Numerous papers focus on the study of syntectonic veins from a deformational point of view. The veins are used as indicators of strain and for determining the origin of folds (e.g., Thorbjornsen and Dunne 1997), faults and shear structures (e.g. Smith 1996, 1997). Veins are also studied to determine the migration pattern of tectonically-driven fluids and their importance in deformation processes. The role of fluids in fault and shear zones is the topic of the papers by Kerrich et al. (1984), McCaig (1988), Carter and Dworkin (1990) and Brown et al. (1994). Structural permeability of fault-fracture meshes and the origin of fluids has been discussed by Nesbitt and Muehlenbachs (1989) and Sibson (1996) among others. The investigation of fluid inclusions which contain tectonically-expelled fluids can provide interesting information on the evolution of the deformation conditions of rocks (e.g. Xu 1997, Muchez and Sintubin 1998). This study was focused on the physico-chemical conditions of syntectonic veins, which formed during a late stage of the Variscan deformation in the Moravian Karst area. The Moravian Karst area belongs to the Moravo-Silesian Palaeozoic and is underlain by crystalline granitoid rocks of the Brunovistulicum (Dudek 1980). The Devonian and Carboniferous limestones have been deformed together with this basement. Abundant syntectonic veins were formed within these Palaeozoic limestones. They have very often complex shapes and geometries. They may be irregular, sigmoidal in shape or arranged in a dense network or en-echelon arrays. The mineral assemblage of these veins is very simple; they only contain milky calcite. The white hue of the calcite is produced by a large number of tiny fluid inclusions (Ł 1mm). Several samples were analysed from the southern (Mokra, Hady), central (Skalka area) and northern part (Amateur Cave area) of the Moravian Karst. Microthermometric analyses of fluid inclusions in the calcites produced different results in these areas. The temperatures of homogenisation (T H ) of primary twophase H 2 O-NaCl fluid inclusions in the Skalka area and in the Amateur Cave range between 60°C and 110°C. T H values of the fluid inclusions in calcites from Mokra and Hady exhibit slightly higher values between 80° and 140°C. Without pressure corrections we can consider these values as the lowest formation temperatures of the syntectonic calcites. Salinity of the enclosed solutions is lower in the southern part (1.4 to 7.5 eq. wt.% NaCl) than in the central and northern areas (6.5 to 17.8 eq. wt.% NaCl). The identical dull orange-brown luminescence of syntectonic calcites and of the surrounding limestones and the similar range of their stable isotopic composition (δC = -1.5‰ to +2.6 ‰ VPDB, δO = -9.6 to -3.9 ‰ VPDB) suggest that the fluids from which the syntectonic calcites precipitated were buffered by their host limestones (Muchez et al. 1995). The syntectonic fluids could have been expelled from the limestones during their deformation. The difference in the salinity and T H in the samples can be explained by the different geological position. Higher values of T H are produced by heating of the fluids by the basement in the southern area. The veins and limestones investigated in the south are situated a few metres to one hundred metres above the unconformity. In such geological setting, fluids could have partly migrated through the basement rocks, modifying the temperature of fluids and their chemistry. Heating by the basement can be explained by its magmatic reactivation that is reported from the Late Carboniferous and Permian (e.g., Přichystal 1994) and by the geothermal gradient. That is estimated at 46°C/km during the Late Palaeozoic in this region (Střelcova et al.1997). The samples studied from the central and northern areas (Skalka, Amateur Cave) are located ~300 to 600 m above the basement. Syntectonic fluids with low salinities comparable to those in these areas have been recorded from syntectonic Variscan calcite veins at the Variscan thrust front in Belgium (Muchez et al. 1997).
ABSTRACT South of the Caledonian Brabant‐Wales Massif a more than 200 m thick Tournaisian to Lower Visean replacive dolomite unit can be followed for several hundred kilometres from the Boulonnais (France) to Aachen (Germany). Field observations, of features such as karst cavities occurring at the top of the Lower Visean dolomite which are filled by Lower Visean crinoidal limestone, indicate that dolomitization and karstification took place during the Early Visean. This early development of the dolomite is in agreement with the presence of stylolites cutting the dolomite fabric. The minor element composition of the majority of the dolomites remains almost uniform throughout the entire studied area. Values for Fe, Mn, Na and Sr are normally in the range 700–4700 ppm, 15–400 ppm, 80–300 ppm and 50–200 ppm, respectively. The δ 13 C values (range‐0.72 to +5.31% o ) mainly reflect the carbon isotopic composition of the precursor limestones. The δ 18 O values, in contrast, are highly variable: ranging from‐19.15 to +0.85% o . This rather large range of δ 18 O values is explained by multiple‐step re‐equilibration/recrystallization during progressive burial and subsequent uplift of the dolomites. These processes are also responsible for the high 87 Sr/ 86 Sr values of the dolomites which range from about 0.7088 to 0.7098. They are distinctly more radiogenic than Lower Visean marine carbonates (0.7076–0.7078). Correlation, however, of δ 18 O values or 87 Sr/ 86 Sr ratios with dolomite and/or cathodoluminescenec (CL) textures has not been very successful. This suggests that recrystallization may remain unrecognized if only petrographic techniques are used. Nevertheless, certain CL textures can be related to specific interactions with the ambient recrystallizing fluids.
Research Article| November 01, 1994 Mississippi Valley-type Pb-Zn mineralization in eastern Belgium: Indications for gravity-driven flow Ph. Muchez; Ph. Muchez 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium Search for other works by this author on: GSW Google Scholar M. Slobodnik; M. Slobodnik 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium2Department of Geology and Paleontology, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic Search for other works by this author on: GSW Google Scholar W. Viaene; W. Viaene 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium Search for other works by this author on: GSW Google Scholar E. Keppens E. Keppens 3Geochronology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium Search for other works by this author on: GSW Google Scholar Author and Article Information Ph. Muchez 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium M. Slobodnik 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium2Department of Geology and Paleontology, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic W. Viaene 1Fysico-chemische Geologie, Katholieke Universiteit Leuven, Celestijnenlaan 200C, B-3001 Heverlee, Belgium E. Keppens 3Geochronology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (11): 1011–1014. https://doi.org/10.1130/0091-7613(1994)022<1011:MVTPZM>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Ph. Muchez, M. Slobodnik, W. Viaene, E. Keppens; Mississippi Valley-type Pb-Zn mineralization in eastern Belgium: Indications for gravity-driven flow. Geology 1994;; 22 (11): 1011–1014. doi: https://doi.org/10.1130/0091-7613(1994)022<1011:MVTPZM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mississippi Valley-type deposits are widespread in Carboniferous strata in eastern Belgium. Five successive Fe-rich, fracture-filling calcite generations have been recognized in the veins containing the Pb-Zn mineralization of Bleiberg. Fluid-inclusion evidence indicates that all the calcites formed from fluids with salinities between 16.0 and 23.1 equivalent wt% NaCl. The trapping temperature of the fluid inclusions decreases from ∼125 °C in the first two calcite generations to ≤50 °C in the last two vein cements. The δ13C values of the calcites vary between -0.1‰ and -8.3‰ relative to PDB (Peedee belemnite). The oxygen isotopic composition of the ambient fluids, calculated from the trapping temperature and the isotopic composition of the calcites, varies between -5.2‰ and +7.6‰ relative to SMOW (standard mean ocean water). The low δ13C values of the calcites are explained by the contribution of 12C from CO2 released during the oxidation of organic matter in the upper Carboniferous shales and the coupled reduction of sulfate in the mineralizing brine. The highly variable oxygen isotopic composition of the ambient fluids, the low δ18C value of the water from which one calcite cement precipitated, and the intense water-rock interaction necessary to leach metals indicate that the original fluids had a low δ18C, and that those fluids became enriched in 18O by water-rock interaction. Waters with such low δ18C, values must have had a meteoric origin. Flow of these waters into the deeper subsurface was likely gravity driven and took place from the uplifted parts of the Variscan orogen toward the foreland basin. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
