Geochemical features of the depression basin-related magmatism in Southeastern Rhodope Massif and Circum-Rhodope Belt: the Tertiary Evros volcanic rocks (Western Thrace, Northeastern Greece)

The Tertiary Evros volcanic rocks (EVR) crop out in western Thrace, in close association with depression sedimentary basins, which developed during the Tertiary extension. K/Ar ages range from 33.4 to 19.5 Ma, establishing an Oligocene (33.4-25.4 Ma) and an Early Miocene (22.0-19.5 Ma) volcanic activity. EVR are distributed in three main volcanic areas, namely Loutros-Feres-Dadia, Kirki-Esimi and Mesti-Petrota, after the corresponding basins. The EVR chemical composition ranges from basaltic andesite to rhyolite through andesite, latite, trachydacite and dacite. Basaltic andesites have two pyroxenes, whereas andesites bear either pyroxene or biotite-hornblende. Pyroxenes and biotite are the mafic phases in latites and trachydacites, whereas dacites bear mostly biotite and hornblende and locally pyroxene. Rhyolites have mainly biotite and rarely hornblende. All rocks are porphyritic with glassy, holocrystalline or semicrystalline textures. Two main groups of rocks have been distinguished, the PxBt group comprising basaltic andesites, pyroxene andesites, latites, trachydacites and dacites, and the HblBt group comprising hornblende-biotite andesites, dacites and rhyolites. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and, locally, shoshonitic features. Mantle normalised trace element patterns display LILE enrichments relative to HFSE and negative spikes of Ta, Nb, and Ti, features associated with orogenic magmatism. The (87Sr/86Sr)i and (143Nd/144Nd)i of both PxBt and HblBt groups are variable, ranging from 0.70540 to 0.70773 and from 0.51260 to 0.51242, respectively, for the PxBt samples; for the HblBt samples the ranges are: 0.70639-0.70832 and 0.51249-0.51235, respectively. Geochemical fingerprints and Sr-Nd isotope ranges of EVR are in favour of an enriched mantle as the source region. Distinct geochemical trends of PxBt and HblBt groups indicate different evolutionary histories. Geochemical patterns, along with the relationships between Sr and Nd isotopes, and between these isotopes and SiO2, provide evidence of contamination of mafic melts by interaction with crust during magma differentiation. MFC processes, with crustal melts having variable geochemical and isotope characteristics, may account for compositional variations between PxBt and HblBt rocks and within the two groups.