Coherent subduction underplating of CBU-correlative blueschist-facies metasedimentary slices, Pelion, Greece

Studies of exposed high pressure-low temperature (HP-LT) metamorphic complexes are critical for advancing our understanding of subduction processes, such as underplating, metamorphism, and exhumation. Exhumed blueschist-facies metasedimentary and volcanic rocks exposed on the Pelion peninsula (eastern Thessaly, Greece) represent one of the largest coherent exposures of subduction-complex rocks in the eastern Mediterranean and are key for understanding early Cenozoic Hellenic subduction processes. In this study, we present new detrital zircon and apatite U-Pb data to reconstruct the stratigraphic anatomy and provenance of these rocks and to understand their correlation with other Aegean (Cycladic) HP-LT rocks and the Pelagonian Zone of mainland Greece.

Detailed new U-Pb zircon and apatite data show two distinct, coherent, and stratigraphically upright structural slices, with (1) the South Pelion slice consisting of Permian-Late Cretaceous strata overlying Carboniferous basement and (2) the North Pelion slice comprising Triassic-Late Cretaceous strata overlying Neoproterozoic basement. Both slices exhibit Late Cretaceous strata at the top of the section characterized by cosmopolitan detrital zircon (DZ) signatures. Zircon U-Pb data of rim overgrowths suggest subduction-metamorphism occurred during the early Cenozoic with temperatures not reaching >450°C, as indicated by non-reset or -recrystallized apatite U-Pb ages and the absence of garnet.

Comparison of compiled DZ data from the CBU and our data from the Pelion blueschists supports a correlation in the pre-subduction paleogeography, with protolith deposition during Permo-Carboniferous intra-arc extension and early Mesozoic Adria-Pindos rifting. The data show that the Pelion blueschists, representing lateral equivalents of the CBU, are comprised of two coherently underplated upper-crustal slivers, separated by Late Cretaceous flysch, and metamorphosed during Cenozoic Hellenic subduction beneath the Pelagonian convergent margin.