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Timing and magma evolution of the Chelopech volcanic complex (Bulgaria)

Stoykov, Stanislav
Peytcheva, Irena
Von Quadt, Albrecht
Frank, Martin
Published in Schweizerische mineralogische und petrographische Mitteilungen. 2004, vol. 84, p. 101-117
Abstract The Chelopech volcanic complex is located in the Central Srednogorie magmatic zone and hosts one of the largest Cu–Au deposits in Europe. Field observations and sedimentary relationships allow to distinguish three units of the volcanic complex: (I) dome-like bodies, (II) lava to agglomerate flows, and (III) the Vozdol lava breccias and volcanites. The volcanic rocks are porphyritic with plagioclase and amphibole phenocrysts, quartz and biotite are rare. The lava flows contain fully crystallised, fine-grained enclaves of more basic composition. Their mineral chemistry indicates mingling and mixing between two parental magmas. The geochemical evolution of the Chelopech volcanic complex developed from intermediate to basic lavas, but the evolution of the magmatism was more complex including magmatic differentiation, assimilation, mingling and mixing. The trace element distribution is typical for an active continental margin. The magmatic activity commenced at the northern border of the Chelopech region with the intrusion of dome-like bodies at 92.2 ± 0.3 Ma (U–Pb single zircon ID-TIMS dating). The products of the second and the third units are geochronologically indistinguishable within the error uncertainties, and representative samples yield a crystallisation age of 91.3 ± 0.3 Ma. REE abundances reveal a striking positive Ce-anomaly in zircons of unit 2 and zircon core parts of unit 3, which relates to a higher oxidation state of the parental magma. Sr and Nd isotopic compositions suggest a mixed mantle and crustal source of the Turonian magma. Initial Sr ratios range between 0.70470 and 0.70554, and 90(Nd) varies between –2.27 and –3.55. 90(Hf) values of concordant zircons corroborate this data and range between +2.90 to +5.02 in the andesite of the first unit and from +1.06 to +1.38 in the volcanites of the second and third unit.
Keywords Late Cretaceous volcanitesChelopechpetrologyU–Pb zircon geochronologygeochemistry
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Research group Mineral Resources and Geofluids
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STOYKOV, Stanislav et al. Timing and magma evolution of the Chelopech volcanic complex (Bulgaria). In: Schweizerische mineralogische und petrographische Mitteilungen, 2004, vol. 84, p. 101-117. https://archive-ouverte.unige.ch/unige:24001

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Deposited on : 2012-11-14

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