Oblique Collision and Deformation Partitioning

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Oblique collision and deformation I. Pérez-Cáceres et al. partitioning in the SW Iberian Variscides

Title Page I. Pérez-Cáceres, J. F. Simancas, D. Martínez Poyatos, A. Azor, and F. González Lodeiro Abstract Introduction

Departamento de Geodinámica, Facultad de Ciencias, Universidad de Granada, Campus de Conclusions References Fuentenueva s/n, 18071 Granada, Spain Tables Figures Received: 27 November 2015 – Accepted: 30 November 2015 – Published: 9 December 2015 Correspondence to: I. Pérez-Cáceres ([email protected]) J I

Published by Copernicus Publications on behalf of the European Geosciences Union. J I

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3773 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Abstract SED Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny 7, 3773–3815, 2015 in SW Iberia, which is characterized by a number of successive left-lateral transpres- 5 sional structures developed at Devonian to Carboniferous times. These structures Oblique collision and resulted from the oblique convergence between three continental terranes (Central deformation Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation partitioning 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 I. Pérez-Cáceres et al. 10 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 Title Page boundary conditions modeled, our results must be considered as a semi-quantitative Abstract Introduction approximation to the issue, though very significant from a regional point of view. The Conclusions References 15 total collisional convergence surpasses 1000 km, most of them corresponding to left- lateral displacement parallel to terrane boundaries. The average vector of convergence Tables Figures is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique col-

lision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in J I the Variscan orogen. This particular kinematics of SW Iberia is understood in the con- 20 text of an Avalonian plate promontory currently represented by the South Portuguese J I Zone. Back Close

Full Screen / Esc 1 Introduction Printer-friendly Version Oblique convergence/divergence between lithospheric plates or continental blocks are common tectonic scenarios, usually named transpression/transtension (Harland, 1971; Interactive Discussion 25 Sanderson and Marchini, 1984). Strain resulting from transpression is usually modeled as a combination of a three-dimensional coaxial component and an orthogonal sim- 3774 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion ple shear component (Tikoff and Fossen, 1999). Less frequently, oblique convergence has been modeled as a combination of two simple shears, with lateral (wrenching) SED and frontal (thrusting) kinematics (Ellis and Watkinson, 1988). The oblique conver- 7, 3773–3815, 2015 gence/divergence that characterizes transpression usually involves deformation par- 5 titioning into thin bands concentrating lateral displacements and broader domains concentrating frontal displacements (e.g. Holdsworth and Strachan, 1991; Tikoff and Oblique collision and Teyssier, 1994). deformation Following the works by Sanderson and Marchini (1984) and Fossen and Tikoff partitioning (1993), many models increasingly sophisticated have been developed to analyze high- I. Pérez-Cáceres et al. 10 strain transpressional zones. A number of boundary conditions have been introduced, such as lateral extrusion (Dias and Ribeiro, 1994; Jones et al., 1997; Teyssier and Tikoff, 1999), inclined walls (Jones et al., 2004), oblique extrusion and/or oblique simple Title Page shear (Czeck and Hudleston, 2003, 2004; Fernández and Díaz-Azpiroz, 2009; Jiang and Williams, 1998; Lin et al., 1998), no slip at the boundaries with undeformed walls Abstract Introduction 15 (Dutton, 1997; Robin and Cruden, 1994) and migrating boundaries (Jiang, 2007). Conclusions References SW Iberia (Fig. 1) resulted from a complex transpressional evolution during the Variscan collision at Devonian to Carboniferous times (e.g. Pérez-Cáceres et al., 2015). Tables Figures This evolution involved the oblique convergence between three continental terranes, namely, from north to south, the Central Iberian Zone (CIZ), the Ossa-Morena Zone J I 20 (OMZ), and the South Portuguese Zone (SPZ). These terranes show transpressional left-lateral kinematics with deformation partitioning, thus contrasting with the dextral J I component that characterizes most of the Variscan collision in other regions of the Back Close orogen (e.g. Shelley and Bossière, 2000). Full Screen / Esc This work aims to describe and approximately quantify the Variscan transpressional 25 deformation in SW Iberia. We are particularly interested in evaluating the left-lateral Printer-friendly Version component of the transpressional deformation, in order to achieve an approximate image of the relative position of the terranes involved in this oblique collision. To do so, Interactive Discussion the use of sophisticated transpressional models might not be justified, since these models demand stringent geological data hardly available for a large-scale tectonic

3775 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion analysis (e.g. Jiang and Williams, 1998; Fernández et al., 2013). For this reason, simple monoclinic-ﬂow models (Dewey et al., 1999) and other approximate tools may yield SED regionally valuable approximations. 7, 3773–3815, 2015

2 Variscan events in SW Iberia Oblique collision and deformation 5 The Variscan/Alleghanian Orogen resulted from the closure of the Rheic Ocean partitioning that separated Laurentia/Baltica and Gondwana during Ordovician to Devonian times (Fig. 1a). The subsequent collision amalgamated these two continents along with in- I. Pérez-Cáceres et al. tervening minor oceanic realms and micro-continents in-between (e.g. Franke, 2000; Matte, 1991, 2001; Murphy and Nance, 1991; Stampfli and Borel, 2002). 10 Prior to the Rheic Ocean formation, the arc-type Cadomian orogeny variedly over- Title Page printed the northern margin of Gondwana during the Ediacaran (e.g. Linnemann et al., 2014). In Iberia, this orogeny resulted in the development of thick syn-orogenic arc- Abstract Introduction related basins (e.g. in the CIZ; Rodríguez-Alonso et al., 2004) and calc-alkaline arc- Conclusions References related magmatism that concentrated in the OMZ and southernmost CIZ (Bandrés Tables Figures 15 et al., 2004; Pin et al., 2002; Sánchez Carretero et al., 1990; Simancas et al., 2004). As for the Variscan evolution, the boundaries between the CIZ, OMZ and SPZ terranes are considered as sutures (Fig. 1). The CIZ is a continental domain that formed J I part of northern Gondwana, while the OMZ is commonly interpreted as a continental J I piece that rifted (and drifted to some extent) from Gondwana (i.e., the CIZ) in the early Back Close 20 Paleozoic (Matte, 2001; Robardet, 2002). Subsequent collision between these two terranes resulted in the suture unit known as Badajoz-Córdoba Shear Zone (BCSZ) or Full Screen / Esc Central Unit (Fig. 1c) (Azor et al., 1994; Burg et al., 1981). The BCSZ includes some early Paleozoic amphibolites (Ordóñez Casado, 1998) with a geochemical signature Printer-friendly Version akin to oceanic crust (Gómez-Pugnaire et al., 2003). A first collisional stage is attested Interactive Discussion 25 by eclogite relics in the BCSZ (1.6–1.7 GPa; Abalos et al., 1991; Azor, 1994; López Sánchez-Vizcaíno et al., 2003) and large-scale Devonian recumbent folds and thrusts in the colliding blocks (OMZ and southern CIZ; Simancas et al., 2001, and references 3776 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion therein). The eclogites were exhumed during the subsequent, latest Devonian to Early- Middle Mississippian intense ductile left-lateral shearing that characterizes the BCSZ SED (Burg et al., 1981), coeval to normal faulting, basin development and mafic magmatism 7, 3773–3815, 2015 at both sides of the BCSZ. Renewed Pennsylvanian compression is attested by upright 5 folds and left-lateral strike-slip faults. Overall, the CIZ-OMZ boundary is interpreted as a Gondwana-related second-order suture of the Variscan Orogen (e.g. Simancas et al., Oblique collision and 2005). deformation The OMZ-SPZ boundary (Fig. 1) has been classically interpreted as the suture partitioning of the Rheic Ocean. This boundary is constituted by three units (Fig. 1c): (i) the I. Pérez-Cáceres et al. 10 Beja-Acebuches (BA hereafter) unit, metamorphosed mafic and ultramafic rocks that crop out all along this major contact (Azor et al., 2008; Castro et al., 1996; Crespo- Blanc, 1991; Fonseca and Ribeiro, 1993; Munhá et al., 1986; Quesada et al., 1994); Title Page (ii) the Pulo do Lobo unit, a low-grade metasedimentary unit with minor MORB-like metabasalts (Braid et al., 2010; Dahn et al., 2014; Eden, 1991; Eden and Andrews, Abstract Introduction 15 1990; Silva et al., 1990); and (iii) the allochthonous Cubito-Moura unit, which contains Conclusions References high-pressure and MORB-like rocks emplaced onto the OMZ border (Araujo et al., 2005; Fonseca et al., 1999; Ponce et al., 2012). Recent work including new structural Tables Figures and radiometric data has improved our knowledge on the geometry and timing of deformations affecting the OMZ-SPZ suture (Pérez-Cáceres et al., 2015), which is now J I 20 viewed as a Rheic criptic suture, blurred by Carboniferous tectonothermal imprints. Thus, the envisaged evolution of the OMZ-SPZ boundary can be summarized as fol- J I lows (Fig. 2): Back Close

i. Following Rheic Ocean consumption in Devonian time, the southern border of Full Screen / Esc the OMZ partially subducted (high-pressure rocks). Some of the subducted rocks 25 were later scrapped oﬀ along with Rheic Ocean rocks and emplaced (the al- Printer-friendly Version lochthonous Cubito-Moura unit) onto the southern OMZ (Fig. 2a). The kinemat- Interactive Discussion ics of emplacement, recorded in an early stretching lineation, is top-to-the-ENE, which corresponds to a tectonic regime of oblique left-lateral convergence.

3777 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion ii. An Early-Middle Mississippian transtensional event temporarily interrupted the convergence and created a very narrow aisle of oceanic-like crust (actually repre- SED sented by the BA unit) just at the OMZ-SPZ boundary (Fig. 2b) (Azor et al., 2008). 7, 3773–3815, 2015 Moreover, c. 340 Ma maﬁc and acid magmatism intruded/extruded at both sides 5 of the oceanic strip. Oblique collision and iii. Convergence was resumed immediately, giving way to northwards obduction of deformation the BA unit, as well as north-verging folds and tectonic imbrications in the Pulo do partitioning Lobo unit (Fig. 2c). I. Pérez-Cáceres et al. iv. Subsequently, south-vergent transpressional structures developed (Fig. 2d). The 10 BA unit was folded synchronous with left-lateral high-temperature shearing, which

evolved to greenschist facies conditions and concentrated in the southern part of Title Page the unit. Oblique convergence propagated southward across the SPZ in the Penn- sylvanian. At latemost Variscan time, left-lateral displacements newly focused on Abstract Introduction

the OMZ-SPZ boundary as brittle strike-slip faults. Conclusions References

Tables Figures 15 3 Deformation partitioning in SW Iberia

One of the most striking features of SW Iberia is the partitioning of deformation into J I four well-defined domains, namely, from north to south: (i) CIZ-OMZ boundary, (ii) OMZ J I terrane, (iii) OMZ-SPZ boundary, and (iv) SPZ terrane (Fig. 1c). Back Close The CIZ-OMZ boundary, marked by the BCSZ, shows a prominent S-L fabric with 20 occasional L-type tectonites, developed at Late Devonian to Mississippian time. The Full Screen / Esc stretching lineation is subhorizontal and kinematic indicators consistently indicate left- lateral displacement (Azor et al., 1994; Burg et al., 1981). Left-lateral strike-slip faults Printer-friendly Version developed at Pennsylvanian times at this boundary, giving way to its final cartographic Interactive Discussion appearance. 25 The OMZ records Devonian and Carboniferous compressional deformations separated by a Mississippian transtensional stage. Both, Devonian and Carboniferous folds 3778 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion and thrusts trend obliquely to the OMZ boundaries, suggesting a transpressional setting. The Devonian SW-vergent recumbent folds are associated with S or S-L tectonic SED fabrics, the stretching lineation showing high pitch angles. The Carboniferous folds are 7, 3773–3815, 2015 upright with an associated S-type tectonic fabric (Expósito, 2000; Expósito et al., 2002). 5 The OMZ-SPZ boundary is underlined by the narrow belt of the BA unit (Bard, 1977; Quesada et al., 1994). Carboniferous high- to low-temperature shearing and folding Oblique collision and affected this unit, concluding with brittle faults. Ductile shear zones originated a promi- deformation nent S-L tectonic fabric, with stretching lineation displaying mostly moderate or low partitioning pitch angles (Crespo-Blanc and Orozco, 1988; Díaz-Azpiroz and Fernández, 2005). I. Pérez-Cáceres et al. 10 The common factor to all these structures is a kinematics dominated by left-lateral displacements. The SPZ is a Carboniferous south-vergent fold-and-thrust belt (Oliveira, 1990; Title Page Simancas et al., 2003). The axial traces of folds are slightly oblique to the northern boundary of the terrane, thus featuring transpressional deformation. The strain ellip- Abstract Introduction 15 soids are oblate and rocks are usually S-tectonites with faint development of upright Conclusions References stretching lineation (Simancas, 1986). The brief description advanced above illustrates partitioning of the bulk regional de- Tables Figures formation in SW Iberia (Fig. 1c). Thus, ductile and brittle sinistral strike-slip shear bands characterize the CIZ-OMZ and OMZ-SPZ boundaries, while deformation inside the J I 20 OMZ and SPZ terranes includes a significant component of frontal shortening. Defor- mation partitioning such as the one displayed in SW Iberia is believed to be favored J I by low angles of plate convergence (Teyssier et al., 1995), but a more comprehensible Back Close kinematic analysis can be gained by analyzing deformation data in more detail. Full Screen / Esc

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3779 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion 4 Kinematics of the CIZ-OMZ collision SED 4.1 Ductile shearing at the CIZ-OMZ boundary 7, 3773–3815, 2015 The BCSZ is a NW–SE trending band of highly deformed schists, gneisses, migmatites and amphibolites that constitutes the CIZ-OMZ boundary (Fig. 1c). It exhibits, consis- Oblique collision and 5 tently along 200 km of visible outcrop, an intense mylonitic S-L fabric (locally L fab- ◦ deformation ric) with subhorizontal stretching lineation (pitch less than 15 ) and left-lateral kine- partitioning matics (Azor et al., 1994; Burg et al., 1981). The age of the ductile shearing in the BCSZ ranges from at least latest Devonian to Middle Mississippian, according to diﬀer- I. Pérez-Cáceres et al. ent metamorphic geochronological data: 340–330 (Ar/Ar on biotite) (Blatrix and Burg, 10 1981), 370–360 Ma (Ar/Ar on hornblende), 340–330 (Ar/Ar on muscovite) (Quesada and Dallmeyer, 1994), c. 340 (U/Pb on zircon) (Ordóñez Casado, 1998; Pereira et al., Title Page 2010). Nevertheless, the previous high-pressure metamorphism would have occurred Abstract Introduction prior to Late Devonian time. South of the BCSZ, the OMZ depicts pro-wedge Devonian SW-vergent folds and thrusts (Expósito et al., 2002); to the north, the southernmost Conclusions References 15 CIZ shows conjugate retro-wedge NE-vergent folds (Martínez Poyatos, 1997). Tables Figures The kinematics of the BCSZ is analyzed here in two diﬀerent ways: (i) considering the recorded strain, under the light of the simple shear model; and (ii) considering a more J I complete, though poorly constrained, subduction-exhumation path. J I i. Simple shear in the BCSZ. The BCSZ stands out as a prominent feature of de- Back Close 20 formation partitioning in SW Iberia, which concentrates the simple shear compo-

nent of the deformation. The very consistent mylonitic fabric with subhorizontal Full Screen / Esc stretching lineation (Azor et al., 1994; Burg et al., 1981) suggests approximate

monoclinic strain (Lin et al., 1998), and can be approximately analyzed by means Printer-friendly Version of the strike-slip simple shear model. The finite strain in this shear zone can be Interactive Discussion 25 assessed from the very elongated shape of some orthogneissic bodies located inside the BCSZ (e.g. the Ribera del Fresno orthogneiss), which suggests X/Z ≈ 11 and γ ≈ 3 assuming simple shear. However, this is a rather conservative estima- 3780 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion tion, since these bodies are relatively rigid strain markers surrounded by schists. For this reason, we will take γ = 4 in the following calculation. The thickness of the SED BCSZ is another important parameter to take into account: the maximum outcrop- 7, 3773–3815, 2015 ping thickness is 15 km, but the original one was probably greater (20–25 km) be- 5 cause late Variscan brittle faults currently bound the ductile shear zone (Fig. 1c). Thus, considering an original thickness of 25 km and a mean shear strain γ = 4, Oblique collision and a tentative left-lateral displacement of 100 km results. The transpression model of deformation inclined walls (Jones et al., 2004) is another way to examine the BCSZ, since this partitioning crustal-scale shear zone has been seismically imaged dipping to the NE (Siman- I. Pérez-Cáceres et al. 10 cas et al., 2003). According to this transpression model, the subhorizontal stretching lineation would be only compatible with an angle of convergence less than 10◦, i.e. the simple shear component should have been extremely dominant. Thus, the Title Page left-lateral displacement derived from this model does not differ significantly from the one obtained with the strike-slip simple shear model. Abstract Introduction

15 ii. Two simple shears during a subduction-exhumation path. Besides left-lateral dis- Conclusions References placement, the movement between the CIZ and the OMZ must have included Tables Figures some dip-slip component of shearing, enabling first the burial and then the exhumation of the high-pressure rocks. Note, however, that the exhumation path has not resulted in a generalized L fabric, as it typically occurs under transten- J I 20 sional kinematics (e.g. Teyssier and Tikoff, 1999). For that reason, we use in our J I estimates the double strike-slip and dip-slip shear model of Ellis and Watkinson Back Close (1988). According to this model and considering a shear zone dip of 45◦ (Fig. 2, curve 3 in Ellis and Watkinson, 1988), the subhorizontal stretching lineation that Full Screen / Esc characterizes the BCSZ would indicate a convergence/divergence angle of 15– ◦ ◦ 25 35 . We take 25 for our calculations in Fig. 3a; if the high-pressure rocks of the Printer-friendly Version BCSZ reached depths of ≈ 55 km (1.6–1.7 GPa), then a left-lateral displacement Interactive Discussion of around 115 km is inferred during the exhumation of these rocks. If a simi- lar calculation is considered for the previous path of burial, the whole subduction/exhumation path would amount to ≈ 230 km of left-lateral displacement. 3781 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion From the above estimations, a great discrepancy exists between the results of the two models considered: 100 and 230 km, respectively. Actually, most or all of the shear- SED ing recorded in the BCSZ may correspond to the Carboniferous exhumation path (see 7, 3773–3815, 2015 above the reported cooling metamorphic ages), thus explaining most of the difference. 5 Anyway, because these calculations provide only a rough estimate, we will take an intermediate rather conservative value of ≈ 150 km for the ductile left-lateral displace- Oblique collision and ment concentrated at the CIZ-OMZ boundary. deformation partitioning 4.2 Deformation inside the OMZ I. Pérez-Cáceres et al. The OMZ records Devonian and Carboniferous compressional events (folds and 10 thrusts), separated by the Early-Middle Mississippian transtensional stage (Pérez- Cáceres et al., 2015). The Devonian deformation gave way to SW-vergent recumbent Title Page folds and thrusts, while the Carboniferous one originated upright or slightly vergent Abstract Introduction folds and reverse faults (Fig. 1c). The two sets of folds have subparallel axes with NW or SE plunges (Expósito et al., 2002). Their axial traces trend oblique to the OMZ bound- Conclusions References

15 aries, evidencing a transpressional setting. Furthermore, the trend of these structures Tables Figures is Z-shaped, in accordance with a left-lateral component of transpression increasing towards the borders (Fig. 1c). The Devonian tectonic fabric is S or S-L type, the stretch- J I ing/mineral lineation is at high angles to the fold axes, and the strain ellipsoids are generally oblate with very variable strain intensity (2.5 ≤ X/Z ≤ 9) and no signiﬁcant J I

20 XZ areal change on the section (Expósito, 2000). Regarding the Carboniferous tec- Back Close tonic fabric, it is generally a planar fabric, less intense than the Devonian one, with steeply plunging X axis. Full Screen / Esc There is no transpressional model that ﬁts the complex and heterogeneous evolution of the OMZ. As a basic kinematic analysis, we propose the evolution schematically Printer-friendly Version

25 displayed in Fig. 4, which accounts for the following geometrical features: (i) the axial Interactive Discussion traces of the Carboniferous folds (as depicted by the Terena syncline) (Fig. 1c) are smoothly curved, trending NNW–SSE at the central OMZ and WNW–ESE towards its borders; (ii) the Devonian folds and thrusts trend subparallel to the Carboniferous ones, 3782 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion though the Devonian axial surfaces are folded (Type 3 interference fold pattern; Ram- say and Huber, 1987) (Fig. 1c); and (iii) the northern and southern OMZ boundaries SED are not parallel (Fig. 1c), the obliquity having been enhanced during the Carboniferous 7, 3773–3815, 2015 transpression (Fig. 4c and d). Moreover, the two boundaries of the OMZ were ductile 5 shear zones for most of its tectonic evolution, though at Pennsylvanian time left-lateral brittle faults developed at both boundaries. Oblique collision and The Carboniferous shortening can be divided into the two stages shown in Figs. 4c deformation and 5: (i) ﬁrst, a set of folds formed due to SW–NE compression, its original orien- partitioning tation being preserved in the central OMZ (Fig. 5a); (ii) then, these folds rotated het- I. Pérez-Cáceres et al. 10 erogeneously to reach Z shape in map view, congruent with left-lateral transpression (Fig. 5b). These two stages are described below.

i. The width of the central OMZ as measured perpendicular to the original trend of Title Page the Carboniferous folds is ≈ 150 km (Fig. 5a). As regards finite strain, the available Abstract Introduction data are insufficient for an accurate evaluation of shortening. Let’s take a conser- 15 vative shortening of ≈ 35 %, just enough to generate the weak axial-plane Car- Conclusions References boniferous foliation observed in these rocks. Accordingly, a shortening of ≈ 80 km Tables Figures would have taken place (perpendicular to the folds), while a left-lateral displacement parallel to the CIZ-OMZ boundary of ≈ 56 km is inferred. Therefore, the width J I of the OMZ before Carboniferous folding would have been ≈ 230 km. J I 20 ii. In the second stage, the trend of the Carboniferous folds rotated heterogeneously. This rotation can be modeled according to the transpressional equation of Fossen Back Close 0 and Tikoff (1993), but the simpler equation cotΦ = αcotΦ + γ of Sanderson and Full Screen / Esc Marchini (1984) will be used here in view of our main interest in evaluating finite 0 lateral displacements (Φ and Φ are the final and original angles of the rotated Printer-friendly Version 25 line, α is the vertical stretch and γ is the shear strain parallel to the boundary). To analyze this deformation, the OMZ has been divided into five bands, each one Interactive Discussion characterized by a particular reorientation angle (Fig. 5b). Since frontal shortening

– Band I (Φ0 = 10◦, Φ = 40◦, width = 40 km) would have undergone an intense 7, 3773–3815, 2015 shear strain of γ = 4, which results in 160 km of left-lateral displacement. 0 ◦ ◦ Oblique collision and 5 – Band II (Φ = 30 , Φ = 40 , width = 13 km) would have undergone approximately deformation zero shear strain (only frontal shortening). partitioning – Band III is considered to have preserved the original orientation. I. Pérez-Cáceres et al. – Band IV (Φ0 = 30◦, Φ = 50◦, width = 17 km) would have undergone a shear strain of γ = 0.53, originating 9 km of left-lateral displacement. 0 ◦ ◦ Title Page 10 – Finally, band V (Φ = 15 , Φ = 50 , width = 23 km) is characterized by γ = 2.53 and a left-lateral displacement of 58 km. Abstract Introduction

Overall, these calculations based on the sinistral rotation of the Carboniferous folds Conclusions References

amount to 227 km. Added to the 56 km of left-lateral displacement calculated above, Tables Figures the total left-lateral Carboniferous displacement would amount to ≈ 280 km. 15 Devonian deformation in the OMZ can be analyzed taking into account the subpar- J I allelism of Devonian and Carboniferous fold axes (Fig. 4d). Like for the Carboniferous structures, we assume that the original trend of the Devonian structures is observed J I ◦ at the central part of the OMZ (40 with respect to the northern border of the OMZ). Back Close Devonian shortening would be perpendicular to this trend. The width of the OMZ along Full Screen / Esc 20 the shortening direction before Carboniferous deformation would be the current width (150 km) plus the Carboniferous shortening (80 km), thus reaching up to 230 km. On the other hand, an approximate mean strain ratio X/Z ≈ 5 can be proposed from the Printer-friendly Version

available range of strain measures (2.5 ≤ X/Z ≤ 9; Expósito, 2000), which results in Interactive Discussion Z = 0.44 if the XZ area remained unchanged and a Devonian shortening of 290 km. 25 Given the oblique orientation of the shortening direction with respect to the CIZ-OMZ boundary, the resulting left-lateral relative displacement between the northern and 3784 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion southern OMZ is ≈ 185 km. This figure is clearly a rough estimate, as evidenced by the many approximations introduced along this section. However, an accurate calcu- SED lation is not currently possible and the obtained figure can be roughly considered as 7, 3773–3815, 2015 regionally significative.

5 4.3 Left-lateral brittle faults at the CIZ-OMZ boundary Oblique collision and deformation Left-lateral strike-slip faults characterize the late Variscan evolution of SW Iberia. These partitioning brittle structures concentrated at the northern and southern boundaries of the OMZ (Fig. 1c). The system of strike-slip faults at the CIZ-OMZ boundary was analyzed by I. Pérez-Cáceres et al. Jackson and Sanderson (1992) based on a power-law distribution of fault displace- 10 ments from outcrop to map scale. As a result, they evaluated 87 km of along strike brittle displacement. Title Page

Abstract Introduction 5 Kinematics of the OMZ-SPZ collision Conclusions References

5.1 Subduction/exhumation at the southern OMZ continental margin Tables Figures

At Middle-Late Devonian times, the southern continental margin of the OMZ subducted J I 15 under the SPZ, as witnessed by exhumed high-pressure metasedimentary rocks of the OMZ cover included in the allochthonous Cubito-Moura unit (Fig. 2a) (Araujo et al., J I

2005; Booth et al., 2006; Fonseca et al., 1999). The kinematics of this event can be Back Close gauged by the early stretching lineation developed during exhumation, which, once restored later folds, trends ≈ N70◦ E and shows top-to-the-ENE sense of shearing Full Screen / Esc ◦ ◦ 20 (Fig. 6a; Ponce et al., 2012). This orientation forms an angle of ≈ 30 with the ≈ N100 E trend of the OMZ-SPZ boundary (Fig. 6b). Based on the model of thrust-and-wrench Printer-friendly Version

shearing parallel to a subduction zone, this orientation of the stretching lineation would Interactive Discussion correspond to a convergence angle of 45–55◦, depending on the dip of the subduction zone (curve 3 in Figs. 1 and 2 by Ellis and Watkinson, 1988). By contrast, the model of 25 simple inclined transpression (frontal shortening and strike-slip shearing with inclined 3785 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion walls) (Jones et al., 2004) suggests a more oblique convergence at an angle ≤ 20◦. Since it is unclear which one of these two models ﬁts better the SW-Iberia tectonic SED scenario, we will take an intermediate convergence angle of 35◦ for the next tentative 7, 3773–3815, 2015 calculation. 5 A rough estimate of the left-lateral displacement between the SPZ and the OMZ during this stage can be proposed based on: (i) a simple subduction-exhumation channel Oblique collision and with opposite senses of burial and exhumation (Fig. 3b), (ii) a convergence angle of deformation 35◦, (iii) an intermediate dip of 45◦ for the subduction plane, and (iv) a maximum depth partitioning of ≈ 50 km for the high-pressure rocks, corresponding to the maximum recorded pres- I. Pérez-Cáceres et al. 10 sure of 1.4 GPa in the Cubito-Moura unit (Fonseca et al., 1999; Ponce et al., 2012; Ru- bio Pascual et al., 2013). According to these assumptions, a simple calculation yields 71 km of lateral displacement during burial and the same amount during exhumation, Title Page i.e. altogether ≈ 140 km of left-lateral displacement of the OMZ with respect to the SPZ during this Devonian event. Abstract Introduction

Conclusions References 15 5.2 Emplacement of the Beja-Acebuches mafic/ultramafic belt Tables Figures Along the OMZ-SPZ boundary, a linear intrusion of mafic and ultramafic rocks (the BA unit; Figs. 1c and 7; Quesada et al., 1994) was emplaced during the transtensional J I stage that dominated all SW Iberia during the earliest Carboniferous (Azor et al., 2008) (Fig. 2b). There are no kinematic indicators but an undefined left-lateral transtension is J I

20 suggested in order to maintain the same lateral displacements as in the previous (see Back Close above) and subsequent (see below) convergent stages. Full Screen / Esc 5.3 Obductive thrust of the Beja-Acebuches unit Printer-friendly Version The convergence between the OMZ and the SPZ was resumed very soon after the formation of the BA unit. The renewed convergence resulted in hot obductive thrust of Interactive Discussion 25 the BA unit onto the OMZ border (Fig. 2c) (Fonseca and Ribeiro, 1993; Pérez-Cáceres

5.4 Ductile shearing and large-scale folding at the OMZ-SPZ boundary 7, 3773–3815, 2015

Recent structural research has provided a detailed model for the Carboniferous evolu- Oblique collision and 5 tion of the OMZ-SPZ boundary. After the obductive thrust referred above, the conver- deformation gent evolution became characterized by the interplay between large-scale folding and partitioning left-lateral shearing (Fig. 8) (Pérez-Cáceres et al., 2015). The entire OMZ-SPZ boundary was aﬀected by an E–W trending steeply to mod- I. Pérez-Cáceres et al. erately inclined south-vergent fold (Quintos fold), aﬀecting the BA unit (Figs. 2d, 8b 10 and 9). In the eastern sector (Aracena area) only the reverse limb of this fold ap- pears (Fig. 9), though in the western sector (Sherpa area) the complete fold structure Title Page has been mapped (Pérez-Cáceres et al., 2015). Coeval to the Quintos fold, ductile Abstract Introduction shearing came about concentrated in the BA unit, which evolved from high- to low- temperature (the so-called Southern Iberian shear zone; Crespo-Blanc and Orozco, Conclusions References

15 1988; Díaz-Azpiroz and Fernández, 2005; Fernández et al., 2013). The age of these Tables Figures deformations is constrained in the range 340–335 Ma (Late Visean), according to the available geochronological data (Castro et al., 1999; Dallmeyer et al., 1993). J I The high-temperature rocks of the Southern Iberian shear zone (granulite and high- temperature amphibolite facies) are middle-grained and display intense foliation and J I

20 compositional layering; sometimes, a mineral lineation is deﬁned by the orientation of Back Close amphibole. The low-temperature rocks (amphibolite and greenschist facies) are ﬁne- grained and show a well-developed S-L mylonitic fabric with abundant microstructures Full Screen / Esc indicating left-lateral shear sense (Crespo-Blanc, 1991; Díaz-Azpiroz and Fernández, 2005). They concentrated towards the southern part of the unit (Fig. 9). The orientation Printer-friendly Version

25 of the foliation is somewhat varied in the western sector (Fig. 10a) but in the eastern Interactive Discussion sector it strikes NW–SE and dips ≈ 55◦ to the NE (Fig. 10b). The pitch of the high- temperature mineral lineation is medium to high, while the stretching/mineral lineation in the low-temperature rocks has medium to low pitch angles (Fig. 10a and b). Most 3787 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion low-temperature lineations plunge to the E or SE, except south of Cortegana where the lineation plunges to the NW. This anomalous local plunge has been interpreted SED as a local flow induced by the proximity of a stiff gabbroic body (Díaz-Azpiroz and 7, 3773–3815, 2015 Fernández, 2005). 5 The prominent S-L mylonitic fabric and the left-lateral asymmetric microstructures suggest that simple shear dominated this deformation. Apart from the Cortegana sec- Oblique collision and tor, the mineral/stretching lineation plunges to the east, though the different pitch angle deformation of high-and low-temperature lineations deserves attention. The evolution displayed in partitioning Fig. 8 indicates that the high-temperature fabric would have been developed when the I. Pérez-Cáceres et al. 10 shear zone had low dip, while the low-temperature one would have been formed in a steeper shear zone, as the Quintos fold was getting tighter. Accordingly, the transpression model of simple inclined walls (Jones et al., 2004) provides with a possible Title Page explanation for the observed pitch variation: at an angle of convergence β ≈ 10◦ and a shortening S < 0.2 (simple-shear dominated transpressional zones), the model pre- Abstract Introduction ◦ ◦ ◦ 15 dicts pitch angles of 50–60 when the dip of the shear zone is 20 ≤ δ ≤ 30 , and pitch Conclusions References angles of 10–35◦ when the dip of the shear zone is 50◦ ≤ δ ≤ 80◦. This model also suggests that the pitch of the lineation is not indicative of oblique thrusting; then the Tables Figures moderate uplift of the southern border of the OMZ with respect to the SPZ would be rather ascribed to the Quintos fold and later brittle thrusting (Figs. 8 and 9) (Pérez- J I 20 Cáceres et al., 2015). Díaz-Azpiroz and Fernández (2005) have also examined the Southern Iberian shear zone under the light of the model of Jones et al. (2004), while J I Fernández et al. (2013) have tested the model of triclinic flow of Fernández and Díaz- Back Close Azpiroz (2009). In both cases, an important difference with our interpretation is that Full Screen / Esc they do not envisage the existence of the Quintos fold and its concomitant evolution 25 with shearing (Figs. 8 and 9). Printer-friendly Version Regardless of the transpression model considered, the left-lateral displacement due to the Southern Iberian shear zone cannot be accurately calculated. Assuming that the Interactive Discussion mafic layering corresponds to dykes intruded in gabbro and considering that layering and foliation are almost parallel, a γ ≥ 4 can be proposed (simple shear) (Fig. 10c).

3788 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Considering that the maximum thickness of the BA unit is ≈ 2000 m across its ghost stratigraphy (metabasalts-gabbros-ultramafites), a plausible shear strain γ = 5 would SED correspond to a left-lateral displacement of only 10 km, which is a rather modest figure. 7, 3773–3815, 2015 Reasonably higher values of γ would not result in greater regionally significant lateral 5 displacements. Oblique collision and 5.5 Deformation inside the SPZ deformation partitioning The SPZ is a fold-and-thrust belt made up of low-grade slates, metasandstones and metavolcanic rocks of Devonian to Carboniferous age (Fig. 11a). The fold-and-thrust I. Pérez-Cáceres et al. system is rooted in a detachment level located at the middle crust (IBERSEIS seismic 10 profile; Simancas et al., 2003). Deformation propagated southwards from late Visean to Moscovian time (Oliveira, 1990). At the western part of the SPZ, its structural trend Title Page deviates from the common WNW–ESE trend, due to the influence of the N–S oriented Abstract Introduction Porto-Tomar dextral Fault (Ribeiro et al., 1980) (Fig. 1b). For this reason, we do not consider this western part in the following analysis. Conclusions References

15 Relevant features of the SPZ deformation include (Simancas et al., 1986) (Figs. 1c Tables Figures and 11): (i) the foliation trends N105◦ E and dips 50◦ to the north on average; (ii) the tectonic fabric is planar (S-tectonites), sometimes exhibiting a faint stretching lineation no- J I ticeable in piroclastic rocks; S-L tectonites are observed only at localized thrust bands; ◦ (iii) when visible, the stretching lineation shows high-pitch angles of 65–90 ; (iv) ﬁnite J I

20 X strain ellipsoids are oblate with the axis always upright; (v) folds axes display a re- Back Close markably variable plunging, with smooth curved hinges observed at outcrop; and (vi) fold traces are slightly oblique clockwise with respect to the OMZ-SPZ boundary, thus Full Screen / Esc suggesting left-lateral transpression. The deformation of the SPZ is partitioned into strain, buckle folds and thrusts at lo- Printer-friendly Version

25 cal scale, but considered as a whole it can be approximated to a bulk homogeneous Interactive Discussion deformation that can be analyzed in the light of a suitable transpressional model. In this respect, the northern wall of the SPZ transpressional zone is the currently steep Southern Iberian shear zone, the southern wall is loosely defined at the southernmost 3789 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion SPZ, and the base of the transpressional zone is the mid-crustal detachment imaged in the IBERSEIS seismic section (Fig. 11a). Furthermore, significant lateral escape of the SED deformed rock-volume (Jones et al., 1997) can be rejected, since folds show smooth 7, 3773–3815, 2015 curved hinges. Finally, as the X finite strain axis roughly but consistently coincides 5 with the dip direction, then the bulk strain symmetry may be considered approximately monoclinic (Lin et al., 1998, 1999). Thus, the boundary conditions of the SPZ fit reason- Oblique collision and ably well with those in the models of Sanderson and Marchini (1984), who factorized deformation bulk strain into finite pure shearing followed by simple shearing, and Fossen and Tikoff partitioning (1993), who modeled simultaneous superposition of the strain components. The latter I. Pérez-Cáceres et al. 10 model is in general a more realistic way of modelling transpression, because in nature simultaneous superposition of shear components must be the rule. Nevertheless, the pure shear component probably diminishes as shortening increases, i.e. the ratio Title Page simple shear/pure shear would increase with increasing deformation, as it has been suggested for natural transpression zones (Dutton, 1997; Jiang, 2007). Actually, the Abstract Introduction 15 evolution of the SPZ might have been of this type, as suggested by the fact that defor- Conclusions References mation ended with pure sinistral strike-slip faulting. If this is the case, modelling natural deformation here by simultaneous superposition with constant simple shear/pure shear Tables Figures ratio is not obviously advantageous with respect to the finite factorization of pure shear followed by simple shear. Accordingly, we have modeled the bulk deformation of the J I 20 SPZ as superposition of pure shear followed by simple shear (Sanderson and Mar- chini, 1984), the bulk shear strain thus obtained gives us the approximate value of the J I bulk left-lateral displacement (Fig. 12a). Back Close Strain data from the SPZ have been projected in the finite strain grid of Sanderson Full Screen / Esc and Marchini (1984) (Fig. 12b), suggesting a bulk transversal shortening of ≈ 40 % −1 ◦ 25 (α ≈ 0.6) and a shear strain of Y ≈ 1 (bulk angular shear strain ψ = 45 ). For the Printer-friendly Version α−1 and Y values deduced above, the transpressional model used predicts that the 0 ◦ long axis of the horizontal strain ellipse (map view) would be oriented at θ = 18 with Interactive Discussion a vertical X strain axis, in reasonable agreement with the data (Fig. 12c). Thus, the bulk strain of the SPZ can be factorized into a transversal shortening of ≈ 40 % fol-

3790 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion lowed by a strike-slip shearing of Y ≈ 1 (ψ = 45◦). Taking an ≈ 90 km width for the SPZ (excluding the less-deformed SW sector), that shear strain yields a left-lateral relative SED displacement of the OMZ with respect to the SPZ of ≈ 90 km. This finite strain factor- 7, 3773–3815, 2015 ization has been geometrically depicted in Fig. 12d. Modeling our data of the SPZ in 5 terms of simultaneous superposition with constant simple shear/pure shear ratio (Fos- sen and Tikoff, 1993) does not yield significantly different results, but just a bulk angular Oblique collision and shear strain slightly higher (ψ ≈ 50◦). deformation partitioning 5.6 Brittle shearing at the OMZ-SPZ boundary I. Pérez-Cáceres et al. The syn-orogenic flysch attests that deformation reached the southwesternmost SPZ 10 in Moscovian time (Oliveira, 1990). At that time, a well-organized left-lateral strike-slip fault system started to develop at the OMZ-SPZ boundary (Fig. 13), thus suggesting Title Page

renewed deformation partitioning. Abstract Introduction Two faulting stages can be diﬀerentiated (Simancas, 1983). First, two smoothly curved E–W oriented major faults divided the southernmost OMZ into three lens- Conclusions References

15 shaped blocks, their summed slip accounting for 75 % (55–60 km) of the total slip of Tables Figures the left-lateral brittle faulting (Fig. 13a and b). These two faults concentrated the strike- slip component of the transpression, while simultaneous frontal shortening occurred at J I the southwesternmost SPZ (Carrapateira thrust; Ribeiro and Silva, 1983). The second faulting stage is characterized by a set of en-échelon NE–SW shorter faults summing J I

20 ≈ 20 km of slip. Thus, the total strike-slip of all the faults amounts to 80 km. This brittle Back Close shearing just preceded the stuck of the OMZ-SPZ convergence. Full Screen / Esc

6 Discussion and conclusions Printer-friendly Version

From Middle-Late Devonian to Pennsylvanian time, the collisional evolution of SW Interactive Discussion Iberia is characterized by oblique left-lateral convergence between three continental 25 terranes: the CIZ (representing the northern margin of Gondwana), the OMZ (a frag-

3791 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion ment of the Gondwana margin), and the SPZ (the southern margin of Avalonia). Oblique convergence resulted in strain partitioning with the boundaries between the SED terranes accumulating preferentially the left-lateral component, and the interior of them 7, 3773–3815, 2015 exhibiting both frontal and lateral components of deformation.

5 6.1 The big numbers of SW Iberia Variscan transpression Oblique collision and deformation This paper is the first attempt to evaluate regional left-lateral displacement in SW Iberia partitioning due to the oblique collision of continental terranes during the Variscan orogeny. We are aware of the approximate nature of our calculations given the uncertainties in the kine- I. Pérez-Cáceres et al. matic analysis performed, but we contend that the big numbers thus obtained have 10 strong regional significance. As a synthesis, the quantification of the Variscan deformations in SW Iberia described above yields the following results, from north to south Title Page (Fig. 14): Abstract Introduction – The ductile shearing that occurred in the BCSZ during the Upper Devonian- Mississippian time has been quantified to ≈ 150 km of left-lateral displacement, Conclusions References 15 roughly parallel to the CIZ-OMZ boundary. Tables Figures – The late Variscan strike-slip fault system that developed at the CIZ-OMZ boundary produced ≈ 85 km of left-lateral displacement parallel to this boundary. J I – The Devonian SW-vergent folds and thrusts of the OMZ terrane accumulated ≈ J I 290 km of NE–SW directed shortening with a left-lateral component parallel to the Back Close 20 CIZ-OMZ boundary of ≈ 185 km. Full Screen / Esc – The Carboniferous upright folds of the OMZ terrane accumulated ≈ 80 km of NE– SW shortening with a left-lateral component parallel to the CIZ-OMZ boundary of Printer-friendly Version ≈ 55 km. Interactive Discussion – The rotation of the OMZ Carboniferous folds to a Z shape was produced by a left- 25 lateral shearing with ≈ 230 km of displacement subparallel to the OMZ boundaries, plus a limited perpendicular shortening. 3792 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion – The Devonian subduction/exhumation on the southern margin of the OMZ, as represented by the allochthonous Cubito-Moura unit, took place in a left-lateral set- SED ting that amounts to ≈ 140 km of displacement parallel to the OMZ-SPZ boundary. 7, 3773–3815, 2015 – The displacement figures of the transtensional Early-Middle Mississippian stage 5 that gave way to the BA oceanic-like realm cannot be evaluated, though this event Oblique collision and most probably occurred in a continued left-lateral tectonic setting. An alike sce- deformation nario can be envisaged for the subsequent obduction of the BA unit, though with partitioning renewed transpression. I. Pérez-Cáceres et al. – The transpressional Southern Iberian shear zone that deformed the BA unit re- 10 veals a rather conservative ≈ 10 km of left-lateral displacement parallel to the OMZ-SPZ boundary. Title Page – The transpressional fold-and-thrust belt of the SPZ terrane produced ≈ 90 km of Abstract Introduction left-lateral displacement parallel to the OMZ-SPZ boundary with ≈ 40 km of orthogonal shortening. Conclusions References

15 – The late Variscan strike-slip fault system that developed at the OMZ-SPZ bound- Tables Figures ary produced ≈ 80 km of left-lateral displacement parallel to the boundary. J I 6.2 Relative displacements of SW Iberian terranes J I

Considered altogether, the total collisional convergence recorded in SW Iberia is E– Back Close W oriented and surpasses 1000 km. The left-lateral component parallel to terrane Full Screen / Esc 20 boundaries is estimated to be ≈ 1000 km, of which ≈ 465 km accumulated as strike-slip shearing at the two suture boundaries (Fig. 14c). This main conclusion brings up an image of the paleoposition of SW Iberian continental terranes just before the Devonian- Printer-friendly Version

Carboniferous Variscan collision. The remarkable left-lateral oblique kinematics during Interactive Discussion the Variscan plate convergence in SW Iberia, as opposite to the dominant right-lateral 25 kinematics of the Variscan/Alleghanian Orogen (Fig. 1a), is also inferred from our kinematic analysis. We interpret that the reason for the singular kinematics of SW Iberia is 3793 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion the existence of an Avalonian promontory, currently represented by the SPZ (Figs. 1a and 14b). SED Finally, it is important to emphasize that in-between these regions with opposite kine- 7, 3773–3815, 2015 matics (left-lateral oblique convergence in SW Iberia and right-lateral oblique conver- 5 gence in central Europe), an intermediate one with rather frontal convergence must have existed (Fig. 1a), which would had to accommodate the > 1000 km of collisional Oblique collision and convergence evaluated above. In NW Iberia, a major unrooted allochthonous pile with deformation continental and oceanic-like units has been described onto the para-autochthonous partitioning CIZ (Martínez Catalán et al., 1997). Thus, NW Iberia may represent this intermediate I. Pérez-Cáceres et al. 10 region with frontal collision.

Acknowledgements. Financial support by grants CGL2011-24101 (Spanish Ministry of Science and Innovation), RNM-148 (Andalusian Government) and BES-2012-055754 (Doctoral schol- Title Page arship to I. Pérez-Cáceres from the Spanish Ministry of Science and Innovation). We thank C. Fernández for his critical reading of an early draft of this paper. Abstract Introduction Conclusions References

15 References Tables Figures

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A.: Interlinked system of ductile strike slip and thrusting Conclusions References formed by Caledonian sinistral transpression in northeastern Greenland, Geology, 19, 510– 513, 1991. Tables Figures 20 Jackson, P. and Sanderson, D. J.: Scaling of fault displacements from the Badajoz-Cordoba shear zone, SW Spain, Tectonophysics, 210, 179–190, 1992. Jiang, D.: Sustainable transpression: an examination of strain and kinematics in J I deforming zones with migrating boundaries, J. Struct. Geol., 29, 1984–2005, J I doi:10.1016/j.jsg.2007.09.007, 2007. 25 Jiang, D. and Williams, P.F.: High-strain zones: a unified model, J. Struct. Geol., 20, 1105–1120, Back Close 1998. Full Screen / Esc Jones, R. R., Holdsworth, R. E., and Bailey, W.: Lateral extrusion in transpression zones; the importance of boundary conditions, J. Struct. Geol., 19, 1201–1217, 1997. Jones, R. R., Holdsworth, R. E., Clegg, P., McCaffrey, K., and Tavarnelli, E.: Inclined transpres- Printer-friendly Version 30 sion, J. Struct. Geol., 26, 1531–1548, 2004. Interactive Discussion Lin, S., Jiang, D., and Williams, P.F.: Transpression (or transtension) zones of triclinic symmetry: natural example and theoretical modelling, in: Continental Transpression and Transtension

3797 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Tectonics, edited by: Holdsworth, R. E., Strachan, R. A., and Dewey, J. F., Geological Society of London Special Publications, 135, 41–57, 1998. SED Lin, S., Jiang, D., and Williams, P. F.: Discussion on transpression and transtension zones, Journal of Geological Society of London, 156, 1045–1048, 1999. 7, 3773–3815, 2015 5 Linnemann, U., Gehmlich, M., Tichomirowa, M., Buschmann, B., Nasdala, L., Jonas, P., Lützner, H., and Bombach, K.: The cadomian orogen: neoproterozoic to Early Cambrian crustal growth and orogenic zoning along the periphery of the West African Craton – con- Oblique collision and straints from U-Pb zircon ages and Hf isotopes (Schwarzburg Antiform, Germany), Precam- deformation brian Res., 244, 263–278, 2014. partitioning 10 López Sánchez-Vizcaíno, V., Gómez Pugnaire, M. T., Azor, A., and Fernández Soler, J. M.: Phase diagram sections applied to amphibolites: a case study from the Ossa– I. Pérez-Cáceres et al. Morena/Central Iberian Variscan suture (Southwestern Iberian Massif), Lithos, 68, 1–21, 2003. Martínez Catalán, J. R., Arenas, R., Díaz García, F., and Abati, J.: Variscan accretionary com- Title Page 15 plex of northwest Iberia: terrane correlation and succession of tectonothermal events, Geol- ogy, 25, 1103–1106, 1997. Abstract Introduction Martínez Poyatos, D.: Estructura del borde meridional de la Zona Centroibérica y su relación Conclusions References con el contacto entre las Zonas Centroibérica y de Ossa-Morena, PhD Thesis, Univ. de Granada, 295 pp., 1997. Tables Figures 20 Matte, P.: Accretionary history and crustal evolution of the Variscan belt in Western Europe, Tectonophysics, 196, 309–337, 1991. Matte, P.: The Variscan collage and orogeny (480–290 Ma) and the tectonic definition of the J I Armorica microplate: a review, Terra Nova, 13, 122–128, 2001. J I Munhá, J., Oliveira, J. T., Ribeiro, A., Oliveira, V., Quesada, C., and Kerrich, R.: Beja-Acebuches 25 ophiolite, characterization and geodynamic significance, Maleo, 2, 31, 1986. Back Close Murphy, J. B. and Nance, R. D.: A supercontinent model for the contrasting character of Late Full Screen / Esc Proterozoic orogenic belts, Geology, 9, 469–472, 1991. Oliveira, J. T.: Part VI: South Portuguese Zone, stratigraphy and synsedimentary tectonism. in: Pre-Mesozoic Geology of Iberia, edited by: Dallmeyer R. D. and Martínez García, E., Printer-friendly Version 30 Springer, 334–347, 1990. Interactive Discussion Ordóñez Casado, B.: Geochronological Studies of the Pre-Mesozoic Basement of the Iberian Massif: The Ossa-Morena Zone and the Allochthonous Complexes within the Central Iberian Zone, PhD Thesis, ETH, Zürich, 235 pp., 1998. 3798 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Pereira, M. F., Apraiz, A., Chichorro, M., Silva, J. B., and Armstrong, R. A.: Exhumation of high pressure rocks in northern Gondwana during the Early Carboniferous (Coimbra-Cordoba SED shear zone, SW Iberian Massif): tectonothermal analysis and U-Th-Pb SHRIMP in-situ zircon geochronology, Gondwana Res., 17, 440–460, 2010. 7, 3773–3815, 2015 5 Pérez-Cáceres, I., Martínez Poyatos, D., Simancas, J. F., and Azor, A.: The elusive nature of the Rheic Ocean suture in SW Iberia, Tectonics, 34, doi:10.1002/2015TC003947, 2015. Pin, C., Paquette, J. L., Santos Zalduegui, J. F., and Gil Ibarguchi, J. I.: Early Devonian supra- Oblique collision and subduction ophiolite related to incipient collisional processes in the Western Variscan Belt: deformation the Sierra Careon unit, Ordenes Complex, Galicia, in: Variscan-Appalachian Dynamics: The partitioning 10 Building of the Late Paleozoic Basement, edited by: Martínez Catalán, J. R., Hatcher, R., Arenas, R. and Díaz García, F., Geological Society of America Special Paper, 364, 57–71, I. Pérez-Cáceres et al. 2002. Ponce, C., Simancas, J. F., Azor, A., Martínez Poyatos, D., Booth-Rea, G., and Expósito, I.: Metamorphism and kinematics of the early deformation in the Variscan suture of SW Iberia, Title Page 15 J. Metamorph. Geol., 30, 625–638, 2012. Quesada, C. and Dallmeyer, R. D.: Tectonothermal evolutionof the Badajoz-Córdoba shear Abstract Introduction 40 /39 zone (SW Iberia): characteristics and Ar Ar mineral age constraints, Tectonophysics, Conclusions References 231, 195–213, 1994. Quesada, C., Fonseca, P. E., Munhá, J., Oliveira, J. T., and Ribeiro, A.: The Beja-Acebuches Tables Figures 20 Ophiolite (Southern Iberia Variscan fold belt): geological characterization and significance, Boletín Geológico y Minero, 105, 3–49, 1994. J I Ramsay, J. G. and Huber, M. I.: The Techniques of Modern Structural Geology, Vol. 2, Folds and Fractures, Springer, 393 pp., 1987. J I Ribeiro, A. and Silva, J. B.: Structure of the South Portuguese Zone, in: The Carboniferous of Back Close 25 Portugal, edited by: Sousa, M. J. L. and Oliveira, J. T., Memória dos Serviços Geológicos de Portugal, 29, 83–89, 1983. Full Screen / Esc Ribeiro, A., Pereira, E., and Severo, L.: Análise da deformaçao da zona de cisalhament Porto- Tomar na transversal de Oliveira de Azeméis, Comunicações dos Serviços Geológicos de Portugal, 66, 3–9, 1980. Printer-friendly Version 30 Robardet, M.: Alternative approach to the Variscan Belt in southwestern Europe: pre-orogenic Interactive Discussion paleobiogeographical constraints, in: Variscan-Appalachian Dynamics: The Building of the Late Paleozoic Basement, edited by: Martínez Catalán, J. R., Hatcher, R., Arenas, R., and Díaz García, F., Geol. S. Am. S., 364, 1–15, 2002. 3799 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion Robin, P. Y. F. and Cruden, A. R.: Strain and vorticity patterns in ideally ductile transpressional zones, J. Struct. Geol., 16, 447–466, 1994. SED Rodríguez-Alonso, M. D., Peinado, M., López-Plaza, M., Franco, P., Carnicero, A., and Gon- zalo, J. C.: Neoproterozoic-Cambrian synsedimentary magmatism in the Central Iberian 7, 3773–3815, 2015 5 Zone (Spain): geology, petrology and geodynamic significance, Int. J. Earth Sci., 93, 897– 920, 2004. Rubio Pascual, F. J., Matas, J., and Martín Parra, L. M.: High-pressure metamorphism in the Oblique collision and Early Variscan subduction complex of the SW Iberian Massif, Tectonophysics, 592, 187–199, deformation 2013. partitioning 10 Sánchez Carretero, R., Eguíluz, L., Pascual, E., and Carracedo, M.: Ossa-Morena Zone: Ig- neous rocks. in: Pre-Mesozoic Geology of Iberia, edited by: Dallmeyer, R. D. and Martínez I. Pérez-Cáceres et al. García, E., Springer, 292–313, 1990. Sanderson, D. J. and Marchini, W. R. D.: Transpression, J. Struct. Geol., 6, 449–458, 1984. Shelley, D. and Bossière, G.: A new model for the Hercynian Orogen of Gondwanan France Title Page 15 and Iberia, J. Struct. Geol., 22, 757–776, 2000. Silva, J. B., Oliveira, J. T., and Ribeiro, A.: South Portuguese Zone, estructural outline, in: Pre- Abstract Introduction Mesozoic Geology of Iberia, edited by: Dallmeyer, R. D. and Martínez García, E., Springer, Conclusions References 348–362, 1990. Simancas, J. F.: Geología de la Extremidad Oriental de la Zona Sudportuguesa, PhD Thesis, Tables Figures 20 Univ. de Granada, 439 pp., 1983. Simancas, J. F.: La deformación en el sector oriental de la zona Surportuguesa, Boletín Ge- ológico y Minero, 82, 239–268, 1986. J I Simancas, J. F., Martínez Poyatos, D., Expósito, I., Azor, A., and González Lodeiro, F.: The J I structure of a major suture zone in the SW Iberian Massif: the Ossa-Morena/Central Iberian 25 contact, Tectonophysics, 332, 295–308, 2001. Back Close Simancas, J. F., Carbonell, R., González Lodeiro, F., Pérez-Estaún, A., Juhlin, C., Full Screen / Esc Ayarza, P., Kashubin, A., Azor, A., Martínez Poyatos, D., Almodóvar, G. R., Pascual, E., Sáez, R., and Expósito, I.: Crustal structure of the transpressional Variscan orogen of SW Iberia: SW Iberia deep seismic reflection profile (IBERSEIS), Tectonics, 22, 1062, Printer-friendly Version 30 doi:10.1029/2002TC001479, 2003. Interactive Discussion Simancas, J. F., Expósito, I., Azor, A., Martínez Poyatos, D., and González Lodeiro, F.: From the Cadomian orogenesis to the Early Palaeozoic Variscan rifting in Southwest Iberia, J. Iber. 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Geol., I. Pérez-Cáceres et al. 21, 1497–1512, 1999. Tikoff, B. and Teyssier, C.: Strain modeling of displacement-field partitioning in transpressional orogens, J. Struct. Geol., 16, 1575–1588, 1994. Title Page

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a) Avalonian terrane Taconic-Acadian-Caledonian sutures SED Rheic Ocean Variscan suture B A L T I C A Other Variscan sutures Late Paleozoic deformation front Vergence of main structures 7, 3773–3815, 2015 T I A U R E N L A Iberian Massif b) ? 42º N

? ? Porto-Tomar fault ? 200 km Oblique collision and G O N D W CIZ A N A OMZ 38º N deformation SPZ 1000 km 8º W 0º partitioning

c) Devonian structures: I. Pérez-Cáceres et al. Recumbent folds Thrusts Mississippian structures: Left-lateral shear N Normal faults Middle Carboniferous structures:

v Upright to overturned folds v Km Thrusts 0 10 20 30 40 50 Oblique-slip thrusts

v Pennsylvanian structures: Title Page v Left-lateral faults T Associated thrusts erena Syncline C I Z

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Post-Variscan cover 1 Badajoz-Córdoba J I geological Shear Zone Pulo do Lobo unit cross section Figure 1 Cubito-Moura Beja-Acebuches unit allochtonous unit Back Close

Fig. 1: (a) Reconstrucon of the Variscan‐Alleghanian Orogen at the end of the Carboniferous (simplified from Simancas et al., 2005). The Avalonian connental fragment and the inferred Rheic Ocean and other second‐order Variscan sutures are Full Screen / Esc Figure 1. (a) Reconstrucióndepicted. The SW Iberian of thele‐lateral Variscan-Alleghanian shear sutures are highlighted. (b) Geological subdivision Orogen of the Iberian atMassif the. CIZ: end of the Carbonif- Central Iberian Zone; OMZ: Ossa‐Morena Zone; SPZ: South Portuguese Zone. (c) Structural map of the SW Iberia showing erous (simplified fromthe main Simancas units and the different etDevonian al., and Carbonif 2005).erous structur Thees. The loc Avalonianaon of cross‐secon in Fig. continental 11 is indicated. fragment and the inferred Rheic Ocean and other second-order Variscan sutures are depicted. The SW Iberian Printer-friendly Version left-lateral shear sutures are highlighted. (b) Geological subdivision of the Iberian Massif. CIZ: Central Iberian Zone; OMZ: Ossa-Morena Zone; SPZ: South Portuguese Zone. (c) Structural Interactive Discussion map of the SW Iberia showing the main units and the different Devonian and Carboniferous structures. The location of cross-section in Fig. 11 is indicated.

L1 a) HP and MORB allochthons S1 Pulo do Lobo unit

OMZ upper crust Oblique collision and ~370 Ma SPZ crust } deformation partitioning b) I. Pérez-Cáceres et al.

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Mantle 355 - 340 Ma Title Page Lower crust Lower crust Mantle Abstract Introduction d) Pulo do Lobo c) SPZ unit OMZ Pulo do Lobo unit tectonic BA unit shear zone BA unit Conclusions References imbrications brittle late faults Tables Figures 335 - 310 Ma ~340 Ma mafic intrusions in the middle crust (IRB) H=V Synkinematic 0 10 20 30 km Granite J I

J I Figure 2. Fig.Evolutionary 2: Evolutionary model model for thefor OMZ‐SP theZ boundary OMZ-SPZ from Middle‐La boundaryte Devonian from to Pennsylv Middle-Lateanian proposedDevonian by Pérez‐ to Penn- Cáceres et al. (2015). (a) Closing of the Rheic Ocean and Late Devonian collision. (b) Early Carboniferous intracollisional Back Close sylvaniantr proposedanstensional st byage mainly Pérez-Cáceres represented by the et me al.tama (2015).fic BA unit.(a) (c) CarbonifClosingerous ofrene thewed Rheicoblique collision Ocean and Late Devonianpr collision.oducing the obduction(b) Early of the B CarboniferousA unit onto the OMZ. (d) intracollisional High‐ to low‐temperatur transtensionale folding and shearing of stage the BA unit mainly repre- Full Screen / Esc sented byand the south metamaﬁcwards propagation BA of the unit. deforma(c)tion.Carboniferous renewed oblique collision producing the obduction of the BA unit onto the OMZ. (d) High- to low-temperature folding and shearing of Printer-friendly Version the BA unit and southwards propagation of the deformation. Interactive Discussion

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Devonian oblique a) convergence OMZ b) CIZ OMZ I. Pérez-Cáceres et al. SPZ Early Carboniferous 118 km 25º 71 km Devonian oblique oblique divergence 35º subduction of the OMZ 55 km southern border 50 km Burial path 45º 45º Title Page 25º Burial and exhumation 50 km 50 55 km 55 45º path of the HP rocks in 45º Exhumation path of the Cubito-Moura Abstract Introduction allochthonous unit the HP rocks in the Subduction Badajoz-Córdoba Shear Zone path Conclusions References

SUBDUCTION ZONE (CIZ-OMZ boundary) SUBDUCTION ZONE (OMZ-SPZ boundary) Tables Figures

Figure 3. Simple models of burial and exhumation for the high-pressure rocks cropping out at J I the two collisionalboundariesFig. 3: Simple models of burial of and the exhuma OMZ.tion(a) forCIZ-OMZ the high‐pressur boundary.e rocks cropping(b) OMZ-SPZout at the two boundary.collisional See boundaries of the OMZ. a) CIZ‐OMZ boundary. b) OMZ‐SPZ boundary. See text for more explanations. J I text for more explanations. Back Close

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(Transtensional stage) OMZ Oblique collision and

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SPZ SPZ Abstract Introduction

Conclusions References d)Pennsylvanian (not to scale) Tables Figures CIZ 1 Badajoz-Córdoba Shear Zone 1 2 Trend of Devonian J I 2 structures: the Monesterio thrust J I 0 50 OMZ 3 Trend of Carboniferous Km 3 structures: the Back Close Terena synform Full Screen / Esc 4 Beja-Acebuches unit N 4 SPZ Printer-friendly Version

Figure 4. (a–d) Schematic evolutionary model of the deformations inside de OMZ from Devo- Interactive Discussion nian to Pennsylvanian time. See text for further explanations. Fig. 4 (a‐d): Schematic evolutionary model of the deformations inside de OMZ from Devonian to Pennsylvanian time. See text for further explanations. 3805 icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion SED 7, 3773–3815, 2015

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a) b) 40º ? 10º Band I

folds Band II 30º Monesterio thrust (Devonian) Title Page

Band III 40º OMZ Terena fold (Carboniferous) 30º Abstract Introduction Band IV 15º width perpendicular to folds N Band V 50º Conclusions References 50 km Tables Figures

Figure 5.Fig.Stages 5: Stages of Carbonif Carboniferouserous shortening shortening inside the OMZ. inside (a) NE‐S theW compr OMZ.ession(a) gaNE–SWve way to a se compressiont of upright gave way to afolds. set (b) of F uprightolds rotation folds. by heter(b)ogeneousFolds left‐la rotationteral shearing. by heterogeneous The five different bands left-lateral considered to shearing. analyze the The ﬁve J I diﬀerentde bandsformation considered are depicted. to analyze the deformation are depicted. J I

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quartz Subgrain I. Pérez-Cáceres et al. c-axes boundaries

b) Inferred kinematics of the HP rocks emplacement Title Page

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SPZ J I N Back Close 0 km 50 Full Screen / Esc Figure 6. Early collisional (Devonian) stage aﬀecting the Cubito-Moura unit in the OMZ-SPZ boundary, modiﬁed fromFig. Ponce 6: Early et al.collisional (2012). (a) (DeKinematicvonian) st analysisage affecting of the the early fabric indicating Printer-friendly Version top-to-the-ENE sense of movement: stereoplot of quartz C-axes (equal-area, lower hemisphere projection) and rose diagramCubito‐M ofo quartzura u subgrainnit in t boundaries.he OMZ‐SPZ(b) bSchematicoundary, map showing the Interactive Discussion kinematic vector of exhumationmodified offrom the allochthonousPonce et al. Cubito-Moura(2012). (a) Kinema unit. tic analysis of the early fabric indicating top‐to‐the‐ENE sense of movement: stereoplot of quartz C‐axes (equal‐area, lower hemispher3807 e projection) and rose diagram of quartz subgrain boundaries. (b) Schematic map showing the kinematic vector of exhumation of the allochthonous Cubito‐Moura unit. icsinPpr|Dsuso ae icsinPpr|Dsuso ae | Paper Discussion | Paper Discussion | Paper Discussion | Paper Discussion

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High- temperature Pulo do Lobo unit: Other paleozoic Low-grade metasediments BA unit Gabbros mapping lithologies Full Screen / Esc Metabasalts and schists Cubito-Moura unit Granitoids Marbles

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Figure 7. (a)Fig. Schematic7: (a) Schemac map map of the of OM theZ/SP OMZZ boundary/SPZ showing boundary the diﬀerent units showing involved in the the sutur diﬀerente. (b) Geologic unitsal involved Interactive Discussion map of the Aracena‐Cortegana area. Cross‐secons 1‐5 in Fig. 9 are located. in the suture. (b) Geological map of the Aracena-Cortegana area. Cross-sections 1–5 in Fig. 9 are located.

a) Northwards obduction and high-temperature shearing b) High-temperature shearing and south-verging folding Oblique collision and Quintos

N fold deformation v oblique folds v v v v partitioning v v v v v v v v v v v HT shear v v zone in BA OMZ I. Pérez-Cáceres et al. v v v HT folds and v v foliation in OMZ mineral lineation v Original lithlogy of BA unit: v HT shear zone in OMZ early shallow dip of the HT shear zone v v v v: volcanics v g g: gabbros v shear folds Title Page OMZ mineral lineation c) Low-temperature shearing and southwards propagation of the deformation Abstract Introduction

greenschists SPZ striations shear zones Conclusions References v v v v v v v Tables Figures

v F2 thrusts v OMZ J I 310 Ma F1folds

F1 thrusts stretching lineation J I 330 Ma Back Close Fig. 8 (a‐c): Evolutionary model of the BA unit during the Carboniferous transpression, from northward obduction Figure 8. (a–c)to southEvolutionaryward propagation of model the deforma oftion. the BA unit during the Carboniferous transpression, from Full Screen / Esc northward obduction to southward propagation of the deformation. Printer-friendly Version

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Figure 9. DetailedFig. 9: Detailed cross-sections cross‐sections of the of ov theerturned overturned limb of the Quin limbtos fold of in the cen Quintostral sector (Ar foldacena‐Cort in theegana) central of sector Back Close (Aracena-Cortegana)the BA unit, showing of the secondary BA f unit,olds and showing discrete low‐t secondaryemperature (greenschis foldst facies) and shear discrete bands. See low-temperature Fig. 7 for (greenschistloc facies)ation. shear bands. See Fig. 7 for location. Full Screen / Esc

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b) Eastern sector a) Western sector 0° 0° Oblique collision and deformation partitioning

I. Pérez-Cáceres et al. 270° 90° 270° 90°

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Abstract Introduction N = 31 N = 96 180° Low temperature facies: Stretching lineation 180° Equal angle , lower hemisphere projection Conclusions References High temperature facies: Mineral lineation

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Back Close Figure 10.Fig. 10: (a, (a, b) StructurStructuralal data of the data BA unit of (equal‐angle, the BA low uniter hemispher (equal-angle,e stereoplots), lower disnguishing hemisphere mylonic foliaon stereoplots), and stretching lineaon in the western (Beja‐Serpa) (a) and eastern (Cortegana‐Almadén de la Plata) (b) sectors.(c) Interpretaon distinguishingof the BA unit mylonitic amphibolite foliation layering. and stretching lineation in the western (Beja-Serpa) (a) and Full Screen / Esc eastern (Cortegana-Almadén de la Plata) (b) sectors. (c) Interpretation of the BA unit amphibolite layering. Printer-friendly Version

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a) b) South Portuguese Zone Ossa-Morena Zone mean stretching lineation BA unit (X strain axis) IBERSEIS deep seismic profile N SSO-NNE Title Page fold axes

Abstract Introduction 50 km mean cleavage current Moho orientation Conclusions References Fig. 11: (a) Schematic structural cross‐section of the southern OMZ and SPZ (modified from Simancas et al., 2003). See Fig. 1c Figure 11.for (a) location.Schematic (b) Stereoplot structural(equal‐angle, low cross-sectioner hemisphere projection) of the of structur southernal data from OMZ the eas andtern SP SPZZ showing (modiﬁed the from Tables Figures Simancasmean et al.,stretching 2003). lineation See and clea Fig.vage 1c orien fortation, location. as well as fold(b) axes.Stereoplot (equal-angle, lower hemisphere projection) of structural data from the eastern SPZ showing the mean stretching lineation and J I cleavage orientation, as well as fold axes. J I

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 7, 3773–3815, 2015 0.9 a) b) Transpressional components: 10 0.8   1 , 0.5-1 0.6 8 0.7 OMZ SPZ 6 0.6  5  = 4 Oblique collision and 4  = 3 0.5  X / Y deformation 3  = 2 0.4

2  = 1 partitioning 0.3 

1 I. Pérez-Cáceres et al.  = tan 1 2 3 4 5 6 8 10 15 30 X, Y, Z: strain axes strain data Y / Z ´angle between the walls and the maximum horizontal stretch axis,  strike of folds, thrusts and cleavage before deformation Title Page c) d) N Km 0 10 20 30 40 50 Abstract Introduction

50 Ossa-Morena Zone (OMZ) Conclusions References 40 

X strain axis vertical v 30 0.8 X strain axis horizontal v ´ v Tables Figures

´ v 20 0.6

0.4  10  0.2 J I 1 2 3 4 5 6 7 8 South Portuguese Zone (SPZ) estimated ´values  J I after deformation Back Close Fig. 12: (a) Transpressional model of Sanderon and Marchini (1984). (b) Strain data from the SPZ suggest the Figure 12.values (a) ofTranspressional shortening () and shearing model () acc ofor Sanderonding to this model. and (c) Marchini Calculation of (1984). the angle (b)betweenStrain the data from Full Screen / Esc the SPZ suggestboundary of thethe transpr valuesessional of block shortening and the maximum (α) andhorizon shearingtal stretch axis, (γ acc)or accordingding to the estima tot thised  model. (c) and  values. (d) Sketch of the eastern SPZ showing the transpressional deformation. Calculation of the angle between the boundary of the transpressional block and the maximum Printer-friendly Version horizontal stretch axis, according to the estimated α and γ values. (d) Sketch of the eastern SPZ showing the transpressional deformation. Interactive Discussion

a) Beja-Acebuches amphibolites Pulo do Lobo unit Oblique collision and Left-lateral ductile shear zone (Upper Visean) deformation N Thrusts (Upper Visean-Bashkirian) Km Strike-slip brittle faults and associated thrusts partitioning 0 20 40 (Upper Pennsylvanian) ?

b) I. Pérez-Cáceres et al. + + + + + + + + + + + + + + + + + + + + + N + + + + + + + + + + + + + + + + 10 Km + + + + + + + Serpa + + + + v v v v v v v + + + + + v v v v v v v v + + + + v v Ficalho v v v v + + + + v v v v Title Page v v v v v + + + + + v Cortegana v v v v Aracena

+ + + Abstract Introduction c) + + + + + + + + + + + + + + + + + + + Beja-Acebuches Cubito-Moura + + + + + + metamafic unit allochthonous unit Conclusions References + + + + + + + + + + + + + + + + + + Units of the southern border of the OMZ: + + + + High-grade Low-grade + + + + + Tables Figures + + + +

Undeformed plutonic rocks + + + A: granitoids; + + + B: diorites and gabbros J I A B

High-grade fold anticlines Greenschist fold anticlines J I

Fig. 13: (a) Schematic map of the main late Variscan faults affecting the OMZ‐SPZ boundary. (b) Cartography of the central Back Close Figure 13. (a)part ofSchematic the OMZ‐SPZ boundary map of, showing the mainthe main late Ficalho Variscan fault and the faults set of short aﬀectinger faults af thefecting OMZ-SPZ the Aracena‐ boundary. Cortegana sector. (c) Reconstruction of this central part before the brittle faulting. (b) Cartography of the central part of the OMZ-SPZ boundary, showing the main Ficalho fault Full Screen / Esc and the set of shorter faults aﬀecting the Aracena-Cortegana sector. (c) Reconstruction of this central part before the brittle faulting. Printer-friendly Version

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Oblique collision and deformation

a) N NW b) partitioning

A 0 200 km 0 100 200 CIZ km C CIZ I. Pérez-Cáceres et al. D OMZ C C SPZ C D Alpine front Rheic suture OMZ

C Title Page C SPZ c) D CIZ  235 km Abstract Introduction Avalonian spur ?

OMZ Conclusions References  470 km C D  230 km Tables Figures 0 200 Carboniferous Devonian displacements displacements km  90 km SPZ J I Figure 14.Fig. (a)14: (a)Sketch Sketch of the of Iberian the Massif Iberian with loc Massifation of the with CIZ, OMZ, location SPZ and the of NW the Iberia CIZ, alloch OMZ,thon (NW SPZA). (b) Vect andors the NW showing the relative displacements between the southern Iberia terranes, according to our calculations. (c) Sketch J I Iberia allochthonemphasizing (NWA). the left‐later(b)al displacemenVectorsts par showingallel to terrane the boundaries. relative displacements between the southern Iberia terranes, according to our calculations. (c) Sketch emphasizing the left-lateral displace- Back Close ments parallel to terrane boundaries. Full Screen / Esc

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