ALTERACE DETRITICKÉHO TITANITU V KULMU DRAHANSKÉ VRCHOVINY

Abstract

Titanite is a common accessory mineral of magmatic rocks, low- and medium-grade metamorphic rocks and it occurs as a detrital mineral in clastic sediments. Our paper deals with titanite alterations as a result of interaction of diagenetic fluids with detrital titanite during deep burial of sedimentary rocks of Drahany Upland, Protivanov Formation. Detrital titanites and their alteration products were examined by electron microprobe. Titanite dissolution was observed from the rim and along the cracks, accompanied by the formation of an authigenic calcite, TiO2 phase, synchysite-(Ce), and rarely chlorite. With an increasing degree of alteration, detrital titanite occurs as small irregular relics inside a mixture of authigenic minerals. Based on the composition of authigenic minerals, we can suppose diagenetic fluid rich in CO2, F and Ca responsible for alteration of detrital titanite. The maximum temperatures in this area during deep burial of sedimentary rocks reached 250–300 °C, corresponding to the conditions of very low-grademetamorphism. Contents of REE (0.67–3.55 wt. % REE2O3) in detrital titanite are rather high and vary significantly. Authigenic synchysite-(Ce) compared with detrital titanite strongly prefers LREE over HREE, indicating that LREE released during dissolution of detrital titanite were preferentially incorporated into the structure of synchysite-(Ce), whereas HREE were mobilized and removed away by diagenetic fluids.