Oblique collision and deformation partitioning in the SW Iberian Variscides

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 semiquantitative 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.

Ediacaran Obduction of a Fore‐Arc Ophiolite in SW Iberia: A Turning Point in the Evolving Geodynamic Setting of Peri‐Gondwana

“…Shearing during latest D 1 would eventually fracture rocks and induce fault propagation under colder conditions, giving way to D 2 thrusts. The left‐lateral component observed in these thrusts favors a transpressional model for their development (Expósito Ramos, ; Pérez‐Cáceres et al, ). Moreover, the stretching lineation associated with D 1 folds is roughly parallel to their axes.…”

“…Therefore, lateral tectonic flow is not just restricted to D 2 but extends back to the onset of Variscan deformation. Such flow pattern has been interpreted as the consequence of an oblique collision between Gondwana and Laurussia (Díez Fernández & Martínez Catalán, ; Martínez Catalán, ; Pérez‐Cáceres et al, ; Shelley & Bossière, ; Silva & Pereira, ).…”

Coseismic Slip Deficit of the 2017 Mw 6.5 Ormoc Earthquake That Occurred Along a Creeping Segment and Geothermal Field of the Philippine Fault

“…The Philippine Fault is a 1,200 km-long sinistral fault resulting from the partitioning of the oblique convergence between the Philippine Sea Plate and Eurasia (Figure 1) (Aurelio, 2000;Barrier et al, 1991;Besana & Ando, 2005). This mechanism was first proposed by Fitch (1972) and later adopted by other workers to explain the existence of other large strike-slip faults behind oblique convergence zones such as the Karakoram fault system in Kashmir Himalaya (Kundu et al, 2014), the Variscan fault in the SW Iberian (Pérez-Cáceres et al, 2015), the Great Sumatran Fault in Indonesia (Maung, 1987;McCaffrey et al, 2000), the Median Tectonic Line in Japan (Taira et al, 1983), the Alpine Fault in New Zealand (Claypool et al, 2002;Walcott, 1998), and the Ramu-Markham Fault in Papua New Guinea (Dow & Sukamto, 1984). In this mechanism, the PSP-Eurasia oblique convergence of about 9.8 cm/yr (DeMets et al, 2010) is decomposed into two components, namely, (1) a frontal subduction perpendicular to the axis of the Philippine Trench and (2) a sinistral slip accommodated along the NW-SE trending Philippine Fault (Figure 1).…”

The enigmatic curvature of Central Iberia and its puzzling kinematics

“…(6) The South Portuguese Zone represents a foreland fold-and-thrust belt with little internal deformation and metamorphism with Avalonian affinity and a strong left-lateral component of shear (e.g. Pereira et al, 2012;Pérez-Cáceres et al, 2016;Oliveira et al, 2019). Geographically, the external zones of the Gondwana margin are nested to the north into the core of the Cantabrian Orocline, whereas the hinterland zones are to the west and center of the massif (Fig.…”

“…Oliveira et al, 2019a;2019b); and (3) the Baixo Alentejo Flysch, which is located to the southwest and is a syn-orogenic composite turbiditic sequence with ages from ~330 to ~310 Ma (Oliveira et al, 2019b). The boundary between the South Portuguese and Ossa Morena zones is a sinistral shear zone (so-called Beja-Acebuches, Quesada and Dallmeyer., 1994;Pérez-Cáceres et al, 2016) that contains a strongly deformed amphibolitic belt with oceanic affinity (Munha et al, 1986;Munha, 1989;Quesada et al, 2019).…”