Wiek i geneza mineralizacji kalcytowej w Górach Świętokrzyskich w świetle badań litologiczno-petrograficznych i izotopowych

Zdzisław M. Migaszewski, Stanisław Hałas



This report presents the results of lithologic, petrographic, isotopic and chemical investigations performed on calcites from the Holy Cross Mts(Fig. 1). In general, 5 phases, i.e., A - Variscan (Visean/Namurian), B - older Postvariscan (Late Carboniferous through Permian to the bottom of Zechstein conglomerates), C and D - younger Postvariscan (Permian/Triassic and middle/late Early Triassic), and E and F - Cimmerian-Alpine (Late Jurassic and Late Cretaceous), have been distinguished. This division has been confirmed by the highly diverse δ13C i δ18O values of these calcites clustered in 4 populations (Fig. 3 in Migaszewski et aI., 1995). The "rose-like" calcite (phases C and D) are most common (Figs 4-7). This calcite occurs within the same fault system. Nearly all these faults extend in the close to N-S direction cutting different consolidated Variscan structures. This unique structuro-tectonicposition of the "rose-like" calcite indicates a rare geologicevent that took place here in Early Triassic time. Acc. To Migaszewski, the Holy Cross Mts area probably shifted toward NW along the western margin of the East European Platform. This shift must have been coupled with a slight clockwise rotation. These two combined movements of the crystalline basement brought about forming echelon faults featured by a close to N-S strike. The produced heat was enough to warm upthe sea water and to trigger its circulation. The calcites from the Holy Cross Mts formed under different geologic conditions: from a typical marine off-shore zone (phases E+F), through marine relict basins originated at the end of Variscan movements (phase A), to a terrestrial environment (phase B), at the final stage with strongly developed karstic processes (phases C+D). The marine provenance of the E and F phase calcites has been proved by the presence of fossil formation of sea-floor hot springs in Upper Cretaceous rocks (Migaszewski et aI., 1987, 1995) and the 87Sr/86Sr ratio varying from 0.70726911 to 0.70812912. In turn, the continental origin of the C and D phase calcites has been evidenced by their strongly variable isotopic composition (C, O and Sr) and the presence of characteristic elongated inclusions. The development of karstification during precipitation of these calcites has been supported by a large number of different forms resembling flows tones and dripstones, as well as karsticauthigenic and allogenic intercalations, karstic-tectonic brecciasetc(Figs 5-6, 9). The simultaneous determinations of δ18O and homogenization temperatures of gaseous-liquid inclusions in the same calcite crystals indicated that hydrothermal fluids had been of marine provenance (Fig. 2 in Migaszewski et aI., 1995). The mean δ18OSMOW is 1‰ being close to that found in mid-ocean hydrothermal fluids (±1‰); it is completely different from the δ18OSMOW for meteoric waters (-5 to -22‰).