engleski

Diagenesis and low-temperature metamorphism of Mt. Medvednica, Croatia: Mineral assemblages and phyllosilicate characteristics

New mineral paragenetic, illite Kübler index, chlorite "crystallinity", apparent crystallite thickness, lattice strain, and K-white mica geobarometric data proved that the Eoalpine (Paleozoic-Mesozoic) metamorphic complex was affected by medium-pressure, high-temperature anchizonal regional metamorphism, whereas the Jurassic ophiolitic mélange and the Late Cretaceous-Paleocene sedimentary sequence of Mt. Medvednica were diagenetically altered. Mineral chemical investigations carried out on phyllosilicate flakes found in various microstructural positions revealed complete mineral chemical homogenization of chlorite and K-white mica of selected slate samples from the Eoalpine (Paleozoic-Mesozoic) metamorphic complex. One possible explanation of this feature is an Alpine (Cretaceous) regiona1 metamorphic event with polyphase deformational history. Variscan low-temperature metamorphism overprinted by an Alpine (Cretaceous) event, with temperatures at least as high as those of the Variscan one, may be an alternative, although more complicated explanation. However, no isotope geochronological evidence supports this assumption. At present only one metamorphic event can be detected. Its physical conditions were ca. 350-400 °C on the basis of illite Kübler index and chlorite Al(IV) empirical thermometers and 3-4 kbar using K- white mica b cell dimension measurements.

ilIite Kübler index; chlorite

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