Coherent underplating of HP-LT blueschist packages and basement during Hellenic subduction recorded by zircon U-Pb data, Pelion, Greece

Studies of HP-LT metamorphic complexes are crucial in advancing our understanding of subduction processes, such as underplating, metamorphism and exhumation. Detailed new U-Pb zircon data of blueschist facies metasedimentary units at Pelion indicate two distinct stratigraphically upright and coherent structural slices: (1) the South Pelion slice consisting of strata with Permian-Late Cretaceous zircon maximum depositional ages; and (2) the North Pelion slice consisting of strata with Triassic-Late Cretaceous zircon maximum depositional ages. Both slices have Late Cretaceous strata at the top of the section with cosmopolitan detrital zircon signatures. The ages from zircon U-Pb rim overgrowths correlate with existing constraints from subduction metamorphism during the Paleocene-Eocene, with a possible second stage recorded during basal underplating in the Late Eocene-Oligocene. Detrital zircon provenance data and multi-dimensional scaling comparisons demonstrate a tectono-metamorphic linkage between the Pelion rocks and the Cycladic Blueschist Unit, and between the southern Pelion basement and the Cycladic basement. Protolith deposition for Pelion blueschist facies rocks occurred during Permo-Carboniferous intra-arc extension and Adria-Pindos rifting. Our results show that the Pelion blueschist facies rocks, representing lateral equivalents of the Cycladic Blueschist Unit, consist of two separate, coherent upper crustal slivers that were underplated and metamorphosed during Hellenic subduction beneath the Pelagonian margin.