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GEOLOGICAL-TECTONIC BASIS OF TERMO-MINERAL SPRINGS IN VARAŽDINSKE TOPLICE
Antun Šimunić
Sažetak
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.
Ključne riječi
Hrčak ID:
133941
URI
Datum izdavanja:
5.12.1988.
Posjeta: 1.446 *