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 me tabasalt, an early low-pressure assemblage (<0.5 GPa at 350 degrees C), cha racterized by muscovite and zoisite, is followed by high-pressure glaucopha ne, phengite, Na-pyroxene, chlorite, clinozoisite and Al-poor titanite, ind icating pressures of >1.2 GPa at 450 degrees C. Na-pyroxene shows strong co mpositional variations between the end-members Jd(4-70), Aeg(10-49) and Q(1 7-49), respectively. Phengite has high Si content of 3.5 a.p.f.u. The zoisi te with Al2Fe (100[Fe-tot/ (-2+Al-tot+Fe-tot)]) = 3-5%, is rimmed by clinoz oisite, with a maximum of 75% Al2Fe, as well as being enclosed by glaucopha ne. The occurrence of clinozoisite, rimming zoisite, suggests that the tran sformation of orthorhombic to monoclinic epidote depends not only on the te mperature but also on the pressure. In the studied metabasalt, retrograde p hases reflecting greenschist-facies conditions are albite and chlorite. Som e neighbouring metabasites may additionally contain actinolite and biotite.