The large number and distribution of rollback systems in Mediterranean orogens infer the possibility of interacting extensional back‐arc deformation driven by different slabs. The formation of the ...Pannonian back‐arc basin is generally related to the rapid Miocene rollback of a slab attached to the European continent. A key area of the entire system that is neglected by kinematic studies is the connection between the South Carpathians and Dinarides. In order to derive an evolutionary model, we interpreted regional seismic lines traversing the entire Serbian part of the Pannonian Basin. The observed deformation is dominantly expressed by the formation of Miocene extensional detachments and (half) grabens. The extensional geometries and associated synkinematic sedimentation that migrated in time and space allow the definition of a continuous and essentially asymmetric early to late Miocene extensional evolution. This evolution was followed by the formation of few uplifted areas during the subsequent latest Miocene–Quaternary inversion. The present‐day extensional geometry changing the strike across the basin is an effect of the clockwise rotation of the South Carpathians and Apuseni Mountains in respect to the Dinarides. Our study infers that the Carpathian rollback is not the only mechanism responsible for the formation of the Pannonian Basin; an additional middle Miocene rollback of a Dinaridic slab is required to explain the observed structures. Furthermore, the study provides constraints for the pre‐Neogene orogenic evolution of this junction zone, including the affinity of major crustal blocks, obducted ophiolitic sequences and the Sava suture zone.
Key Points
Novel early to late Miocene extensional evolution
Migration in time and space of the normal faulting
Novel component of rollback of a Dinaridic slab
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The architecture of sedimentary basins reflects the relationship between accommodation space and sediment supply, their rates and localization being variable during basin evolution. The mechanisms ...driving the interplay between tectonics and sedimentation in extensional back‐arc basins overlying rheological weak zones inherited from an earlier orogenic evolution are less understood. A typical example is the Pannonian back‐arc basin of Central Europe. It is floored by continental lithosphere and was affected by large amounts of extension driven by the subduction rollback that took place in the Carpathians and/or Dinarides. A novel kinematic and seismic sequence stratigraphic interpretation calibrated by wells allows the quantification of the link between the formation of half grabens and coeval sedimentation in the Great Hungarian Plain part of the basin. While the lower order tectonic‐induced cycles characterize the main phases of extension in various subbasins, the higher‐order cyclicity and associated unconformities define individual moments of fault (re)activation. Our novel interpretation of a temporal and spatial migration of extension during Miocene times explains the contrasting present‐day strike of various subbasins as a result of their gradual clockwise rotation. Incorporating the observed asymmetry, in particular the associated footwall exhumation, infers that the amount of extension is much larger than previously thought. The quantitative link between tectonics and sedimentation has allowed the definition of a novel model of sedimentation in asymmetric basins that can be ported to other natural scenarios of similarly hyperextended back‐arc basins observed elsewhere.
Key Points
Coupled tectonosedimentary evolution of the Pannonian Basin
Kinematics of extension in back‐arc settings
Migration of tectonic phases
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Back‐arc basin evolution is driven by processes active at the main subduction zone typically assuming the transition from an extensional back‐arc, during the retreat of a mature slab, to a ...contractional basin, during high‐strain collisional processes. Such a transition is observed in the Black Sea, where the accurate quantification of shortening effects is hampered by the kinematically unclear geometries of Cenozoic inversion. By means of seismic profiles interpretation, quantified deformation features and associated syn‐tectonic geometries on the Romanian offshore, this study demonstrates that uplifted areas, observed by exploration studies, form a coherent thick‐skinned thrust system with N‐ward vergence. Thrusting inverted an existing geometry made up by successive grabens that were inherited from the Cretaceous extensional evolution. The shortening started during late Eocene times and gradually affected all areas of the Western Black Sea Basin during Oligocene and Miocene times, deformation being coherently correlated across its western margin. The mechanism of this generalized inversion is the transmission of stresses during the collision recorded in the Pontides‐Balkanides system. Syn‐tectonic sedimentation in the Western Black Sea demonstrates that this process was continuous and took place through the onset of gradual shortening migrating northward. Although the total amount of shortening is roughly constant in an E‐W direction, individual thrusts have variable offsets, deformation being transferred between structures located at distance across the strike of the system. The Black Sea example demonstrates that the vergence and offset of thrusts can change rapidly along the strike of such a compressional back‐arc system. This generates apparently contrasting geometries that accommodate the same orogenic shortening.
Key Points
Kinematics and mechanics of back‐arc basin inversion
W Black Sea evolution, from Cretaceous opening to L Eocene‐M Miocene inversion
Far field transmission of continental collision stresses into the back‐arc basin
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The interplay between slab dynamics and intraplate stresses in postcollisional times creates large near‐surface deformation, particularly in highly bent orogens with significant lateral variations in ...mechanical properties. This deformation is expressed through abnormal foredeep geometries and contrasting patterns of vertical movements. Intraplate folding is often the controlling mechanism, particularly when the orogenic belt is locked. The study of these tectonic processes in the SE Carpathians indicates a generalized subsidence period during latest Miocene–Pliocene times driven by the slab‐pull and an intraplate folding due to an overall Quaternary inversion. The latter accommodates ∼5 km ESE‐ward movement of this area with respect to the neighboring units, which creates complicated three‐dimensional deformation patterns potentially driven at a larger scale by the interaction between the Adriatic indentor and the entire Carpathians system. The lithospheric anisotropy inherited from the subduction times concentrates strain and induces large‐scale deformation far away from the active plate margins. This anisotropy is dynamic because of deep mantle processes related to the subducted slab during postcollisional times, such as thermal reequilibration or increase in slab dip.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Sea‐level changes provide an important control on the interplay between accommodation space and sediment supply, in particular, for shallow‐water basins where the available space is limited. Sediment ...exchange between connected basins separated by a subaqueous sill (bathymetric threshold) is still not well understood. When sea‐level falls below the bathymetric level of this separating sill, the shallow‐water basin evolution is controlled by its erosion and rapid fill. Once this marginal basin is filled, the sedimentary depocenter shifts to the open marine basin (outward shift). With new accommodation space created during the subsequent sea‐level rise, sediment depocenter shifts backwards to the marginal basin (inward shift). This new conceptual model is tested here in the context of Late Miocene to Quaternary evolution of the open connection between Dacian and Black Sea basins. By the means of seismic sequence stratigraphic analysis of the Miocene‐Pliocene evolution of this Eastern Paratethys domain, this case study demonstrates these shifts in sedimentary depocenter between basins. An outward shift occurs with a delay that corresponds to the time required to fill the remaining accommodation space in the Dacian Basin below the sill that separates it from the Black Sea. This study provides novel insight on the amplitude and sedimentary geometry of the Messinian Salinity Crisis (MSC) event in the Black Sea. A large (1.3–1.7 km) sea‐level drop is demonstrated by quantifying coeval sedimentation patterns that change to mass‐flows and turbiditic deposits in the deep‐sea part of this main sink. The post‐MSC sediment routing continued into the present‐day pattern of Black Sea rivers discharge.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The transition zone between the Alps and Dinarides is a key area to investigate kinematic interactions of neighboring orogens with different subduction polarities. A study combining field kinematic ...and sedimentary data, microstructural observations, thermochronological data (Rb‐Sr and fission track), and regional structures in the area of Medvednica Mountains has revealed a complex polyphase tectonic evolution. We document two novel stages of extensional exhumation. The first stage of extension took place along a Late Cretaceous detachment following the late Early Cretaceous nappe stacking, burial, and greenschist facies metamorphism. Two other shortening events that occurred during the latest Cretaceous‐Oligocene were followed by a second event of extensional exhumation, characterized by asymmetric top‐NE extension during the Miocene. Top‐NW thrusting took place subsequently during the Pliocene inversion of the Pannonian Basin. The Cretaceous nappe burial, Late Cretaceous extension, and the Oligocene(‐Earliest Miocene) contraction are events driven by the Alps evolution. In contrast, the latest Cretaceous‐Eocene deformation reflects phases of Dinaridic contraction. Furthermore, the Miocene extension and subsequent inversion display kinematics similar with observations elsewhere in the Dinarides and Eastern Alps. All these processes demonstrate that the Medvednica Mountains were affected by Alpine phases of deformations to a much higher degree than previously thought. Similarly with what has been observed in other areas of contractional polarity changes, such as the Mediterranean, Black Sea, or New Guinea systems, the respective tectonic events are triggered by rheological weak zones which are critical for localizing the deformation created by both orogens.
Key Points
Kinematic and thermochronological study of interacting neighboring orogens
Two stages of extensional exhumation influenced the Alpine‐Dinaridic junction
Structures of the Alps extend far into the Dinarides
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This finite element modelling study addresses the contraction of rheologically layered and laterally heterogeneous lithosphere representative for the Pannonian Basin and its surroundings. The time ...interval and strain rate adopted in the experiments reflect the Pliocene–Quaternary inversion of the basin. Several sets of fully coupled elastoviscoplastic thermo-mechanical, plane strain 2D models explore the evolution of buckling, and stress/strain changes across the lithosphere. The viscous rheology of the asthenosphere allows for a detailed simulation of isostatic rebound during deformation.
The numerical models predict the successive development of surface undulations, caused by crustal and/or lithosphere folding, at three different characteristic wavelengths. Among these, the longest wavelength folds occur systematically at the rim of the basin as marginal bulges, while the short wavelength folds overprint the earlier folds and are observed at a later stage during compression. The thermo-mechanical evolution of the lithosphere in response to progressive horizontal contraction is described in terms of a characteristic delay of the changes in the stress regime and a reduction of elastic strain in the strong crustal layers. The models predict a change in stress state along the flanks of the basin, caused by the development of weak basin lithosphere in their vicinity. Comparing the modelling results with tectonic features of the Pannonian Basin has resulted in the identification of three different stages in the Pliocene–Quaternary basin inversion of the Pannonian–Carpathian system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In contractional (subduction/collisional) settings, convergence is accommodated by the formation of thin- and thick-skinned thrust and fold belts. The transmission of such deformation over larger ...distances into orogenic foreland areas is influenced by the inherited rheological characteristics of continental lithosphere. Lateral rheological variations parallel to the strike of continental foreland areas creates contrasting geometries and sequences of deformation that interact during orogenic build-up. We investigate the far-field transmission of strain within a continental lithosphere characterized by a laterally variable rheology through physical analogue modelling. Rheological weak crustal zones were introduced at distance from an advancing backstop to study the progressive along strike linkage and interference of structures during contraction. The results reveal that rheologically weak crustal zones localise far-field contractional deformation. When the size of weak zones, by means of their horizontal extend to depth ratio, is large, deformation localises at the boundaries of the weak zone where they lead to the formation of large-offset faults. Subsequently the faults migrate along-strike into areas that are rheologically stronger. When the size of the weak zone is reduced, a large-scale contractional step-over forms in orogenic forelands, where rheologically contrasting domains transmit out-of-sequence deformation by a gradual migration of thrust offsets and fold amplitudes along their strike. These results show that crustal scale orogenic step-overs do not always reflect variations in the geometry of the plate boundary (indenter) or along-strike gradients in shortening rates. Such features may also form in response to variations in rheology, as the ones created by inherited extensional basins situated at large distances from plate boundaries in the orogenic foreland.
•Crustal weak zone(−s) localise strain at far distance from the indenter.•Contractional step over might reveal the presence of crustal weak zone.•Crustal deformation at weak zone will be associated with lithospheric folding.•The symmetry of lithosphere fold can reveal the lithosphere strength.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Pannonian and Dacic Basins in SE Europe are presently connected by the Danube River across the South Carpathians, to which they are in a back-arc and foreland position respectively. Part of the ...Paratethys realm during the Neogene, open water communication between the basins was interrupted by the Late Miocene uplift of the Carpathians. Different mechanisms have been proposed for the formation of the Danube gateway: capture of the upstream lake or an upstream river or incision of an antecedent river. Estimates on its age range from Late Miocene to Quaternary. A related issue is the effect of the large Mediterranean sea level fall related to the Messinian Salinity Crisis on the Paratethys subbasins, specifically the “isolated” Pannonian Basin.
In a synthetic numerical modelling study, using a pseudo-3D code integrating tectonics, surface processes and isostasy, we addressed the causes and effects of changes in connectivity between two large sedimentary basins separated by an elevated barrier. Specifically, we aimed to find the expression of connectivity events in the sedimentary record in general and the consequences for the evolution of the Pannonian–Dacic area in particular. We studied a range of parameters including the geometry and uplift rate of the barrier, downstream sea level change and lithosphere rigidity.
We found that changes in connectivity are expressed in the sedimentary record through their effect on base level in the upstream basin and supply in the downstream basin. The most important factors controlling the response are the elevation difference between the basins and the upstream accommodation space at the time of reconnection. The most pronounced effect of reconnection through lake capture is predicted for a large elevation difference and limited upstream accommodation space. Downstream increase in sediment supply is dependent on the latter rather than the reconnection event itself.
Of the parameters we tested, the rigidity of the lithosphere was found to be of major importance by its control on sediment loaded subsidence and generation of accommodation space. A downstream sea level change is unlikely to induce capture, but may affect the upstream lake level by enhancing incision in a pre-existing gateway. In the Pannonian–Dacic region, the mechanically weak, continuously subsiding Pannonian lithosphere allowed accommodation of significant volumes of continental sedimentation and as a consequence, transfer of excess sediment to the downstream Dacic Basin was only gradual. The Messinian sea level fall in the Dacic Basin could have been recorded in the Pannonian Basin only if a connection between the basins already existed. More detailed modelling of river incision taking into account lateral differences in erodibility in the South Carpathians will be required to give better time constraints on the formation of the Danube Gateway.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The Carpathians orogenic system, with its along-arc variations in topography developed in the aftermath of continental collision, is associated with unusual foredeep basins, large-scale strain and ...seismicity concentration and high-velocity mantle bodies. The East Carpathians continental collision was non-cylindrical, leading to large-scale variations in thrust nappe kinematics, orogenic uplift patterns and foredeep subsidence, controlled by the mechanics and geometry of the lower plate. Thermo-mechanical modelling demonstrates that in this low-rate convergence regime, the subducted lithosphere had enough time to interact with the mantle to advance towards a thermal resettlement. This is favored by the low degree of metamorphism, mechanical weakness of the lower plate and the lack of active surface processes at the contact with and in the upper plate. In contrast, low-buoyant, thick lower crust and active surface processes keep the continuity of the slab intact and promote the development of typical foredeep basins. The model explains in a self-consistent manner the unusual geometry of the Vrancea seismogenic slab in the bend zone of the Romanian Carpathians. The model is also consistent with the presence of two high-velocity bodies inferred from seismic tomography studies and explains the depth zonation of seismicity in the Vrancea area. Differences between the northern part of East Carpathians and the southeastern bend of the Carpathians arc are largely controlled by lateral variations in crustal structure, topography emplacement and surface processes along the arc. Mechanical heterogeneity of the Carpathians subduction leads to the development of two end member modes of collision, allowing a study of these states and their transition. Lithospheric configuration and tectonic topography appear to be prime factors controlling variations in slab behavior. In the SE Carpathians, at the terminal phase of continental convergence, slab delamination, roll-back and depocenter migration appear to play a more limited role at shallow and lithospheric levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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