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(a) Large‐scale geological map of the Gibraltar arc (modified after Comas et al., 1999). (b) Geological map of the study area (eastern Sierra de Los Filábres), modified after Garcia Monzón et al. (1974), containing shear sense indicators, the locations of dating samples, and the location of other key outcrops. Plotted shear sense indicators are representative average values of numerous measurements per location (for the shear sense data see Table S1). A‐A’ is the location of the cross section on Figure 5a, presented together with a more detailed map of the cross section area (marked by blue box). (c) NNW‐SSE cross section across the study area highlighting the major structural features (sz = shear zone).
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The high‐pressure metamorphic Nevado‐Filábride Complex (NFC) in the Betics mountain range of southeastern Spain exhibits continental and ocean‐derived tectonic units, which are key for understanding the geodynamic evolution of the Western Mediterranean. We address the current debate in the definition of tectonic units, the emplacement of (ultra)maf...
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... At least the lower part of the NFC has been traditionally regarded as a portion of South Iberian crust (Guerrera et al. 1993;Platt et al. 2006;Puga et al. 2011;Rodríguez-Cañero et al. 2018), subducted below a previously tectonized allochthonous terrain (Alborán Domain) comprising the Alpujárride-and Maláguide units (Bouillin et al. 1986;Guerrera et al. 1993;Guerrera et al. 2021). However, a parallel tectono-metamorphic evolution of the Nevado-Filábride and Alpujárride complexes has recently been shown based on similar micro-structural sequences and Eocene to Miocene metamorphic ages (Aerden et al. 2022;Porkoláb et al. 2022;Poulaki et al. 2023). The Maláguide complex is only metamorphosed in its lowermost levels (Nieto et al. 1994;Ruiz Cruz et al. 2005) as counts for several frontal thrust slices of Mesozoic carbonates (Frontal Units/Dorsale Calcaire; Mazzoli et al. 2013) also traditionally included in the Internal Zones. ...
... Blueschist to eclogite facies metamorphism in the complex has been variably dated as Eocene to Miocene (Monié et al. 1991;Puga et al. 2000;Puga et al. 2005;Augier et al. 2005;Platt et al. 2006;Kirchner et al. 2016;Li and Massonne 2018;Aerden et al. 2022;Porkoláb et al. 2022;Poulaki et al. 2023;Farrell et al. 2024). Pressure-temperature path reconstructions vary significantly ( Figure 3a) including isothermal decompression (Augier et al. 2005;Ruiz-Cruz et al. 2015), decompression with cooling (Behr and Platt 2012) or decompression with heating (Gómez-Pugnaire and Fernández-Soler 1987; Santamaría-López et al. 2019), decompression followed by reheating (Bakker et al. 1989;Booth-Rea et al. 2015) or two consecutive Alpine cycles (Puga et al. 2005;Li and Massonne 2018). ...
Integration of microstructural, petrological and geochronological techniques has allowed detailed characterization of the timing and metamorphic features of deformation events in the Betic Cordillera. Phase equilibrium modelling, thermobarometric estimations, in situ U–Pb monazite geochronology and Ar–Ar geochronology (amphibole and micas) have been applied to key samples containing well‐constrained deformation fabrics and garnet porphyroblasts of different timing that can be distinguished based on their specifically orientated inclusion trails. Our study helps constrain the timing and kinematics of initial crustal thickening stages in the Alpujárride complex, followed by orogenic collapse and renewed continental collision around 17 Ma. In the underlying Nevado‐Filábride complex, multiple garnet generations coexisting in a single investigated sample record a similar history ending with garnet growth under low‐pressure/high‐temperature conditions around 13 Ma. New age constraints for microstructural trends fossilized within porphyroblasts refine the sequence of changing shortening directions previously linked to the plate‐motion interplay between the Alborán Domain, Iberia and Africa from Eocene to Middle Miocene.
... Slab detachment is associated with significant exhumation and extension (Buiter et al., 2002;Chatelain et al., 1992;England and Molnar, 1990;Wortel and Spakman, 1992), while the retreat accelerates towards the places where the slab is still attached (Bercovici et al., 2018;Wortel and Spakman, 2000). The transition between continental collision and extension driven by slab retreat is also accompanied by significant rotations, which can often lead to oroclinal bending (e.g., Carey, 1955), such as observed in the Carpathians (Balázs et al., 2018;Márton et al., 2016), the Betics-Rif system (Porkoláb et al., 2022;Vergés and Fernàndez, 2012), or at the transition between Eastern Himalaya to Myanmar (Cao et al., 2009;Otofuji et al., 2010). ...
... However, such a Late Cretaceous-Early Eocene SE-dipping subduction was not recognized so far in the Maghrebian transect. Jolivet and Porkoláb et al. (2022), it was rather an extended OCT domain off southwestern Iberia and its width was restricted. On the other hand, HP-LT metamorphism of the Nevado-Filabride ophiolitic rocks is now dated at 38-27 Ma ( 40 Ar/ 39 Ar dating; Porkoláb et al., 2022), which points to a late Paleogene subduction beneath the Alpujarrides-Malaguides continental units. ...
... Jolivet and Porkoláb et al. (2022), it was rather an extended OCT domain off southwestern Iberia and its width was restricted. On the other hand, HP-LT metamorphism of the Nevado-Filabride ophiolitic rocks is now dated at 38-27 Ma ( 40 Ar/ 39 Ar dating; Porkoláb et al., 2022), which points to a late Paleogene subduction beneath the Alpujarrides-Malaguides continental units. Consistent Sm-Nd bulk-garnet ages were obtained by Aerden et al. (2022) from the Alpujarride-Sebtide complex and from the Nevado-Filabride complex (35-13 Ma). ...
The evolution of the Alpine Tethys margins during the beginning of the African-Eurasian convergence (Upper Cretaceous) was little studied compared to their evolution during the post-Pangea rifting and oceanic expansion, i.e., from the Early Jurassic to the Early Cretaceous. The aim of the present work is first to make up for this shortcoming in the case of the distal European margin of the Alpine Tethys, namely the Briançonnais domain of the Western Alps. We show that this magma-poor passive margin was affected by a systemic extension in Late Cretaceous-Paleocene times. Remarkably, this extensional tectonics shortly preceded Lutetian times, when Briançonnais margin encroached the SE-dipping subduction zone under the Adria microplate (“Alpine subduction”). Secondly, we aim to assess the Late Cretaceous-Paleocene evolution of the north-Tethyan paleomargin in the Maghrebides transects, i.e., south-west of the Briançonnais transect along the same European-Iberian margin. For this purpose, we consider the Triassic-Eocene series of the "Dorsale Calcaire" in the Alboran, Kabylias and Peloritan terranes that constitute with Calabria the Alkapeca blocks formerly located along the southeastern border of Iberia until the Eocene. Reinterpretation of the literature allows us to assert that the Tethyan margin of these blocks was extending like the Briançonnais during the Late Cretaceous-Paleocene, when Africa-Eurasia-Iberia convergence and then subduction of the intervening Tethyan slab were active. We propose here for the first time that the subduction of the Ligurian-Maghrebian slab occurred under the North African margin at that time in the southward continuation of the Alpine subduction. In the Alboran transect, the Rif-Betic Dorsale Calcaire can be seen as the detached cover of the thinned crust of the Alpujarrides-Sebtides Complex. In the same transect, the oceanic domain may have included a continental allochthon of African origin (Ketama Unit). Contrary to some assertions, the North African margin did not experience significant compression during the Cretaceous. During the Eocene, a Subduction Polarity Reversal occurred, which was associated with the relocation of the subduction zone along the Alkapeca block. This was the beginning of the "Apenninic subduction", which triggered the back-arc opening of the Mediterranean basins and corresponds to the backthrusting tectonic phase in the Western Alps.
... However, B. Li and Massonne (2018) proposed an HP/LT event during the Eocene (∼40 Ma) and a second P/T loop with exhumation from 24.1 ± 0.8 Ma. More recently, Aerden et al. (2022) separated garnets based on their magnetic fraction and were able to obtain Sm-Nd ages in Eocene (∼35 Ma) age as well as Miocene ones, and Porkoláb et al. (2022) with Ar/Ar data also found distinct events dated at 38-27 Ma and 22-12 Ma. The final exhumation of the NFC and Alpujárride was accommodated with the formation of low-angle normal faults and strike-slip transfer faults at ∼12 Ma for the NFC (Augier, Agard, et al., 2005;Azañón et al., 2015;Galindo-Zaldívar et al., 1993, 2003Madarieta-Txurruka et al., 2021;Platt et al., 2005;Reinhardt et al., 2007) and 22-18 Ma for Alpujárride (e.g., Platt et al., 2005). ...
... Several locations show slivers of Permian rocks wedged above Triassic but below Devonian strata (Figures 8a and 8b). Similar tectonic slivers have been previously identified in the eastern Sierra de los Filabres and were interpreted as three distinct thrust sheets with Paleozoic on top of Mesozoic cover (de Jong, 1993a(de Jong, , 1993bPorkoláb et al., 2022). Our new data confirm this interpretation and show Permian rocks of the lower unit thrust above Triassic strata (Tahal formation; Figure 8d). ...
... An Eocene HP/Low-Temperature (HP/LT) metamorphic phase in the NFC has been suggested based on 40 Ar/ 39 Ar analyses (Augier, Agard, et al., 2005;Monié et al., 1991;Porkoláb et al., 2022), while other studies have disregarded these data and attributed them to excess Ar because they do not fit evidence for younger Miocene metamorphic ages interpreted as a HP/LT event (Behr & Platt, 2012, de Jong, 2003De Jong et al., 2001;Kirchner et al., 2016;Platt et al., 2006). However, B. Li and Massonne (2018) identified Eocene monazite ages in the Mulhacén succession of the Sierra Nevada that support the Eocene 40 Ar/ 39 Ar data and suggest that the subduction of the NFC must have occurred prior to the Miocene metamorphic event. ...
The interplay between structural and metamorphic processes operating along the deep plate interface in subduction zones remains elusive as much of the geologic record is recycled into the mantle. In some cases, metamorphosed subducted rocks are underplated and exhumed to the surface, providing critical constraints on structural processes and the rheological evolution of subduction interfaces at convergent margins. One such exhumed high-pressure/low-temperature subduction complex is the Cenozoic Nevado-Filábride Complex (NFC) in Southern Spain. This study presents new data from the NFC that elucidate the syn-metamorphic deformation, stacking, and underplating of continental slivers along the subduction interface. The structurally lowest NFC dominantly comprises lithologically monotonous Paleozoic metamorphic basement rocks recorded by apatite U-Pb ages and shows no evidence for large-scale internal duplications suggesting it behaved as a coherent basement succession during subduction. In contrast, structurally higher levels of the NFC are characterized by the stacking of older-on younger coherent slices and distinctly different metamorphic ages. These relationships document syn-subduction structural repetitions and tectonic stacking of imbricate thin slivers (∼100s m) during subduction underplating. Structurally higher levels of the NFC exhibit both Eocene and Miocene metamorphic zircon rims and apatite ages, along with microstructures indicative of relatively higher temperature metamorphism. Large-scale underplating and antiformal stacking of slivers in the subduction channel can provide buoyancy forces to underplate and assist exhumation. We demonstrate that the presubduction stratigraphic architecture is a key control on the style and timing of deformation and metamorphism, facilitating coherent subduction underplating.
... The Alpine orogenic loop formed by the Betics in southern Spain and the Rif in northern Morocco is called the Gibraltar Arc (e.g., García-Dueñas et al., 1992;Comas et al., 1999;Azañón et al., 2002;Platt et al., 2003;Vera, 2004;Chalouan et al., 2008;Williams and Platt, 2018;Jabaloy Sánchez et al., 2019a,b;Soto et al., 2022;Porkoláb et al., 2022). Associated with the contact between the Internal and the External Betics, particularly in the western Betics, there are several structures that we interpret in terms of negative or positive structural inversion on pre-existing faults (Fig. 8a). ...
The same sense movement on any given fault plane occurs much more frequently compared to the cases when the sense reverses. Therefore, positive or negative structural inversions are regarded as special cases within the much more general and typical process of fault reactivation. Extensional reactivation of former reverse faults or, specifically thrust planes in thrust fold belts, designated as “negative inversion”, received much less attention by both the petroleum industry and the academia than the opposite process. Based on the structural review of many case studies of positive and negative inversion they display contrasting kinematic patterns. One of the obvious structural differences is related to the geometry of short-cut structures developed during the more advanced stage of inversion. In the case of positive inversion, a short-cut thrust develops within the footwall of the major inverted fault to better accommodate the ongoing shortening. In contrast, a short-cut normal fault develops within the hanging wall of the partially inverted master fault during negative inversion. Based on a worldwide compilation there are examples of hydrocarbon fields with valid traps associated with negative inversion. Therefore, we suggest that even though negative inversion may not be as important for petroleum exploration as its positive counterpart, yet, it may produce more traps in the internal parts of thrust fold belt than currently perceived. At present, case studies of negative inversion defined by the extensional reactivation of pre-existing thrust planes are relatively rare, compared to the more frequent documentation of positive structural inversion in published literature. Whether this disparity between negative and positive inversion is a result of non-observation in the subsurface, at the expense of the former, or it is caused by a more fundamental structural difference between the two processes, it remains to be seen.
... Exhumation of the complex was synchronous with HP metamorphism in the Nevado-Filábride Complex (López Sánchez-Vizcaíno et al., 2001;Platt et al., 2006;Kirchner et al., 2016), which was exhumed in the late Miocene (Johnson et al., 1997). Recent geochronological and petrological evidence, however, indicates that the Nevado-Filábrides may have experienced an earlier HP metamorphic event in the Eocene, synchronous with that of the Alpujárride Complex (Augier et al., 2005;Li and Massonne, 2018;Porkoláb et al., 2022;Aerden et al., 2022). ...
3D microstructural analysis of porphyroblast inclusion trails using X-ray Computed Tomography is integrated with analysis of field structures to unravel the Alpine deformation history of the Alpuj´arride Complex, which constitutes the partially submerged metamorphic core of the Gibraltar Arc. Prograde metamorphism in the complex has been traditionally linked to a ’D1’ event witnessed by inclusion trails in garnet porphyroblasts. Orientation data for these microstructures reveal three age groups with differently oriented axes of inclusion-trail curvature (known as FIA). The successive development of FIAs trending WNW-ESE, ENE-WSW and NNW-SSE is shown and correlated with the Paleogene-Neogene relative plate-motion paths of Africa, Iberia and the Albor´an Domain as known from paleomagnetic data. During the late-metamorphic evolution of the Alpuj´arride Complex, after garnet growth had ceased, two steeply dipping crenulation cleavages and associated folds with roughly suborthogonal N–S and E-W trends developed, in addition to two subhorizontal ones. Inclusion trails are also found to exhibit a general preference for subvertical and subhorizontal orientations, suggesting a protracted orogenic evolution characterized by multiple stress permutations causing alternations of crustal shortening and gravitational collapse.
... These Variscan basement rocks are overlain by Permo-Triassic (sedimentary age) light-colored schists and quartzites and Mesozoic marbles (Poulaki & Stockli, 2022 and references cited therein). Mafic and ultramafic lenses with Jurassic protolith ages that appear concentrated near the base of the marble formation have been interpreted as marking an ophiolitic suture between Iberia and Alkapeca (e.g., Porkoláb et al., 2022;Puga et al., 2017) or a hyper-extended continental margin (e.g., Pedrera et al., 2020). ...
... These ages were linked to initial burial of the complex along a low geothermal gradient to 17 kbar/530°C, followed by near-isothermal decompression and then re-burial and heating to ca. 9 kbar/650°C. Such a bi-cyclic evolution starting in the Eocene appears further supported by recent Ar-Ar dating of white micas revealing two age populations (38-27 and 23-12 Ma) associated with different tectonic fabrics (Porkoláb et al., 2022), and Eocene U-Pb zircon-rims (Poulaki et al., 2020). Also our garnet ages will be shown to confirm a protracted history of Late-Eocene to Miocene metamorphism in the NFC. ...
... Following up on the above discussion, we interpret the WNW-ESE trend of our "red" FIA set to record orthogonal NNE-SSW crustal shortening in the Late Eocene to Early Oligocene. In the NFC, this time frame is indicated by our new ∼35 Ma garnet age for sample B13c, in accordance with Ar-Ar ages for relic "S1" (Augier et al., 2005;Porkoláb et al., 2022), a mean U-Pb age of ∼40 Ma for high-Y monazite grains (Li & Massonne, 2018), and Eocene U-Pb ages for zircon rims (Poulaki et al., 2020). In the Alpujarride Complex, a similar timing of burial metamorphism is indicated by the 35 Ma Sm-Nd age obtained for high-magnetic garnet in sample F8, in agreement with a mean age of ∼34 Ma for high-Y monazite grains in the Los Reales unit (Massonne, 2014), 34-38 Ma white-mica (Ar-Ar) ages associated with HP/HT assemblages Marrone, Monié, Rossetti, Aldega, et al., 2021), and a 32.4 ± 3.3 Ma U-Pb age of rutile inclusions in garnets from high-pressure rocks in the Kabylias (Bruguier et al., 2017). ...
High‐resolution microstructural analysis of porphyroblast inclusion trails integrated with Sm‐Nd garnet geochronology has provided new insight into the tectonic history of the Betic‐Rif orogen. Three principal age groups of porphyroblasts are demonstrated with distinctly oriented inclusion‐trails. Inclusion‐trail curvature axes or “FIA” (Foliation Inflexion/Intersection Axes) are shown to represent “fossilized” crenulation axes from which a succession of different crustal shortening directions can be deduced. The regional consistency of microstructural orientations and their geometric relationship with multiple sets of macroscopic folds reveal the composite character of the Gibraltar Arc formed by a superposition of different folding directions and associated lineations. Bulk‐garnet ages of 35–22 Ma obtained from five micaschist samples of the Alpujarride‐Sebtide complex (ASC) and of 35–13 Ma from four micaschists of the Nevado‐Filabride complex (NFC) allow to deduce NNE‐SSW directed shortening in the Late Eocene changing to NW‐SE shortening in the early Oligocene, alternating with suborthogonal NE‐SW shortening during the Miocene. These directions can be related to a major swing in the direction of relative Africa‐Iberia plate‐motion known from kinematic modeling of magnetic seafloor anomalies, and subsequent dynamic interference between plate convergence and suborthogonal “tectonic escape” of the Alboran Domain. Coupled to previously established P‐T‐t paths, the new garnet ages support a common tectono‐metamorphic evolution of the ASC and NFC as laterally equivalent orogenic domains until, in the Miocene, the second became re‐buried under the first.
Crustal deformation is characterized by brittle and ductile faults that accommodate at different scales the strain imposed by plate tectonics. The aim of this contribution is to show with the help of different examples how the in situ 40Ar/39Ar dating of synkinematic neocrystallized minerals in ductile shear zones and the step-heating 40Ar/39Ar dating of synkinematic authigenic clays in fault gouges can bring information on the timing of fault activity. However, due to their complex evolution, interpretation of the argon signature in fault zones requires consideration of several effects among which re- or neocrystallization, inheritance and fluid interaction processes are dominant.
