Petrology of Upper Cretaceous island-arc ore-magmatic centers from Central Srednogorie, Bulgaria: Magma evolution and paths

Abstract. Magmatic rocks of Late Cretaceous age from the Central Srednogorie, Bulgaria show marked variations in its geochemistry. The present study is focused on the common features in the magma evolution paths of several ore-magmatic systems: Elatsite, Chelopech, Medet, Assarel, Elshitsa and Capitan Dimitrievo considered as links of a petrological across-arc transect. The whole range of SiO2 is large (40-73%). The evolution from intermediate to more basic stages is a common characteristic for most of the centers, but it is complicated by fractional differentiation and mixing of magmas. High-K calc-alkaline to shoshonitic series predominate, calc-alkaline being only in the middle of the transect. The geochemical peculiarities are typical for an enriched mantle source and indicate a subduction-related volcanic-arc setting. Melting degrees are estimated as small for both ends of the transect and higher for the central parts. The magmatic activity started at the northern end of the transect at 92.1 Ma, gradually became younger and finished at the border to the Rhodopes massif at 78 Ma. The 87Sr/86Sr ratios (0.704-0.706), suggest melts generated in a mantle source, modified by the addition of crustal materials. Pb-isotope analyses and ε-Hf values show an increase of the radiogenic component from North to South. The subduction slab retreat mode