Peri-Amazonian provenance of the Proto-Pelagonian basement (Greece), from zircon U–Pb geochronology and Lu–Hf isotopic geochemistry

Abstract

The basement of the Pelagonian zone of the Hellenides, in the Eastern Mediterranean realm, has been shaped by mid-Neoproterozoic (700Ma) and Variscan (300Ma) igneous activities. In the present study, detrital zircon U–Pb geochronology and Lu–Hf isotope geochemistry of ca. 700Ma-aged granites and of pre-700Ma metasediments from the Pelagonian zone allow a genuine perspective into the provenance and origin of this terrane which hosts one of the oldest sedimentary sequences known in SE Europe. Pelagonian crustal vestiges comprising 700Ma granitoids and their hosting metasediments are termed here “Proto-Pelagonian”.Except from several concordant Tonian-aged detrital zircon grains (as young as 980Ma), which set the Early Tonian as a maximum sedimentation age, a preponderance of the detrital zircon grains separated from four Proto-Pelagonian metasedimentary samples yielded Mesoproterozoic–Paleoproterozoic ages peaking at 1.5Ga. Neoproterozoic-aged detrital zircon grains are generally absent. The detrital zircon isotopic data is thus consistent with an Amazonian source for this sequence. In terms of their detrital zircon age spectra, Proto-Pelagonian metasediments exhibit close similarity to pre-Avalonian metasedimentary sequences (e.g. Gamble Brook Formation) which underlie Late Neoproterozoic "typical Avalonian" successions in Atlantic Canada.The detrital zircon age signal obtained from the pre-700Ma metasediments is however markedly different from that previously obtained from African-derived terranes which are imbricated with the Pelagonian zone in the Eastern Mediterranean region and which are usually devoid of Mesoproterozoic detrital zircon grains (other than Stenian). Likewise, the Proto-Pelagonian basement also differs from Avalonian-type terranes previously identified in the Eastern Mediterranean–SE European region (Istanbul block of the Pontides, Pirgadikia terrane of the Internal Hellinides, North and Central Dobrogea and Danubian basement), which alongside abundant Mesoproterozoic zircon grains contain also Neoproterozoic-aged detrital zircons. Thus, from the point of view of the pre-Variscan geological history, the Pelagonian zone is exotic with respect to surrounding terranes of both, North African and Avalonian origins.