Balance between tectonics and sedimentation during geodynamic evolution of the Adria-Europe convergence zone in central Serbia

The Cretaceous sedimentation along the NE Dinarides margin was associated with subduction and collision of the Neotethys Ocean located between continental units of Adria and Europe (i.e., the Sava subduction system). In this region, we have performed a coupled kinematic and sedimentological study in order to understand the main controlling mechanism of deposition in basins situated above the Sava subduction zone. The Cretaceous sedimentation on the upper plate of the Sava subduction system took place in a fore-arc basin developed in frontal parts of the active European continental margin. The sedimentary facies indicate three cycles of deposition during Early Cretaceous–Cenomanian, Turonian–Santonian, and Campanian-Maastrichtian. Lower Cretaceous–Cenomanian deposition was associated with regional contraction and characterized by the clastic-carbonatic cyclic shelf and slope deposits (i.e., the “para-flysch”). The European fore-arc “para-flysch” sequences, deposited during Berriasian–Aptian times, presently outcrop in the Gledićke Mts and Rudnik area in central Serbia. Following the Albian–Cenomanian regression that created regional unconformity across the entire fore-arc domain, Turonian–Santonian extension resulted in subsidence and syn-depositional bimodal magmatism. Fore-arc syn-subductional extension was triggered by retreating and steepening of the subducting Neotethys lithosphere. The final Campanian–Maastrichtian regression was initiated by large-scale shortening during the onset of Adria-Europe collision. Unlike the European fore-arc domain, the Cretaceous sedimentation over the passive continental margin of the Dinarides was exclusively controlled by continuous shortening and overall transgression over the subducting Adria plate. Deposition starts with transgressive Albian–Cenomanian coarse-clastics and gradually deepens into the clastic-carbonatic shelf deposits. Rapid subsidence since the late Turonian resulted in deposition of slope carbonates followed by the deep pelagic sedimentation of Coniacian to Campanian–Maastrichtian limestones with cherts (i.e., the Struganik facies). The onset of deposition in the Sava subduction trench, as well as the accelerated subsidence in the entire lower Adria plate domain was coeval with Turonian–Coniacian switch to syn-subductional extension in the European fore-arc basin. The trench sedimentation starts with Turonian distal mudstones overlain by Coniacian–Maastrichtian clastic-carbonatic turbidites, as observed in the Rudnik Formation in Central Serbia. The westward expansion and migration of trench deposition towards the lower Adria plate culminated with Middle Campanian–Late Maastrichtian deposition of siliciclastic trench turbidites observed in the Ljig Formation. The onset of the latest Cretaceous–Paleogene Adria-Europe continental collision resulted in large-scale W-wards thrusting that inverted the Cretaceous basins along NE Dinarides margin and emplaced sedimentary infill and basement of the European fore-arc over the Sava trench turbidites. The continued continental collision led to the propagation of thrusting during Eocene, which was characterized by formation of the large offset out-of-sequence thrusts. The eduction that followed break-off of the Neotethys slab beneath the Dinarides triggered Oligocene–Miocene extension which reactivated the inherited thrust contacts as extensional detachments along the entire Dinarides margin. The extension exhumed the lower Adria plate and additionally fragmented and deformed the former Cretaceous basins. The rates of extensional exhumation are decreasing to the NE, from the Dinarides margin towards the Carpathians

Classifying large strains from digital imagery: application to analogue models of lithosphere deformation

We are interested in reconstructing the time evolution of 2D plane deformation of analogue models of tectonic processes. Under relevant forcings, these models develop internal deformation, such as faults, and broader zones of deformation. We use Particle Image Velocimetry (PIV) to derive incremental displacements from top-view images that we use in subsequent steps to calculate the shape changes that come with large deformation. Because PIV describes displacement in a spatial reference, and material moves through the area in view, displacements at any given time refer to fixed locations in space, and not to specific material points. By reconstructing the path of material, we can follow small regions of material while they translate, rotate and change shape. To aid the qualitative interpretation of this deformation, we have developed a novel method that can qualitatively describe shape changes coming from extensional, shortening and horizontal shearing (strike-slip) deformation or combinations of these. This method is based on a logarithmic measure of stretch and results agree well with the visual interpretation of structures that we observe in our models. Thus, we provide tools with which the evolution of 2D tectonic deformation can be interpreted in a physically meaningful manner, but our method may be useful outside the realm of tectonics. Our software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods

Towards resolving Cretaceous to Miocene kinematics of the Adria–Europe contact zone in reconstructions: Inferences from a structural study in a critical Dinarides area

One key element in the current debate analysing the Central Mediterranean evolution is the Cretaceous structure and kinematics of the present-day oroclinal bent contact between Adria- and Europe-derived continental units in the Dinarides, interpreted in different tectonic reconstructions as a subduction-related thrust system or a large-scale strike-slip fault zone. We provide a solution to the debate by a structural and kinematic study in a key area located in central Serbia along the Europe–Adria orogenic suture of the Sava Zone. The results demonstrate that large-scale, top-SW, in- to out-of-sequence thrusting is the dominant mechanism that deformed the observed accretionary wedge-trench sediments during the Late Cretaceous subduction of the Neotethys Ocean and the ensuing Adria–Europe collision. The subsequent Oligocene–Miocene extension of the Pannonian Basin was associated with opposite-sense rotations of different Sava Zone segments, which created the observed ~80° oroclinal bending

Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

Particle image velocimetry (PIV), a method based on image cross-correlation, is widely used for obtaining velocity fields from time-series of images of deforming objects. Rather than instantaneous velocities, we are interested in reconstructing cumulative deformation, and use PIV-derived incremental displacements for this purpose. Our focus is on analogue models of tectonic processes, which can accumulate large deformation. Importantly, PIV provides incremental displacements during analogue model evolution in a spatial reference (Eulerian) frame, without the need for explicit markers in a model. We integrate the displacements in a material reference (Lagrangian) frame, such that displacements can be integrated to track the spatial accumulative deformation field as a function of time. To describe cumulative, finite deformation, various strain tensors have been developed, and we discuss what strain measure best describes large shape changes, as standard infinitesimal strain tensors no longer apply for large deformation. PIV or comparable techniques have become a common method to determine strain in analogue models. However, the qualitative interpretation of observed strain has remained problematic for complex settings. Hence, PIV-derived displacements have not been fully exploited before, as methods to qualitatively characterize cumulative, large strain have been lacking. Notably, in tectonic settings, different types of deformation—extension, shortening, strike-slip—can be superimposed. We demonstrate that when shape changes are described in terms of Hencky strains, a logarithmic strain measure, finite deformation can be qualitatively described based on the relative magnitude of the two principal Hencky strains. Thereby, our method introduces a physically meaningful classification of large 2-D strains. We show that our strain type classification method allows for accurate mapping of tectonic structures in analogue models of lithospheric deformation, and complements visual inspection of fault geometries. Our method can easily discern complex strike-slip shear zones, thrust faults and extensional structures and its evolution in time. Our newly developed software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods

Towards resolving Cretaceous to Miocene kinematics of the Adria–Europe contact zone in reconstructions: Inferences from a structural study in a critical Dinarides area

One key element in the current debate analysing the Central Mediterranean evolution is the Cretaceous structure and kinematics of the present-day oroclinal bent contact between Adria- and Europe-derived continental units in the Dinarides, interpreted in different tectonic reconstructions as a subduction-related thrust system or a large-scale strike-slip fault zone. We provide a solution to the debate by a structural and kinematic study in a key area located in central Serbia along the Europe–Adria orogenic suture of the Sava Zone. The results demonstrate that large-scale, top-SW, in- to out-of-sequence thrusting is the dominant mechanism that deformed the observed accretionary wedge-trench sediments during the Late Cretaceous subduction of the Neotethys Ocean and the ensuing Adria–Europe collision. The subsequent Oligocene–Miocene extension of the Pannonian Basin was associated with opposite-sense rotations of different Sava Zone segments, which created the observed ~80° oroclinal bending

Data supplement to: Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

The dataset consists of the original top-view and cross-section digital photographs of the model presented in Broerse et al. (2020) (Mappingand classifying large deformation from digital imagery: application to analogue models of lithosphere deformation.). The top-view images have been taken at a regular interval of 45 seconds during the entire experiment. Cross-section images have been taken after the experiment was finished. The purpose of the top-view images is to track incremental displacement fields of the model surface in time, estimated by Particle Image Velocimetry (PIV) based on the digital images. The cross-section images serve to inspect the final internal deformation along vertical planes. The images are located in two folders; top-views contains the full range of top-view images as used in the PIV analysis, starting at the original undeformed state until the final deformed state at the end of the experiment. A sub-folder not used in PIV contains images from before the start and after the stop of the experiment, and that are not used in the accompanying manuscript. The folder cross-sections contains an overview image of the locations of all cross-sections taken (IMG 7243) and images of vertical model cross-sections. In total 13 cross-sections have been made, where the cross-section numbering starts from the north, and continues southward (see image IMG 7243). The cross-sections a-a’, b-b’ and c-c’ that are used in Broerse et al. (2020) correspond to numbers 2, 6 and 13, respectively. The cross- section images have been taken with a southward view, while in Broerse et al. (2020) we have mirrored the images to present a northward view on the cross-sections. All photographs are in .jpg format and their names are original generic names created by the camera software at the moment of acquisition. Contact person is Taco Broerse - [email protected]

Alpine tectonic evolution of the Northern Serbo-Macedonian subunit: inferences from kinematic and petrological investigations

The Serbo-Macedonian Massif represents a belt of medium to lower amphibolite facies metamorphics situated along the European continental margin between the Pannonian Basin in the north and the Aegean Sea in the south. Structurally, it comprises the innermost segments of the Dacia mega-unit of the European affinity and is juxtaposed against the Adria-derived units of the Dinarides across the Adria-Europe zone of collision. The peak metamorphic event in the Serbo-Macedonian Massif is Variscan in age, while its magmatism had a complex pre-Alpine evolution, with the youngest stage being related to the crustal extension during the Triassic opening of the northern branch of Neotethys Ocean (or the Vardar Ocean). The subsequent Late Jurassic–Paleogene closure of the Vardar Ocean led to the E-ward subduction of the Neotethys oceanic lithosphere beneath the upper European plate (i.e., the Sava subduction system). The retreating and steepening of subducting lithosphere during the Late Cretaceous triggered syn-subductional extension in the upper plate of the Sava subduction system. The Late Cretaceous extension exhumed and structurally juxtaposed the high-grade Serbo-Macedonian metamorphics against the low-grade metamorphics of the Carpathians Supragetic Unit. The contact is marked by the E-dipping shear zone that can be traced along the eastern margin of Serbo-Macedonian Massif, from the Vršac Mts in the north, across the Jastrebac Mts and further towards the south in the Central Serbo-Macedonian sub-unit of south-eastern Serbia. The Late Cretaceous extension exhumed the Serbo-Macedonian metamorphic core, concurrently creating subsidence in a forearc basin along the frontal part of the European continental margin. Due to its unique position in the interference zone of the two retreating Carpathian and Dinaridic slabs, the Northern Serbo-Macedonian sub-unit between the Vršac Mts in the north and the Jastrebac Mts in the south was strongly influenced by processes associated with the Oligocene–Miocene Pannonian extension. Hence, large segments of the Northern Serbo-Macedonian sub-unit including its contact with the Supragetic Unit were buried beneath the Neogene sediments of the Morava Valley Corridor, as the southern prolongation of the Pannonian Basin. In order to segregate and quantify the effects of the Oligocene–Miocene extension we have conducted a coupled kinematic, petrological and thermochronological study in the segments of Northern Serbo-Macedonian sub-unit adjacent to the Dinarides and Carpathians. The recent tectonic uplift of the Vršac Mts occurred in the Middle to Late Miocene along the WSW-dipping normal faults that control deposition in the adjacent Zagajica depression. The ENE-WSW oriented extension, which was triggered by the retreat of Carpathian slab, exhumed the core of the mountains and exposed the Late Cretaceous Serbo-Macedonian\Supragetic extensional contact. South from the Vršac Mts such exhumation was hampered by the presence of rigid Moesian indenter. Tectonic exhumation of the Jastrebac Mts, together with a cluster of Serbo-Macedonian gneiss domes that emerge from the surrounding Neogene sediments in the western-central part of the Morava Valley Corridor, was induced by corrugated detachment faults during the Oligocene–Miocene E-W oriented Dinaridic extension

Analogue modelling of strain partitioning along a curved strike-slip fault system during backarc-convex orocline formation: Implications for the Cerna-Timok fault system of the Carpatho-Balkanides

Large-scale strike-slip faults are associated with significant strain partitioning in releasing/restraining bends and often display map-view curvatures ending in horse-tail geometries. Such faults are commonly associated with indentation tectonics, where shortening in front of indenters is transferred laterally to transpression, strike-slip and the formation of transtensional/extensional basins. We investigate how these structurally distinct domains are kinematically linked by the means of a crustal-scale analogue modelling approach where a deformable crust is moved against a stable and rigid indenter. The modelling demonstrates that the geometry of the indenter is the major controlling parameter driving strain partitioning and deformation transfer from thrusting and transpression to strike-slip and transtension, whereas the rotation of the mobile plate controls the opening of triangular shaped transtensional basins. Flow of the ductile crust leads to the distribution of deformation over a wider area, facilitating strike-slip splaying into transtension/extension behind the indenter. Our results show a very good correlation with the Moesian indentation in the Carpatho-Balkanides system of South-Eastern Europe, where strain is partitioned around the dextral Cerna and Timok strike-slip faults and transferred to thrusting in the Balkanides part of the Moesian indenter and to transtension/extension in the neighbouring South Carpathians