Budowa geologiczna jednostek reglowych Tatr Zachodnich

• Autorzy: Bac-Moszaszwili M.

Warianty tytułu

EN

Geology of the Subtatric units, Western Tatra Mts., Poland

• Języki publikacji: PL

Abstrakty

PL

Omówiono budowę geologiczną jednostek reglowych w Tatrach na zachód od Doliny Suchej Wody. Składają się one z dwóch zasadniczych części: regli zachodnich zbudowanych z monoklinalnej kriżniańskiej jednostki Bobrowca i leżących na niej jednostek płaszczowiny choczańskiej oraz regli zakopiańskich zbudowanych z większej ilości drobnych jednostek tektonicznych płaszczowiny kriżniańskiej. Obie te części kontaktują ze sobą wzdłuż strefy nasunięcia regli zachodnich na zakopiańskie. Strefa ta jest jedną z poprzecznych dyslokacji o kierunku SW-NE przecinających jednostki reglowe i nadległy kompleks eoceński.W strefie reglowej Tatr dyslokacje te mają złożoną budowę i najczęściej charakter nasunięć lub uskoków pochylonych ku NW. Tworzą one system imbrykacyjny, interpretowany tu jako kontrakcyjny dupleks. Przesunięcia na poprzecznych uskokach powodują prawoskrętną rotację poszczególnych bloków jednostek reglowych.

EN

The Subtatric zone makes up a longitudinal belt along northern edge of the High Tatra Mts (Fig. 1). It is represented by the Križna nad the Choč nappes of the Inner Carpathians. The western subtatric zone. West of the Kościeliska Valley, the Bobrowiec unit makes up the main subtatric mass (Fig. 2). It consists of monoclinal Triassic, Jurassic and Lower Cretaceous units in the typical Križna nappe development. Its Middle Triassic competent dolostones are split into smaller blocks. Amplitude of fault displacement between these block dimnishes upward. The entire zone is cut by a large Siodło dislocation in its central part. Enrichment in iron and manganese ores (Krajewski & Myszka, 1958), is associated wit the dislocation (Fig. 7). The tectonic sole of the Bobrowiec unit is thrust onto the Hightatric zone along a shear plane (Fig. 6). The Bobrowiec unit is overlain by a higher nappe showing lithostratigraphic characteristics of the Choč nappe (Nemčok et al., 1996). In the western part of the Tatra Mts, it consists of Triassic formations, but in the Kościeliska Valley - of Lower Jurassic ones (Fig. 3). The whole nappe structure had been peneplenised during early Paleogene, being then covered with clastic sediments of Middle Eocene age (Fig. 4). At the Siodło dislocation, and the one that terminates the western Subtaric zone in the east (between the Kościeliska and Mała Łąka Valleys), changes occur in the composition and thickness of the basal Eocene beds (Bac, 1971). The Zakopane Subtatric zone. The Zakopane Subtatric zone makes up a complicated tectonic structure consisting of several nappe units composed of Triassic and Lower Jurassic formations in the Križna nappe development (Fig. 8). The zone consists of two belts of Middle Triassic dolostones with the so-called Czerwona Przełęcz syncline inbetween. The latter is built of Upper Triassic and Lower Jurassic shaly beds. Knowledge of the Subtatric Triassic lithostratigraphy (Kotański, 1963) allowed to state that this part of the Subtatric zone is composed of isoclinal slice elements usually in tectonically normal position (Guzik & Kotański, 1963). Tectonic model of the western Subtatric zone in the Western Tatra Mts. The set of tectonic scales in the Zakopane Subtatric zone makes a form of duplexes in the sense of contraction tectonics (see Boyer & Elliott, 1982; Mitra, 1986). It is proved by isoclinal, normal position of the majority of the scales, with shearing planes cutting horizons of incompetent Lower Triassic and Keuper shales, with passing of overthrust planes into shearing planes. The cross-sections (Fig. 10) are limited to structural elements visible in the field. They show a distinct imbrication of tectonic units in the Zakopane Subtatric zone. One must, however, subtract the effect of postorogenic tectonic processes and, first of all, of a rotational post-nappe tilt of the Tatra massif which caused the nothward dip of the Mesozoic Subtatric sequence that primarily was nearly flat or only slightly tilted toward the south (Bac-Moszaszwili et al., 1982). Within the Zakopane Subtatric zone, the duplexing process had embraced the sequence from the Triassic to the Lower Jurassic. Younger formations are unknown from that zone. Such a process did not take place in the Western Tatra Mts where the Lower Subtatric nappe include sedimentary formations from Middle Triassic through the Lower Cretaceous inclusively. The two above mentioned Subtatric zones namely the Zakopane and the western one, contact with each other in a tectonically complicated area of Upłaz Miętusi. It was argued (Bac, 1971) that there is no superposition of these two zones as supposed earlier by Rabowski (1954) and Kotański (1965). The tectonic structure of Upłaz Miętusi is best explained by an en bloc thrust of the western Subtatric zone onto the Zakopane one (Figs 2-5, 8, 9). The basal Eocene beds also take part in this thrust (Bac-Moszaszwili et al., 1979), and reverse folds so common in the Bobrowiec unit (Bac, 1971; Piotrowski, 1987) are associated with it. Displacement of an upper part of the Bobrowiec unit, recognized in the Chochołowska Valley, also shows a reverse character (Figs 2, 5). Folds in the Zakopane subtatric zone are of similar character (Fig. 11). The Subtatric units of the Zakopane zone are cut in several places by transverse, rather broad dislocations (Figs 8, 9), of fault overthrust character. As follows from studies by Iwanow (1965), and Bac-Moszaszwili & Rudnicki (1979), the above mentioned thrust zones are tilted toward NW, similarly as it is the case with the thrust of the western subtatric zone over the Zakopane one. They separate units differing in structure (Fig. 9) and are accompanied by small retrofolds usually of drag fold type (Fig. 11). The amplitudes of displacements vary in particular units. They are largest in the lowermost Suchy Wierch unit and smallest within the basal Eocene. This suggests a gradual development of this zone that started already during the nappe process, and was subsequently rejuvenated. The development of reverse structures, and transformation of the transverse dislocation zones into flat overthrusts dipping from NW toward SE, may have been caused by the formation of the Parnica Sigmoide at the western termination of the Tatra Mts (Bac-Moszaszwili, 1993) as well as by other tectonic phenomena that took place at the Inner/Outer Carpathian boundary. The last post-Paleogene stage of displacements along the mentioned transverse dislocations, shown in fig. 12, was a clockwise rotation of the Subtatric blocks. This may be one of effects of transpression and block displacements at the Inner/Outer Carpathian boundary. This direction agrees well with results of palaeomagnetic (Grabowski, 1995) and geotectonic studies (Birkenmajer, 1985). The morphological observations done by the authoress (1995) in the Subtatric units led to acceptation of such direction of recent rotation along the north-Tatra lineament.

Słowa kluczowe

PL

geologia; Tatry Zachodnie

EN

geology; Tatra Mts.

• Wydawca: Instytut Nauk Geologicznych PAN
• Czasopismo: Studia Geologica Polonica
• Rocznik: 1998
• Tom: Vol. 111
• Strony: 113--136

Twórcy

autor

Bac-Moszaszwili M.

• Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland