Publication details
Petalite and its alteration from complex (Li) pegmatites in the Moldanubian zone
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| Year of publication | 2015 |
| Type | Appeared in Conference without Proceedings |
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| Description | Three pegmatites from the Moldanubian Zone - Nová Ves near Český Krumlov, Jeclov near Jihlava and Dobrá Voda near Velké Meziříčí were examined in detail to cover whole extend of the region. Detailed EMP study revealed that petalite is replaced by fine-grained (Jeclov) to fine- to coarse-grained (Nová Ves, Dobrá Voda) spodumene-quartz aggregate. This aggregate is typically porous at both latter localities, whereas in the Jeclov pegmatite tectonic mylonitization significantly overprinted the original texture. At Nová Ves and Dobrá Voda pegmatites, the aggregate contains small rounded inclusions of petalite, 15-40 µm in size. The mineral assemblage petalite + spodumene + quartz has several implications. (i) Occurrence of primary petalite suggests P < 2.5-3 kbar (depth ~7-9 km) of the pegmatite emplacement and primary crystallization for all over the region of the Moldanubian Zone. (ii) The complex pegmatites are evidently restricted to a narrow depth level in the whole region. (iii) The assemblage Ptl +Spd+Qz is highly sensible for tectonic overprint. (iv) Inclusions of petalite in quartz and spodumene may represent relics of primary petalite but also a product of recrystallization of secondary spodumene + quartz due to decreasing of volume at 18-19 vol. % during the reaction Ptl › Spd + 2Qz and consequent isothermal drop of pressure back from the stability field of spodumene to the stability field of petalite. |