Tektonika zachodniego zakończenia antykliny chęcińskiej i otaczających ją struktur obrzeżenia mezozoicznego

Włodzimierz R. Kowalski


Tectonics of western end of Chęciny anticline and surrounding structures of Mesozoic margins of the Holy Cross Mts.

The elevation of the Holy Cross Mts (Central Poland) is a net result of movements uplifting Middle-Polish anticlinorium and meta-Carpathian zone (Kutek and Głazek 1972). The uplift of this area was accompanied by erosion, which exposed Paleozoic strata of the so-called Paleozoic Core of the mountains. The Paleozoic Core is surrounded by exposures of Mesozoic strata, i. e. the so-called Mesozoic margins of the Holy Cross Mts. Paleozoic rooks subjected to repeated tectonic movements since Ordovician to Tertiary times (Kutek and Głazek 1972, pp. 629—630 and references cited therein) display much stronger tectonic disturbances than the Mesozoic rocks. The paper discusses the structure of western part of the Chęciny anticline, belonging to the Paleozoic Core of the Holy Cross Mts, and neighbouring folds built up of Mesozoic strata. The Chęciny anticline stretches along SW margin of the Paleozoic Core (see Fig. 1). The structure is of the type of horst with limbs delineated by WNW—ESE faults (Fig. 3a). Summative post-Mesozoic downthrust of the southern limb in relation to central part of the anticline is estimated at 1,0—1,5 km, and that of the northern limb — at 0,5 km. The southern limb shows stronger tectonic disturbances that the northern one. The disturbances are expressed by steep and locally even reversed dips and overthrusts of the Devonian on Mesozoic strata. Tectonic deformations at the contact of Paleozoic and Mesozoic strata were recently discussed by E. Stupnicka (1972; see also Kutek and Głazek 1972, p. 632, Fig. 14). The structure of the Chęciny anticline highly resembles models (Fig. 2) obtained by A. R. Sanford (1959), who modelled vertical dislocations in sedimentary rocks overlaying rigid substratum. The models show that both reversed faults and overthrusts may result from sufficiently large vertical faults. Depending on the magnitude of downthrust, vertical or reversed faults may originate, and downthrusts exceeding 1,2—1,5 km may lead to overthrusts. Generally, the higher amplitude of faults the larger the overthrust. The western end of the Chęciny anticline is surrounded by fold structures (Fig. 3c) built of Mesozoic strata (Stupnicka 1972). Southwards of the anticline there is a wide depression of the brachysyncline charakter, with flat central part and ussually steeply sloping limbs. Northwards there is a large area of relatively flat lying Triassic strata cut by a number of WNW—ESE oriented faults. The Łososina river walley runs along dislocation zone of strike-slip character. The Chęciny anticline ends at this line. To the west of the dislocation zone there outcrop Mesozoic strata involved in a number of small-size synclines and anticlines. Along the whole Mesozoic margins of the Holy Cross Mts the fold structures involving Mesozoic strata are short in relation to their width. Further from horst structures of the Paleozoic Core or from larger dislocation zones the tectonic disturbances fairly rapidly cease and Mesozoic strata become gently inclined and involved in wide-radius flat synclines and anticlines. Two principal directions of dislocations, WNW-ESE and NW—SE, may by distinguished in the Holy Cross Mts area (Fig. 5). The former is marked in the areas devoid of thick Mesozoic cover (the Holy Cross Mts and Carpathian Foreland). The latter (NW—SE) is commonly observed along the whole Middle-Polish anticlinorium, built of extremely thick Mesozoic series (Kutek and Głazek 1972). Post-Mesozoic uplift of the Middle-Polish anticlinorium resulted in the appearance of NW—SE oriented faults cutting the Mesozoic cover. The faults played important role in tectonic development of the area. However, in axial part of the Paleozoic Core, in areas where initially thick Mesozoic cover was removed by erosion, the relaxation of stresses also took place along older, WNW—ESE oriented faults. The overlapping two systems of faults resulted in formation of a mosaic of blocks in the substratum. Translocations of these blocks resulted in modelling of Mesozoic sedimentary cover, giving rise to numerous brachysynclines and brachyanticlines with flat central parts and strongly disturbed limbs. The continuous character of deformations of the Mesozoic cover was facilitated by the occurrence of soft clay complexes in the older Paleozoic (Czarnocki 1927a; Stupnicka 1972). The formation of folds involving Mesozoic rocks was also enhanced by compression in the direction varying from 40° to 65°, the effects of which are recorded in a number of places along the margins of the Holy Cross Mts. The studies carried out in the Gnieździska area (see Figs 1 and 4) showed that the compression resulted in formation of stylolite surfaces already in the early phase of folding. However, stylolite linear elements were fully developed not before the formation of fold structures.

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