engleski

Characteristics of Middle Triassic volcaniclastic deposits in the External Dinarides (Croatia and Bosnia and Herzegovina)

Middle Triassic volcaniclastic rocks were investigated by means of petrography, biostratigraphy and geochemistry at three localities (Donje Pazarište, Bosansko Grahovo and Zelovo) in the External Dinarides. Petrographic features of volcaniclastics at all three localities are quite different and suggest different genesis. Biostratigraphic analysis, based on conodonts and rare ammonoids, indicate similar, upper Anisian, Illirian stratigraphic position of Donje Pazarište and Bosansko Grahovo sections while the Zelovo section is stratigraphically younger - Upper Fassanian. Geochemical data (EMP – electron microprobe analysis) show that pyroclastic material from Donje Pazarište comprises minerals mostly of acidic magma, while at the locality Zelovo crystaloclasts show more complex composition with the normal and reverse zoned plagioclase crystals. Various types of volcaniclastic deposits, their different mineral composition and other petrographic characteristics can be interpreted in the light of different genesis in a bathymetricaly different Middle Triassic basins accompanied by different volcanic processes.

External Dinarides; Middle Triassic; volcaniclastics; petrography; biostratigraphy; geochemistry

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