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 veintype mineralisation.

Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

“…We claim that the geometry of the Central Iberian curve is the results of a combination of processes. The curvature of the inner arc (Galicia‐Trás‐os‐Montes; Figure 1), if rotational, has to be the result of a process before ~318 Ma, probably during the early stages of collision and involving no vertical axis rotations (Pastor‐Galán, Dias da Silva, et al, ; Jacques, Muchez, et al, ; Jacques, Vieira, et al, ). The outer arc curvature, at least in the Iberian Range, is the result of much younger Alpine tectonics: These are commonly disregarded in studies of the Variscan orogen of Iberia.…”

The enigmatic curvature of Central Iberia and its puzzling kinematics

“…With the re-emergence of the Central Iberian curve debate, several studies have re-evaluated the well-documented structures of the Central Iberian Zone to constrain the origin and kinematics of curvature. The majority of studies focused on the hinge zone of the curve in the area surrounding Galicia-Tras-os-Montes (e.g., Dias da Silva et al, 2014;Jacques et al, 2018a), but some do explore areas in the outer-arc (e.g., Palero-Fernández et al, 2015;Gutiérrez-Alonso et al, 2015). The following section synthesizes the findings of new field, structural, and geochronological analyses from around 1256 D. Pastor-Galán et al: The enigmatic curvature of Central Iberia the hinge of the Central Iberian curve and its surrounding regions.…”

The enigmatic curvature of Central Iberia and its puzzling kinematics

“…The majority of studies focused on the hinge zone of the curve in the area surrounding Galicia Tras-os-Montes (e.g. Dias da Silva et al, 2014;Jacques et al, 2018a), but some explored more outer-arc areas (e.g. Palero-Fernández et al, 2015;Gutiérrez-Alonso et al, 2015).…”

“…. The age of the C3 event ranges from 315 and 290 (e.g Jacques et al, 2018a),. concomitant with the formation of the Cantabrian Orocline (e.g Pastor-Galán et al, 2015a)…”

“…Ductile deformation, including folding with axial planar cleavage (e.g. Dias daSilva et al, 2014;Pastor-Galán et al, 2019b) and shear zones, occurred at the early stages of C3(315-305 Ma;Gutiérrez-Alonso et al, 2015; Díez-Fernández and Pereira, et al, 2018b) followed by brittle deformation that formed cross-joint sets and vein swarms with Sn-W mineralizations(Jacques et al, 2018a;2018b). The conjugated shear zones, some of them with hundreds of kilometers of displacement, had activity during the period 315-305 based on direct Ar-Ar dating of the shear zones (Gutiérrez- and cross-cutting relationships with precisely dated igneous rocks (Díez-Fernández and…”