Dušan Plašienka

Development of basement-involved fold and thrust structures exemplified by the Tatric–Fatric–Veporic nappe system of the Western Carpathians (Slovakia)

Abstract The Tatric-Fatric-Veporic convergence zone of the Central Western Carpathians involved a basinal area that originated by Lower Jurassic rifting of Variscan continental crust. In mid-Cretaceous times shortening affected first the southern, Veporic margin of the basin, which was converted to the toe of the orogenic wedge prograding from the hinterland. A system of ductile basement/cover large-scale folds formed here by rotation of pre-existing, closely spaced, domino-type normal faults. However, the advancement of the wedge was likely accomplished by formation of a new thrust fault rooted in the ductile lower and/or middle crust. Afterwards, the basement of the lower plate Fatric basin was underthrust below the Veporic wedge; its sedimentary fill was detached and stacked to create the later Križna decollement cover nappe. Underthrusting continued until the lower plate–Tatric margin collided with the orogenic wedge toe. Large basement slabs were peeled off this margin, shortened internally and thrust at moderate distances over the South Tatric ridge area. Pre-existing domino blocks were only slightly inverted here and passively transported above new thrust faults, which formed along weak crustal layers. It is inferred that the origin and geometry of large-scale, basement-involved structures generated in wide, intracontinental convergent zones is largely dependent on the lower versus upper plate position with distinctly different thermo-mechanical regimes operating during deformation.

Passive and active margin history of the northern Tatricum (Western Carpathians, Slovakia)

The Tatricum, an upper crustal thrust sheet of the Central Western Carpathians, comprises pre-Alpine crystalline basement and a Late Paleozoic-Mesozoic sedimentary cover. The sedimentary record indicates gradual subsidence during the Triassic, Early Jurassic initial rifting, a Jurassic-Early Cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods, and Middle Cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland. Passive rifting led to the separation of the Central Carpathian realm from the North European Platform. A passive margin, rimmed by peripheral half-graben, was formed along the northern Tatric edge, facing the Vahic (South Penninic) oceanic domain. The passive versus active margin inversion occurred during the Senonian, when the Vahic ocean began to be consumed southwards below the Tatricum. It is argued that passive to active margin conversion is an integral part of the general shortening polarity of the Western Carpathians during the Mesozoic that lacks features of an independent Wilson cycle. An attempt is presented to explain all the crustal deformation by one principal driving force - the south-eastward slab pull generated by the subduction of the Meliatic (Triassic-Jurassic Tethys) oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere.

Kinematics and metamorphism of a cretaceous core complex: The veporic unit of the Western Carpathians

Abstract The Veporic basement and its Permian-Mesozoic cover experienced medium-pressure, collision-related metamorphism during the Cretaceous. Geothermobarometric calculations of Alpine mineral assemblages indicate peak conditions of 8–12 kbar and 550–600°C in the deepest-exposed basement, and up to 8 kbar and 450–500°C in the Permian metasediments. After having reached the metamorphic peak conditions (at around 110 Ma, 40 Ar/ 39 Ar on amphiboles), the thermally softened Veporic unit was exhumed probably due to the underplating of a buoyant Tatric-Fatric crust. Exhumation was triggered by extensional denudation of former upper-crustal thrust units, overlying the Veporic unit. Unroofing was accomplished due to orogenparallel, top-to-east extension along low-angle, ductile normal shear zones. The area collapsed and rapidly cooled at 90-80 Ma ( 40 Ar/ 39 Ar on micas). As revealed by the structural record, the doming and tectonic exhumation of the Veporic core occurred in an overall contractional regime and was followed by additional Late Cretaceous—Early Tertiary shortening events.

Progradation of the Alpidic Central Western Carpathians orogenic wedge related to two subductions: constrained by 40Ar/39Ar ages of white micas

To reveal a model of the polystage evolution of an orogenic wedge subsequent to two subductions, 40Ar/39Ar dating of white micas (Wmca) across the shear zones in the Central Western Carpathians (CWC) has been carried out. This wedge is limited by the two suture zones, as a remnant after subducted oceanic crust of the Neotethyan Meliatic (in the S) and South-Penninic (in the N) oceans. It is composed of a system of basement and cover nappes, separated by major shear zones. Wmca aggregates from different microstructural and grain-size domains of lower- to medium-grade blastomylonites were dated by the 40Ar/39Ar method. The minimum age of NW-ward thrusting of the Gemeric and Meliatic nappes over the South-Veporic nappes in the southern part of this wedge was detected around 100 Ma. The NE-SW trending sinistral transpression, combined with a top-to-the SE extensional exhumation was dated at 90 – 85 Ma in the South-Veporic unit. Collision continued at ca. 95-90 Ma in the central part of the North-Veporic unit, while in the frontal part and in the Tatric and Infratatric units it was identified at 80 – 70 Ma. Lateral extrusion of the Tatric unit towards the NE occurred in Early Eocene, at ca. 50 Ma, indicating a final evolutionary stage of this wedge. The younging of ages from S to N revealed that footwall-propagating thrust-faults were responsible for the growth of the orogenic wedge.

Structural pattern and emplacement mechanisms of the Krížna cover nappe (Central Western Carpathians)

Structural pattern and emplacement mechanisms of the Krížna cover nappe (Central Western Carpathians) The Central Western Carpathians are characterized by both the thick- and thin-skinned thrust tectonics that originated during the Cretaceous. The Krížna Unit (Fatric Superunit) with a thickness of only a few km is the most widespread cover nappe system that completely overthrusts the Tatric basement/cover superunit over an area of about 12 thousands square km. In searching for a reliable model of its origin and emplacement, we have collected structural data throughout the nappe body from its hinterland backstop (Veporic Superunit) to its frontal parts. Fluid inclusion (FI) data from carbonate cataclastic rocks occurring at the nappe sole provided useful information about the p-T conditions during the nappe transport. The crucial phenomena considered for formulation of our evolutionary model are: (1) the nappe was derived from a broad rifted basinal area bounded by elevated domains; (2) the nappe body is composed of alternating, rheologically very variable sedimentary rock complexes, hence creating a mechanically stratified multilayer; (3) presence of soft strata serving as décollement horizons; (4) stress and strain gradients increasing towards the backstop; (5) progressive internal deformation at very low-grade conditions partitioned into several deformation stages reflecting varying external constraints for the nappe movement; (6) a very weak nappe sole formed by cataclasites indicating fluid-assisted nappe transport during all stages; (7) injection of hot overpressured fluids from external sources (deformed basement units) facilitating frontal ramp overthrusting under supralithostatic conditions. It was found that no simple mechanical model can be applied, but that all known principal emplacement mechanisms and driving forces temporarily participated in progressive structural evolution of the nappe. The rear compression operated during the early stages, when the sedimentary succession was detached, shortened and transported over the frontal ramp. Subsequently, gravity spreading and gliding governed the final nappe emplacement over the unconstrained basinal foreland.

Study of pressure-induced amorphization in sulfur usingab initiomolecular dynamics

We report results of ab initio constant-pressure molecular dynamics simulations of sulfur compression leading to structural transition and pressure-induced amorphization. Starting from the orthorhombic S-I phase composed of S8 ring molecules we find at room temperature and pressure of 20 GPa a transformation to monoclinic phase where half of the molecules develop a different conformation. Upon further compression, the monoclinic phase undergoes pressure-induced amorphization into an amorphous phase, in agreement with experiments. We study the dynamics of the amorphization transition and investigate the evolution of intra and intermolecular distances in the monoclinic phase in order to provide a microscopic insight into the rings disintegration process leading to amorphization. In the amorphous form we examine the structural properties and discuss its relation to the experimentally found amorphous form and to underlying crystal phases as well. The amorphous form we find appears to correspond to the experimentally observed low density amorphous form.

Ophiolitic detritus in Kimmeridgian resedimented limestones and its provenance from an eroded obducted ophiolitic nappe stack south of the Northern Calcareous Alps (Austria)

Abstract The causes for the Middle to Late Jurassic tectonic processes in the Northern Calcareous Alps are still controversially discussed. There are several contrasting models for these processes, formerly designated “Jurassic gravitational tectonics”. Whereas in the Dinarides or the Western Carpathians Jurassic ophiolite obduction and a Jurassic mountain building process with nappe thrusting is widely accepted, equivalent processes are still questioned for the Eastern Alps. For the Northern Calcareous Alps, an Early Cretaceous nappe thrusting process is widely favoured instead of a Jurassic one, obviously all other Jurassic features are nearly identical in the Northern Calcareous Alps, the Western Carpathians and the Dinarides. In contrast, the Jurassic basin evolutionary processes, as best documented in the Northern Calcareous Alps, were in recent times adopted to explain the Jurassic tectonic processes in the Carpathians and Dinarides. Whereas in the Western Carpathians Neotethys oceanic material is incorporated in the mélanges and in the Dinarides huge ophiolite nappes are preserved above the Jurassic basin fills and mélanges, Jurassic ophiolites or ophiolitic remains are not clearly documented in the Northern Calcareous Alps. Here we present chrome spinel analyses of ophiolitic detritic material from Kimmeridgian allodapic limestones in the central Northern Calcareous Alps. The Kimmeridgian age is proven by the occurrence of the benthic foraminifera Protopeneroplis striata and Labyrinthina mirabilis, the dasycladalean algae Salpingoporella pygmea, and the alga incertae sedis Pseudolithocodium carpathicum. From the geochemical composition the analysed spinels are pleonastes and show a dominance of Al-chromites (Fe3+–Cr3+–Al3+ diagram). In the Mg/(Mg+ Fe2+) vs. Cr/(Cr+ Al) diagram they can be classified as type II ophiolites and in the TiO2 vs. Al2O3 diagram they plot into the SSZ peridotite field. All together this points to a harzburgite provenance of the analysed spinels as known from the Jurassic suprasubduction ophiolites well preserved in the Dinarides/Albanides. These data clearly indicate Late Jurassic erosion of obducted ophiolites before their final sealing by the Late Jurassic–earliest Cretaceous carbonate platform pattern.

Experimental and computational studies on toughness enhancement in Ti-Al-Ta-N quaternaries

Design of hard ceramic material coatings with enhanced toughness, which prevents crack formation/propagation leading to brittle failure during application, is a primary industrial requirement. In this work, experimental methods supported by ab initio density functional theory (DFT) calculations and electronic structure analyses are used to investigate the mechanical behavior of magnetron sputtered Ti-Al-Ta-N hard coatings. The as-deposited Ti1-x-yAlxTayN (y = 0–0.60) films exhibit a single phase cubic sodium chloride (B1) structure identified as TiAl(Ta)N solid solutions. While the hardness H of Ti0.46Al0.54N (32.5 ± 2 GPa) is not significantly affected by alloying with TaN (H of the quaternary nitrides varies between 26 ± 2 and 35 ± 4 GPa), the elastic stiffness monotonically decreases from 442 to 354 GPa with increasing Ta contents, which indicates improved toughness in TiAlTaN. Consistent with the experimental findings, the DFT results show that Ta substitutions in TiAlN reduce the shear resistance due...

Structural evolution in high-pressure amorphous CO 2 from ab initio molecular dynamics

By employing ab initio molecular dynamics simulations at constant pressure we investigated behavior of amorphous carbon dioxide between 0-100 GPa and 200-500 K. We focused on evolution of the high-pressure polymeric amorphous form known as a-carbonia on its way down to zero pressure, where it eventually converts into a molecular state. During the simulations we observed a spectrum of amorphous forms between two limiting polymeric forms with different proportion of three and four-coordinated carbon atoms. Besides that we also found a new mixed molecular-polymeric form that shows pronounced metastability at certain conditions. The observed behavior suggests CO2 as possible candidate for polyamorphism. We discuss structural and physical properties of the observed amorphous forms as well as their relations to crystalline phases.

Evolution of Late Cretaceous–Palaeogene synorogenic basins in the Pieniny Klippen Belt and adjacent zones (Western Carpathians, Slovakia): tectonic controls over a growing orogenic wedge

Ab stract: The Pieniny Klippen Belt and neigh bour ing zones of the West ern Carpathians rep re sent an an cient accretionary wedge that de vel oped dur ing the meso-Alpidic (Coniacian–Eocene) tec tonic ep och. Af ter an over view of the ex ten sive lit er a ture data, the au thors pres ent an in ter pre ta tion of the synorogenic sed i men tary re cord of these zones as be ing re lated to var i ous en vi ron ments of the fore land ba sin sys tem con sist ing of the trench-foredeep and wedge-top depositional ar eas. The pe riph eral trench-foredeep depozones mi grated from the South PenninicVahic oce anic realm to wards the Oravic con ti nen tal frag ment in an intra-Penninic po si tion, where the synorogenic de pos its were laid down with coars en ingand thick en ing-up ward trends be fore be ing overthrust by the prop a gat ing orogenic wedge tip. The de vel op ment of wedge-top, pig gy back bas ins (Gosau Supergroup) was con trolled by the dy nam ics of the un der ly ing wedge, com posed of fron tal el e ments of the Fatric and Hronic cover nappe sys tems of the Cen tral West ern Carpathians (Austroalpine units). Sev eral compressional and extensional events are doc u mented in the com plex sed i men tary and struc tural rock re cords within the wedge and re lated bas ins. The suc ces sive transgressive-regressive depositional cy cles and cor re spond ing de for ma tion stages are in ter preted in terms of a dy namic accretionary wedge that main tained the crit i cal taper only tran siently. The super criti cal taper states are re flected in re gres sion, shallowing and ero sion in the wedge-top area, while the trench was sup plied with large amounts of clastics by var i ous grav ity-flow types. On the other hand, the col lapse stages tend ing to subcritical wedge taper are in di cated by wide spread ma rine trans gres sions or in gres sions in the wedge-top area and a gen eral deep en ing of all bas ins to bathyal con di tions. Ac cord ingly, the evo lu tion of the en tire trench-foredeep and wedge-top ba sin sys tems was prin ci pally con trolled by the com plex in ter play of the re gional tec tonic evo lu tion of the Al pine-Carpathian orogenic sys tem, lo cal wedge dy nam ics and eustatic sea-level fluc tu a tions.