Initial SE-dipping slow subduction of the Ligurian–Tethys lithosphere beneath Africa from Late Cretaceous to middle Oligocene twisting to a later faster E-dipping subduction of the subcrustal ...lithosphere is proposed as an efficient geodynamic mechanism to structure the arcuate Betic–Rif orogenic system. This new subduction-related geodynamic scenario is supported by a kinematic model constrained by well-dated plate reconstructions, tectonic, sedimentary and metamorphic data sets. The slow initial SE-dipping subduction of the Ligurian–Tethys realm beneath the Malaguide upper plate unit is sufficient to subduct Alpujarride and Nevado-Filabride rocks to few tens of kilometers of depth in middle Eocene times. The shift from SE- to E-dipping subduction during latest Oligocene–early Miocene was possibly caused by both the inherited geometry of the highly segmented Ligurian–Tethys domain and by the fast roll-back of the subducted lithospheric slab. The early Miocene rather synchronous multiple crustal and subcrustal processes comprising the collision along the Betic front, the exhumation of the HP/LT metamorphic complexes, the opening of the Alboran basin, its flooring by HP Alpujarride rocks and subsequent HT imprint, can be explained by the fast NW- and W-directed roll-back of the Ligurian–Tethys subcrustal lithospheric slab. The W retreat of the Ligurian–Tethys lithosphere in middle–late Miocene times could partly explain the initiation of its lateral tear and consequent subcrustal processes. From latest Miocene onward the Betic–Rif system evolved under both the northerly push of Africa resulting in tightening at crustal and subcrustal levels and by the distinct current dynamics of the steep lithospheric slab. The SW-directed scape of the Rif fold belt is one of the most striking evidences linked to the recent evolution of the squeezed Betic–Rif system between Africa and Iberia.
► Kinematic model for the Betic–Rif orogen with initial SE-dipping subduction ► Highly stretched Ligurian–Tethys lithosphere subducted beneath N-moving Africa ► Late Cretaceous to mid Oligocene slow subduction and HP metamorphic peak ► Subduction shifted to E-dipping in late Oligocene due to ocean segmentation. ► Coeval roll-back, Alboran back-arc extension and exhumation of HP rocks
The study of fluvial network rearrangement provides a key to understand past and future landscape evolution. Large perturbations of hydrographic basins such as the change from endorheism to exorheism ...have repercussions in the steady or disequilibrium state of the basins and their drainage divides. Such transitions from internal to external drainage imply a major lowering of the geomorphological base level causing a major retreating knickpoint wave that separates the upstream low-relief area (inherited from the endorheic period) from the downstream incised area. Subsequently, the water divide migrates to reach an equilibrium in which erosion rates at both sides of the divide are similar. Previous fluvial analyses suggest that both the Duero and Ebro drainage networks, the two largest catchments in Iberia, experienced a change from endorheism to exorheism sometime between the Late Miocene and the Pliocene. Fluvial capture evidence argues for a Pliocene westward migration of the Ebro-Duero divide implying an area decrease for the Duero fluvial network (victim) in favor of the Ebro (aggressor). We used river profiles, knickpoint distribution and Chi-map calculation to understand the different degree of erosion of the Duero and the Ebro catchments and the dynamics of their drainage network. The results show an equilibrated Ebro drainage network in contrast with a disequilibrium in the erosional state of the Duero drainage, which remains reorganizing and adapting to the newly-imposed Atlantic base level. We identified at least two knickpoint wave trains in the Duero drainage resulting from the onset of exorheism: a fast-propagating wave through the cover and a low-propagating wave affecting the bedrock. Field evidence and topographic analysis suggest a westward migration of the Ebro-Duero divide, resulting in an ongoing headward erosion of the Ebro against the Duero catchment. Chi analysis provides the degree of disequilibrium of the drainage network indicating a large-scale aggressor role for the Duero and a victim role for the Ebro. We interpreted this seeming contradiction as the result of a different time scale perspective: local divide observations indicate a victim Duero in the short-term, whereas basin-scale dynamics support a victim role for the Ebro fluvial network in the long-term (multi-million-year time-scales).
•The Ebro Basin is closer to equilibrium than the Duero Basin, which remains adapting to the Atlantic base-level.•We suggest a fast-propagating knickpoint wave through the cover and a low-propagating wave affecting the bedrock.•The rate of knickpoint retreat on the cover is twice as high as the rate of retreat on the bedrock.•Local divide dynamics argue for a victim Duero at short-term and basin-scale dynamics argue for a victim Ebro at long-term.
This paper deals with the tectono-sedimentary evolution of the Dehdasht Basin, located at the boundary between the Izeh Zone and the Dezful Embayment, in the Central Zagros. The structural evolution ...of the basin is closely related to the coeval sedimentation of Neogene Fars Group foreland basin deposits. The analysis of five geological cross-sections reveals the interaction between tectonics, Gachsaran Formation diapirism and coeval sedimentation as well as the influence of hidden basement-involved faults. The great thickness of the Miocene Gachsaran evaporites contributes to the internal structure of the Dehdasht Basin as well as decouples the Competent Group structure at depth from the Passive Group structure cropping out at surface. The basin forms a synclinorium limited by high amplitude NW-SE trending anticlines filled with Neogene deposits. Its internal structure is characterized by relatively thin growth synclines-minibasins separated by Gachsaran diapiric ridges formed under a combination of shortening and diapirism. The amount of shortening across the basin ranges between 7.5 and 13.1 km (16–24%) whereas the restored preserved thickness of Gachsaran evaporites increases southeastwards from 2 to 2.85 km. This high thickness is interpreted as partly accumulated by gravity gliding from the rising surrounding anticlines. Observed changes in structural relief across and along the Dehdasht Basin suggests its development above an array of hidden and linked basement faults including segments of the Mountain Frontal Flexure with NW-SE Zagros trend under the northern and southern boundary anticlines and a transfer fault with N-S Arabian trends at the SE border. The observed structural variations both along-strike and across the Dehdasht Basin at a local scale are similar to those already found at larger scales along the major Kazerun Fault Zone.
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•The Dehdasht Basin in the Central Zagros is a synclinorium filled with syntectonic Neogene deposits.•Constructed regional cross-sections show structural variations along-strike, transversely and vertically.•The surficial structures are decoupled from the underlying ones along the Miocene Gachsaran evaporites.•High accumulation of the evaporites is partly due to the gravity gliding from the rising surrounding anticlines.•The basin is developed above an array of hidden and linked NW-SE and N-S basement faults.
The structural evolution of basement-involved, or thick-skinned, fold-and-thrust belts is often affected by preexisting, inherited extensional faults within the basement. Here, a crustal-scale ...two-dimensional finite difference model with a visco-elasto-brittle/plastic rheology is applied to investigate the formation of fold-and-thrust belts as a result of tectonic inversion, from intracontinental extension to compression. We examine the influence of frictional strain weakening, varying surface process intensity and different crustal rheologies. Intense strain weakening results in narrow and deep basins with wide shear zone spacing during the extension phase and fault reactivation and localized uplift during inversion. Little weakening of shear zones results in thrusts cross-cutting pre-existing normal faults and the development of newly-formed thrusts in distal parts of the fold-and-thrust belt during inversion. Enhanced surface mass movement localizes deformation and uplift in the central part of mountain belts. Implementation of a weak upper crust (quartzite) leads to less localized deformation compared to a strong crust (quartz-diorite). We compare modelling results to the basement-involved Kopet Dagh Mountains, NE Iran, and discuss potential lateral variation of fault reactivation and erosion rates being responsible for deeper tectonic exhumation in the eastern part of the mountain belt, relative to the West and Central Kopet Dagh.
•Crustal-scale numerical models test strain weakening effect on tectonic inversion.•Basin formation and fault reactivation is strongly dependent on weakening amount and surface processes.•Results help understanding lateral variation of exhumation in the Kopet Dagh Mountains, NE Iran.
Two passive seismic profiles have been acquired in the eastern Pyrenees as part of the Pyrope and Orogen projects to investigate the crustal structure differences between this area and the central ...and western Pyrenees. Up to 28 broad-band stations were deployed along two orthogonal lines, with an interstation spacing close to 10 km. High frequency receiver functions allowed us to obtain the main lithospheric interfaces along those lines. The NNE-SSW profile shows a well-defined Moho beneath Iberia, slightly deepening northwards. Beneath the Axial zone the Moho appears to be segmented but does not show evidence of crustal imbrication. Further North, the Moho appears again as a continuous interface located around 30 km depth. This image clearly differs from the conspicuous imbrication between the Iberian and Eurasian crusts observed westward. The E-W profile shows a smooth Moho thinning from a 40 km depth to the west of the profile to 23 km close to the coastline, evidencing the crustal thinning related to the Neogene extensional processes. Additional constraints on the geometry of the crust/mantle boundary in the Eastern Pyrenees are obtained from local moderate magnitude earthquakes recorded along the seismic lines during the experiment. In particular, a fan profile built from an event located near the Mediterranean coast suggests that crustal thickness differences between Iberian and Eurasian crusts can still be recognized 30 km westward of the Mediterranean coast, in an area that seems to mark the limit between regions dominated by compressive and extensive processes. We propose a model in which the observed dissimilar Moho structure beneath the Eastern Pyrenees is interpreted as the result of a different Mesozoic pre-shortening margin configuration. Seismic results are consistent with recently proposed tectonic models including an intermediate continental block separating Iberia and Europe by two basins with extremely thin crust or exhumed mantle.
•Crustal structure beneath eastern Pyrenees•Receiver function stacks•Local events modeling•Geological interpretation of the results•Eastward limit of the crustal imbrication beneath the Pyrenees
Reinterpretation of the Organyà Basin, based on new detailed field observations and subsurface data, emphasizes the key contribution of Upper Triassic evaporites in the tectono‐sedimentary evolution ...of the South‐Central Pyrenees. Results are integrated in a 65‐km long restored cross‐section through the Serres Marginals, Montsec and eastern Organyà salt‐related depocenters. The reconstructed part of the Jurassic–Cretaceous northern Iberian salt‐rich rifted margin shows a template characterized by inherited Permo‐Triassic basement normal faults and an initial salt thickness of 0.7 km to the south and 1.5 km to the north. The Organyà Basin is part of the South Pyrenean Diapiric Province, a large system of salt related depocenters and minibasins, that is limited to the north by the more than 120‐km long Senterada salt wall complex separating the supra‐salt and sub‐salt domains in the Southern Pyrenees. Three main stages of diapiric activity are recognized along the northern Iberian margin from Asturias to the Eastern Pyrenees: a Jurassic early salt mobilization; a latest Jurassic–middle Albian main diapiric evolution associated with rifting; and a Campanian–Miocene diapiric reactivation during basin inversion that produced salt welds and thrust welds and translated the salt province some 60 km to the south.
Key Points
Reinterpretation of the Organyà Basin indicates occurrence of a large and continuous salt tectonics province in the South‐Central Pyrenees
Late Jurassic early salt mobilization followed by Early Cretaceous passive diapirism and diapir reactivation from late Campanian
The restored 65 km wide salt‐bearing passive margin indicates asymmetrical Iberia‐Eurasia conjugate margins
In natural doubly vergent orogens, the relationship between the pro‐ and retro‐wedges is, as yet, poorly constrained. We present a detailed tectonostratigraphic study of the retro‐wedge of the ...Eastern Pyrenees (Europe) and link its evolution to that of the pro‐wedge (Iberia) in order to derive insight into the crustal‐scale dynamics of doubly vergent orogens. Based on cross‐section restoration and subsidence analyses, we divide the East Pyrenean evolution into four phases. The first phase (Late Cretaceous) is characterized by closure of an exhumed mantle domain between the Iberian and European plates and inversion of a salt‐rich, thermally unequilibrated rift system. Overall shortening (~1 mm/yr) was distributed roughly equally between both margins over some 20 Myr. A quiescent phase (Paleocene) was apparently restricted to the retro‐wedge with slow, continuous deformation in the pro‐wedge (~0.4 mm/yr). This phase occurred between closure of the exhumed mantle domain and onset of main collision. The main collision phase (Eocene) records the highest shortening rate (~3.1 mm/yr), which was predominantly accommodated in the pro‐wedge. During the final phase (Oligocene), the retro‐wedge was apparently inactive, and shortening of the pro‐wedge slowed (~2.2 mm/yr). Minimum total shortening of the Eastern Pyrenees is ~111 km, excluding closure of the exhumed mantle domain. The retro‐wedge accommodated ~20 km of shortening. The shortening distribution between the pro‐ and retro‐wedges evolved from roughly equal during rift inversion to pro‐dominant during main collision. This change in shortening distribution may be intrinsic to all inverted rift systems.
Key Points
Cross‐section restoration reveals ~111 km minimum shortening in the Eastern Pyrenees, excluding closure of an exhumed mantle domain
The shortening distribution between pro and retro evolved from roughly equal during rift inversion to pro‐dominant during main collision
This change in shortening distribution from equal to pro‐dominant may be intrinsic to all inverted rift systems
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