Abstract
Abstract. Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed in the Devonian to Carboniferous period. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate salient currently represented by the South Portuguese Zone.
Highlights
Oblique convergence/divergence between lithospheric plates or continental blocks are common tectonic scenarios, usually named transpression/transtension (Harland, 1971; Sanderson and Marchini, 1984)
From the Middle–Late Devonian to Pennsylvanian period, the collisional evolution of SW Iberia is characterized by oblique left-lateral convergence between three continental terranes: the CIZ, the Ossa-Morena zone (OMZ) and the South Portuguese zone (SPZ)
– The ductile shearing that occurred in the Badajoz-Córdoba Shear Zone (BCSZ) during the Upper Devonian–Mississippian period has been quantified to ≈ 150 km of left-lateral displacement, roughly parallel to the CIZ–OMZ boundary
Summary
Oblique convergence/divergence between lithospheric plates or continental blocks are common tectonic scenarios, usually named transpression/transtension (Harland, 1971; Sanderson and Marchini, 1984). This evolution involved the oblique convergence between three continental terranes, namely, from north to south, the Central Iberian Zone (CIZ), the Ossa-Morena Zone (OMZ) and the South Portuguese Zone (SPZ). These terranes show transpressional left-lateral kinematics with deformation partitioning (Burg et al, 1981; Matte, 1991; Crespo-Blanc, 1992; Azor, 1994; Quesada et al, 1994; Expósito et al, 2002; Silva and Pereira, 2004; Ponce et al, 2012), contrasting with the dextral component that characterizes most of the Variscan collision in other regions of the orogen (e.g., Shelley and Bossière, 2000). Simple monoclinic-flow models (Dewey et al, 1999) and other approximate tools may yield regionally valuable approximations
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