POST-MAGMATIC ALTERATIONS IN THE BASIC VOLCANITES OF THE RAKHIVSKO-CHYVCHYNSKYI COMPLEX
DOI:
https://doi.org/10.30970/min.73.04Keywords:
metabasalts, post-magmatic alterations, feldspars, pumpellyite, chlorite, miner-alogical geothermometer, Rakhivsko-Chyvchynslyi magmatic complex, Ukrainian CarpathiansAbstract
We studied the post-magmatic alterations in the basic volcanites of the Rakhivsko-Chyvchynskyi complex (MZ), which are exposed in the basin of the Kamianyi Stream (right trib-utary of the Tisza River) in the Ukrainian Carpathians. The rocks gravitate towards the thrust zone of the Maramureş Massif on the flysch rocks of the Rakhiv Zone. Metabasalts predominate among the studied volcanites – greenish-grey, greenish-purple massive or breccia-like rocks with a porphyritic texture, amygdaloidal structure and spheroidal parting. According to the results of petrographic, microprobe and X-ray studies, it was determined that the main minerals of metabasalts are feldspars, chlorites, pumpellyite, carbonates, quartz, muscovite; titanite, titanomagnetite, goethite, rutile, chrome spinellides, mixed-layer formations, and apatite also occur. Amygdules in rocks are mainly filled with quartz-pumpellyite-chlorite-carbonate aggregate. Microliths or laths of plagioclase with a composition from albite to bi-tovnite prevail among the feldspars. Pumpellyite, according to the results of microanalytical studies, is represented by Al-pumpellyite. There are two morphological variations of it: (1) small grains formed as a result of the replacement of plagioclase with the formation of pseudomorphoses in it together with chlo-rite, muscovite, albite, and carbonates; (2) slightly larger crystals in amygdules together with chlorite and albite. Among the chlorites, pycnochlorite, diabantite, brunsvigite and ripidolite were identified. With the help of mineralogical geothermometers, the temperature of mineralization during the formation of paragenesis of secondary minerals in metabasalts was calculated: according to the two-feldspar geothermometer – 310–265 °С, according to chlorite one – 318–171 °С. On the PT-diagram for metamorphic facies, the mineral paragenesis of the Rakhivsko-Chyvchynslyi complex falls into the field of prehnite-pumpellyite facies.
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