On the Rootless Nature of a Devonian Suture in SW Iberia (Ossa‐Morena Complex, Variscan Orogen): Geometry and Kinematics of the Azuaga Fault

Abstract

Recognizing the major architecture of a collisional orogen relies on an understanding of its suture zone(s). The final structure and local geometry of a suture zone is typically the result of multiple deformation events, from the subduction that records convergence to the syncollisional and postcollisional structures responsible for the lithospheric thickening and/or thinning that follow (

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 Díez Fernández et al. (2021)

“…Actually, most of the stereoplots presented by Díez Fernández et al. (2021) in their Figure 7 are incongruent with the inferred sizes and rounded geometries of the hinge zones, since S 2 orientation shows a bimodal distribution that denotes dominant moderate to steep dips, with almost no subhorizontal dips.…”

“…A mylonitic deformation affected the whole central unit and gave way to a penetrative planar-linear tectonic fabric (S 2 in Díez Fernández et al, 2021), which is the structural feature more commonly observed and measured in the field (Azor et al, 1994;Burg et al, 1981;Pereira et al, 2008). Díez Fernández et al (2021) mistakenly attribute the "earlier exhumation from eclogite facies conditions to the lower-middle crust" to this mylonitic fabric. Actually, this deformation occurred at variable conditions from high-temperature (sillimanite zone) at the lower part of the unit to low-grade ones at the upper part (garnet-biotite zone), and has been interpreted as related to the exhumation of the unit up to upper crustal levels (Azor, 1994;Azor et al, 1994).…”

“…Díez Fernández et al. (2021) consider that the late folds are km‐scale and have subvertical axial planes, thus proposing a flat‐lying attitude for both the planar‐linear fabric (S 2 ) and the subparallel lithological layering in the Central Unit, once the late folds are restored. Nevertheless, Azor (1994) and Azor et al.…”

“…The planar-linear fabric was deformed by late-metamorphic folds, generally with open geometries and coaxial with respect to the stretching lineation. Díez Fernández et al (2021) consider that the late folds are km-scale and have subvertical axial planes, thus proposing a flat-lying attitude for both the planar-linear fabric (S 2 ) and the subparallel lithological layering in the Central Unit, once the late folds are restored. Nevertheless, Azor (1994) and Azor et al (1994) showed that most of the late-metamorphic folds in the Central Unit are very asymmetric, with subhorizontal to gently SW-dipping axial surfaces, that is, long limbs dip moderately to the NE, while short limbs are subvertical (Figure 2a) or steeply dipping to the SW (Figure 2b).…”

“…Therefore, the S 2 stereoplots presented by Díez Fernández et al (2021) in their Figure 7 cannot be used to ascertain the geometry of the late folds. Actually, most of the stereoplots presented by Díez Fernández et al (2021) in their Figure 7 are incongruent with the inferred sizes and rounded geometries of the hinge zones, since S 2 orientation shows a bimodal distribution that denotes dominant moderate to steep dips, with almost no subhorizontal dips. 2.…”