) aiding lithosphere thinning during subduction initiation. THIN will use a combination of paleomagnetic, magnetic fabric, structural geological, and geochronological techniques to reconstruct the tectonic rotations in the mantle section of the Oman ophiolite and ultimately produce a four-dimensional (three dimensions over time) model of deformation that will shed key lights on one of the most fundamental geological processes for our planet.