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8. Two BS2000 cross sections through the first 1000 km of the Western Mediterranean mantle taken along strike of the Italian Peninsula: A) section through western Italy and the central Alps; B) section through the Adriatic basin and the central-eastern Alps. For further explanation see caption of Figure 6.
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During the Cenozoic, the Western Mediterranean region has experienced a complex subduction history which involved the destruction of the Late Triassic/Jurassic Ligurian ocean and the West Alpine-Tethys. Lithosphere remnants of this evolution have been detected in the upper mantle by seismic tomography imaging. However, no general consensus exists o...
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Detailed seismic tomography reveals that the 2001 Mw 7.7 Bhuj earthquake was associated with a 10-14% increase in Vp and Vs and a 10% decrease in Vp/Vs in the 10 to 35 km depth range covering a 2750 km2 area beneath the aftershock zone. This anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic compositio...
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... However, which deep mantle processes, such as delamination, slab break-off, convective removal of lithosphere, and slab rollback, are driving the extensional environment remain inconclusive (Platt et al., 2013). Although the recent detailed seismic tomographic models (Gutscher et al., 2002;Spakman and Wortel, 2004;Bezada et al., 2013;Palomeras et al., 2014;Villaseñor et al., 2015) confirm the existence of a subducted slab, the question of whether the slab belongs to the oceanic or continental crust lithosphere remains unanswered. Thus, distinguishing the origins of these deep mantle anomaly will be crucial for deciphering the dynamics of the slab-mantle interaction across the western Mediterranean. ...
The Rif–Betics–Alboran region has been vital in the tectonic evolution of the western Mediterranean. Seismic images support the idea of continuous slab rollback being a prominent force in this region. However, the detailed slab structure and the physical mechanisms generating local deep (> 600 km) earthquakes remain unclear. Here, we analyze waveforms recorded from dense seismic networks above the deep earthquake beneath Granada in 2010 to study the slab structure. We discover a thin low-velocity layer (LVL) at the base of the slab to explain both the long codas observed in Morocco and the secondary arrivals observed in Spain. This LVL indicates the presence of hydrous magnesium silicates extending to ∼600 km depth, which suggests that dehydration embrittlement promotes the occurrence of deep-focus earthquakes. Our findings contradict the traditional slab model with the LVL sitting on the top of the slab, suggesting that the Alboran slab has been overturned.
... Past tomographic models 15,[18][19][20][21] and other imaging techniques [22][23][24][25][26][27][28][29][30] have suggested the lateral discontinuity of subduction with a slab window along the central Apennines 31 , marked by a low-velocity zone at lithospheric depth mirrored by the lack of intermediate-depth seismicity 27,32 . Anyway, recent models proposed that the same features could be related to heterogeneities of the Adria continental lithosphere 33 , which also affected the different evolution of subduction between the northern and southern portions of the chain. ...
Physical properties and structure of the lithosphere are the first step to constrain the evolution of mountain belts. Here we show detailed shear wave velocity profiles of the lithosphere in the Apennines that clarify a controversial aspect of continental subduction: the intricate mechanism of crust delamination from the downgoing plate. From the analysis of complete and dense teleseismic Receiver Function data set, we find that the delamination of the continental lithosphere is favored by the development of a low seismic shear wave velocity zone in the middle-lower crust. We observe a double Moho below the external portions of the present mountain range, suggesting the progressive formation of the shallow interface. The delamination edge is located in the forearc, far eastward than expected, implying that the re-equilibration of the thermal unbalance, generated by the mantle substitution, may last 10-7 Myr.
... The model also replicates several geophysical observations, namely, the slab imaged with tomography (Spakman and Wortel, 2004) (Fig. S2), the toroidal flow around the slab edges inferred from SKS splitting (Diaz et al., 2010; see also Lo Bue et al., 2022) (Fig. S3), and the fast westward velocity of the Gibraltar arc observed with a global navigation satellite system (GNSS) (Billi et al., 2023) (Fig. S4). ...
Subduction initiation is a cornerstone of the Wilson cycle. It marks the turning point in an ocean’s lifetime, allowing its lithosphere to be recycled into the mantle. However, formation of new subduction zones in Atlantic-type oceans is challenging, given that it commonly involves the action of an external force, such as the slab pull from a nearby subduction zone, a far-field compression, or the impact of a plume. Notwithstanding, the Atlantic already has two subduction zones, the Lesser Antilles and the Scotia arcs. These subduction zones have been forced from the nearby Pacific subduction zones. The Gibraltar arc is another place where a subduction zone is invading the Atlantic. This corresponds to a direct migration of a subduction zone that developed in the closing Mediterranean Basin. Nevertheless, few authors consider the Gibraltar subduction to be still active because it has significantly slowed down in the past millions of years. Here, we use new gravity-driven geodynamic models that reproduce the evolution of the Western Mediterranean, show how the Gibraltar arc formed, and test if it is still active. The results suggest that the arc will propagate farther into the Atlantic after a period of quiescence. The models also show how a subduction zone starting in a closing ocean (Ligurian Ocean) can migrate into a new opening ocean (Atlantic) through a narrow oceanic corridor. Subduction invasion is likely a common mechanism of subduction initiation in Atlantic-type oceans and a fundamental process in the recent geological evolution of Earth.
... Beneath Adria, slab break-off has been proposed to migrate southward from the Central Apennines during the Late Miocene and Pliocene (Chiarabba et al., 2008;Guillaume et al., 2010). Beneath the Northern Apennines, tomographic data image a fast anomaly (van der Meer et al., 2018) that may correspond to a deep and almost vertical slab, suggesting that the slab may still be continuous, although Spakman and Wortel (2004) suggest that that the North Apennines slab reaches a depth of only ∼300 km and is separated from a deeper anomaly corresponding to an Alpine slab. The slab beneath Calabria imaged by tomography is clearly continuous and highlighted by the Wadati-Benioff plane dipping towards the NW, showing that the subduction that initiated 35 Ma ago is still going on (e.g., Faccenna et al., 2001a;Neri et al., 2009;Jolivet et al., 2015). ...
We present analogue models simulating the Neogene subduction that occurred in the Western Mediterranean region, in order to understand how it impacted the regional tectonics. Although models do not include the lithospheric plate overriding the subduction zone, their surface deformations share many similarities with the Neogene tectonics of Western Europe and Iberia. We observe that the tectonic evolution is largely controlled by the roll-back of the slab, that occurred much faster than the Africa-Eurasia convergence. Models reproduce the opening of the Western Mediterranean Basins and the dispersion of the AlKaPeCa continental fragments. They also show that oceanic subduction favors the counterclockwise rotation of Adria. In more elaborated models, we introduced a pre-existing weakness along the Africa and Adria margins, to reproduce the break-off of the oceanic slab that followed the beginning of continental subduction both in Northern Africa and Italia. Slab break-off is followed by the exhumation of the subducted continent. We observe that the influence of subduction on the kinematics of Adria largely decreases following slab break-off. In models, the total counterclockwise rotation of Adria varies between 7° and more than 30°, depending on the timing of slab break-off. Since the process of subduction modifies the displacement of Adria, it also impacts the tectonic evolution of the regions that bound this plate, especially in the Alpine belt: in the Western Alps, an older Late Cretaceous to Eocene “Pyrenean-Provençal” tectonic phase accommodating N-S shortening is classically described resulting from the convergence between Africa and Eurasia. It is followed by the Neogene “Alpine phase” accommodating E-W shortening. Since this major tectonic change is not explained by a modification of the global Africa-Eurasia convergence, it should be explained instead by more local causes. Our models show that during slab-roll back and before slab break-off, the azimuth of convergence between Adria and Europe shifts from ~N-S to ~ENE-WSW. Hence, they suggest that the oceanic subduction in the Western Mediterranean may explain the “Oligocene revolution” described by Dumont et al. (2011), leading to E-W shortening in the Western Alps and to the activation of the Periadriatic right-lateral shear zones in the Central Alps. We conclude that the western Mediterranean region is a spectacular example showing how the tectonics of mountain ranges and plate boundaries may be controlled by distant subduction processes.
... The mechanisms of slab rollback and the ensuing creation of back-arc basins and mountain belts along subduction fronts serve as examples of the model of convergence (e.g. Rosenbaum et al., 2002;Spakman and Wortel, 2004;Schettino and Turco, 2011;Faccenna et al., 2004). Since the Paleogene, the tectonic evolution of northern Tunisia had shared common structural features with the Maghrebian belts that stretch over the western Mediterranean from the Strait of Gibraltar to Tunisia (Wortel and Spakman, 2000;Faccenna et al., 2014;Van Hinsbergen et al., 2014;Booth-Rea et al., 2018). ...
In order to better understand the intricate structural architecture of northern Tunisia, we use a multidisciplinary approach that includes field observations, geomorphic, sedimentological, and gravity data across this area. We offer a model of progressive thrusting in which four deformation phases occurred in the context of plate convergence (i) Uplift of the Jebel Ichkeul Triassic succession via a NE-trending thrust fault during the Eocene; (ii) Advance of Numidian thrust sheets during the late Oligocene-Middle Miocene, causing the formation of the Lake Ichkeul/Jalta as being piggy-back basin; (iii) Initial out-of-sequence thrusting during the Late Miocene, resulting in the formation of the Sejnane and El Mejel basins with syntectonic Pliocene infill; and (iv) Subsequent out-of-sequence thrusting during the Early Pleistocene, leading to the formation of the Oued (River) Zyatine basin with a syntectonic Quaternary deposits. We used the gravity data analysis to mark the thicknesses of syntectonic deposits and their bounding thrust faults. The kinematic analysis indicates the occurrence of progressive multiphase out-of-sequence thrusting events with thrusts verging to the southeast. The combination of climate and mechanical fractures induced gradually long-term damage and changed the original landscape of the evidenced out-of-sequence thrusts. Furthermore, the existence of local normal faults in the backlimbs and reverse faults in the forelimbs, together with the drainage network type, earthquakes, the slope erosion, and the aggraditional terrace system, implies a gradual landscape evolution of thrust topography. This physical evolution occurred following an active tectonics across the exhibited out-of-sequence thrusting since the Pliocene.
... Evidence of southeast-ward rollback of the southern part of the Ionian plate is recorded in tomographic images and earthquakes (e.g., Schellart, 2010). Furthermore, a tear propagating from the northern to the southern magmatic provinces is confirmed by available tomographic images of the Apennine subduction zone, and numerical model calculations and surface uplift support the presence of a slab detachment propagating along the Apennines (e.g., Spakman and Wortel, 2004). ...
... 1) Partial melting of the veined lithosphere occurred due to further opening of the slab window and the increase of the heat from the inflowing asthenosphere with the tear widening from north to south (e. g., Nikogosian and van Bergen, 2010;Spakman and Wortel, 2004). This second stage is required to explain the extreme geochemical variability observed in the olivine-hosted MIs (extreme K 2 O enrichments and variable Th/Nb) that require the melt source to be mineralogically heterogeneous on a small scale. ...
Boron represents an important tracer of crustal recycling processes in subduction zones, because it is readily mobilised from the subducted lithosphere and different components in the slab are isotopically distinct. Profiles of boron content and isotope ratio across magmatic arcs generally show that B concentrations decrease with increasing slab depth, which implies decreasing amount of slab-derived fluids. To date, however, data on continental-collision zones and post-collisional subduction settings are scarce. This study examines Plio-Quaternary Italian magmatism to quantify crustal recycling in a complex subduction setting. Magmatic products vary from (ultra)potassic along the Tyrrhenian side in the north, to calcalkaline and Na-alkaline in the south. Combined major and trace element and [B] content and δ 11 B values are reported in 99 Melt Inclusions (MIs), analyses from a wide range of Italian lavas. [B] vary from 4 to 298 µg/g and δ 11 B from-29.2 to-3.9‰. The B isotopic values are considerably lower than previously reported in arcs and other post-collisional setting mag-matism. We infer a role for phengite in the source of all studied Italian magmas (with the exception of Mt. Etna lavas). This white mica is stable to high pressures in subducted sediments of altered oceanic crust and records dehydration and 11 B depletion due to dehydration processes. MIs hosted in highly fosteritic olivines (Fo >74; median of 89) from across Italy reveal that primary melts tap heterogeneous mantle including subducted oceanic and continental components that were introduced during the Alpine, and Adriatic and Ionian subduction phases. The combined geochemical data record the involvement of sediments that variably metasomatized the mantle wedge. We propose that slab detachment and consequent heat input from the inflow of hot asthenosphere was responsible for phengite breakdown in subducted sediments and locally produced metasomatism of the mantle wedge, imposing a characteristic B isotope signature to the overlying mantle. Continued heating due to asthenosphere inflow led to melting of the metasomatized mantle wedge and generation of the Italian mag-matism. Mt. Etna represents an exception being dominated by asthenosphere upwelling through a slab window with minimal influence from active subduction.
... Its most significant geodynamic feature is the presence of a near-vertical fast-velocity slab reaching depths of 600 km and clearly imaged by the early tomographic studies in the zone (e.g., Blanco & Spakman, 1993). Although most models agree on that slab-roll back is the driving mechanism of the Gibraltar Arc System (e.g., Chertova et al., 2014), the discussion on its origin and evolution is still open, as the origin of the rollback has been related to a long N-NW dipping subduction zone extending from Gibraltar to the Balearic Islands (e.g., Faccenna et al., 2004), to a shorter NW dipping slab confined to the Balearic margin (e.g., Spakman & Wortel, 2004) or to a SE dipping subduction under the north-African margin (Vergés & Fernàndez, 2012). ...
Using seismic data from 1,186 stations deployed across the westernmost Mediterranean, we construct a high‐resolution 3‐D radially anisotropic model from a joint inversion of receiver functions and Rayleigh and Love wave dispersions. The Rayleigh and Love data are extracted from both ambient noise interferograms and earthquake waveforms, and a new three‐station ambient noise interferometry method is used to further improve the data coverage. The obtained crustal thickness map reproduces independently the Moho depth maps compiled from previous data, showing crustal roots beneath the Pyrenean‐Cantabrian range and the Gibraltar Arc and thicker crust beneath the Variscan Iberian Massif than in the area affected by Alpine orogenesis. The Vsv crustal model outlines the Iberian Massif as a high shear wave velocity block and shows extremely low velocities in the Gulf of Cadiz and Gibraltar Arc. At mantle levels, a sharp boundary between the Aquitanean Basin and the Massif Central is imaged, with low Vsv beneath the Massif Central probably reflecting a remaining signature of the magma. To the south of Iberia, the geometry of the Alboran slab is captured by the model, while beneath the Atlas Mountains, widespread low Vsv and positive radial anisotropy is observed, favoring the edge‐driven convection model explaining the lithospheric thinning. The most relevant contribution of this work is mapping, for the first time at this scale, the radial anisotropy anomalies at crustal level, with higher values observed in the Alpine Iberia, dominated by present‐day extensional tectonics.
... This lithospheric removal caused a radial crustal extension that ended in the Late Miocene due to the dominance of the Eurasia-Nubia convergence [75]. (ii) Subduction models of lithosphere below the Alboran Domain present many variations considering rollback and/or slab detachment [78][79][80][81][82]. The subduction begins due to a northward dipping slab attached to the African margin, which later was fragmented. ...
... The subduction begins due to a northward dipping slab attached to the African margin, which later was fragmented. The Alboran Domain moved westward associated with the rollback of one slab fragment [78,79,82,83]. The westward tearing detached the northward dipping slab from Africa, while in the Iberian margin, it is still partly attached. ...
... In short, our data support a terminal subduction model of Iberian lithosphere beneath the Alboran Domain [79,80,82,84,85], producing rollback and subsidence in the Western Alboran Basin and uplift in the central Betic Cordillera. The latter is also affected by a NW-SE compression due to the Eurasia-Nubia convergence [28,171]. ...
The Betic Cordillera was formed by the collision between the Alboran Domain and the South Iberian paleomargin in the frame of the NW–SE convergent Eurasia–Nubia plate boundary. The central region is undergoing a heterogeneous extension that has not been adequately analysed. This comprehensive study addressed it by collecting structural geologic, seismologic, and geodetic data. The region west of the Sierra Nevada is deformed by the extensional system of the Granada Basin, which facilitates E–W to NE–SW extension. Moreover, the southern boundary of Sierra Nevada is affected by a remarkable N–S extension related to E–W normal to normal–dextral faults affecting the shallow crust. However, geologic and geodetic data suggest that the western and southwestern Granada Basin boundary constitutes a compressional front. These data lead to the proposal of an active extensional collapse from the uplifted Sierra Nevada region to the W–SW–S, over an extensional detachment. The collapse is determined by the uplift of the central Betics and the subsidence in the Alboran Basin due to an active subduction with rollback. Our results indicate that the central Betic Cordillera is a good example of ongoing extensional collapse in the general context of plate convergence, where crustal thickening and thinning simultaneously occur.
... were blocked or choked by continental collisions, the subduction zone narrowed leaving a remnant only 125 km wide in the southernmost Tyrrhenian Basin(Chiarabba et al., 2008;Spakman & Wortel, 2004).Strike slip faults (dextral in Sicily, sinistral in northern Calabria) flank the remnant slab, and are related to STEP's (Subduction Transform Edge Propagators-Billi et al., 2006; Govers & Wortel, 2005; Loreto et al., 2021; Orecchio et al., 2015). Despite the variety of different structural elements, three graben with intervening horsts are highlighted (Figure 6), with faults perpendicular to the arc separating graben from horsts. ...
Segmented magmatic arcs create arc‐parallel variable loads and influence associated foreland basins through flexural isostasy along strike, in addition to standard subduction‐perpendicular foredeep/forebulge/backbulge models. Segmentation occurs in both continental and island arcs (Aleutians, Calabria, Japan, Kuril/Kamchatka, Lesser Antilles, Solomon Islands and Sumatra/Java). Some segments have variable gravity anomalies and elastic thicknesses ( T e ). In standard theory, the load created by an orogenic belt/magmatic arc depresses the lithosphere modelled as a thin elastic plate floating on a fluid mantle substrate, leading to an arc‐perpendicular foredeep, forebulge and backbulge. Arc‐parallel topographic and gravitational features should influence loading along strike in a similar way, resulting in a checkerboard pattern of foredeeps, forebulges and backbulges in both pro‐arc and retro‐arc foreland basins. This pattern exercises profound controls on sediment and facies distribution in a here‐to‐fore un‐envisaged manner, with implications for resource exploration in foreland basins.
... Slab breakoff was then used to explain postcollisional magmatism and exhumation of high-pressure rocks in the European Alps by Davies and von Blanckenburg (1995). Garzanti et al. (2018), and references therein, gave a comprehensive global overview of where slab breakoff has been invoked to explain changes in plate kinematics and tectonic deformation in regions including the Alps (Spakman et al., 1988;Wortel and Spakman, 1992;Davies and von Blanckenburg, 1995;Sinclair, 1997;Fox et al., 2015), the Mediterranean region (Carminati et al., 1998;Wortel and Spakman, 2000;Spakman and Wortel, 2004;Rosenbaum et al., 2008;Chertova et al., 2014;van Hinsbergen et al., 2014;Spakman et al., 2018), the Anatolia-Zagros orogen (Şengör et al., 2003;Faccenna et al., 2006), and Himalaya and Tibet (Jiménez-Munt and Platt, 2006;Van Hinsbergen et al., 2014;Wu et al., 2014;Liang et al., 2016;Qayyum et al., 2022). Many of these studies confirm the hypothesis that a complete slab break off is preceded by the lateral propagation of a slab tear or detachment within the subducted plate (Yoshioka and Wortel, 1995), ascribing shortlived, long-wavelength exhumation events or sudden pulses in sediment supply to this process. ...
... Based on seismic tomographic imaging, Spakman and Wortel (2004) suggested that slab tearing might have occurred in the Gibraltar Arc region as a consequence of the continental convergence between Africa and Iberia and the subsequent slab rollback (Elsasser, 1971;Karig, 1971) declined during early Miocene. The uplift observed in the internal Betic basins after late Tortonian are best constrained from the present elevation of tectonically undeformed Miocene marine sediment in that region (marine to non-marine transition), often above 600 m elevation (Garcés et al., 1998;Iribarren et al., 2009). ...
... The biostratigraphic studies by Krijgsman et al. (2018) and van der Schee et al. (2018) revised the age of the uplift and provided a new age constraint on the western Betic intramountain basins to be older than 7.51 Ma (late Tortonian). This has been interpreted as the result of a westward migration of a lateral tear of the hanging slab seen in tomography underneath the Gibraltar Arc (Spakman and Wortel, 2004;Garcia-Castellanos and Villaseñor, 2011;Bezada et al., 2013). Slab tearing occurred in previous thermomechanical models by Chertova et al. (2014) and Spakman et al. (2018), but the cause and timing of slab tearing was not investigated by them. ...
Lithospheric slab tearing, the process by which a subducted lithospheric plate is torn apart and sinks into the Earth’s mantle, has been proposed as a cause for surface vertical motions in excess of 100 s of meters. However, little is known about the mechanisms that help initiate and control the propagation of slab tearing and the associated uplift. This study aims to explore these processes by means of 3D thermo-mechanical geodynamic modelling of a slab retreat oblique to a continental margin, using the Gibraltar Arc region (Betic Cordillera) as a scenario for inspiration. Our results suggest that the obliquity of the continental passive margin relative to the subduction trench leads to an asymmetric distribution of subduction forces and strength, facilitating the initiation of slab tearing. The model results predict a lateral migration of the tearing point at a velocity ranging between 38 and 68 cm/yr for a sublithospheric-mantle viscosity of up to 1e+22 Pa s. This fast slab tearing propagation yields uplift rates of 0.23–2.16 mm/yr above the areas where the subducted slab is torn apart, depending on mantle viscosity. Although a more detailed parametric exploration is needed, this range of uplift rates is compatible with the uplift rates required to overcome seaway erosion along the Atlantic-Mediterranean marine corridors during the Late Miocene, as proposed for the onset of the Messinian Salinity Crisis.
