GEOLOŠKO - TEKTONSKA OSNOVA TERMOMINERALNIH VRELA U VARAŽDINSKIM TOPLICAMA

Autor: Antun Šimunić
Jazyk: chorvatština
Rok vydání: 1988
Zdroj: Radovi Zavoda za znanstveni rad Varaždin
Issue 2
ISSN: 1848-7890
0352-9509
Popis: A N T U N Š I M U N IĆ GEOLOGICAL-TECTONIC BASIS OF THERMO-MINERAL SPRINGS IN VARAŽDINSKE TOPLICE In the neighborhood of Varaždinske Toplice (Fig, 1) lie the northern slopes of Kalnik and the central part of Varaždinskotopličko mountains. The oldest rocks that crop out to the surface are dolomites and lime^stones from the Upper Triassic. The same rocks were found by drilling in Varaždinske Toplice, and most of the thermo-mineral water is contained in these rocks. The Upper Triassic layers have been hit by numerous tectonic stirs for which reason they are heavily crushed and split. This tectonization has greatly increased their capacity for accumulation. The connection between the dolomites and lime-stones in the area of the northern slopes of Kalnik, and the dolomites found by drilling in Varaždinske Toplice is presumed. The Lower Miocene olasts are transgressive on the Triassic carbonates. They consist of various pebbles, sands, marl, tuff and ribs of coal. Because these sediments alternate laterally and vertically, their porosity is rather poor. Large cobbles, measuring 10—30 cm in diameter, orginating from destruction of high^rank metamorphic rooks, appear at the boundary of the dolomites and limestones. Such rocks are not known in either Kalnik or the Ivančica area, so it is presumed that the »Moslavačko-Vrbovečki shelf« extended in the Lower Miocene to the southern slopes of Kasnik. Because of the transgressive character of the Lower Miocenean clasts, their greatest thickness is not known, although it is not presumed to exceed 400 m. After the very intensive tectonic movements in the Middle Miocene, the whole area was under the marine transgression. At first, Kalnik was an elevation from where large clastic materials were eroded and denuded, but at the beginning of the Sarmatian the whole area was completely overflown. Sedimentation, together with gradual sweetening, lasted unitl the Upper Pontian. During the Upper Neogene, approximately 1800 m of strata were deposited. Of these, roughly 600 m of Upper Pontian sediments are completely eroded. The great thickness of Upper Pontian sediments (650—700 m) suggests very intense synsedimentation movements. During the Badenian, Sarmatian and Lower Pannonian, marl and limestones were mainly deposited while sands and sandy marl mostly appear during the Pontian. The tectonic movements of great intensity occur after the Upper Pontian. It is difficult to reconstruct the chain of tectonical events, but it is clear that even the younger sediments of the Neogene were folded and rifted. Neotectonic movements formed plicated structures of great dimensions, the segments of which are shown on the Index Map (Fig. 1). These are the anticline Varaždinske Toplice— Margečan and antiform Ljubelj, and, between them, the syncLine Lobor—Zajezda—Pötkovec. These folds are very important for the explanation of the system of thermal-water heating. After the folding ceased, the elevation of Kalnik and Varaždinskotopličko mountains took place. The various movements of separete blocks towards normal and inclined clefts happened contemporaneously. It should be emphasized that »leaps« of the blocks were not so big as to cut off the connections among the Triassic dolomites, which are the main containers of the thermal waters. The Ljubelj area is the part most elevated by the neotectonic movements, and it is there where water accumulater. Limestones and doloimites conduct water down under the bottom of the Neogene syncline (about 1300 m). The water is heated as it travels downwards. Afterwards, it rises up to the top of the anticline and reaches the surface throughe the small fault. For the water to be able to run through the system of linked containers, hydrostatic pressure is of great importance. This pressure arises due to the differences of 200—350 m in height above sea level in the dolomites. Triassic dolomites from the Ljubelj area are the most elevated (558 m) and the thermal spring is 198,7 m above sea level. According to A. R u b i n i ć (1961) the geothermal gradient for northern Croatia is 25,6 to 27 ^'C. Water wofuld have to go as for as 1300 to 1400 m deep in order to be heated from 8* to 56 «C. This is the very thickness of the Neogene strata located in the Lobor—Zajezda—Petkovec synicline.
Databáze: OpenAIRE
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