Geochronology, geochemistry and isotope tracing of the Oligocene magmatism of theudBuchim–Damjan–Borov Dol ore district: Implications for timing, duration and source ofudthe magmatism

摘要

Timing, source and magmatic evolution of the intrusions in the Buchim–Damjan–Borov Dol ore district of theudFormer Yugoslav Republic of Macedonia (F.Y.R.O.M.) have been studied. They intrude the Circum Rhodope Unitudclose to the contact with the Vardar Zone and are a part of the Late Eocene–Oligocene Macedonian Rhodope–udNorth Aegean belt. The magmatism at Buchim–Damjan–Borov Dol occurred between 24.04 ± 0.77 andud24.51 ± 0.89 Ma, as indicated by chemical-annealing (CA)–LA ICP-MS zircon dating. Major element, trace andudrare earth element analyses have been performed on the various intrusive rocks. All ore bearing magmas wereudclassified as trachyandesitic, except the youngest intrusion which is not associated with mineralization; theudBlack Hill locality (24.04 ± 0.77 Ma) shows a trachytic composition. The distribution of the trace elements,udenrichment of large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE), indicatesudsubduction-related magmatism; most of the magmas follow a calc-alkaline fractionation trend with shoshoniticudaffinities; additionally, Sr/Y (10 to 90) and La/Yb values show somesimilarities to adakite-likemagmas. Sr and Ndudisotope ratios (Sri = 0.70658 to 0.70740 and Ndi = 0.512425–0.512497) showthat themagmatic productswereudslightly contaminated by continental crust material, e.g., the Variscan/Cadomian basement. In the Late Eocene–udOligocene belt the magmatism between 29 and 35 Ma is dominated by crustal melting with an increase in theudmantle contribution between 20 and 27 Ma. We suggest the following scenario for the magmatic history of theudBuchim–Damjan–Borov Dol ore district: a slab rollback of an oceanic slab located further to the SW which ledudto extensional and compressional features in upper levels of the continental crust. In the middle to upper crustudthree consecutive crystallization stages occurred at variable depths as indicated by amphibole zonation. Mixingudof newly formed crust with mantle-like affinities and continental crust material in variable degrees during theudascent of the magma can explain all geochemical characteristics. The magma crystallized as dykes or stocksudnear the Earth's surface (>1 km) after its final emplacement and contemporaneous hydrothermal activity ledudto different mineralization styles depending on the lithology of the host rocks.