Martin Ondrejka

Magmatic and post-magmatic Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE oxide minerals in A-type metagranite: an example from the Turčok massif, the Western Carpathians, Slovakia

Abstract An electron microprobe study of Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE accessory-mineral assemblages revealed the compositional variations and evolution in post-orogenic, hypersolvus Permian A-type metagranite from Turčok, in the Gemeric Unit, of the Western Carpathians, eastern Slovakia. Prismatic zircon I and allanite-(Ce) are primary magmatic phases. However, the late-magmatic to early-subsolidus processes led to the formation of a more complex younger assemblage: bipyramidal zircon II, xenotime-(Y), thorite, gadolinite-hingganite-(Y), Nb-Ta-Y-REE oxide phases [fergusonite-(beta)/samarskite-(Y), aeschynite/polycrase-(Y), and Nb-rich rutile?] and possibly monazite-(Ce). However, monazite-(Ce) and the partial alteration of allanite-(Ce), xenotime-(Y) and the Nb-Ta-Y-REEminerals are probably connected with a younger Alpine metamorphic overprint of the granite. Thorite appears as a solid solution in the thorite-xenotime-zircon series; it is also enriched in Al. Fergusonite-(beta)/samarskite-(Y) and especially aeschynite/polycrase-(Y) show increased P, Si and Al contents.

SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatism

SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatism Representative granitic rock samples from the Malé Karpaty Mountains of the Western Carpathians (Slovakia) were dated by the SHRIMP U-Th-Pb isotope method on zircons. Oscillatory zoned zircons revealed concordant Mississippian magmatic ages: 355±5 Ma in Bratislava granodiorite, and 347±4 Ma in Modra tonalite. The results document nearly synchronous, successive Meso-Hercynian plutonic events from S-type to I-type granites. The Neo-Proterozoic inherited zircon cores (590±13 Ma) were identified in the Bratislava S-type granitic rocks whereas scarce Paleo-Proterozoic inherited zircons (1984±36 Ma) were detected within the Modra I-type tonalites.

Permian A-type rhyolites of the Muráň Nappe, Inner Western Carpathians, Slovakia: in-situ zircon U–Pb SIMS ages and tectonic setting

Abstract Three representative A-type rhyolitic rock samples from the Muráň Nappe of the inferred Silicic Unit of the Inner Western Carpathians (Slovakia) were dated using the high-precision SIMS U–Pb isotope technique on zircons. The geochronological data presented in this paper is the first in-situ isotopic dating of these volcanic rocks. Oscillatory zoned zircon crystals mostly revealed concordant Permian (Guadalupian) ages: 266.6 ± 2.4 Ma in Tisovec-Rejkovo (TIS-1), 263.3 ± 1.9 Ma in Telgárt-Gregová Hill (TEL-1) and 269.5 ± 1.8 Ma in Veľká Stožka-Dudlavka (SD-2) rhyolites. The results indicate that the formation of A-type rhyolites and their plutonic equivalents are connected to magmatic activity during the Permian extensional tectonics and most likely related to the Pangea supercontinent break-up.