Comment on "On the Rootless Nature of a Devonian Suture in SW Iberia (Ossa-Morena Complex, Variscan Orogen): Geometry and Kinematics of the Azuaga Fault" by Diez Fernandez et al. (2021)

The paper recently published by Diez Fernandez et al. (2021) in Tectonics focuses on the post-metamorphic folding and faulting of the suture-related unit located at the Ossa-Morena-Central Iberian Zone boundary, namely the central unit, with the aim of restoring the pre-folding geometry, alleged to be flat-lying and belonging to a single rootless nappe covering most of the Iberian Variscan Massif. Nevertheless, the geometrical analysis presented by these authors is difficult to reconcile with field and seismic reflection data. This comment argues that the central unit rocks do not depict a flat-lying attitude once the late folds are removed, but a NE-dipping tectonic/lithological layering that extends down to the middle crust. The kinematics of the highly-dipping Azuaga Fault, which limits to the SW the central unit, is dominantly left-lateral with a subordinate downthrowing of the NE block. Therefore, this fault did not contribute to uplift the Central Unit rocks during the late Variscan evolution, as assumed in the transpressional model applied by Diez Fernandez et al. (2021). Actually, the central unit was almost completely exhumed during a prelate folding ductile shearing (S-2), which evolved from high-temperature conditions to low-grade conditions. The rootless nature of the central unit and its continuation underneath the entire OMZ can be discarded. Consequently, the Ossa-Morena zone is not part of a large-scale allochthonous nappe, but a Variscan continental block bounded to the NE by the rooted suture represented by the central unit, and to the SW by the Rheic suture.