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Litho-stratigraphic effect on Variscan fluid flow within the Prague synform, Barrandian: Evidence based on C, O, Sr isotopes and fluid inclusions

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Original title:Litho-stratigraphic effect on Variscan fluid flow within the Prague synform, Barrandian: Evidence based on C, O, Sr isotopes and fluid inclusions
Authors:Marek Slobodník, Rostislav Melichar, Vratislav Hurai, Ronald Bakker
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Original language:English
Field:Geology and mineralogy
Type:Article in Periodical
Keywords:Bohemian Massif; Palaeozoic; Variscan orogeny; veins; fluid inclusions; stable isotopes

The Palaeozoic sedimentary sequence of the Prague synform (Ordovician- Devonian) in the centre of the Bohemian massif underwent Variscan deformation and thermal overprint events. Variscan veins widespread throughout the sedimentary strata have precipitated from syntectonic aqueous and hydrocarbon-rich fluids. Homogenization temperatures of aqueous inclusions increased from 70 up to 226 degC in the Cambrian rocks underlying the Prague synform. Seawater, modified due to intensive water-rock interaction, was the main fluid component. Fluid flow was limited and restricted to the lithostratigraphic compartments forming a rock-buffered system. Stable isotopic modelling (C, O) and final interpretations of the confined hydrostratigraphic fluid migration was supported by the 87Sr/86Sr ratio in veins and wall rocks. Siliciclastic Cambrian and Ordovician rocks and the associated intersecting veins yielded similar isotopic signatures, and consequently the fluid migration is restricted to layer- and formation-scales. Gradually downwards increasing fluid temperature and compositional changes reflect burial at oil-window conditions. An open fluid system could be expected in proximity of major faults of the Prague syncline and at the top of the sedimentary sequence.

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