1. metamorphic Ceol., zyxwvutsrqp 1995, zyxwvutsr 13, 701-714 Phase petrology and P- T conditions of mafic blueschists from the Meliata unit, West Carpathians, Slovakia S. W. FARYAD Department of Geology and Mineralogy, Technical University, zyxwvu Letna' 9, 04084 KoEce, Slovakia ABSTRACT zyxwvutsrqp Blueschists occumng as layers in calcite marbles of the Meliata unit zyxw occur along the so-called Roznava tectonic line situated in the southern part of the Gemericum, Slovakia. Mineral assemblages and compositions from seven blueschists localities and one occurrence of amphibolite facies rocks overprinted by blueschist metamorphism were investigated. The most common minerals in the blueschists are blue amphibole, epidote and albite. Some Fe2'- and Al-rich rocks also contain garnet and chloritoid, respectively. Na-pyroxene with a maximum 50% jadeite component was also found. The blue amphiboles correspond mostly to aossite and also to glaucophane and ferroglaucophane in some samples. Almandine- and spessartine-rich garnet has very low zyxwvu MgO content (<3 wt%). The Si content in phengite ranges between 3.3 and 3.5pfu calculated on the basis of 11 oxygens. The zoning patterns of blue amphibole, garnet and chloritoid suggest their formation during a prograde stage of metamorphism. The zy P -T conditions of metamorphism are estimated to be about 380-460" C and 10-13 kbar. Pressures of 7.5-8.5 kbar and temperatures of 350-370" C were obtained for some actinolite- and aegirine-rich rocks. Apart from chlorite, other mafic minerals formed during retrograde metamorphism are biotite and occasionally also actinolite. Key words: low-grade high-pressure metamorphism; metabasites; metamorphic conditions; phase rela- tions; West Carpathians. Abbreviations Ab =albite Act = actinolite Aeg = aegirine Alm = almandine Aug = augite Bt =biotite Cal =calcite Chl =chlorite Ctd = chloritoid Cz = clinozoisite En = enstatite Ep = epidote Fac = ferroactinolite Fgl = ferroglaucophane Fs = ferrosilite GI = glaucophane Gr =garnet Grs = grossularite Hbl = horblende Hem =hematite Jd = jadeite Lws = lawsonite Mrb = magnesioriebeckite Ms = muscovite Pg = paragonite Ph =phengite Prp =pyrope Px =pyroxene Qtz =quartz Rb = riebeckite Rt = rutile Ttn = titanite Sps = spessartine Tr = tremolite Wo = wollastonite INTRODUCTION Mafic rocks with blue amphiboles, interpreted as being metamorphosed at blueschist facies conditions, have been known for some time from the south-eastern part of Slovakia (Kamenicky, 1957; Reichwalder, 1973). These rocks occur along a tectonic zone between the Inner and Central West Carpathians (Fig. 1) and provide a unique opportunity for investigating the interaction between tectonism and metamorphism in this area. To date, work on the postulated blueschist rocks has been limited to petrographic analysis with no mineral chemical data or rigorous petrological analysis, thus the origin and evolution of these rocks remains speculative. As well as being interpreted as a subduction complex (Mahel, 1986), the rocks have also been attributed as the products of overthrusting by higher nappe units (Reichwalder, 1973). The aims of this work have been to undertake a rigorous petrological analysis of these so-called blueschists in order to determine mineral chemistry and to provide a realistic estimate of the P-T conditions of metamorphism. This is to confirm or otherwise the postulated blueschist facies character of the metamorphism and the implications for the tectonic evolution of this West Carpathian area. To characterize the geotectonic setting of the protoliths and of the pre-blueschist facies terrane, the geochemical and lithological nature of the blueschists have been studied. GEOLOGY The blueschist facies rocks occur within the Meliata unit of Triassic-Jurassic age that occurs as a fault slice between the Gemericum and Silica nappes, situated in the eastern part of Slovakia (Fig. 1). The Meliata unit and the Pieniny Klippen Belt to the north (Fig. 1, inset).are regarded as two oceanic sutures separating the West Carpathians into three units, namely the External, Central and Inner units 701