Acta Musei Moraviae

Multiphase solid inclusions in garnet pyroxenite – evidence of carbonate-silicate metasomatism in the mantle, Saxothuringian Zone, Bohemian Massif

The studied pyroxenite forms ~1–2 cm thick veins cutting garnet peridotite in a quarry north of the village of Zoblitz. The locality is situated in the German part of the Erzgebirge Crystalline Complex, Saxothuringian Zone, Bohemian Massif. Multiphase solid inclusions (MSI) enclosed in garnet represent crystallized remnants of fluids or melts present in the rocks under HT and HP conditions at great depths. The MSI contain more than 20 different minerals. The average modal amounts are: pargasite (49 vol. %), Ba-mica (22 vol. %) and carbonates (magnesite 12 vol. % and dolomite 5 vol. %). Olivine, apatite, and spinel make up above 2 vol. %. The remaining phases are represented by less than 1 vol. %. The calculated bulk composition of multiphase solid inclusions (from Zoblitz) shows significant enrichment in BaO, K₂O, SrO, TiO₂, CO₂, LREE, Th, U and Pb compared to the mantle. The enrichment in elements incompatible in the mantle supports element transfer between the crust and mantle due to metasomatism. Mineral carriers of these incompatible elements include: Ba-mica (Ba, K), pargasite (Na, K), monazite-(La) (LREE, Th, U), apatite (LREE, Sr) and thorianite (Th and U). This carbonate-silicate metasomatic medium was rich in volatile components: H₂O, Cl (Ba-mica and pargasite), and P (apatite, monazite-(La)). The MSI represent remnants of the original carbonate–silicate melt trapped in the second garnet generation formed during initial decompression. Carbonate–silicate metasomatism contributed to the formation of complex mineral assemblage in MSI and records crust–mantle interaction under HP and HT conditions in subduction setting and modification of the lithospheric mantle of the Bohemian Massif.