Rafał Szaniawski

Interplay between the thermal evolution of an orogenic wedge and its retro-wedge basin: An example from the Ukrainian Carpathians

The Carpathian-Pannonian region is made up of the wide extensional Pannonian Basin surrounded by the Carpathian mountain belt. The Pannonian Basin formed in the Miocene by extension in a retro-wedge position while thrusting was still active at the Carpathian front. The Ukrainian region is an ideal area to reconstruct the relationship between the Pannonian Basin and the Carpathians, due to the relatively simple structural setting and to the progressive but neat transition between the two domains. This study uses low-temperature thermochronometry and vitrinite reflectance analysis to investigate the effect of the opening of the Pannonian Basin on the thermal and burial-exhumation histories of the Ukrainian Carpathians. The results show heating and burial maxima in the central units of the wedge (up to ~170 °C and 6 km, respectively), tapering out toward both the innermost and the outermost thrust sheets. Cooling and exhumation occurred by means of a first rapid stage between ca. 12 and 5 Ma (exhumation rates of up to ~1 mm/yr), followed by a slower stage from ca. 5 Ma to the present (exhumation rates within 0.5 mm/yr). Timing and spatial pattern of exhumation are compatible with post-thrusting erosion enhanced by isostatic uplift. The extent of exhumation progressively decreases toward the Pannonian Basin, characterized by a thinned crust. No further significant influence of the Pannonian Basin opening on the thermal and burial history of the Ukrainian Carpathians may be inferred based on our results, whereas the comparison of the tectonothermal evolution of the two domains suggests that they are both controlled by the same lithospheric processes.

Coupling sequential restoration of balanced cross sections and low-temperature thermochronometry: The case study of the Western Carpathians

In this paper, a new approach is applied to test a proposed scenario for the tectonic evolution of the Western Carpathian fold-and-thrust belt–foreland system. A N-S balanced section was constructed across the fold-and-thrust belt, from the Polish foreland to the Slovakia hinterland domain. Its sequential restoration allows us to delineate the tectonic evolution and to predict the cooling history along the section. In addition, the response of low-temperature thermochronometers (apatite fission-track and apatite [U-Th]/He) to the changes in the fold-and-thrust belt geometry produced by fault activity and topography evolution are tested. The effective integration of structural and thermochronometric methods provides, for the first time, a high-resolution thermo-kinematic model of the Western Carpathians from the Early Cretaceous onset of shortening to the present day. The interplay between thick- and thin-skinned thrusting exerts a discernible effect on the distribution of cooling ages along the profile. Our analysis unravels cooling of the Outer Carpathians since ca. 22 Ma. The combination of thrust-related hanging-wall uplift and erosion is interpreted as the dominant exhumation mechanism for the outer portion of the orogen. Younger cooling ages (13–4 Ma) obtained for the Inner Carpathian domain are mainly associated with a later, localized uplift, partly controlled by extensional faulting. These results, which help unravel the response of low-temperature thermochronometers to the sequence of tectonic events and topographic changes, allow us to constrain the tectonic scenario that best honors all available data.

Syn-folding remagnetization events in the French-Belgium Variscan thrust front as markers of the fold-and-thrust belt kinematics

New paleomagnetic studies have been carried out within the Ardennes segment of the N France - S Belgium Variscan fold-and-thrust belt to set constraints on the fold-thrust belt kinematics and reveal the casual relationships between vertical-axis rotations and major strike deviated zones localised along the general trend of the belt. Magnetite-bearing Devonian and Carboniferous limestones yielded two characteristic, secondary components of the natural remanent magnetization : a low temperature component recorded most probably during the late stages of folding and a high temperature component, acquired during incipient stages of deformation. Both post- and synfolding magnetizations were identified in the Lower Devonian hematite bearing sandstones. Ages of magnetization, inferred from the analysis of characteristic remanence inclinations compared to the reference curves for the stable parts of the Old Red Sandstones Continent (ORC), suggest the previous remagnetization event to be due to the burial of sedimentary rocks under the thick molassic foreland basin of Namurian-Westphalian age and the second to the final out-of-sequence activation of the thrust front in Stephanian times. Irrespective of the age of the magnetizations, orientations of paleomagnetic directions are dominantly governed by second-order structural trends. Clockwise rotations are observed in relatively narrow zones featuring deviated orientations of fold axes, other sites show paleomagnetic directions akin to those known from the ORC. We interpret this feature as a result of local transpressive deformations and related rotations, which occurred at lateral borders of propagating thrust-sheets. The latter deformation zones are suggested to be controlled by deep-seated discontinuities inherited from the Devonian Rheno-hercynian basin development. The Ardennes thrust belt was thus not rotated as a whole unit with respect to the ORC after the Namurian, preserving the initial orientation of the continental margin.

Building and exhumation of the Western Carpathians: new constraints from sequentially restored, balanced cross‐sections integrated with low‐temperature thermochronometry

Western Carpathian orogeny has been the subject of intense scientific debate due to the occurrence of enigmatic features, leading several authors to provide contrasting geological models. In this paper, a new interpretation for the tectonic evolution of the Western Carpathians is provided based on: (i) an analysis of the stratigraphy of the Mesozoic-Tertiary successions across the thrust belt domains; (ii) a reappraisal of the stratigraphy and sedimentology of the tectonic melange (i.e. the so-called Pieniny Klippen Belt) marking the suture between the Inner and Outer Carpathians; and (iii) the construction of a series of balanced and restored cross-sections, validated by 2D forward modeling. Our analysis provides a robust correlation of the stratigraphy from the Outer to the Inner Carpathians, independently of the occurrence of oceanic lithosphere in the area, and allows for the reinterpretation of the tectonic relationships among the Inner Carpathians, the Outer Carpathians and the Pieniny Klippen Belt and the exhumation mechanisms affecting this orogenic belt. In order to constrain the evolution during the last 20 Ma, our model also integrates previously published and new apatite fission track and apatite (U-Th-Sm)/He data. These latter indicate a Middle-Late Miocene exhumation of the Pieniny Klippen Belt. In this study, the recent regional uplift of the Pieniny Klippen Belt is described for the first time using a 2D kinematic model for the tectonic evolution of the Western Carpathians.

Formation of intracontinental basins in the opposite corners of the Tabas block as coeval structures controlled by transpressional faulting, Iran

The interaction of strike-slip faults in their restraining junctions allowed for the coeval formation of the Tabas and Abdoughi Basins and led to their inversion during the late Cenozoic. The intracontinental basins filled with Neogene and Quaternary deposits were controlled by large-scale dextral transpression along major faults that bounded the Tabas block, which is a part of the Central Iranian block. The anastomosing strike-slip fault pattern facilitated the development of both basins in opposite corners of the Tabas block. The subsided areas were formed as a result of interaction between the restraining junctions of strike-slip faults and thrusts. Flexural loading caused by the uplifted series of thrust sheets resulted in the depression of the opposite fault slabs, which permitted deposition of Neogene sediments. Deformation according to the “bookshelf” mechanism can be considered as a consequence of accommodation of the shortening of the area north of the Main Zagros thrust and externally imposed shearing along the Great Kavir (Doruneh) fault during the collision of the Arabian and Eurasian plates. Related processes of transpression and counterclockwise rotation of the tectonic blocks included in the Central Iranian block favored the interaction of strike-slip faults. The change of far-field stress and continuous transpression caused inversion of the basins and formation of Neogene folds in the northern and southern corners of the Tabas block. The geomorphic features observed along these strike-slip faults and on the thrust surfaces bounding the folds display their recent activity, consistent with present-day seismicity and geodetic measurements within the Central Iranian block.

Applying the anisotropy of magnetic susceptibility technique to the study of the tectonic evolution of the West Spitsbergen Fold-and-Thrust Belt

We demonstrate the use of the anisotropy of magnetic susceptibility (AMS) method to determine the orientation of the principal tectonic strain directions developed during the formation of the West Spitsbergen Fold-and-Thrust Belt (WSFTB). The AMS measurements and extensive rock-magnetic studies of the Lower Triassic rocks reported here were focused on the recognition of the magnetic fabric, the identification of ferromagnetic minerals and an estimation of the influence of ferro- and paramagnetic minerals on magnetic susceptibility. At most sites, the paramagnetic minerals controlled the magnetic susceptibility, and at only one site the impact of ferromagnetic minerals was higher. The AMS technique documented the presence of different types of magnetic fabrics within the sampled sites. At two sites, a normal (Kmin perpendicular to the bedding) magnetic fabric of sedimentary origin was detected. This was associated with a good clustering of the maximum AMS axes imposed by tectonic strain. The Kmax magnetic lineation directions obtained here parallel the general NNW–SSE trend of the WSFTB fold axial traces and thrust fronts. The two other investigated sites possessed mixed and inverted fabrics, the latter of which appear to reflect the presence of iron-bearing carbonates.

Palaeomagnetic dating of brittle tectonics structures : case studies on Ferques fault (Boulonnais, France) and two faults from the Holy Cross Mountains (Poland)

Abstract Calcite and sedimentary fills in fractures cutting the Upper Devonian carbonates in the Holy Cross Mountains (HCM) and Boulonnais (B) were dated palaeomagnetically by comparison with the Apparent Polar Wander Path (APWP) for Baltica in order to constrain age of faults. Here we present results obtained from calcite and sedimentary fills of two selected faults as case studies. Hematite-bearing elastics and calcite possessed well-defined components of natural remanent magnetization (NRM) that were preserved up to thermal demagnetization at ca. 500 °C. Two components in Rzepka calcite (HCM) and one component residing in elastics within Ferques Fault (B) could be determined. Comparison of directions of these components with reference directions calculated from the APWP for Baltica constrains the upper age limit for the Ferques Fault to Middle Triassic, while Rzepka and Jazwica faults may be no younger than Late Permian. Generally, the remanence from fracture fills may be useful for dating related tectonics, karst phenomena or mineralization processes.