Geochemical comparison of felsic Eocene granite intrusions in the Rhodope massif, southern Bulgaria and northern Greece

We compare whole rocks geochemistry of several felsic granite bodies of similar age (53-42 Ma) that are emplaced into the intermediate and upper plate of the Central Rhodope metamorphic core complex (CRMCC), namely: the Smilyan granite in the southernmost part of the Madan unit; the Pripek granite in the Startsevo unit, the Yugovo granites in the Assenitsa unit and the Paranesti granite from the Barutin-Buynovo-Elatia-Skaloti-Paranesti plutonic complex partially hosted by the Madan and Assenitsa units. The time span of granite intrusions overlaps the period of synmetamorphic partial melting in the CRMCC (~50-36 Ma) and clearly predates the anatectic melts crystallization in the core of the complex (38-36 Ma). The temporal and spatial proximity suggests genetic/feedback relations between intrusive granites and migmatites.
   The geochemical features of the compared granites show predominantly felsic compositions (SiO₂ > 70 %) and alkaline-calcium to Ca-alkaline and alkaline characteristics. The Smilyan, Pripek and Paranesti granites are meta- to peraluminous (A/CNK 0.80-1.29), and Yugovo granites are only peraluminous (A/CNK 1.06-1.26). High Ba (≥1000 ppm) and Sr (>600 ppm) content is a common feature of granite LILE (Ва, Sr, Rb) geochemistry. Negligible negative to positive Eu-anomaly (Eu/Eu* 0.8-1.2) and high LREE/HREE ratios (up to 54.1) are typical of the chondrite-normalized REE patterns. Increasing Rb/Sr (0.04→1.53) and Rb/Ba (0.03→0.45) ratios towards the most felsic granites mark a trend of feldspar fractional crystallization. The LILE distribution patterns of Pripek and Paranesti granites indicate more evolved differentiation than the Smilyan granite. Decreasing Zr and Hf contents and Zr/Hf ratios towards the higher-silica compositions reflect typical magmatic trends with zircon fractionation and enhance the close geochemical resemblance of the granite intrusions. All of them display volcanic-arc and collision-related affinity according to the most popular discriminations based on incompatible trace elements. The isotopic data available support granite magma generation from predominantly igneous precursors of mixed mantle-crust characteristics.
   On the other hand the granite intrusions show remarkable geochemical similarities with in situ formed anatectic melts from the CRMCC diatexitic core (felsic peraluminous compositions, low HFSE and REE, high LILE contents and LREE/HREE ratios, and negligible negative to positive Eu anomaly) that infer to a common mechanism of granite magma generation, e.g. crustal melting. The younger age of the anatectic melts (37-38 Ma) precludes direct feedback relations between intrusive granites and migmatites. A low temperature crustal melting involving mainly felsic minerals from orthometamorphic substratum could explain the granite magma origin and its similarities with the younger
anatectic melts from the CRMCC core.
   Acknowledgements: This work was supported by the National Science Fund of the Ministry of Education and Science in Bulgaria, projects DO 02-363/2008 and DO 02/-327/2008.