Paleotemperatury minerałów węglanowych i barytów na przykładzie Gór Świętokrzyskich

Abstract

PALEOTEMPERATURES OF CARBONATE MINERAIS AND BARITES FROM THE HOLY CROSS MTS (CENTRAL POLAND) Summary This report summarizes the results of paleotemperature investigations performed on carbonate minerals and barites from the Holy Cross Mts (Fig. 1). In order to correctly determine crystallization temperatures on the basis of the δ18O values, the δ18OSMOW of hydrothermal fluid should be known. Data derived from contemporary hot springs from mid-ocean ridges have indicated that the "zero delta" (with ±1 fluctuations) seems to be the best assumption. Moreover, many researchers emphasize that this value has not changed with geologic time [3, 12, 18-20, 30]. Homogenization temperatures of gaseous-liquid inclusions and δ18O determinations carried out on the same crystals of "rose-like" calcites from the Holy Cross Mts indicated that the δ18OSMOW of fluid (hybridized seawater) had varied from 0 to 2‰ (Fig. 2). The "oxygen thermometer" based on the "delta zero" assumption was applied to Middle and Middle/Upper Devonian dolomites from the Holy Cross Mts. The obtained results were the basis for a new concept of the origin of dolomites [22-24]. Two structural forms that support the hydrothermal-synsedimentary model have been presented in this report (Figs 4 and 5). Isotopic determinations, which included isotopic-petrographic microprofiles (Fig. 6), have also been performed on calcites from the Holy Cross Mts. Based on lithologic and petrographic investigations, six main phases of calcite mineralization, each featured by a specific pattern of the δ13C and δ18O , have been distinguished (Fig. 3). Cretaceous calcites (δ18O = -5.95 to -6.31‰, vs -2.71 to -42‰ in marls) associated with silica concentrations are best represented by a fossil hot spring chimney (Fig. 7). The scope of isotopic determinations also included barites. Their δ18OSMOW values range from 11.81 to 20.07‰ which corresponds to 127-52°C [2]. The most interesting is a barite fossil hot spring mound from Skałka Rykoszyńska (southwestern part of the study area), which was formed at a temperature of about 95-96°C (δ18OSMOW = 14.70 to 14.58‰) in late Early Triassic time. This age was confirmed by lithologic-petrographic and sulfur isotope age curve [4]. As for meteoric calcites, a unique role is played by the so-called "calcite groats" from cave "Chelosiowa Jama" near Kielce. These randomly scattered grains reveal very negative δ18O (from -10.85 to -20.98‰) and (δ13C (from -3.67 to -9.89‰). They were formed as a result of rapid crystallization that had been triggered by decompression of the cave - the so-called "soda water bottle" model [5]. Hydrothermal action coupled with sedimentary processes led to forming hybrid rocks. This new concept on the origin of some rocks opens new prospects in petrologic investigations.