International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

GEOCHEMISTRY OF TRIASSIC RADIOLARIAN CHERTS IN NORTH-WESTERN CROATIA

Pages: 327 - 342

Authors: JOSIP HALAMIC, VESNA MARCHIG, SPELA GORICAN

Abstract: The analysed Triassic (Illyrian, Lower Fassanian, Upper Carnian) radiolarian cherts on Zumberak, Ivanscica, Kalnik and Medvednica Mts. (NW Croatia) are rocks with high SiO2 content (mean >90 %) and the major part of silica is of biogenic origin. Besides this siliceous component, two others stand out in the radiolarian cherts. One of them is detritic (terrigenous input) and it consists mainly of Al, Ti, K, Zr, Hf, Cr, Th, Rb, Nb and Sc. The other, hydrothermal one, is composed of Fe, Mn, P, Cu, Pb, Zn, Ni, Co and Sr. The terrigenous component is a significant REE carrier. The radiolarian cherts on Kalnik and Medvednica Mts show a positive Ce-anomaly (Ce/Ce*) which indicates a sedimentation in a narrow trough relatively close to the continent. The negative Ce-anomaly on Zumberak and Ivanscica Mts suggests a reduced terrigenous input. The radiolarian cherts in the last mentioned areas are sedimented directly onto the dolomites and limestones of the carbonate platform. This means that the terrigenous input was probably weaker, because of the width of the disintegrated carbonate platform (larger distance to the continent) or because of a topographically higher position (bypass of fine terrigenous material) with respect to Medvednica and Kalnik.

Keywords: South-western Pannonian region, NW Dinarides, Croatia, Triassic, radiolarian cherts, geochemistry, major and trace elements, REE

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