Unraveling protolith ages of meta-gabbros from Samos and the Attic–Cycladic Crystalline Belt, Greece: Results of a U–Pb zircon and Sr–Nd whole rock study

• New isotopic ages provide key information for an improved geodynamic interpretation.
• We report the first U–Pb zircon ages for meta-gabbros from Samos, Greece.
• Late Cretaceous protolith ages are documented for meta-ophiolitic rocks.
• Sr–Nd isotope and REE data of meta-gabbros cannot be used as proxy for tentative age assignments.
• A genetic link with the major Greek or Turkish ophiolites remains uncertain.

The focus of this study is on meta-ophiolitic rocks from Samos and the Attic–Cycladic Crystalline Belt, Greece. SHRIMP U–Pb zircon geochronology, Sr–Nd isotope and bulk-rock geochemistry have been applied to meta-gabbros that occur as blocks and lenses in blueschist-facies mélanges on Samos and Evia, and in the greenschist-facies Upper Unit on Tinos. The geodynamic significance of these meta-ophiolite fragments within the overall pattern of the Eastern Mediterranean region is unclear. Regional correlations within the Cyclades archipelago and with the Jurassic meta-ophiolites of the Balkan region or the Cretaceous occurrences in Turkey are uncertain. Although field, petrological and geochemical similarities among some mélange occurrences suggest a common genetic relationship, such interpretations remain speculative if not supported by robust geochronological data. SHRIMP U–Pb zircon dating of three meta-gabbro blocks from Samos yielded Cretaceous ages with weighted mean 206Pb/238U ages of 78.3 ± 1.3 Ma, 76.8 ± 1.4 Ma and 77.8 ± 1.4 Ma and almost identical intercept ages, interpreted to indicate the time of magmatic crystallization. These results further substantiate models suggesting a correlative relationship with mélanges on the islands of Syros and Tinos, central Aegean Sea, where similar rocks yielded almost identical U–Pb zircon ages.Published and new Sr–Nd isotope data of meta-gabbros from Andros, Samos, Tinos (Lower Unit) and from mainland Greece (Pindos, Othris) reveal distinctive differences among ion probe-dated samples with Jurassic and Cretaceous protolith ages. Three groups can clearly be distinguished in a 87Sr/86Sr vs. 143Nd/144Nd diagram. However, these geochemical parameters do not allow assigning tentative age estimates for yet undated meta-gabbros from southern Evia and the Upper Unit of Tinos. The situation is further complicated by the observation that the Jurassic and Cretaceous meta-gabbros do not show other discriminating geochemical characteristics that could provide plausible arguments for an approximate age assignment to undated rocks.