Two Contrasting Mineral Assemblages in the Meliata Blueschists, Western Carpathians, Slovakia

S. W. Faryad1 and G. Hoinkes2
2 Institute of Crystallography, Mineralogy and Petrology, University of Graz, Universitätplatz 2, 0811 Graz, Austria
1 Department of Geology and Mineralogy, Technical University Košice, Letná 9, 04200 Košice, Slovakia.

Abstract: 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°C 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°C Na-pyroxene shows strong compositional variations between the end-members Jd4–70, Aeg10–49 and Q17–49, respectively. Phengite has high Si content of 3.5 a.p.f.u. The zoisite with Al2Fe (100[Fetot/ (−2+Altot+Fetot)]) = 3–5%, is rimmed by clinozoisite, with a maximum of 75% Al2Fe, as well as being enclosed by glaucophane. The occurrence of clinozoisite, rimming zoisite, suggests that the transformation of 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.

Keywords: zoisite-clinozoisite • muscovite-phengite • omphacite • prograde metamorphism • Meliata unit

Mineralogical Magazine; August 1999 v. 63; no. 4; p. 489-501; DOI: 10.1180/002646199548664
© 1999, The Mineralogical Society
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