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The Miocene granitoid rocks of Mt. Bukulja (central Serbia): evidence for pannonian extension-related granitoid magmatism in the northern Dinarides

Vladica Cvetkovi^1,*, Giampiero Poli², George Christofides³, Antonis Koroneos³, Zoltan Pécskay⁴, Kristina Resimi-ari¹ and Vladisav Eri⁵

¹ Faculty of Mining and Geology, University of Belgrade, uina 7, 11000 Belgrade, Serbia
² Department of Earth Sciences, University of Perugia, Piazza Universita’, 06100 Perugia, Italy
³ Faculty of Sciences, School of Geology, Department of Mineralogy, Petrology and Economic Geology, Aristotle University, Thessaloniki, Greece
⁴ Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), Bem ter 18/c, 41001 Debrecen, Hungary
⁵ RIO SAVA Exploration, Bulevar Mihajla Pupina 10i, 11000 Belgrade, Serbia

^* Corresponding author, e-mail: cvladica{at}mkpg.rgf.bg.ac.yu

The study presents evidence about the origin and evolution of the Miocene (20–17 Ma) granitoid pluton of Mt. Bukulja, situated within the southern Pannonian/northern Dinarides region (central Serbia, south-central Europe). The pluton is composed of slightly peraluminous two-mica granite (TMG), metaluminous hornblende-biotite and biotite-bearing (H-BG) granite and rare aplite granite. A lamprophyre dyke (BLD) similar in composition and age to other Serbian primitive minettes has been found in the vicinity of Mt. Bukulja. The available and newly determined radiometric age suggests that the TMG was emplaced around 20 Ma whereas the age of the H-BG is inadequately constrained. TMG and H-BG show similar petrographic characteristics but evidence of open system magma processes is found only in the H-BG. In comparison to the H-BG, the TMGs are less enriched in most trace elements, including REE, and have a more fractionated REE-pattern and stronger negative Eu-anomaly. The TMGs display a wider range of initial Sr-Nd isotope ratios (⁸⁷Sr/⁸⁶Sr_{20 Ma} = 0.70652–0.71368 and ¹⁴³Nd/¹⁴⁴Nd_{20 Ma} = 0.51223–0.51283) than the H-BG (⁸⁷Sr/⁸⁶Sr_{20 Ma} = 0.70768–0.70781 and ¹⁴³Nd/¹⁴⁴Nd_{20 Ma} = 0.51242–0.51256). Geochemical modeling suggests that the H-BG could have derived from a BLD-like melt by mixing plus fractionation processes assuming a batch of TMG-like magma as the acid end-member. On the other hand, the geochemical variability of the TMG is reproduced by an AFC model with an assimilation/fractionation ratio (r) of 0.5 and with high amount of crustal component (~20–50 %) starting from the least evolved TMG rocks. In the modeling, the average composition of the least evolved TMG samples was used to represent the parental magma composition whereas the composition of adjacent metamorphic rocks was adopted as possible contaminant. The composition of the least evolved TMG implies that the TMG parental magma likely originated by melting of a mafic lithology such as earlier basalts underplating in the lower crust. The high proportions of crustal assimilation along with other geochemical and geological evidence suggest that the Mt. Bukulja TMG originated within the same geotectonic setting as acid volcanics of the north Pannonian Basin. The results of this study support the hypothesis that the Mt. Bukulja pluton is related to tectonomagmatic events controlled by the early extensional phases in the opening of the Pannonian basin.

Key-words: granite, peraluminous, assimilation, crust, Balkan Peninsula, igneous petrology, geochemistry.