Superimposed folding and W-Sn vein-type mineralisation in the Central Iberian Zone associated with late-Variscan oroclinal buckling: A structural analysis from the Regoufe area (Portugal)

Abstract

The Cantabrian orocline is a major orocline that bends the Variscan belt of Western Europe. Despite a wealth of studies, its timing and relationship with the late-Variscan folding stages in the Iberian Massif are still debated. This study provides an integrated structural analysis of the Variscan fold generations and associated W-Sn bearing vein systems within the southern Central Iberian Zone (Regoufe, Portugal), giving insight into their kinematic relationship with oroclinal buckling. Two superimposed fold generations with mutually parallel, steep to vertical fold axes have been identified. Isoclinal F1 folds with E-W striking axial planes formed during coaxial shortening and are spatially localised. F3 folds with NW-SE axial planes are associated with late-Variscan transpressional deformation and constrain the structural outline of the major folds. Temporal and kinematic considerations indicate that vertical-axis, asymmetric F3 folding corresponds with the expected deformation style within the southern limb of the Cantabrian orocline. The Regoufe area is characterised by two types of W-Sn vein-type mineralisation. Granite-hosted hydrothermal quartz veins show a concentric distribution and are associated with the stress regime during granite emplacement. The vein system within the metasedimentary host rock, however, is emplaced along a regional, subhorizontal cross-fold joint system. This cross-fold joint system developed orthogonal to the subvertical F3 fold axes, and is interpreted to be coeval with oroclinal buckling. These results impact the understanding of (i) the relative significance and geometry of the main deformation stages in the Iberian massif, reconciling the timing and kinematics of F3 regional folding with oroclinal buckling, and (ii) the kinematic relationship between late- to postorogenic deformation and W-Sn vein-type mineralisation.