Two contrasting mineral assemblages in the Meliata blueschists, Western Carpathians, Slovakia

Low-grade metamorphic rocks from the Meliata unit (Western Carpathians) are characterized by the presence of typical blueschist-facies minerals. In metabasalt, an early low-pressure assemblage (<0.5 GPa at 350 ~ characterized by muscovite and zoisite, is followed by high-pressure glaucophane, phengite, Na-pyroxene, chlorite, clinozoisite and Al-poor titanite, indicating pressures of>1.2 GPa at 450 ~ Na-pyroxene shows strong compositional variations between the end-members Jd4 70, Aeglo 49 and Q17 49, respectively. Phengite has high Si content of 3.5 a.p.f.u. The zoisite with AlaFe (100[Fetot/ (-2+Altot+Fetot)]) = 3-5%, is rimmed by clinozoisite, with a maximum of 75 % AI2Fe, as well as being enclosed by glaucophane. The occurrence of clinozoisite, rimming zoisite, suggests that the transformation f orthorhombic to monoclinic epidote depends not only on the temperature but also on the pressure. In the studied metabasalt, retrograde phases reflecting greenschist-facies conditions are albite and chlorite. Some neighbouring metabasites may additionally contain actinolite and biotite