Ti–Zr–Nb-bearing accessory minerals in high-K trachyandesitic rocks from the Western Outer Carpathians, Moravia, Czech Republic
| Autor: | Bogusław Bagiński, Krzysztof Nejbert, Edyta Jurewicz, Ray Macdonald |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Zirconolite
010504 meteorology & atmospheric sciences Geochemistry Silicic Fractionation engineering.material 010502 geochemistry & geophysics 01 natural sciences law.invention Baddeleyite Geochemistry and Petrology law Titanite engineering Crystallization Geology Ilmenite 0105 earth and related environmental sciences Zircon |
| Zdroj: | European Journal of Mineralogy. 30:135-147 |
| ISSN: | 0935-1221 |
| DOI: | 10.1127/ejm/2017/0029-2693 |
| Popis: | The occurrence of chevkinite-group minerals (CGM), zirconolite and Nb-rich ilmenite is reported in Miocene high-K trachyandesites from the Uherský Brod area, Czech Republic, their occurrence reflecting the high Nb and Zr abundances in the host rocks. All three were late-magmatic phases, crystallizing from silicic residual melts. Strong zonation in some crystals is ascribed mainly to kinetic factors and in the case of the CGM by the replacement of less Fe-rich, more calcic (“perrieritic”) compositions by compositions richer in Fe and poorer in Ca (“chevkinitic”) as temperatures fell during crystallization. Zirconolite has high ThO 2 (≤7.75 wt%) and UO 2 (≤3.78 wt%) abundances and is commonly zoned, with significant fractionation of Th from U and within the LREE. The minerals may have crystallized at relatively high f o 2 , low p H 2 O, and at temperatures around 840°C. Zirconolite was stabilized relative to zircon by the Ti–Ca-rich nature of the melts and to baddeleyite by the high SiO 2 activity. Formation of Zr-bearing titanite, as recorded in other potassic suites, was precluded by the preferential entry of Ti into the CGM. |
| Databáze: | OpenAIRE |
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