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•2D numerical modelling was applied to the Dehdasht Structural Basin, Central Zagros.•The Dehdasht Basin is developed by contribution of syntectonic shallow diapirism and surface ...processes.•Thin Cambrian salt beneath the Dehdasht Basin could help formation of this broad basin.•Shortening triggers the initial growth of diapirs when sediment subsidence is low.•Increasing syntectonic sedimentation decreases the effect of shortening.
The Dehdasht Basin, a small structural basin located in the southeast of the Dezful Embayment in the Zagros fold-and-thrust belt, has a complex tectonic structure characterized by both compressional and halokinetic features. 2D numerical models are used to test how geometrical and rheological parameters affected the Miocene-Pliocene evolution of this deep basin. The analysed parameters include rates of syntectonic sedimentation and erosion, thickness and viscosity of the lower detachment (Hormuz salt) and of the upper detachment (Gachsaran evaporites) developing diapiric salt walls, salt extrusions and minibasins-growth synclines that characterize the internal structure of the Dehdasht Basin. Assuming reasonable dimensions and rheologies (0.5 km Hormuz basal detachment with moderate viscosity of 1019 Pa·s, and Gachsaran upper detachment with a minimum original thickness of 1.5 km and viscosity between 5 · 1018 and 1019 Pa·s), our models reveals that an almost intermediate ratio between the rates of surface processes and deformation well approximate the geological and geophysical observations. A local decrease in the thickness of the Hormuz salt below the Dehdasht Basin with respect to surrounding regions was of great importance for its structural evolution. We suggest that the large volume of Gachsaran evaporites presently filling the basin was partly due to their gravitational flow from the emerging surrounding anticlines into the basin. The numerical experiments also demonstrate that in a compressional setting, shortening is the main factor for the rapid initial growth of the diapirs, although, with increasing syntectonic sedimentation the effect of shortening diminishes.
We propose a review to discuss the large number of studies dealing with the fluid history in extensional and compressional sedimentary basins that evolved along the Iberian-Eurasian plate boundary ...during the full Mesozoic-Cenozoic Wilson Cycle in the Pyrenean fold belt and the Basque-Cantabrian Basin. We integrate classic and modern geochemical and geochronological datasets used in fluid studies with the current tectonic knowledge of the studied area.
Late Hercynian fluid systems were dominated by Carboniferous-early Permian magmatic intrusions related to large-scale lithospheric delamination at the end of the collision, which caused the accumulation of skarns at depths of 8000–10,000 m during contact metamorphism. During the Mesozoic extension, early and widespread shallow burial dolomitization of Jurassic and Early-Cretaceous carbonates occurred at burial depths of 500–1000 m due to seawater influx. From Albian to Cenomanian, along the North Pyrenean extensional fault zone, contact metamorphism processes occurred in association with mantle-derived and deep-crustal fluids at temperatures higher than 300 °C, which interacted with Triassic evaporites and formation and marine waters and depths of 2000–3000 m. Away from this fault, fluid systems were dominated by hydrothermal dolomitization and the accumulation of ZnPb mineralization along diapir walls and faults, whereas in the less extended and proximal domains of the extensional system, fluids were formation waters at temperatures up to 150 °C. The Alpine compressional fluid history registers the increasing influence of meteoric fluids as the foreland basin became overfilled and fluid flow occurred at depths of 2.5–4 km in tectonic units detached in Triassic evaporites and of >4 km in units rooted at depth with the Paleozoic basement. Along and across strike differences in the fluid evolution of the Pyrenees are attributed to changes in the structure of the cover and basement tectonic units, the westward decrease of shortening and in the oblique directions of Upper Triassic successions, which acted as very efficient seals for deep-sourced fluids.
Subvertical walls of diapirs are baffles for fluid flow, whereas fracturing and deposition of porous halokinetic successions are effective conduits. Evaporite detachments compartmentalize paleohydrological systems during tectonic deformation, although they may be breached by fluids reaching lithostatic pressures. In large evaporite-bearing provinces, fluid systems may share common patterns during successive extensional and compressional tectonic events, as documented in the Western Mediterranean Mesozoic extensional rift system. In this area, metal-bearing and deep-sourced fluids interacted with Triassic sulphates and organic matter, triggering the accumulation sulphides in rock porosity. However, more research is needed in other large-scale evaporitic provinces of different ages to identify common fluid flow patterns.
The geodynamic evolution of the Western Mediterranean related to the closure of the Ligurian-Tethys ocean is not yet fully resolved. We present a new 3D numerical model of double subduction with ...opposite polarities fostered by the inherited segmentation of the Ligurian-Tethys margins and rifting system between Iberia and NW Africa. The model is constrained by plate kinematic reconstructions and assumes that both Alboran-Tethys and Algerian-Tethys plate segments are separated by a NW-SE transform zone enabling that subduction polarity changes from SE-dipping in the Alboran-Tethys segment to NW-dipping in the Algerian-Tethys segment. The model starts about late Eocene times at 36.5 Ma and the temporal evolution of the simulation is tied to the geological evolution by comparing the rates of convergence and trench retreat, and the onset and end of opening in the Alboran Basin. Curvature of the Alboran-Tethys slab is imposed by the pinning of its western edge when reaching the end of the transform zone in the adjacent west-Africa continental block. The progressive curvature of the trench explains the observed regional stress reorientation changing from N-S to NW-SE and to E-W in the central and western regions of the Alboran Basin. The increase of the retreat rates from the Alboran-Tethys to the Algerian-Tethys slabs is compatible with the west-to-east transition from continental-to-magmatic-to-oceanic crustal nature and with the massive and partially synchronous calc-alkaline and alkaline magmatism.
•We propose a 3D numerical model of opposing subduction simulating the tectonic setting of the Western Mediterranean.•The retreat rates of the slabs are consistent with the duration of opening of the Alboran and Algerian basins.•The progressive curvature of the Alboran-Tethys slab is consistent with the regional stress evolution of the Alboran Basin.
The halokinetic structure of inverted salt‐related continental margins is frequently obliterated by compressional overprinting. The Cretaceous Sopeira and Sant Gervàs subbasins of the Ribagorça Basin ...(south central Pyrenees) show evidence of salt‐related extensional tectonics and diapiric growth along the Iberian Margin of the Mesozoic Pyrenean rift. We present an integrated field‐based tectonic‐sedimentary study to reconstruct the evolution of the Ribagorça Basin system previous to, and in the early stages of, the Pyrenean orogeny. The ~4 km thick Albian‐Cenomanian Sopeira minibasin infill thins toward the basin borders, especially toward the eastern, N‐S trending, Llastarri salt weld. The 90° tilt to the south of the Sopeira basin bottom records the growth of the buried north dipping Sopeira listric fault from Albian to Santonian times, when it evolved as an extensional rollover associated with the Aulet salt roller. The ~3 km thick Cenomanian‐Campanian succession filling the Sant Gervàs flap displays 130° bed fanning attitude from overturned Cenomanian carbonate platform strata to upright Campanian turbidite beds. The Sant Gervàs flap development since Cenomanian times was related to the fall of a large salt pillow after the main Soperia minibasin stage. Jurassic‐Campanian diachronous subsidence is also observed in the adjacent Montiberri, Faiada, and Tamurcia depocenters. Correlation with the Pedraforca, Cotiella, and Basque‐Cantabrian Basins along the southern Pyrenees suggests that a significant segment of the Iberian side of the Pyrenean rift experienced a gravity‐driven extension from Albian to late Santonian. The Ribagorça Basin provides an excellent field analogue for presently buried salt‐related structures of extended passive margins.
Key Points
Protracted halokinesis from Cretaceous extension to compression is recorded in Ribagorca Basin
Diachronous Ribagorca Basin depocenters were part of a large diapiric province in southern Pyrenees
Gravitational extension ruled the South Pyrenean rift margin from late Albian to late Santonian
This study integrates field structural data, petrographic and geochemical (δ18O, δ13C, Δ47, 87Sr/86Sr, and elemental composition) analyses and U–Pb dating of calcite veins cutting the Bóixols-Sant ...Corneli anticline (Southern Pyrenees) in order to date and to investigate the spatio-temporal relationships between fluid flow and fold evolution. This E-W trending anticline grew from Late Cretaceous to Paleocene at the front of the Bóixols thrust sheet deforming pre-growth and growth sedimentary sequences. U–Pb dating reveals Late Cretaceous to late Miocene deformation ages, which agree with the age of growth strata deposition and the sequence of deformation interpreted from field and microstructural data. Dates coeval (71.2 ± 6.4 to 56.9 ± 1.4 Ma) and postdating (55.5 ± 1.2 to 27.4 ± 0.9 Ma) Upper Cretaceous to Paleocene growth strata are interpreted to record: (i) the growth of the Bóixols-Sant Corneli anticline during the Bóixols thrust emplacement, and (ii) the tightening of the anticline during the southern tectonic transport of the South-Central Pyrenean Unit. Other ages (20.8 ± 1.2 to 9.0 ± 4.6 Ma) postdate the folding event and have been associated with the collapse of the Bóixols-Sant Corneli anticline. The geochemistry of calcite veins indicates that the fluid flow behavior varied across the Bóixols-Sant Corneli anticline through its growth, showing a compartmentalized fluid system. In the hinge of the anticline and in the upper Santonian to middle Campanian syn-orogenic sequence along the footwall of the Bóixols thrust, the similar petrographic and geochemical features between all calcite cements and host rocks point towards a locally-derived or well-equilibrated fluid system. Contrarily, along large faults such as the Bóixols thrust, and in the anticline limbs, the geochemistry of vein cements indicates a different scenario. Cements in large faults yielded the lightest δ18O values, from −8 to −14 ‰VPDB, and variable enrichment in δ13C, 87Sr/86Sr, elemental composition and δ18Ofluid. This is interpreted as the migration of fluids, through fault zones, that evolved from distinct fluid origins. Cements in the fold limbs exhibit δ18O and δ13C between −8 and −6 ‰VPDB and between −10 and + 2 ‰VPDB, respectively, the lowest Sr contents and the lowest precipitation temperatures, suggesting that the anticline limbs recorded the infiltration and evolution of meteoric waters. The paleohydrological system in the Bóixols-Sant Corneli anticline was restricted to the Bóixols thrust sheet. The Upper Triassic evaporitic basal detachment likely acted as a lower fluid barrier, preventing the input of fluids from deeper parts of the Pyrenean crustal thrust system. This study provides a well-constrained absolute timing of fracturing and fluid flow during basin inversion and folding evolution and highlights the suitability of U–Pb geochronology to refine the age of fractures and veins and their sequential evolution in orogenic belts.
•Twenty-three new U-Pb dates provide a well-constrained timing of deformation in an anticline that preserves pre-, syn- and post-folding fractures that do not exhibit a symmetrical orientation with respect to the fold axis, which have important implications for the interpretation of fold-fracture systems.•We further constrain the age and duration of fold evolution in the Bóixols-Sant Corneli anticline.•The geochemistry of calcite veins reveals that the fluid flow behavior varied across the different structural positions of the Bóixols-Sant Corneli anticline, evidencing a compartmentalized fluid system.•The paleohydrological system in the Bóixols-Sant Corneli anticline only involves fluids sourced above the detachment levels, which may act as a lower boundary for the fluid system, preventing the input of fluids from deeper parts of the belt.
Differentiating compressional growth strata from halokinetic sequences is not straightforward in foreland fold‐and‐thrust belts where compressional and diapiric processes were coeval. Although there ...are numerous studies on the role of salt layers in fold‐and‐thrust belts, very few focus on syntectonic evaporites where they are thick enough to develop diapirism. The tectonic structures of the northern Dezful Embayment, along the footwall of the Zagros Mountain Front Fault, show a complex evolution interpreted in this study by the concurrence of folding, thrusting and pre‐ and syn‐shortening diapirism of the lower Miocene Gachsaran evaporites. We explore this tectonic–diapiric–sedimentary interplay by combining field studies and remote‐sensing mapping, detailed stratigraphy and sedimentology, high‐quality seismic data, and step‐by‐step balanced tectono‐sedimentary restorations. Initial diapirism occurred soon after the deposition of at least 1.5 km thick Miocene Gachsaran evaporites during the sedimentation of up to 5 km thick Aghajari, Lahbari and Bakhtyari formations, which display syntectonic mixed growth strata and halokinetic sequences. These sedimentary sequences filled salt‐related minibasins, from which the Azanak Minibasin is the deepest, limited by growing salt walls and salt anticlines (Azanak thrust‐weld and the Saland–Lali anticline). Palaeocurrents and clasts compositions document fluvial diversions and exposure and erosion of Gachsaran evaporites along the active salt walls. Although, by further shortening, the precursor salt walls squeezed and reactivated as thrust‐welds structuring a duplex of overriding minibasins. During the deposition of the middle‐late Miocene Aghajari Formation, Kazhdumi and Pabdeh source rocks were buried to oil‐expulsion depths, and Sarvak and Asmari reservoirs were mildly folded in large and open anticlines. The Gachsaran system in the northern Dezful Embayment is collated with the structures of preshortening Hormuz salt and syn‐shortening Fars salt to highlight the important role of these ductile units in the tectonic evolution of the Zagros fold belt that is compared to syn‐compressional salt‐related Pyrenees, Carpathians, Sivas and Kuga fold belts.
The evolution of the Amiran and Mesopotamian flexural basins of the Zagros belt is approached by coupled 2‐D forward modeling of orogenic wedge formation, lithospheric flexural isostasy, and stream ...power erosion/transport/sedimentation. Thrust geometries and sequence of emplacement derived from geometric and kinematic models presented here are the inputs to our evolutionary model, constrained by basin geometry, sediment volume, and topography. Modeling results confirm that the Zagros flexural basins evolution is consistent with two stages of deformation: (1) the obduction stage involving the Kermanshah accretionary complex and a basement unit and (2) the collision stage, emplacing the Gaveh Rud and Sanandaj‐Sirjan domains in the hinterland and forming a basement duplex in the outer part. Results provide quantitative insights into processes involved in mountain and basin building. The lithospheric equivalent elastic thickness (Te) changed from 20 km during the Amiran stage (~90–50 Ma) to 55 km during the Mesopotamian subsidence stage (last 20 Myr). The Amiran basin results from flexure of the Arabian plate below the load of the Kermanshah cover and basement thrust sheets. During this stage, material eroded in the inner parts was enough to fill the flexural trough. The Mesopotamian basin formed in front of the outermost basement units flexing the Arabian plate. During this latter stage, material eroded from the orogenic wedge was not enough to fill the Mesopotamian basin. An additional longitudinal sediment supply of up to 200 m/Myr is required to fill the flexural basin.
Key Points
Two major thrust emplacement stages triggered the Zagros Foreland basins
Variations of the elastic thickness controlled foreland basins geometries
An extra load is required to explain ~20% of the current Arabian plate flexure
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