Atolové granáty v bazaltových metapyroklastikách z lokality Čučma - Vincent (Slovenská republika)

Atoll garnets in basalt metapyroclastics from the locality Čučma - Vincent (Slovak Republic) consist of relict cores and zonal rings. Research was focused on comparison of chemical changes in these garnet microstructures. Relict cores have composition Sps41.4-45.2Grs40.6-43.0Adr6.4-13.6 Alm1.9-6.1, inner BSE light zone in the rings has composition Grs38.2-44.9Sps39.6-43.7Alm6.3-12.4 Adr6.5-9.6 and outer BSE dark zone in the rings has composition Sps34.3-40.3Grs33.3-38.3Adr8.5-17.3 Alm12.7-17.1. The highest content of Mn2+ in the atoll garnets was observed in the relict cores (1.21 - 1.33 apfu) and subsequent decreasing trend in contents of Mn2+ from the inner parts of the rings (BSE dark zone; 1.16 - 1.29 apfu) to their edge (BSE light zone; 1.02 -1.20 apfu) is present. The opposite trend was observed for Fe2+ content. Inner parts of the garnets are replaced by actinolite and calcite with slightly higher content of Mn (Act up to 0.07 apfu; Cal up to 0.02 apfu). Matrix of basalt metapyroclastics was primarily formed by hedenbergite which was later replaced by actinolite.