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

LOWER TRIASSIC POTASSIUM-RICH RHYOLITES OF THE SILICIC UNIT, WESTERN CARPATHIANS, SLOVAKIA: GEOCHEMISTRY, MINERALOGY AND GENETIC ASPECTS

Pages: 27 - 36

Authors: PAVEL UHER, MARTIN ONDREJKA, JAN SPISIAK, IGOR BROSKA, MARIAN PUTIS

Abstract: Detailed study of Lower Triassic high-K rhyolites of the Drienok and Muran Nappes, the Silicic Unit, Inner Western Carpathians, reveals their alkaline and anorogenic nature. The rhyolites occur within shallow-marine to continental shale, sandstone and limestone platform sequences. The rocks are unusually K-rich (4.9–8.7 wt.% K2O), enriched in Si, Rb, REE‘s, Y and Zr and depleted in Al, Ca, Na, P and Sr. Rhyolite phenocrysts are represented by β-quartz and alkali feldspars. Zircon typology (mainly P5 and D types) indicates a hot and dry magma environment which corresponds to a high zircon saturation temperature: 820–895 °C. Accessory monazite-(Ce), xenotime-(Y), rutile, ilmenite, magnetite, hematite and barite were identified. The results indicate an origin of the high-K rhyolites in an extensional tectonic regime during the early-Alpine rifting stage. The exceptionally high K in contrast to very low Ca and Na contents in the rhyolites is probably a result of late-magmatic and/or post-magmatic (hydrothermal) overprint by K-rich fluids. This K-enrichment of Early to Middle Triassic volcanic rocks is a characteristic feature of the South Alpine–Inner Carpathian domaine during their Early Alpine continental rifting stage.

Keywords: Western Carpathians, Silicic Unit, rhyolites, geochemistry, mineralogy, alkali feldspars, zircon

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