engleski

Alpine metamorphism of organic matter in metasedimentary rocks from Mt. Medvednica (Croatia)

The diagenetic to low-temperature metamorphic alteration of Mt. Medvednica (Internal Dinarides, Croatia) has been studied by vitrinite reflectance, ordering data of organic matter determined by X-ray powder diffraction, and Raman spectroscopy of extracted carbonaceous material. In metapelites of the Medvednica Metamorphic Complex (MMC), maximum vitrinite reflectance varies between 6.9 and 9.8%. By X-ray powder diffraction, the finely dispersed carbonaceous material is classified as d1-graphite. Based on the “ Raman Spectroscopy of Carbonaceous Material Thermometer” , peak metamorphic temperatures of ca. 410 °C are estimated. The degree of organic maturation and the estimated peak temperature correlate fairly well with the Cretaceous (120– 80 Ma) high-temperature anchizonal to epizonal metamorphism of the unit, determined by illite Kübler index, chlorite “ crystallinity” and K-white mica – chlorite thermobarometry. In the tectonically higher Jurassic Ophiolitic Mélange and in the unconformably overlying Cretaceous– Paleocene Sequence, random vitrinite reflectance between ca. 0.7 and 2.2% suggest a stratigraphical trend of the data and therefore a common burial history. In the Jurassic Ophiolitic Mélange and the Cretaceous– Paleocene Sequence, the synmetamorphic carbonaceous material is classified as d3-graphite. In both units, organic thermometers provide peak temperatures of ca. 100– 240 °C. These estimates are in accordance with phyllosilicate reaction progress indicators, showing no systematic variation in the stratigraphic succession.

metamorphism; organic matter; vitrinite reflectance; Raman spectroscopy; structural ordering; Internal Dinarides; Mt. Medvednica; Croatia

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