A reconstruction of Iberia accounting for W-Tethys/N-Atlantic kinematics since the late Permian-Triassic

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Introduction
Plate tectonic reconstructions are based on the knowledge of magnetic anomalies that record age, rate and direction of seafloor spreading.Where these constraints are lacking or their recognition ambiguous, kinematic reconstructions rely on the description and interpretation of the structural, sedimentary, igneous and metamorphic rocks of rifted margins and orogens https://doi.org/10.5194/se-2020-24Preprint.Discussion started: 6 March 2020 c Author(s) 2020.CC BY 4.0 License.Atlantic.Extension and salt movements in the North Sea basins during the Late Triassic further point to the propagation of the North Atlantic rift (Goldsmith et al., 2003).
The persistence of shallow-marine to non-marine deposition during this period contrasts with the large accommodation space that is required at larger scale to sediment the giant evaporitic-province in the late Permian (Jackson et al., 2019) and in the Late Triassic (Štolfová and Shannon, 2009;Leleu et al., 2016;Ortí et al., 2017).Crustal thinning expected for this period therefore does not follow McKenzie's prediction of subsidence (McKenzie, 1978).
A first hypothesis to explain the difference with this model is that crustal attenuation induced density reduction of the thinned lithosphere by mantle phase transitions to lighter mineral phases during lithosphere thinning (Simon and Podladchikov, 2008) or due to the trapping of melt in the rising asthenosphere before breakup (Quirk and Rüpke, 2018) in addition to magmatic re-thickening of attenuated crust by underplating.Another possible hypothesis for the Permian-Triassic topographic evolution of the Iberian basins relies on the complex post-Variscan evolution of the Iberian lithosphere.Recent studies have shown that during the existence of Pangea supercontinent (∼300 to ∼200 Ma), temperature in the asthenospheric mantle increased due to the thermal insulation by the continental lid (Coltice et al., 2009;Ganne et al., 2016).Such mantle thermal anomaly could have further inhibited lithospheric mantle re-equilibration after late-Variscan mantle delamination over a long-time span.
Once mantle temperature dropped as a consequence of the Pangea breakup and magmatic emission at the Triassic/Jurassic boundary, lithospheric mantle started to cool and thicken, causing isostatic subsidence of the thinned Iberian crust and resulting in topographic drop.
This argues for a protracted period of ∼100 Myr (late Carboniferous to Late Triassic) of continental lithosphere thinning and magmatism prior to Jurassic break-up of the North Atlantic but contemporaneous with the Tethyan evolution.One main consequence is that the late Permian-Triassic extension has been so far underestimated in plate reconstructions, despite evidence for continuous extension.
3 From late Permian-Early Triassic rifting to Late Jurassic-Early Cretaceous rifting in Iberia The Permian-Triassic basins of Iberia are exposed in the inverted Mesozoic rift basins of the Basque-Cantabrian and Pyrenean belts, the Iberian Ranges, the Catalan Range and the Betic Cordillera (Figs. 1B and 3A).The coincidence between the orientations of the Alpine orogenic segments and the spatial distribution of  suggest that the Cenozoic orogenic cycle largely inherits the earliest stages of the Tethyan rift evolution.In addition, these Permian-Triassic depocentres are superposed over Variscan structures (Fig. 1B), suggesting antecedent tectonic control of the Tethyan continental rift segment by the late Variscan evolution.
We analyse subsidence reconstructed based on a compilation of well data and synthetic stratigraphic section in the Aquitaine Basin (Brunet, 1984), Cameros and Iberian basins (Salas and Casas, 1993;Salas et al., 2001;Omodeo-Salé et al., 2017), West Iberia (Spooner et al., 2019), and the Betics (Hanne et al., 2003), to estimate 1D mean tectonic subsidence evolution in these areas (Fig. 3B, see Supplementary Material for individual tectonic subsidence curves in each region).For each region, we calculated the mean tectonic subsidence, following the approach of Spooner et al. (2019) for which wells that do not sample https://doi.org/10.5194/se-2020-24Preprint.Discussion started: 6 March 2020 c Author(s) 2020.CC BY 4.0 License. the entire stratigraphy are corrected based on the oldest well of the region.We then calculated the mean crustal stretching (β factor, Fig. 3C) for each tectonic subsidence curve based on isostatic calculation (Watts, 2001).
During the late Permian-Early Triassic, a first phase of significant tectonic subsidence, up to 500 m, is recorded in the Maestrat basin and on the Iberia paleomargin of the Betic basins (Salas and Casas, 1993;Van Wees et al., 1998;Salas et al., 2001;Hanne et al., 2003;Soto et al., 2019) (Fig. 3B-C).The westward migration of marine deposition in the Iberian basins during the middle Triassic (Anisian-Carnian, 240-230 Ma) (Sopeña et al., 1988) argues that Tethyan rifting propagated westward inboard Iberia.The same evolution is suggested by the stratigraphy and the depositional evolution constraints from the Catalan and Basque-Cantabrian basins (Sopeña et al., 1988), and in the Aquitaine domain (Fig. 3B) although ill-defined for the Permian times.
During the Late Triassic (220-200 Ma), the regional tectonic subsidence in all regions is found associated with the deposition of evaporites that spread all over Iberia, in the Betics, West Iberia and in the Aquitaine Basin (Fig. 3A).The distribution of salt terrane in Iberia and its surrounding (Fig. 3A) highlights a very large subsiding domain for this period.A maximum mean subsidence of 700 m is inferred in the Maestrat basin for the Triassic times.The relatively rapid subsidence in the Triassic contrasts with the slower subsidence observed during the Early-Middle Jurassic.A notable exception is depicted by the slight increase of subsidence between 200 and 150 Ma in the Betics (Fig. 3B-C), consistent with rifting across the Iberia-Africa boundary (Ramos et al., 2016;Fernández, 2019).
A third Late Jurassic-Early Cretaceous phase (150-110 Ma) is marked by the increase of tectonic subsidence in the Iberian basins, coeval with the expected timing of strike-slip deformation and rifting in Cameros (e.g., Rat et al., 2019;Aurell et al., 2019) and Columbrets (Etheve et al., 2018) basins as well as the initiation of mantle exhumation in the Atlantic domain (Fig. 1A) (Murillas et al., 1990;Mohn et al., 2015).The most recent extension is recorded in the Aquitaine Basin at 120-100 Ma that reflects the onset of oceanic spreading in the Bay of Biscay (Fig. 3B-C).
Subsidence analyses show thinning events in Iberia that reveal control by Tethys and Atlantic rifting (late Permian-Late Triassic) and later by the intra-Iberian-Pyrenean rift events (Late Jurassic-Early Cretaceous).In the Iberian basin, this latter event is characterized by a relatively large and short-lived subsidence (1.5 km in 30 Myrs) localized in narrow basins that suggests the strike-slip nature of the boundary between Ebro and Iberia in the Late Jurassic.The long-lasting rift evolution however show an average low stretching factor of about 1.2.

Kinematics of Iberia between Atlantic and Tethys
A plate reconstruction from late Permian to Cretaceous is presented in Fig. 4 based on a kinematic modelling using GPlates version 2.1 (Müller et al., 2018).This reconstruction aims to present the partitioning of the deformation within Iberia into a larger coherent kinematic model of the Tethys and Atlantic Oceans.A critical step in determining the pre-rifting configuration is to restore rifted margins.Here, we adopted the reconstructed continental crust geometry of Nirrengarten et al. (2018) based on a kinematic model of southern North Atlantic.Polygons from the model of Seton et al. (2012) were re-defined by including new https://doi.org/10.5194/se-2020-24Preprint.Discussion started: 6 March 2020 c Author(s) 2020.CC BY 4.0 License.smaller polygons (continental microblocks) separated by deformed areas in Iberia and Adria to account for internal deformation (Fig. 1B).
As full-fit cannot be reconstructed along the whole Iberia margin (Fig. 4A), we restore used full-fit only between Northwest Iberia (Galicia) and North America (Flemish Cap) to minimize the strike-slip movement between Iberia and Europe, rather than a full-fit in the Southwest Iberia that leads to significant overlapping between the Flemish Cap and Galicia.
Our kinematic model is based on the following constraints (Table 1): (1) geological constraints on the timing of deformation and subsidence during late Permian-Triassic time in the intra-and peri-Iberian basins mentioned above (Fig. 3); (2) age of rifting, mantle exhumation, onset of oceanic spreading in the Atlantic; (3) the present-day position of ophiolites bodies and the timing of the rifting, oceanic spreading and subduction for the Tethyan-related oceanic domains (Paleotethys, Neotethys, Pindos, Meliata, Vardar); (4) at 100 Ma, Iberia should be close to its present-day along-strike position relative to Europe, so that the orthogonal Pyrenean shortening is accommodated in the late Mesozoic-Cenozoic times.
We then integrate kinematic evolution for published models in both the Atlantic and the Tethys according to the following workflow: 1) the reconstruction of the western Tethys prior to the Late Jurassic is based on the kinematic evolution of the Mediterranean region since the Triassic from Van Hinsbergen et al. ( 2019) that we corrected for overlap over the western France, Iberian and Adriatic domains; 2) for the Late Jurassic and Cretaceous times, we compiled rotation poles for Adria and Africa from Handy et al. (2010) and for the North America-Europe system from Barnett-Moore et al. (2016); 3) Adria and Africa were then corrected for the position of Africa according to Heine et al. (2013).

Permian-Late Triassic (270-200 Ma)
The Neotethys Ocean opening initiated in the early Permian in the northern Gondwana margin, resulting in the northward drift of the Cimmerian terrane and the subduction of the Paleozoic Paleotethys Ocean (Stampfli et al., 2001;Stampfli and Borel, 2002).This occurred contemporaneously with the establishment of the Carboniferous-Permian magmatic activity in the North Sea rift and Midland Valley rift areas (Evans et al., 2003;Heeremans et al., 2004;Upton et al., 2004).
As the Neotethys rift propagated westwards, diffuse continental rifting took place in whole Western Europe defined by the position of the Paleozoic Variscan and Caledonian orogenic belts in the West, the Tornquist suture in the East and a diffuse transtensional transfer zone along the Africa-Iberia-Adria boundary (Fig. 4A).This is recorded by several late Permian rift domains located in the southern North Atlantic (Rasmussen et al., 1998;Leleu et al., 2016), in the Adriatic (Scisciani and Esestime, 2017) in the North Sea (Hassaan et al., 2020), in the Germanic rift basins, including the Zechstein basin (Evans, 1990;Van Wees et al., 2000;Jackson et al., 2019) and in Iberia (Figs. 2, 3 and 4A).Back-arc extension associated with the subduction of the Paleotethys (Van Hinsbergen et al., 2019) (Fig. 4B) triggered extension and formation of oceanic basins in the Pindos and Meliata domains during the Early ( 250 Ma) and Late Triassic (Carnian, 220 Ma), respectively (Channell and Kozur, 1997;Stampfli et al., 2001).As proposed by Schmid et al. (2008), the Pindos ocean was probably a western branch of the Neotethys rather than a unique ocean.The strike-slip reactivation of the Tornquist Zone could also be a far-field effect of Paleotethys closure (e.g., Phillips et al., 2018).(Stampfli and Borel, 2002;Schmid et al., 2008).The large rift-related subsidence in the Iberian basins (Fig. 3B) is kinematically consistent with the stretching lineations documented from Triassic strata (Soto et al., 2019).Ebro is already individualized from Iberia and moved eastwards relative to Iberia and Europe through right-lateral and left-lateral strike-slip movements, respectively.

Early Jurassic (200-160 Ma)
This period marks a gradual change from Tethyan-dominated to Atlantic-dominated tectonism in Iberia.As the Neotethys propagated in the Vardar Ocean, the Pindos and Meliata oceans started to close (Fig. 4C) (Channell and Kozur, 1997).Major dynamic changes occurred with the CAMP event (Olsen, 1997;Marzoli et al., 1999;McHone, 2000;Leleu et al., 2016;Peace et al., 2019) that led to breakup in the Central Atlantic Ocean during the 190-175 Ma interval (Pliensbachian-Toarcian) (Fig. 4C-D) according to Labails et al. (2010) and Olyphant et al. (2017), respectively.The propagation of the Central Atlantic rift northwards caused extension to propagate in the southern North Atlantic (Murillas et al., 1990;Leleu et al., 2016) and laterally, eastward in the Alpine Tethys (Schmid et al., 2008;Marroni et al., 2017) by some reactivation of Triassic Neotethyan rift structures.Evidence for nearly synchronous intrusions of MORB-type gabbro, in a western branch of the Alpine Tethys, is described at 180 Ma in the internal zones of eastern Betics (Puga et al., 2011), associated with the rapid subsidence in the Betics (Fig. 3B).However, whether this is related to incipient oceanic spreading or magmatism in hyper-extended margin is controversial.By contrast, both the thermal and stratigraphic evolutions (also Fig. 2) suggest that central Iberia remained little affected by the propagation of the Early Jurassic Atlantic rift Iberian basins (Aurell et al., 2019;Rat et al., 2019).A kinematic change from oblique to orthogonal E-W extension in the Alpine Tethys is marked by the onset of oceanic spreading between the Bajocian-Bathonian (170-166 Ma) and the Oxfordian (161 Ma) as suggested by the ages of MORB magmatism in the Alps (Schaltegger et al., 2002) and first post-rift sediments (Bill et al., 2001).As such the Jurassic Alpine Tethys has temporal and genetic affinities with the Atlantic Ocean evolution, rather than the Neotethys.The required differential movement between the opening the Alpine oceanic domains, the central Atlantic and the closure of the Neotethys and Vardar Oceans at 160 Ma induced the reactivation of the former diffuse transfer zone between Iberia and Africa into a localized transform plate boundary (Fig. 5A).

Late Jurassic-Early Cretaceous (160-100 Ma)
A major tectonic change occurred in the Late Jurassic-Early Cretaceous when the North Central Atlantic successfully rifted the continental domain located offshore Southwest Iberia in present-day coordinates (between 160 and 100 Ma, Fig. 5), as recorded by mantle exhumation and subsequent oceanic spreading at 150 Ma (e.g., Murillas et al., 1990;Mohn et al., 2015;Barnett-Moore et al., 2016) (Fig. 5B).At that time, the east-directed movement of Iberia relative to Ebro induced left-lateral trans-tensional faulting in a corridor shaped by the Iberian basins (Tugend et al., 2015;Aurell et al., 2019;Rat et al., 2019).We further infer a residual strike-slip movement between Ebro and Europe until the Mid-Cretaceous (118 Ma) when the Bay of Biscay opened and rotation of Iberia occurred (Sibuet et al., 2004;Barnett-Moore et al., 2016).The eastwards motion of Iberia relative to Adria resulted in the closure of the southern Alpine Tethys (Fig. 5C).Eastward rotation of Africa induces subduction along the northern Neotethyan margin (Schmid et al., 2008) (Fig. 5B-D).
Until 120 Ma (Early Cretaceous) eastward accommodation space is constantly created by the formation of rift segments in the Southwest Alpine domain (Valaisan domain and Southeast basins of France) and then Provence domains (Tavani et al., 2018).In the southern part of the Western Alps, reactivation of Tethyan normal faults are shown to be Late Jurassic-Early Cretaceous in age (Tavani et al., 2018).At 110 Ma, deformation migrates in the South Provence Basin making a straighter continuity of the Pyrenean system toward the East (Tavani et al., 2018).
5 Implications for strike-slip movements and the Europe-Iberia plate boundary Table 2 summarizes the timing, amounts and sense of strike-slip component of the Ebro kinematics relative to Europe and Iberia inferred from our model.Our reconstructions suggest a total left-lateral strike-slip movement of 278 km between Europe and Ebro.90 km were accommodated during the late Permian-Triassic period (Fig. 4A-C, 270-200 Ma).86 km were accommodated during the Jurassic (Figs. .We quantify 99 km and 19 km for the 140-120 and 120-100 Ma time intervals, respectively, leading to a total of 128 km of strike-slip movement during the Lower Cretaceous, in the range of amounts deduced from offshore and onshore geological observations (Olivet, 1996;Canérot, 2016).By 118 Ma, most of the strike-slip faulting is terminated as extension became orthogonal and Ebro is close to its present-day position (Jammes et al., 2009;Mouthereau et al., 2014).The maximum strain rate of 5 km.Myr −1 is obtained for the 140-120 Ma time interval, revealing progressive strain localization in the Pyrenean basins before mantle exhumation (Jammes et al., 2009;Lagabrielle et al., 2010;Mouthereau et al., 2014;Tugend et al., 2014).
The Iberia-Ebro boundary has a more complex tectonic history than the Europe-Ebro boundary.The rapid eastward displacement of Ebro during the late Permian to Late Jurassic period (Figs. 4 and 5) induces a total of 67 km (12, 33, 17, and 5 km during the 270-250, 250-200, 200-180, and 180-160 Ma time interval, respectively) right-lateral strike-slip between Ebro and Iberia (i.e., Galicia).This displacement has been partitioned with extension within the Iberian basins along a NW-directed intra-continental deformation corridor.This is consistent with stretching markers in Triassic rocks in this area (Soto et al., 2019).From 160 to 100 Ma, the northward propagation of the Central Atlantic spreading ridge into the southern North Atlantic resulted in a net left-lateral slip of 245 km and increasing strain rates of up to 9 km.Myr −1 , indicating the southern Ebro boundary became the main tectonic boundary in Iberia, accommodating eastwards displacement of Iberia into the Alpine Tethys region.Despite the requirement of such large movements in the Iberian Range geological evidence are lacking.This likely reflect the role played by the Triassic evaporites that decouples the large extension in the pre-salt basement from thinskinned extension in sedimentary cover as shown around Iberia by numerical studies (e.g., Grool et al., 2019;Duretz et al., 2019;Jourdon et al., 2020;Lagabrielle et al., 2020).Brunet, 1984), Betics (Hanne et al., 2003), Cameros basin (Salas and Casas, 1993;Salas et al., 2001;Omodeo-Sale et al., 2017), Maestrat basin (Salas and Casas, 1993;Salas et al., 2001) and West Iberia (Spooner et al., 2018) Olivet, 1996;Srivastava et al., 2000;Schettino and Turco, 2009;Fernandez, 2019 North Sea  Nirrengarten et al., 2018;Hassan et al., 2019;Sandoval et al., 2019 Tethys & peri-Tethys

Table 1 .
Geodynamic and timing constrains used in the kinematic reconstruction model

Table 2 .
Quantification of strike-slip displacement between the European and Ebro and between the Iberia (Galicia) and Ebro.