Publication details
Compositional evolution (Li, Be) in cordierite-group minerals from metamorphic and magmatic rocks of the Bory Granulite Massif, Moldanubian Zone, Czech Republic and its implications for origin of related granitic pegmatites
| Authors | |
|---|---|
| Year of publication | 2025 |
| Type | Article in Periodical |
| Magazine / Source | Chemical Geology |
| MU Faculty or unit | |
| Citation | |
| web | https://doi.org/10.1016/j.chemgeo.2025.122668 |
| Doi | http://dx.doi.org/10.1016/j.chemgeo.2025.122668 |
| Keywords | Cordierite; Sekaninaite; EPMA; LA-ICP-MS; Compositional trends; Granulite; Migmatite; Pegmatite |
| Description | Samples of cordierite-group minerals (CGM) from various rocks in the Bory Granulite Massif (BGM), Moldanubian Zone - granulite (1), leucosome to pegmatitic leucosome in migmatites (2), small zoned granitic pegmatites (2) and large, complexly zoned granitic pegmatites (11) were examined by the means of EPMA and LA-ICP-MS. CGM are morphologically and compositionally highly variable from subhedral grains, ~0.5–5 cm in size, of cordierite (XMg57) from granulite, subhedral grains, < ~5 cm, of cordierite-sekaninaite (XMg56–44) from leucosome to pegmatitic leucosome, cordierite (XMg60) from graphic unit and subhedral grains to large conic subhedral crystals, up to 0.7 m long, of sekaninaite (XMg28–3) mainly from albite unit of complexly zoned pegmatites. Concentrations of Be and chiefly Li in CGM vary significantly - granulite (Be = 84–89 ppm, Li = 204–242 ppm), leucosome to pegmatitic leucosome (Be = 184–317 ppm, Li = 204–338 ppm), complexly zoned pegmatites (outer and blocky units - Be =150–200, Li = 577–904 ppm; albite unit - Be ?51 ppm, Li = 572–3662 ppm; ?0.79 wt% Li2O). The following substitution mechanisms were revealed: homovalent R2+ substitutions - major Mg = Fe in all types of CGM, minor Mg + Fe = Mn in sekaninaite with low XMg, moderate to minor heterovalent substitution NaLi = ? R2+and insignificant substitution NaAl = ? Si in sekaninaite from complexly zoned pegmatites. Textural evolution from small bodies of leucosome to large complexly zoned pegmatites with Li-rich sekaninaite, and to Li-rich lepidolite pegmatites in BGM somewhat resembles evolution of simple anatectic pegmatites to albite-spodumene pegmatites from the Austroalpine Unit Pegmatite Province (Eastern European Alps); however, pegmatites from BGM with Li-bearing sekaninaite and lepidolite + petalite crystallized at lower P ~ 2 kbar. Variations in concentrations of Be and Li in the individual paragenetic types of CGM and chiefly high Li and very low Be in sekaninaite manifest that pegmatitic melts underwent several steps of magmatic fractionation evident chiefly in complexly zoned pegmatites. |