Journal of Geosciences, 54 (2009), 221–243 DOI: 10.3190/jgeosci.048 Original paper Tourmalinites in the metamorphic complex of the Svratka Unit (Bohemian Massif): a study of compositional growth of tourmaline and genetic relations Renata ČOpJakOvá1,2*, David BuRIánek1, Radek ŠkODa1,2, Stanislav HOuzaR3 1 Czech Geological Survey, Leitnerova 23, 658 59 Brno, Czech Republic;
[email protected] 2 Institute of Geological Sciences, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic 3 Department of Mineralogy and Petrography, Moravian Museum, Zelný trh 6, 659 37 Brno, Czech Republic * Corresponding author Tourmalinites (rocks with an association Tu + Qtz + Ms ± Grt ± Bt ± Ky ± Sil ± Pl ± Kfs) from the Svratka Unit form stratiform layers hosted in mica schists. The chemical composition of tourmaline from tourmalinites varies from Al- rich schorl to dravite. The tourmaline usually exhibits three compositional domains, which are, from centre to the rim: a chemically inhomogeneous brecciated core (zone I), a volumetrically minor internal rim zone II, and a dominant outermost zone III. X Y W X Y W The compositional variability of tourmaline in all the zones is controlled by the ( Al OH) ( Na Mg F)-1 and Y Y Fe Mg-1 substitutions. The tourmaline of the zone I corresponds to highly vacanced X-site, Al-rich schorl with lower F (up to 0.43 apfu), which is interpreted as an older, low-temperature hydrothermal tourmaline. Tourmaline of the zone II corresponds to dravite rich in F (reaching up to 0.66 apfu) crystallizing during the prograde metamorphism. Lastly, the Al-rich schorl–dravite of the zone III grew most likely during retrograde metamorphism.