Acta Montanistica Slovaca (Apr 2016)
Paleopiezometry – the new investigation method applied to the Penninic suture zone in comparison to the Meliata-Hallstatt suture zone
Abstract
The method of paleopiezometry reveals new pleopiezometric data of differential stresses within the calcite veins in outcrops with developed fold structure near the village of Chmeľnica – eastern sector of the Pieniny Klippen Belt – PKB(the Inner Western Carpathians – IWC ). The results of paleopiezometric investigations on deformed calcite veins from the PKB at Chmeľmica village within ductile deformed host rocks representing numeric data about the differential stresses from the final stages of ductile deformation of the calcite veins, penetrating the whole volume of host rocks. The number of deformation twins per 1 mm of the perpendicular diameter of the grain (D=31-52) at the grain-size (450.5-516.m) has been produced by the recrystallization at differential stresses sigma = 203.48-228.44 MPa. The new results are given for comparison with previous ones, related with subducted and consequently exhumed rock blocks belonging to Jurassic Mélange proven from the southern Northern Calcareous Alps (NCA)– Hallstatt and Tirolic unit in the Eastern Alps (EA)(184.15–233.88 MPa) and the Meliatic Unit from the frontal parts of the Bôrka nappe, thrusted over the Gemeric Supernit in the IWC (347.49–439.55 MPa). Both measured units are repres enting the parts of the Jurassic Neotethyan Belt, striking from the Carpathians to the Hellenides. The difference between differential stresses simultaneously indicates that the total dynamic recrystallization of allochthonous marbles from the Kurtova skala hill should occur in conditions of the subduction zone, but their post-exhumation transport on autochthonous carbonates without their whole-volume plastic deformation should occur in “could conditions” corresponding with the transport of the superficial nappe. The high differential stresses caused the origin of deformation twins nearly in each calcite grain (Twinning Incidence up to 100 %), as well as the high no. of deformation twins per 1 mm of the perpendicular diameter of the grain (D = 173.0 –646.25) was developed to the very small size of grains (23.7–42.7.m). These results of differential stresses represent the highest values until found in the Inner Western Carpathians. The numeric paleopiezometric data obtained from the eastern sector of the PKB, as well as from the area of Pailwand, were measured in ductile deformed calcite veins, manifest the pressure conditions tightly before the “frozing” of the ductile deformation state at the final stage of thedeformat ion process. That mirrors not only in the markedly lower values of differential stresses, but also in the grain sizes of thin-sections within calcite veins from the PKB – the IWC (450.5–516.m), as well as from the oceanic fragments of the Pailwand, the NCA, the EA (323.38 – 571.25.m), which are much coarser in comparison with grain sizes of thin-sections from Bôrka nappe (23.7 – 42.7.m; but also 174.0 – 403.20.m in the case of grains, which undergone the static recrystallization in the rear parts of the Bôrka nappe). Based on all these measurements, the method of paleopiezometry seems to be a usable tool for determination of differential stresses, which contribute to reveal a geological and tectonic interpretation of geodynamic history.
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