Acta Musei Moraviae

Muscovite-plagioclase layers in dolomite marble near Prosetín (Olešnice Unit, Moravicum) concordant injections of aplite or metaevaporites?

Layers of concordant muscovite-plagioclase rock are enclosed in dolomite marble near Prosetín (Olešnice unit, Moravicum). These rocks were previously interpreted as strongly altered injections of silica-poor aplites (oligoclasites). Muscovite-plagioclase rock is white, fine-grained, composed by prevailing oligoklase and small content of muscovite, phlogopite and aggregates of blue tourmaline (dravite). Plagioclase exhibits continuous metamorphic zonation (core An_15–28–rim An_34–37). Common scapolite (Me_41–49) rich in Cl (1.30–2.20 wt. %) do not contain SO3 anion. It forms small nests, containing also phlogopite and zoisite. Mineral assemblages correspond to multiphase regional metamorphism. Part of scapolite is clearly later mineral which replaces plagioclase; albite, chlorite, vermiculite, rare pumpellyite-(Al) and illitesmectite are the youngest retrograde minerals. High Na/K and Mg/Fe ratio and very low content of TiO₂ and P₂O₅ characterise the whole chemical composition of the rock. The studied layers are interpreted as metamorphosed synsedimentary layers of rock compound of carbonate (especially dolomite) and clay with abundant admixture of halite. Similar albite- and/or scapolite-rich rocks (albitite, marialite marbles, dravite-bearing albite-scapolite biotitic gneisses) are developed in whole northern part of Olešnice Unit.