geochemical and isotope characteristics of representative carbonates in young alkaline volcanites from northern bohemia
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carbonates of young alkaline volcanics from northern Bohemia have carbon of primary magmatic character with a shift to light isotopes, in association with fractionation processes. The oxygen isotopes show equilibration with meteoric - hydrothermal water at low temperatures. Representative samples reveal the following characteristics:
- dolomites associated with melilititic lamprophyres - polzenites of the Osečná Complex are characterized by high REE, high La/Yb ratio, and by δ13C values in the primary magmatic range (carbonatite affinity), but with δ18O values and 87Sr/86Sr ratios corresponding to lower-temperature processes and some crustal contamination
- calcites in phlogopitite, originated as alteration product of olivine melilitolite of the Osečná complex by late-magmatic fluids, are characterized by very low REE, low La/Yb ratio, low δ13C values and by 87Sr/86Sr ratio corresponding to the parental rock; high δ18O values indicate lower-temperature origin
- calcites from the contact zone of polzenite dyke with sandstones of the Czech Cretaceous Basin, with geochemical characteristics typical for sedimentary origin, are characterized by low REE, low La/Yb ratio and very high δ13C, δ18O values, and 87Sr/86Sr ratios
- rhodochrosite-dolomite-calcite series of post-magmatic hydrothermal origin, associated with base metal ore vein in the Roztoky Volcanic Centre of the České středohoří Mts., is characterized by moderate REE contents and Yb/La ratios, high Sr and Ba contents and by 87Sr/86Sr ratio reflecting some crustal contamination; δ13C values indicate probably minor admixture of sedimentary C in carbon of deep-seated origin, while the O isotope data point to participation of a low δ18O fluid of meteoric derivation.
- dolomites associated with melilititic lamprophyres - polzenites of the Osečná Complex are characterized by high REE, high La/Yb ratio, and by δ13C values in the primary magmatic range (carbonatite affinity), but with δ18O values and 87Sr/86Sr ratios corresponding to lower-temperature processes and some crustal contamination
- calcites in phlogopitite, originated as alteration product of olivine melilitolite of the Osečná complex by late-magmatic fluids, are characterized by very low REE, low La/Yb ratio, low δ13C values and by 87Sr/86Sr ratio corresponding to the parental rock; high δ18O values indicate lower-temperature origin
- calcites from the contact zone of polzenite dyke with sandstones of the Czech Cretaceous Basin, with geochemical characteristics typical for sedimentary origin, are characterized by low REE, low La/Yb ratio and very high δ13C, δ18O values, and 87Sr/86Sr ratios
- rhodochrosite-dolomite-calcite series of post-magmatic hydrothermal origin, associated with base metal ore vein in the Roztoky Volcanic Centre of the České středohoří Mts., is characterized by moderate REE contents and Yb/La ratios, high Sr and Ba contents and by 87Sr/86Sr ratio reflecting some crustal contamination; δ13C values indicate probably minor admixture of sedimentary C in carbon of deep-seated origin, while the O isotope data point to participation of a low δ18O fluid of meteoric derivation.
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