Structural evolution of the Turňa Unit constrained by fold and cleavage analyses and its consequences for the regional tectonic models of the Western Carpathians

Abstract

Abstract:The Turňa Unit (Turnaicum, Tornaicum) is one of the three nappe systems involved in the geological structure of the inner zones of the Western Carpathians. The unit is formed by a system of partial nappes and duplexes, which overlie the Meliata Unit s.l. and are overridden by the Silica Nappe. The Slovenská skala partial nappe in the investigated area includes clastic sediments of the mid-Carboniferous, Permian and Early Triassic age, followed by mostly deep-water Middle-Upper Triassic succession predominantly composed of carbonates. Structural analysis of cleavage planes and folds was carried out predominantly in the Lower Triassic Werfen Formation. The measured deformational structures are polygenetic and were principally formed in three successive deformation stages. The first deformation stage is represented by bedding-parallel, very low-grade metamorphic foliation that was related to nappe stacking and formation of the Mesozoic accretionary wedge during the latest Jurassic and earliest Cretaceous. The second deformation stage is represented by systems of open to closed, partly asymmetric folds with SW-NE oriented, steeply NW-or SE-dipping axial-plane cleavage. Regionally, the folded bedding planes are usually moderately SE-ward dipping, the NW-ward and subvertical dips are less common. The mesoscopic fold structures predominantly occur in the SW-NE trending anticlinal and synclinal hinge zones of large-scale folds. These structures evolved in a compressional tectonic regime with the NW-SE to N-S orientation of the maximum compressional axis. The third observed deformation stage was activated during ENE-WSW oriented shortening. This stage is chiefly represented by open, kink-type folds. Some inferences for regional structures and tectonic evolution of the area are discussed as well.

Continuity and Episodicity in the Early Alpine Tectonic Evolution of the Western Carpathians: How Large‐Scale Processes Are Expressed by the Orogenic Architecture and Rock Record Data

“…From bottom to top these are the Meliatic, Turnaic, and Silicic nappe systems. The Meliata Superunit (Meliaticum) includes three different types of units, although their mutual transitions and/or tectonic mixing are present as well (see also Lačný et al, 2016). These are (1) the high-pressure and low-temperature (HP/LT) metamorphosed unit (Bôrka Nappe) in the lowermost structural position, overridden by and partly imbricated with (2) ophiolite-bearing polygenic mélanges (Jaklovce Unit), and (3) sedimentary mélange-olistostrome complexes with poorly presented ophiolitic material (Meliata Unit s.s., Telekesoldal complex in the Rudabánya Mts).…”

Origin and Age Determination of the Neotethys Meliata Basin Ophiolite Fragments in the Late Jurassic–Early Cretaceous Accretionary Wedge Mélange (Inner Western Carpathians, Slovakia)

“…The Meliatic nappe outliers are overlain by the Turňa (in Slovakia)/Torna (in Hungary) Nappe [34,63,64], and the Turnaicum is composed of very low-grade to low-grade Upper Carboniferous, Permian, and Lower Triassic clastic sequences, lower Anisian platform carbonates and upper Anisian to Upper Triassic pelagic limestones and shales. These are partly imbricated with the underlying Meliatic complexes [34,40,63,65]. The uppermost tectonostratigraphic unit is the Silica Nappe [6,66] composed of Triassic-Jurassic successions, and this nappe system continues in the Aggtelek-Rudabánya Hills north of the Bükk Mountains and the Darnó line in Hungary [34].…”

Geological evolution of the southwestern part of the Veporic Unit (Western Carpathians): based on fission track and morphotectonic data

“…with Putiš et al 2014Putiš et al , 2015Lačný et al 2016). In these early convergent stages, the Veporic Unit suffered an internal shortening and thickening documented by upright folding.…”

“…1). This Eo-Alpine nappe pile is tectonically overlain by the Jurassic Meliata subduction-accretionary complex (Kozur & Mock 1973Faryad 1995;Faryad & Henjes-Kunst 1997;Lačný et al 2016) and by the Silicic thin-skinned nappe system (e.g., Mello 1979) and is exposed from beneath the post-nappe Palaeogene and Neogene sedimentary formations and Neogene to Quaternary volcanites or volcano-sedimentary covers (Dublan et al 1997a,b).…”