Liviu Matenco

Thermo-mechanical controls on the mode of continental collision in the SE Carpathians (Romania)

Abstract 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.

Tertiary tectonic evolution of the external East Carpathians (Romania).

Abstract Paleostress calculation and analysis of mesoscopic structures are integrated with depth interpreted geological profiles based on seismic studies and well correlation to derive a Tertiary tectonic model for the East Carpathians. Following Early Miocene and older orogenic phases, the first tectonic event that affected the studied area is characterised by a WSW–ENE-oriented shortening of Middle Miocene (Late Burdigalian) in age. Resulting deformations induced ENE-ward thrusting of Tarcau and Marginal units, as well as the internal part of the Subcarpathian nappe. A second shortening event with an E–W to WSW–ENE contraction direction took place in the Late Miocene (Sarmatian), characterised by further foreland thrusting of the Subcarpathian nappe and out-of-sequence deformation in the Tarcau and Marginal Folds nappes. Along strike, differences in deformation mechanisms are controlled by the friction coefficients along the main detachment layers, by the lateral variations in the wedge thickness and by the involvement in the northern part of the thrusting system of the thick, competent East European platform. Tear faulting occurred in both tectonic events, the main resulting structure being the triangle zone developed south of the Trotus valley. The Latest Miocene (Latest Sarmatian)–Early Pliocene is characterised by a strike–slip stress field with NNE–SSW compression and WNW–ESE tension axis, left-lateral faults being dominant. The last deformation which affected the studied area is characterised by NNW–SSE shortening during the Pliocene, major deformations taking place mainly in the SW-most bending zone.

Subsidence analysis and tectonic evolution of the external Carpathian-Moesian Platform region during Neogene times

Abstract The Miocene–Pliocene subsidence of the tectonic platforms in the Romanian Carpathians foreland is analysed using standard 1D backstripping techniques for individual wells, combined in two regional sections and six contour maps. The subsidence patterns were integrated together with previous paleostress and kinematic studies, in order to derive the Tertiary kinematics of the buried faults in the Carpathians lower plate. The study revealed accelerated subsidence during the Early Miocene in the western part of the Moesian Platform/Getic Depression, in direct relationship with the opening of a WSW–ENE trending extensional basin. The largest subsidence recorded in the front of the Carpathians took place during the Late Miocene, due to final E-ward emplacement of the thrust sheets. The Late Miocene subsidence showed anomalous high values between the Intramoesian and Trotus faults as a result of the orogenic collision with the East-European Platform northward and acceleration of the subduction process in the SE Carpathians corner. Further Pliocene subsidence continued only in the latter region, the depocenter being shifted southward near the junction with the South Carpathians foreland.

Exhumation of the Danubian nappes system (South Carpathians) during the Early Tertiary: inferences from kinematic and paleostress analysis at the Getic/Danubian nappes contact

Abstract A detailed kinematic study based on the analysis of brittle structures, combined with a description of structures in the adjacent foredeep, allows for the definition of three major tectonic episodes during the Late Cretaceous–Tertiary evolution of the central part of the South Carpathians. Following Middle Cretaceous and older orogenic phases, the first tectonic event that affected the studied area was a Late Cretaceous NNW–SSE oriented contraction, which led to the final major emplacement of the Danubian and Getic nappes. During the Paleogene–Early Miocene, an extension event induced rapid exhumation of the Danubian units, leading to the formation of large normal faults dipping towards both the foreland and the hinterland. This extension, together with dextral rotation of the South Carpathians around the western corner of the Moesian platform, allows for the NE-ward movement of the internal continental blocks with respect to the foreland platforms. In the Late Miocene, E-ward translation of the internal South Carpathians units with respect to the Moesian Platform was accommodated through a large-scale E–W oriented strike–slip corridor within the South Carpathians. The general Paleogene–Early Miocene NE to E-ward rotation and the Late Miocene E-ward translation of the Rhodopian fragment allowed for the accommodation of roll-back and contraction taking place in the East Carpathians.

Modes of basin (de)formation, lithospheric strength and vertical motions in the Pannonian-Carpathian system: Inferences from thermo-mechanical modelling

Abstract After a rapid multiphase evolution and a transition from passive to active rifting during late Early Miocene to Pliocene times, the Pannonian Basin has been subjected to compressional stresses leading to gradual basin inversion during Quaternary times. Stress modelling demonstrates the significance of the interaction of external plate-boundary forces and the effect of gravitational stresses caused by continental topography and crustal thickness variation. Flexural modelling and fission-track studies have elucidated the complex interplay of flexural downloading during collision, followed by rapid unroofing by unflexing and isostatic rebound of the lithosphere. The stretching and subsidence history of the Pannonian Basin, the temporal and spatial evolution of the flexure of the Carpathian lithosphere, and the lithospheric strength of the region reflect a complex history of this segment of the Eurasia-Africa collision zone. The polyphase evolution of the Pannonian-Carpathian system has resulted in strong lateral and temporal variation in thermo-mechanical properties in the area. Modelling results suggest that, as a whole, the Pannonian Basin has been an area of pronounced lithospheric weakness since Cretaceous time, shedding light on the high degree of strain localization in this region. This basin, the hottest in continental Europe, has a lithosphere of extremely low rigidity, making it prone to multiple tectonic reactivations. Another feature is the noticeable absence of lithospheric strength in the mantle lithosphere of the Pannonian Basin. Modelling studies suggest pronounced lateral variations in lithospheric strength along the Carpathians and their foreland, which have influenced the thrust load kinematics and post-collisional tectonic history. The inferences and models discussed in this paper are constrained by a large geophysical database, including seismic profiles, gravity and heat-flow data.

Role of the 3D distributions of load and lithospheric strength in arcuate orogenic arcs: poly-stage subsidence in the Carpathians foredeep.

Abstract It has been widely documented that the depth of foredeeps does not always reflect the topography of the neighboring orogens. In many cases, the topographic load is insufficient to explain basin subsidence. Such is the case of the SE Carpathians where an anomalously deep (almost 13 km) foreland basin has evolved since the Middle Miocene (Badenian). A peculiar feature of this basin is its position relative to the orogen. In contrast to typical foredeeps, which deepen towards the belt, the maximum depth of this basin is 10–20 km out of the orogen. The subsidence in the Carpathians Bend foreland is characterized by two stages: the first is Middle Miocene (Badenian) in age and is related to NE–SW extension when fault-bounded basins were formed. Modeling shows that the foreland underwent small pre-orogenic uniform thinning. The modeling also predicts

The link between tectonics and sedimentation in back‐arc basins: New genetic constraints from the analysis of the Pannonian Basin

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.

The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea.

Understanding the natural evolution of a river-delta-sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River-western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during orogenic evolution, as commonly observed in the Mediterranean area and discussed elsewhere.

Kinematics of a former oceanic plate of the Neotethys revealed by deformation in the Ulukışla basin (Turkey)

Kinematic reconstruction of modern ocean basins shows that since Pangea breakup a vast area in the Neotethyan realm was lost to subduction. Here we develop a first-order methodology to reconstruct the kinematic history of the lost plates of the Neotethys, using records of subducted plates accreted to (former) overriding plates, combined with the kinematic analysis of overriding plate extension and shortening. In Cretaceous-Paleogene times, most of Anatolia formed a separate tectonic plate—here termed “Anadolu Plate”—that floored part of the Neotethyan oceanic realm, separated from Eurasia and Africa by subduction zones. We study the sedimentary and structural history of the Ulukisla basin (Turkey); overlying relics of this plate to reconstruct the tectonic history of the oceanic plate and its surrounding trenches, relative to Africa and Eurasia. Our results show that Upper Cretaceous-Oligocene sediments were deposited on the newly dated suprasubduction zone ophiolites (~92 Ma), which are underlain by melanges, metamorphosed and nonmetamorphosed oceanic and continental rocks derived from the African Plate. The Ulukisla basin underwent latest Cretaceous-Paleocene N-S and E-W extension until ~56 Ma. Following a short period of tectonic quiescence, Eo-Oligocene N-S contraction formed the folded structure of the Bolkar Mountains, as well as subordinate contractional structures within the basin. We conceptually explain the transition from extension, to quiescence, to shortening as slowdown of the Anadolu Plate relative to the northward advancing Africa-Anadolu trench resulting from collision of continental rocks accreted to Anadolu with Eurasia, until the gradual demise of the Anadolu-Eurasia subduction zone.

Tectonic Models for the Evolution of Sedimentary Basins

The tectonic evolution of sedimentary basins is the intrinsic result of the interplay between lithospheric stresses, lithospheric rheology, and thermal perturbations of the lithosphere–upper mantle system. The thermomechanical structure of the lithosphere exerts a prime control on its response to basin-forming mechanisms, in both extension and compression. Tectonic reactivation has strongly affected the structure and fill of many sedimentary basins. The long-lasting rheological memory of the lithosphere appears to play a far more important role in basin reactivation than hitherto assumed. The temporal evolution of the strength of continents and the spatial variations in stress and strength at continental margins, rifts, and orogenic belts govern the mechanics of basin development in time and space. Polyphase deformation is a common feature of many sedimentary basin systems. Compressional reactivation of extensional basins during their postrift phase appears to occur in many intraplate rifts and passive margins, reflecting temporal and spatial changes in the orientation and magnitude of the intraplate stress regime. Similarly, foreland basins are frequently characterized by preorogenic extension. The actual subsidence patterns of these polyphase systems are often more complex than predicted by end-member models that only consider the basin formation mechanism. Folding of the lithosphere, involving positive and negative deflections, appears to be of more importance in the large-scale deformation of intraplate domains than hitherto realized. In the intraplate domain of continental Europe that was thermally perturbed by Cenozoic upper mantle plume activity, lithospheric folding, for instance, plays an important role and strongly affects the pattern of vertical motions, in terms of both the basin subsidence and the uplift of broad arches. Tectonic processes operating during basin formation and during the subsequent deformation of basins can generate significant differential topography in basin systems. In view of the close link between erosion of topographic highs and sedimentation in subsiding areas, constraints are needed on uplift and coeval subsidence to validate quantitative process-oriented models for the evolution of sedimentary basins. Integration of analog and numerical modeling provides a novel approach to assess the feedback mechanisms between deep mantle, lithospheric, and surface processes.