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Mišur, Ivan
06/2017Web Resource
Metasedimentne stijene Medvednice, koje se nalaze na prostoru Zagorje-Mid-Transdanubijske zone, zabilježile su nekoliko faza deformacija od kojih je najintenzivnija uzrokovala metamorfizam unutar facijesa zelenih škriljavaca. U radu su obrađene litostratigrafske jedinice Stari potok, Slani potok, Risnjak i Vila Rebar. Posebna pozornost je posvećena kloritoidnom škriljavcu iz jedinice Stari potok. Napravljene su petrografske i geokemijske analize (XRD, ICP-MS). Uvjeti metamorfizma određivani su pomoću geotermometara za klorit i parove klorit-kloritoid te geobarometara za muskovit (fengit). Konstruiran je dijagram pseudopresjeka za uzorak kloritoidnog škriljavca, izoplete udjela Mg u kloritu i kloritoidu te izoplete Si u muskovitu (fengit). Starost progradne faze metamorfizma izmjerena je na monacitima (EMP), pri čemu je dobivena starost srednje do gornje jure (153 ± 6,9 Ma). Mjerenje sadržaja izotopa U-Th-Pb napravljeno je na zajednici detritnih cirkona pomoću LA-ICP-MC-MS-a. Dobiveni starosni podaci cirkona dali su vrijednosti koje su grupirane u devet podgrupa, unutar šest starosnih grupa. Na temelju najmlađe starosne podgrupe cirkona procijenjena je maksimalna starost taloženja. Iz petrografskih analiza na uzorcima metasedimenata litostratigrafskih jedinica Stari potok, Risnjak, Vila Rebar i Slani potok, utvrđena je metamorfna mineralna asocijacija koju čine kvarc, bijeli tinjac, klorit, ± albit, ± biotit, ± kloritoid, ± turmalin, ± monacit, ± ksenotim, ± apatit. Sačuvani akcesorni detritarni minerali su cirkon i rutil. Mineralna asocijacija ukazuje na nizak stupanj metamorfizma unutar facijesa zelenih škriljavaca. Geokemijski podaci sugeriraju da su protoliti istraživanih metasedimentnih stijena uglavnom bili srednje do intenzivno trošeni zreli sedimenti, nastali taloženjem nakon trošenja stijena pretežito granitoidnog sastava, ugrađenih u vulkanski luk. Metasedimentary rocks from Mt. Medvednica, located in Zagorje-Mid-Transdanubian zone, had undergone multiphase deformation history. The most intense deformation phase is manifested by the most intense metamorphic phase, which reached greenschist metamorphic facies. This thesis investigated Stari potok, Slani potok, Risnjak and Vila Rebar lithostratigraphic units, with special attention given to the occurrence of chloritoid schist in Stari potok unit. Petrographic and geochemical analysis were conducted (XRD, ICP-MS). Metamorphic conditions were investigated with geothermometers for chlorite and pairs of chlorite-chloritoid, while geobarometric conditions were calculated on muscovite (phengite). Pseudosection diagram, isopleths of XMg in chlorite and chloritoid, as well as XSi in muscovite (phengite) were modeled using software package PerpleX. Late Jurassic (153 ± 6.9 Ma) metamorphic age was determined based on sinmetamorphic monazite grains analysis. Ratios of U/Th/Pb from detrital zircon grains were measured on LA-ICP-MC-MS, resulting in recognition of nine subgroups within six detrital zircon age groups. Youngest subgroup of detrital zircons gave insight into deposition time of the protolith sediment. Petrographic analysis of metasediment samples of litostratigraphic units Stari potok, Slani potok, Risnjak and Vila Rebar indicated metamorphic mineral association of quartz, white micas, chlorite, ± albite, ± biotite, ± chloritoide, ± turmaline, ± monazite, ± xenotime, ± apatite. Accessory mineral phases are zircons and rutile. Mineral association is typical for low greenschist metamorphic facies. Geochemical data indicate that protolith sediments were mature, middle to intensively weathered sediments, produced by deposition after weathering of mainly volcanic arc granitoid rocks.
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