Vznik metamorfní minerální asociace granátovců z desenské jednotky silezika

The usually medium-grained garnetites form up to several cm thick layers in quartz-magnetite mineralizations of the Desna Unit in the Silesicum. The garnetite mineral assemblage consists of epidote, quartz, garnet, magnetite, biotite, ilmenite, apatite and retrograde chlorite. The mineralogical and petrological results demonstrate that garnetites are metamorphosed submarine exhalites. Garnet from the garnetites has compositions with nearly equal amounts of spessartine and almandine components and can by interpreted as result metamorphic reactions partially consuming of the Mn-rich epidote. Thermobarometric calculations from the garnetites yielded peak amphibolite facie metamorphic conditions ca. 540–600 °C and up to 3 kbar. Chemical composition of fluids estimated for this metamorphic event is H2O = 82 až 95 mol. %, CO2 = 4 až 17 mol %, NaCl = 1 až 2 mol. %. The biotite was partially replaced by chlorite during younger retrograde metamorphic event under greenschist facie.