Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Variscan veins and hydrothermal fluids from the Lower Palaeozoic sediments of the Prague Synform, Barrandien
Abstract
Field work took place at several localities of SW part of the Prague Synform (e.g. Homolák quarry, Srbsko). Preliminary research on hydrothermal veins revealed that calcites are dominant mineral phase (in limestones). Hydrothermal veins are mostly apparently deformed. So far two fluid systems have been found in fluid inclusions (FIS) of calcites, aqueous and liquid hydrocarbons. Sizes of measurable FIS are around 5 micrometers. Homogenisation temperature (Th) of primary and/or pseudosecondary aqueous FIS is between 77-119 °C and fluids have generally lower salinities (0,2-7,9 wt.% NaCl equiv.). Primary inclusions rich in hydrocarbons show Th between 41-107 °C. Calculated values of S1sO of parent aqueous solutions are between -5,79 and +5,64 %% SMOW. When fluids are isotopically buffered by wall rocks than isotopic composition of fluids show more positive values S18O. Preliminary results suggest accord with other authors (e.g. Suchý et al. 2002) that tectonically deformed veins were generated in condition of the oil window. Relationships between tectonic evolution and hydrothermal veins of the Prague Synform will be subject of the further study.
