METARHYOLITES OF VRANICA MOUNTAIN IN PALEOZOIC OF CENTRAL BOSNIA

Metarioliti Vranice planine su stijene naglašene porfirne strukture u kojima se kao fenokristali nalaze kvarc, K-feldspat i vrlo rijetki albit. Osnova je mikrokristalna, karakterizirana sitnolistićastim fengitom, biotitom i područjima u kojima granofirski prorastaju kvarc i feldspati. Akcesorni minerali su ilmenit, rutil, apatit, cirkon i klorit. Metarioliti su peraluminijske stijene (PI=1,5-4,1), naglašenog kalcijskog karaktera (K2O/Na2O=1,3-13,8). Inkompatibilni elementi su vrlo obogaćeni u odnosu na prosjećni sustav hondrita, što ukazuje na krustalno porijeklo magmi metariolita. Iako se fengiti najčešće nalaze u stijenama visokog tlaka, fengiti metariolita Vranice planine najvjerojatnije pripadaju rjeđoj grupi fengita koji se nalaze u stijenama niskih do srednjih tlakova.Metharyolites of Vranica mountain are roks of emphasized porphyritic texture containing phenocrysts of quartz, K.feldspar and very rarely albite. The groundmass is microcrystallinic, characterized by finegrained phengite, biotite and area consisting of granophyric intergrowths of quartz and feldspar. Accessory minerals are ilmenite, rutila, apatite, zircon and chlorite. Metarhyolites are peraulminous rocks (PI=1.-4.1) having dominantly potassium character (K2O/Na2O=1,3-13,8). Incompatible elements are enriched relative to the normalizing chondrite composition, pointing to the crustal origin of metarhyolite magma. Although phengites typically occur in high pressure rocks, it seems that phengites of metarhyolites of Vranica mountain belong to the seldom group of phengites occurring in the low to medium pressure rocks