Hydrothermal alteration of tourmaline from pegmatitic rocks enclosed in serpentinites: Multistage processes with distinct fluid sources

2020 
Abstract Hydrothermal alteration of primary tourmaline (dravite, oxy-dravite, fluor-dravite,” uvite“, schorl, oxy-schorl, fluor-schorl) and associated plagioclase and quartz is examined in coarse-grained pegmatitic plagioclase-tourmaline rocks, simple granitic pegmatites and zoned beryl-columbite pegmatites, all cutting serpentinite from the Moldanubian Zone, Czech Republic. Tourmaline is replaced by a wide spectrum of minerals—prehnite, pumpellyite-(Al), K-feldspar, chlorite, muscovite, natrolite, arfvedsonite, titanite, epididymite, and hydrous Mg-silicates—and idealized replacement reactions of tourmaline are presented. Secondary mineral assemblages replacing tourmaline and chlorite geothermometry suggest evolution of the PT conditions of tourmaline alteration from T ~ 400–350 °C to 200–100 °C and P
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