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Late Variscan deformation events in the Bardo Syncline revealed by biotite K-Ar dating of Ludlow-age tuffite (Holy Cross Mountains, Poland)

Wójcik Emil, Pacek Adrian, Pelc Andrzej

Geological Quarterly

2021

Vol. 65, No. 1

art. no.15

In the Bardo Syncline (Holy Cross Mountains, Poland), two beds of tuffite (named the Niewachlów tuffites) have been discovered within greywackes of Ludlow (Silurian) age. K-Ar dating of the lower bed yielded an age of 292.8 ±4.0 Ma, while the upper bed provided an age of 341.9 ±4.3 Ma. The dates pertain to metamorphic alteration of the tuffite, related to reactivation of the Daleszyce Fault Zone. In this zone, biotite crystals present in the foliation zones were recrystallized and their K-Ar isotopic system was rejuvenated in a temperature range of ~270-300°C. The dates that were obtained define the ages of two tectono-metamorphic episodes and reflect the timing of displacements along the fault which, in turn, reflect two deformation phases during the Variscan Orogeny (Mississippian and Early Permian). Moreover the dates may be correlated with Late Variscan magmatic activity in the Holy Cross Mountains and adjacent areas. The deformation of the Daleszyce Fault Zone may be regarded as resulting from displacements of lithospheric blocks within the Trans European Suture Zone during the Late Variscan reconstruction of the Baltica palaeocontinent margin.

The origin and chemical composition of Carpathians chloride CO2-rich waters in the light of stable chlorine isotope studies (37Cl and 35Cl)

Dembska-Sięka Paulina, Pelc Andrzej, Rajchel Lucyna

Geological Quarterly

2020

Vol. 64, No. 1

197--204

Investigations into chloride CO2-rich water occurring in the Polish and Slovakian Carpathians were carried out to gain a better understanding of the Cl- sources. The primary Cl- concentration in sea water, processes accompanying diagenesis, together with water-rock-gas interactions, have undoubtedly influenced the present content of chlorides. The Cl-- concentrations in the waters analysed vary from 35.5 to 4148.3 mg/l, lower than in sea water, with a mean ~19000 mg/l. The measured δ37Cl values range from -1.15 to -0.26‰, below the typical sea water value of 0‰. It might be concluded that the chemical and isotopic composition of these waters are the result of reactions during diagenesis (e.g., ion exchange or diffusion through low-permeability clay layers) as well as meteoric water influx.