The Western Carpathians are an arc-shaped mountain range, the northern branch of the Alpine-Himalayan fold and thrust system called the Alpide belt, which evolved during the Alpine orogeny. In particular, their pre-Cenozoic evolution is very similar to that of the Eastern Alps, and they constitute a transition between the Eastern Alps and the Eastern Carpathians.
The geological evolution of individual parts of the chain is complex, a result of tectonic processes like folding, thrusting and the formation of sedimentary basins of various types during the Mesozoic and Cenozoic. These processes sometimes affected not only the sedimentary fill of the basins, but also, in some cases, the former basement.
Many aspects of the geological structure of the Western Carpathians have not been completely studied and are subject to ongoing research and debate. The appropriate classification of a number of specific tectonic units is still not clear.
Geological definition
The Western Carpathians are separated from the Alps by the valley of the river Danube (only from the geographical point of view; the geological boundary is the so-called Carnuntum gate) and the Raaba line.Mísař, Z., 1987: Regionální geologie světa. Academia, Praha, 708 pp. To the east, the boundary with the Eastern Carpathians is placed formally in the valley of the river Uzh, but many tectonic divisions consider the Hornád fault system on the line Košice – Prešov the real geological boundary. The northern boundary is the thrust front that separates the nappes from the Carpathian Foredeep. In the Czech Republic the line Znojmo-Přerov-Karviná approximately forms the western boundary of the Western Carpathians. The southern boundary is not distinct (because of the interfingering boundary between the Carpathians and lowlands of the Pannonian Basin). According to some views it is south of the Bükk and Mátra mountains in Hungary.
Geological structure
There are several interpretations of the tectonic structure of the Western Carpathians. For quite a long time, the triple division has been used (Outer, Central and Inner Western Carpathians),Mišík, M., Chlupáč, I., Cicha, I., 1984: Historická a stratigrafická geológia. Slovenské pedagogické nakladateľstvo, Bratislava, 541 pp.Maheľ, M., 1986: Geologická stavba československých Karpát. Paleoalpínske jednotky 1. Veda, Bratislava, 503 pp.Plašienka, D., Grecula, P., Putiš, M., Kováč, M. a Hovorka, D., 1997: Evolution and structure of the Western Carpathians: an overview. in Grecula, P., Hovorka, D., Putiš, M. (Eds.) Geological evolution of the Western Carpathians. Mineralia Slovaca - Monograph, Košice, pp. 1 – 24Plašienka, D., 1999: Tektochronológia a paleotektonický model jursko-kriedového vývoja centrálnych Západných Karpát. Veda, 125 pp. while some geologists prefer the classical double division (Outer and Inner Carpathians).Biely, A. (Editor) 1996: Explanation to geological map of Slovakia. Dionýz Štúr Publishers, Bratislava, 76 pp.Hók, J., Kahan, Š., Aubrecht, R., 2001: Geológia Slovenska. Univerzita Komenského, Bratislava, 43 pp.Vozár, J., Vojtko, R., Sliva, Ľ., (Editors) 2002: Guide to geological excursion. XVIIth Congress of Carpathian-Balkan Geological Association. Dionýz Štúr Publishers, Geological survey of Slovak republic, Bratislava, 163 pp. Other ideas of division may differ, such as morphotectonic (based on geology and geomorphology) or regional geology. Tectonic division applied in this article is based on the division of Plašienka and others in 1997, later modified in 1999 and in 2002 together with Kováč,Kováč, M., Plašianka, D., 2002: Geological structure of the Alpine-Carpathian-Pannonian junction and neighbouring slopes of the Bohemian Massif. Comenius University, Bratislava, 88 pp. although it cannot be considered definitive.
The three main areas of the Inner, Central, and Outer Western Carpathians are divided by two sutures. The Meliata suture is an area of closure of the Triassic-Jurassic Meliata Ocean during the Kimmerian phase. It constitutes the boundary between the Central and Inner Western Carpathians. The position of the boundary is disputable; different authors place the Meliata suture in different areas. It is identified with the Rožňava line, Lubeník-Margecany Line, or possibly placed even more to the South. The second important suture is called the Peri-Pieninic lineament, roughly copying the structure of Pieniny Klippen Belt. This important dislocation divides the Central and Outer Western Carpathians. Deeper under the sediments it constitutes the boundary between the Central Carpathian basement rocks and the foreland – the Bohemian Massif and East European craton (Podolia platform). Since the 1980s the dividing line has been considered the suture of the Vahic Ocean – the Eastern continuation of the Piemont-Liguria Ocean.
Foreland The foreland of the Western Carpathians in the West and North is composed of the Bohemian Massif and Cracow Plateau. In the Northeast it is formed by the rock of the East European craton. These areas were consolidated earlier than the Carpathians. The Bohemian Massif, which is the youngest part of the foreland, evolved during the Hercynian orogeny about 200 million years before the orogeny in the Carpathians.
Outer Western Carpathians The Outer Western Carpathians were formed during orogeny that took part since the Upper Cretaceous (Senonian) and Miocene periods, which is later than the Central Western Carpathians. Pieniny Klippen Belt was affected by thrusting together with the Central Carpathians and later folded and thrust again together with the Flysch Belt.
Foredeep Thrust of the Carpathians on their foreland caused a flexure of the lower continental plate under the frontal part of the nappes. This area, called the Carpathian Foredeep, was filled by thick formations of molasse, prevailingly marls, sandstones and conglomerates that were formed in the Oligocene to Miocene periods by erosion of the growing Carpathians. Nevertheless, the foredeep is not generally folded; flysch nappes thrust from the south partially folded the rock underneath. The whole zone of the foredeep is developed in the foreland of the Alps, and runs through the Moravia to the Ostrava Basin and further East to Poland, Ukraine, and Romania.
Flysch Belt
The Flysch Belt was named after a characteristic alteration of sandstone and claystone, so called flysch, occurring in the Cretaceous to Paleogene (possibly Miocene) age in the area. The belt is the accretionary wedge of the Carpathians. The Flysch Belt also contains a small volume of Cenozoic volcanic rocks. The zone originally consisted of a set of more sedimentary basins that were in constant tectonic transformation. Raised parts of the basins formed elevations, which were eroded and supplied deeper parts of the basin with clastic sediments that were brought by turbidity currents. Orogeny affected the area at the end of the Paleogene and in the beginning of the Neogene in the so-called Savian phase. Other portions were also affected by the Styrian phase, which caused partial thrusting over the Foredeep. Nappes were formed by gradual compression of the sedimentary basins that caused their inversion and separation of sedimentary successions from their basement and their movement for distance of 20 – 30 km, and possibly more. Nappes were formed in two phases: the outer (Northern) or lower group of nappes called the Silezia-Krosno Belt, and the overriding internal (Southern) Magura Belt. Nappes are thrust over their foreland in the form of tectonic slices. At least part of the Flysch Belt was an Eastern continuation of the Alpine Penninic Zone, probably the Valais branch. A direct continuation of the Alpine Rhine-Danube Flysch can be seen. The Flysch Belt continues through Bohemia, Slovakia, and Poland, and joins the Moldavian Flysch in Ukraine and Romania.
Central Western Carpathians The Central Western Carpathians, sometimes referred as the Slovakocarpathian system, are a zone bounded by the Pieniny Klippen Belt from the North and the Meliata Belt from the South. The Pieniny Klippen Belt is a relatively thin but important dividing line separating the Outer Western Carpathians from the internal zones of orogeny. Together with the similar units of the Peri-Klippen zone it constitutes the Považie-Pieniny Belt. The largest portion of the Western Carpathians consists of the zone built of granitic and metamorphic rock (that metamorphic grade is generally higher in the North and lower in the South), and sedimentary cover overridden by thrust nappes of Mesozoic carbonate rocks. The zone consists of the Tatra-Fatra Belt of core mountains, the Vepor Belt, and the Gemer Belt. In their predominantly crystalline basement zones called the Tatric, Veporic, and Gemeric, thrusting (thick-skinned) is also present, but not as apparent. Geophysical investigation confirmed that the Gemeric is thrust over the Veporic, and the Veporic over the Tatric.Tomek, Č., 1993: Deep crustal structure beneath the central and inner West Carpathians. Tectonophysics, 226, pp. 417–431 The Central Western Carpathians formerly constituted a portion of the East European craton continental shelf, and were situated more to the West, in the area of the present Switzerland, laterally joining the Outer Carpathians (represented by the Oravic). During the release of tension within the Alpine collision tectonic events, the stress was released to the flanks of the thrust belt, which caused the tectonic escape of the material. Central Western Carpathians were consequently pushed in the Northeast direction from the Alpine to Carpathian domain.
Považie-Pieniny Belt The Považie-Pieniny Belt has a complicated imbricated structure, represented especially by the Pieniny Klippen Belt. It consists of Oravic, Gossau Group, and Magura units, as well as Inner-Carpathian units (e.g. Manín and Drietoma unit etc.). Placement of the Pieniny Klippen Belt into the Central Western Carpathians is ambiguous, because most authors consider Pieniny Klippen Belt as part of the Outer Carpathians. The Považie-Pieniny Belt is divided into three zones: the Brezová, Peri-Klippen, and Klippen zones.