Kontaktni metamorfizam gornjokrednih sedimentnih stena Rudnika

Abstract

Kontaktni metamorfizam gornjokrednih sedimentnih stena na planini Rudnik ispitivan je na uzorcima iz pet bušotina. Definisano je šest varijeteta krednih stena (protolita) koji čine dve litološke jedinice izgrađene od klastičnog, karbonatnog i klastičnokarbonatnog materijala. Vulkanskom aktivnosti na Rudniku formirana su vulkanska tela koja se utiskuju duž slojevitosti sedimentnih stena, a neka ih presecaju u vidu dajkova. Starost ovog vulkanskog događaja određena je na 23.9 miliona godina. Ovaj miocenski vulkanizam doveo je do kontaktno metamorfnih promena sedimentnih stena i obrazovanja skarnova i hornfelsa. Skarnovi su klasifikovani kao epidotski, granat-vezuvijanski i granat-piroksenski, dok su hornfelsi bliže definisani po facijama na one iz albit-epidotske hornfels facije, hornblenda hornfels facije i piroksenske hornfels facije. Merenjem temperatura fluidnih inkluzija, utvrđeno je da su u vreme formiranja granata temperature hidrotermalnih fluida bile veoma visoke >560° C. Poslednja hidrotermalna faza pronađena je u kvarcu sa temperaturom homogenizacije fluidnih inkluzija oko 228° C. Granati u kontaktno metamorfnim stenama Rudnika su grosularsko-andraditskog sastava. Ispitivanjima granata na mikrosondi utvrđeno je da centar zrna ima grosularski, a obod andraditski sastav. Oštra granica između grosulara i andradita ukazuje na naglu promenu uslova kontaknog metamorfizma tokom kristalizacije granata. Termobarometrijskim modelovanjem dobijen je dijagram stabilnosti koji ukazuje na temperaturu od 430±30° C i pritisak do 800 bara. Tokom prve faze progradnog metamorfizma formirani su granati i pirokseni, a u drugoj retrogradnoj fazi formiraju se epidot i hlorit. Bitno je napomenuti da je tokom ispitivanja otkriven vezuvijan, čije prisustvo na Rudniku ranije nije zabeleženo.

Contact metamorphism of the Upper Cretaceous sedimentary rocks from Rudnik Mt was studied on core samples from five boreholes. Six varieties of Cretaceous rocks (protoliths) in two distinct lithological units were distinguished. Numerous volcanic bodies that left behind volcanic event in Rudnik before 23.9 Ma are emplaced either along bedding planes in sedimentary rocks, or in a form of cutting dikes. Miocene volcanism resulted in contact metamorphism of sedimentary rocks and formation of skarn and hornfelses. Skarns are classified on epidote, garnet-vesuvianite and garnet-pyroxene skarns, while further division of hornfelses was based on facies. Thus, albite-epidote hornfels, hornblende hornfels and pyroxene hornfelses were distinguished. Thermometric measurements of fluid inclusions reflected on high temperature of hydrothermal solutions, exceeding 560° C, during the garnet growth. The last hydrothermal phase was detected by homogenization temperature of fluid inclusions in quartz at 228° C. Garnets in contact metamorphic rocks from Rudnik consider grossularite-andradite garnets. Microprobe studies revealed on grossularite in the core of garnet crystals, and their rims of andradite composition. Sharp boundary between these two garnet compositions reflects on rapid changes in conditions of contact metamorphism during garnet crystallization. According to pressure-temperature diagram based on thermobarometric modeling the temperature of 430±30° C and pressure up to 800 bars were inferred. During the first stage, i.e. prograde metamorphism formed garnet and pyroxene, whereas in the second, retrograde phase epidote and chlorite derived. It should be mentioned that mineral vesuvianite has not been recorded in Rudnik before doing these researches.