RECENZOWANE ARTYKUŁY NAUKOWE Geneza węglanów rozproszonych w dolnośląskich bazaltoidach kenozoicznych: badania izotopowe węgla i tlenu

Abstract

The origin of scattered carbonates in the Cenozoic Silesian basaltoids and their ultramafic xenoliths: carbon and oxygen isotope analysis.S u m m a r y. Carbon and oxygen isotope composition of scattered grain carbonates in the Cenozoic Silesian basaltoids and their ultramafic xenoliths were estimated. The δ13CPDB and δ18OSMOW values of these carbonates showed wide ranges from –24.16 to –7.86‰ and from 15.37 to 34.31‰, respectively. These values significantly differ from the δ13C and δ18O values typical for carbonates of magmatic origin. The carbonates analysed occurred only in basaltoids cutting through carbonates-rich sedimentary rocks. Accordingly, we considered two different models: theoretical (based on mathematical calculation) and empirical (based on δ13C values analysed), to explain the origin of carbonates in the basaltoids under study. The first model showed that carbonates could crystallize under following conditions: (i) mixing of magmatic fluids with DIC-rich groundwaters, (ii) pH decrease caused by mixing, (iii) degassing of CO2 from the mixed waters. The second model involves chemical weathering with an active role of water saturated with DIC of biological origin. The presented models indicate convergent conclusion, that the sources of carbon in carbonates from the Paleogene and Neogene Silesian basaltoids and their ultramafic xenoliths were probably of contaminant (external) origin.