Tertiary volcanic rocks from Samothraki island (north Aegean, Greece): Sr and Nd isotope constraints on their evolution.

In Samothraki Island (northeast Aegean Sea, Greece) voluminous Tertiary volcanic products are present, associated to the widespread volcanic activity as a result of post-collision extensional processes. The rocks have characteristics of calc-alkaline to high-K calc-alkaline and shoshonite series. Three groups can be distinguished, based on geochemical and isotopic data: a) the "older" group, comprising basalts to latites, b) the "younger" group having latites to rhyolites, and c) the "intermediate" group that interim the two. The oldest volcanic products are around 25 Ma whereas the last ones are 17 Ma. Variation diagrams reveal distinct trends between the older and younger group, while the intermediate one generally overlap the former. The REE patterns are very similar and tightly banded showing quite enrichment relative to chondrite (LaN = 61 - 336). (La/Yb)N, ?REE and Eu/Eu* clearly define the three groups. MORB-normalised spiderdiagrams are strongly enriched in LILE and show Nb and Ti negative anomalies characteristic of subduction related environments. The Sr and Nd isotopic ratios range respectively from 0.70876 to 0.70978 and 0.512184 to 0.512290 for the "younger", 0.70581 to 0.70603 and 0.512550 to 0.512593 for the "intermediate" and 0.70501 to 0.70522 and 0.512651 to 0.512693 for the "older" group. A continuous evolution for the Tertiary volcanic rocks of Samothraki Island is ruled out. Isotope and trace element models showed that the more evolved rocks of the "older" group were formed through MFC (r = 0.3; F = 0.4) involving two melts originated in different parts of a heterogeneously metasomatized mantle source. The "younger" group was evolved mainly through mixing of 20-30% of a melt, originated in the same metasomatized mantle source, with a crustal melt from a theoretical average "alpine crust". Further crust assimilation by the hybrid magma cannot be excluded.