PUMPELLYITE FROM METABASALTS OF THE UKRAINIAN CARPATHIANS

Abstract

In general, the pumpellyite series (hydrous silicates of Ca and Al) includes such mineral species as pumpellyite-(Al), pumpellyite-(Fe2+), pumpellyite-(Fe3+), pumpellyite-(Mg), and pumpellyite-(Mn). We studied pumpellyite from the Mesozoic metabasalts of the Ukrainian Carpathians in order to recreatethe facies conditions of mineral formation. The studied rocks are metabasalts of the Rakhivsko-Chyvchynskyi and Uholskyi magmatic complexes, which were studied using mineralogical, petrographical and petrogeochemical methods. In the rocks of the Rakhivsko-Chyvchynskyi complex, two morphological varieties of pumpellyite-(Fe) were found, while in the Uholskyi complex an intermediate mineral species between pumpellyite-(Al) and pumpellyite-(Fe2+) was found. The temperature of mineralization during the formation of pumpellyite-containing parageneses was determined: according to ternary feldspar geothermometry — 260 and 310 °C and according to chlorite geothermometry — from 170 to 320 °С. On the PT-diagram for metamorphic facies, the mineral paragenesis of both studied magmatic complexes fall into the field of prehnite-pumpellyite facies. The absence of clear pumpellyite-actinolite subfacies associations indicates that the pressure in the mineral formation system did not exceed 300 MPa.