Observations in sedimentary basins affected by deformation show that the fault-induced depositional accommodation, at various spatial and temporal scales, is closely linked to basin kinematics. The ...tectonically-driven sediment infill displays the history of deepening and shoaling facies that are controlled by the activation of faults and changes in their offset rates. Simply stated, this results in shifting sedimentary facies towards the source area or towards the basin centre in response to increasing or decreasing depositional space. We propose a first-principle conceptual model for tectonic successions, controlled by the balance between the rates of creation of depositional space and sediment supply. These sediment bodies are bounded by succession boundaries and comprise sourceward or basinward shifting facies tracts that are separated at a point of reversal. Due to the relatively steep slopes associated with the evolution of faults, changes in sediment supply rates and mass-wasting are common in these systems and may complicate the normal rhythm of the shifting facies tracts. Once tectonic quiescence is achieved, and if the basin is connected to the open ocean, eurybatic or eustatic base level changes may take over and play a greater role in sedimentary rhythm and cyclicity. We illustrate the efficacy of the new concept with a review of examples from extensional, contractional and strike-slip basins. We show that the basic tectonic succession model is applicable at all temporal and spatial scales and whether the tectonics cause subsidence or uplift, and in all types of tectonic settings that determine the evolution of sedimentary basins.
Earthquake nests are anomalous clusters of seismicity located far from active collisional systems in intraplate, locked suture zones, or the deep part of relic subducted slabs, challenging classic ...earthquake generation mechanism theories. The Vrancea Seismic Zone in Romania is such an upper-mantle seismic nest located in the SE Carpathians, releasing the largest strain in continental Europe. To better understand earthquake generation and the relationship with lithospheric deformation, we estimate earthquake source parameters in Vrancea and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. In the crustal domain, maximum horizontal stress is in agreement with surface fault kinematics and GPS-derived S-SE trending horizontal plate velocities relative to Eurasia, implying that tectonic stress is vertically coherent on a crustal scale. The stress regime changes from transpression beneath the orogen to transtension towards the foreland where movement is accommodated along major crustal faults, and tension further away from the epicentre, in the Moesian Platform and the North Dobrogea Orogen. Inside the seismogenic body vertical tension and an overall compressive regime dominates, implying that vertical elongation may be the driving mechanism for brittle failure and that stress is transmitted along the sinking slab to the surface. However, the retrieved stress ratios are low: ~0.2 for mantle earthquakes Mw>4 and ~0.4 for Mw<4, challenging the brittle failure assumption. Increased pore fluid pressure has been shown to lower stress ratios, implying that dehydration embrittlement may contribute to generating intermediate-depth seismicity in the Vrancea slab. Comparisons with seismic tomography and anisotropy studies show excellent correlations between maximum horizontal stress directions, possible slab strike orientation, and seismic anisotropy, especially below ~130km depth, suggesting ambient mantle flow may also promote in-slab stress build-up and seismic potential.
•The Vrancea seismic body is vertically extending in a horizontal compressive regime and stress is transmitted to the surface.•Crustal tectonic stress is coherent with foreland fault kinematics and horizontal plate motion relative to Eurasia.•Stress regime changes from transpression to transtension towards the foreland, consistent with a weakly-coupled slab scenario.•Low stress ratios from Mw > 4 events suggest high pore fluid pressure plays a role in intermediate-depth earthquake nucleation.•Maximum horizontal stress is similar to seismic azimuthal anisotropy at depths below 130 km, suggesting mantle flow may promote in-slab stress and seismic potential.
A correlation of tectonic units of the Alpine-Carpathian-Dinaridic system of orogens, including the substrate of the Pannonian and Transylvanian basins, is presented in the form of a map. Combined ...with a series of crustal-scale cross sections this correlation of tectonic units yields a clearer picture of the three-dimensional architecture of this system of orogens that owes its considerable complexity to multiple overprinting of earlier by younger deformations.
The synthesis advanced here indicates that none of the branches of the Alpine Tethys and Neotethys extended eastward into the Dobrogea Orogen. Instead, the main branch of the Alpine Tethys linked up with the Meliata-Maliac-Vardar branch of the Neotethys into the area of the present-day Inner Dinarides. More easterly and subsidiary branches of the Alpine Tethys separated Tisza completely, and Dacia partially, from the European continent. Remnants of the Triassic parts of Neotethys (Meliata-Maliac) are preserved only as ophiolitic mélanges present below obducted Jurassic Neotethyan (Vardar) ophiolites. The opening of the Alpine Tethys was largely contemporaneous with the Latest Jurassic to Early Cretaceous obduction of parts of the Jurassic Vardar ophiolites. Closure of the Meliata-Maliac Ocean in the Alps and West Carpathians led to Cretaceous-age orogeny associated with an eclogitic overprint of the adjacent continental margin. The Triassic Meliata-Maliac and Jurassic Western and Eastern Vardar ophiolites were derived from one single branch of Neotethys: the Meliata-Maliac-Vardar Ocean. Complex geometries resulting from out-of-sequence thrusting during Cretaceous and Cenozoic orogenic phases underlay a variety of multi-ocean hypotheses, that were advanced in the literature and that we regard as incompatible with the field evidence.
The present-day configuration of tectonic units suggests that a former connection between ophiolitic units in West Carpathians and Dinarides was disrupted by substantial Miocene-age dislocations along the Mid-Hungarian Fault Zone, hiding a former lateral change in subduction polarity between West Carpathians and Dinarides. The SW-facing Dinaridic Orogen, mainly structured in Cretaceous and Palaeogene times, was juxtaposed with the Tisza and Dacia Mega-Units along a NW-dipping suture (Sava Zone) in latest Cretaceous to Palaeogene times. The Dacia Mega-Unit (East and South Carpathian Orogen, including the Carpatho-Balkan Orogen and the Biharia nappe system of the Apuseni Mountains), was essentially consolidated by E-facing nappe stacking during an Early Cretaceous orogeny, while the adjacent Tisza Mega-Unit formed by NW-directed thrusting (in present-day coordinates) in Late Cretaceous times. The polyphase and multi-directional Cretaceous to Neogene deformation history of the Dinarides was preceded by the obduction of Vardar ophiolites onto to the Adriatic margin (Western Vardar Ophiolitic Unit) and parts of the European margin (Eastern Vardar Ophiolitic Unit) during Late Jurassic to Early Cretaceous times.
Subsidence and uplift patterns and thermal history of sedimentary basins are controlled by tectonics, mantle dynamics and surface processes, such as erosion, sediment transport and deposition and ...their links to climatic variations. We use combined thermo-mechanical and stratigraphic numerical modelling techniques to quantify the links between tectonic and surface processes. We aim to assess the thermal evolution and subsidence rates of asymmetric extensional basins during the syn- and post-rift times by simulating different erosion and sedimentation rates. We analyse the 3D sedimentary architecture and facies distribution of the depocenters. Model results are validated by observations in the Pannonian Basin of Central Europe. Extensional reactivation of inherited suture zones creates asymmetric basin systems controlled by large-scale detachments or low-angle normal faults, where crustal and lithospheric mantle thinning are often rheologically decoupled. Subsidence rates and basement heat flow in the depocenters show large variabilities during asymmetric extension and post-rift evolution controlled by their initial position from the suture zone and migration of deformation. Transient heat flow anomalies mirror crustal exhumation of footwalls, sediment blanketing and erosion effects in the basins. Enhanced erosion and sedimentation facilitate lower crustal deformation and elastic flexure of the weak, extended lithosphere leading to accentuated differential uplift and subsidence during the syn- and post-rift basin evolution. Tectonics, climate and autogenic processes control transgressive-regressive cycles at different timescales together with the overall sedimentary facies distribution. In our models assuming wet climate the high subsidence rate often outpaces moments of eustatic water-level fall preventing relative base-level fall and enhances the effects of autogenic processes, such as lobe switching processes.
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•Linking lithosphere-asthenosphere processes with sedimentation and erosion.•Heat flow evolution of asymmetric extensional basins is reconstructed.•Extensional pulses create stratigraphic sequences.•Stratal stacking patterns are simulated including eustatic and autogenic processes.
The Vrancea region of the south-eastern Carpathians is a remarkable site of intra-continental intermediate-depth seismicity. A large set of geological, geophysical, and geodetic observations has been ...accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath Vrancea, the crustal and mantle dynamics, and the linkage between deep and surface processes in the region. In this article we review geology and tectonics of the Vrancea region including post-collisional to recent deformations, syn- to post-collisional magmatism, and orogenic exhumation along the East and South Carpathians. The regional seismicity is analysed, and the recent seismic studies including reflection, refraction, body and surface wave tomography are reviewed. We discuss new geodetic measurements of horizontal and vertical movements in the region, geoelectric studies, density/gravity and thermal modelling. Qualitative and quantitative (including retrospective) geodynamic models developed for Vrancea are analysed. The knowledge of regional tectonics, geodynamics, seismicity, lithospheric deformation, and stress regime in the Vrancea earthquake-prone region assists in an assessment of strong ground motion, seismic hazard and risk. The earthquake simulation, seismic hazard, and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface. Finally we discuss unresolved problems in Vrancea in order to improve our understanding of the regional evolution, present tectonics, mantle dynamics, intermediate-depth seismicity, and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the Vrancea region. The problems to be solved include: (i) the origin of the high-velocity body revealed by seismic tomography studies (oceanic versus continental); (ii) the lithospheric scale mechanism driving the Miocene subsidence of the Transylvania basin; (iii) sub-crustal structure between 40 and 70km; (iv) contemporary regional horizontal and vertical movements; and (v) a comprehensive seismic hazard assessment in the region.
One of the most common observation in Mediterranean areas is the migration of contractional deformation and associated slabs through time toward external orogenic areas, associated with lower plate ...crustal accretion. The Dinarides orogen of Central Europe is an optimal place to study such a sequence of contractional deformation. Compared with other areas, contraction in the Dinarides was less overprinted by subsequent extension, while a remnant of the subducted slab is observed in a far external orogenic position. Understanding the deformational evolution of the Dinarides is hampered by the reduced availability of kinematic studies. Therefore, we have performed a surface kinematic study in the external parts of the Dinarides. By correlating with available geophysical and evolutionary constraints, we constructed two large‐scale, kinematically controlled regional transects. The results demonstrate a long‐lived evolution of shortening that affected the Dinarides lower orogenic plate. While the Late Jurassic‐earliest Cretaceous deformation was associated with an earlier obduction moment, the latest Cretaceous onset of continental collision has gradually focused deformation at inherited rheological weakness zones. We show that shortening was interrupted by a period of Miocene extension that affected all orogenic areas and created the Dinarides Lake System. The extension was followed by renewed shortening, which started during the latest Miocene and remains presently active, whose kinematics in the central and SE part of the Dinarides is revealed for the first time by our study. These results indicate a lower plate crustal accretion mechanism that was spatially and temporally connected with gradual slab retreat in the Dinarides.
Key Points
The migration of contractional deformation in the Dinarides can be associated with lower plate crustal accretion during slab rollback
Along the Dinarides orogenic strike there is a lateral variability of contractional deformation
The entire Dinarides orogen was affected by Miocene extension and subsequent inversion
From the Oligocene onwards, the complex tectonic evolution of the Africa–Eurasia collision zone led to paleogeographic and biogeographic differentiation of the Mediterranean and Paratethys, two ...almost land-locked seas, in the area formerly occupied by the western Tethys Ocean. Episodic isolation of the basins triggered strong faunal endemism leading to the introduction of regional stratigraphic stages for the Paratethys. Chronostratigraphic control on the Paratethys stages remains rudimentary compared to the cyclostratigraphically constrained Mediterranean stages. This lack of chronostratigraphic control restricts the insight in the timing of geodynamic, climatic, and paleobiogeographic events and thereby hinders the identification of their causes and effects. In this paper, we here derive better age constraints on the Badenian, Sarmatian and Pannonian Central Paratethys regional stages through integrated 40Ar/39Ar, magnetostratigraphic, and biostratigraphic research in the Transylvanian Basin. The obtained results help to clarify the regions Middle Miocene geodynamic and paleobiogeographic evolution. Six new 40Ar/39Ar ages were determined for tuffs intercalating with the generally deep marine basin infill. Together with data from previous studies, there is now a total of 9 radio-isotopically dated horizons in the basin. These were traced along seismic lines into a synthetic seismic stratigraphic column in the basin center and serve as first order tie-points to the astronomically tuned Neogene timescale (ATNTS). Paleomagnetically investigated sections were treated similarly and their polarity in general corroborates the 40Ar/39Ar results. The integrated radio-isotopic and magnetostratigraphic results provide an improved high-resolution time-frame for the sedimentary infill of the Transylvanian Basin. Early Badenian deep water sedimentation is characterized by accumulation of the Dej Tuff Complex in response to a period of intensive volcanism, the onset of which is constrained between the first occurrence (FO) of Orbulina suturalis at 14.56Ma and 14.38±0.06Ma. During the subsequent Badenian Salinity Crisis (BSC) up to 300m of salt accumulate in the basin center. The faunal turnover that marks the Badenian–Sarmatian Boundary is dated at 12.80±0.05Ma. A second phase of intense volcanism occurs at 12.4Ma and leads to deposition of the middle Sarmatian tuff complex (Ghiriş, Hădăreni, Turda and Câmpia Turzii tuffs). Rates of sediment accumulation strongly diminish in the basin center at the onset of the Pannonian stage coincident with an approximately 20° CW tectonic rotation of the Tisza–Dacia plate. Concurrent enhanced uplift in the Eastern a'nd Southern Carpathians leads to the isolation of the Central Paratethys and triggers the transition from marine to freshwater conditions. An additional Pannonian to post-Pannonian 6° of CW rotation is related to the creation of antiform geometries in the Eastern Carpathians which are notably larger in the north than in the south. An 8.4Ma age is determined for the uppermost Pannonian sediments preserved in the central part of the Transylvanian Basin. Two sections belonging to middle Pannonian Zone D, and the lower part of Zone E (Subzone E1) are found to cover the 10.6–9.9Ma time-interval.
► 40Ar/39Ar and magnetostratigraphic results provide a new chronology for the Miocene Transylvanian Basin, Romania. ► Stratigraphic relations between sections are established through subsurface tracing to a synthetic section in the basin centre. ► The Badenian-Sarmatian extinction event is dated at 12.80±0.05Ma. ► 20° CW tectonic rotation of the Tisza-Dacia plate is pinpointed to take place around 11.3Ma ago.
The tectono‐sedimentary evolution of asymmetric extensional systems driven by the activity of major normal faults or detachments associated with footwall exhumation is often characterized by a ...sequence of slower, faster, and ultimately again slower subsidence rates in the center of hanging wall half‐grabens during their synkinematic and postkinematic evolution. We have studied this specific evolution by the means of 3‐D stratigraphic numerical modeling that accounts for the variability of the sediment and water flux combined with climatic and sea level variations, and sediment compaction. The model setup is constrained by observations from the Pannonian back‐arc basin of central Europe. Our modeling predicts the formation of low‐order tectonic and higher‐order sea level and climate‐driven transgressive‐regressive sedimentary cycles. Furthermore, we model and analyze the autocyclic nature of the depositional systems. Retrograding‐prograding cycles are visible on the proximal flank of the half‐grabens by their different spatial and temporal expressions, while depocenters record large water depth variations linked to the specific and episodic activity of normal faults and their migration with time. The application to a system of multiple half‐grabens in the Pannonian Basin, which are activated in different locations, at different times and with different kinematics, demonstrates a complex interplay between direct sediment sourcing and the sediments' ability to bypass trapping subbasins and paleo‐reliefs created by eroded footwalls.
Plain Language Summary
The formation and evolution of sedimentary basins is of prime interest as they record different Earth processes. The understanding of rifting mechanics and associated evolution of extensional sedimentary basins is also important for the assessment of their potential for georesources including freshwater. The spatial and temporal variabilities of vertical movements in asymmetric extensional systems control landscape evolution coupled to sedimentary and climatic processes. This paper aims to quantify the effect of tectonics and climatic variations on the overall architecture of such basins. Our numerical modeling demonstrates the low‐order tectonic and higher‐order sea level and climate‐driven influence on the sedimentary transport routes and overall architecture. The application of our model in the Pannonian Basin of central Europe shows how tectonic inheritance control sedimentary transport routes.
Key Points
Quantification of tectonic and climatic controls on sedimentation in asymmetric extensional basins
New insights into distribution of lithologies, sedimentary facies, and unconformities in half‐grabens
Verifying the new insights in the Pannonian Basin tectono‐sedimentary evolution
When continents collide, the arrival of positively buoyant continental crust slows down subduction. This collision often leads to the detachment of earlier subducted oceanic lithosphere, which ...changes the subsequent dynamics of the orogenic system. Recent studies of continental collision infer that the remaining slab may drive convergence through slab roll-back even after detachment. Here we use two-dimensional visco-elasto-plastic thermo-mechanical models to explore the conditions for post-collisional slab steepening versus shallowing by quantifying the dynamics of continental collision for a wide range of parameters. We monitor the evolution of horizontal mantle drag beneath the overriding plate and vertical slab pull to show that these forces have similar magnitudes and interact continuously with each other. We do not observe slab rollback or steepening after slab detachment within our investigated parameter space. Instead, we observe a two-stage elastic and viscous slab rebound process lasting tens of millions of years, which is associated with slab unbending and eduction that together generate orogenic widening and trench shift towards the foreland. Our parametric studies show that the initial length of the oceanic plate and the stratified lithospheric rheology exert a key control on the orogenic evolution. When correlated with previous studies our results suggest that post-detachment slab rollback may only be possible when minor amounts of continental crust subduct. Among the wide variety of natural scenarios, our modelling applies best to the evolution of the Central European Alps. Furthermore, the mantle drag force may play a more important role in continental dynamics than previously thought. Finally, our study illustrates that dynamic analysis is a useful quantitative framework that also intuitively explains observed model kinematics.
The south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity ...in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3
Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9
Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3
Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (<
0.03
Ma) interrupted at 1.6–1.2
Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3
Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6
Ma) and South Harghita area at a distance of ca. 200
km imply a regional connection with the inversion tectonics.
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