engleski

Illite "crystallinity" investigations of rocks from Mt. Medvednica, northern Croatia

On Mt. Medvednica four pre-Neogene tectono-stratigraphic units are present: 1) ophiolite mélange, 2) Paleozoic metamorphic complex, 3) Late Cretaceous-Paleocene flysch, and 4) Triassic mainly carbonate rocks. Rocks from the first three units have been studied by illite "crystalinity" (IC) method, an empirical XRD-based method used for evaluation of conditions of very-low grade metamorphism in phyllosilicate bearing rocks. The IC can be expressed by different indices but usually it is expressed by Kübler index (KI). This index is defined as the full width at half-maximum (FWHM) of the first basal reflection of illite-muscovite at 10 &Aring ; measured in &ordm ; &#916 ; 2&#952 ; . The major problem of IC method is the dependence of peak profile on many geological factors (temperature, stress, time, weathering, lithology and mineralogy) as well as on variations in instrumental conditions and sample preparation. Keeping all these problems in mind the sample preparation was consistent with recommendations of IC working group, and the IC results of this study were calibrated by measuring polished rock standards. Illite "crystallinity" measurements carried out on samples from Mt. Medvednica indicate that ophiolitic mélange complex and the overlying Cretaceous&#8211 ; Paleocene sequence are not metamorphosed. Measured KI values (>0.42 &ordm ; &#916 ; 2&#952 ; ) are characteristic for diagenetic alteration. IC measurements performed on the samples from the Paleo&#8211 ; Mesozoic complex of Mt. Medvednica are in good agreement with other geological data, KI values (0.25-0.30 &ordm ; &#916 ; 2&#952 ; ) fall into the high anchizone.

illite "crystallinity"; Mt. Medvednica

nije evidentirano