Acta Musei Moraviae

Tourmalinites from the southern part of Svratka Crystalline Complex

Tourmalinites from the southern part of the Svratka Crystalline complex form stratiform layers hosted in mica schist. They probably represent a part of metamorphosed volcano-sedimentary complex primary rich in F and B. Whole rock composition of tourmalinites is close to the surrounding mica schists. P-T conditions 600–630 °C and 5–6 kbar calculated from associated mica schist were interpreted as retrograde metamorphism. Chemical composition of tourmaline strongly varies from high X-site vacant Al-rich schorl to dravite which indicate tourmaline growths over a range of P-T-X conditions. Tourmaline shows three distinct compositional domains (zone I, II, III): chemically inhomogeneous broken core (zone I), volumetrically minor zone II overgrown the core and volumetrically dominant outer zone III, chemically relatively homogeneous. Tourmaline type I correspond to Al-rich schorl with high vacancy and relatively low F (≤0.35 apfu) and it is interpreted as older, low temperature hydrothermal tourmaline. Tourmaline type II is dravite rich in F (≤0.5 apfu) and corresponds to prograde metamorphism. Tourmaline I overgrown by tourmaline II is usually enclosed in other minor minerals (kyanite, muscovite, biotite, garnet). Tourmaline III – Al-rich schorl-dravite formation probably occurred during retrograde metamorphism. Variability of all three tourmaline types is controlled mainly by the substitutions ^X◻^YAl^WOH ^XNa_-1^Y (Mg,Fe)_-1^WF_-1 and ^YFe^YMg_-1.