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

Studies of high pressure-low temperature (HP-LT) metamorphic complexes are critical for 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, with (1) the South Pelion slice consisting of strata with Permian-Late Cretaceous zircon maximum depositional ages (MDAs) and (2) the North Pelion slice comprising strata with Triassic-Late Cretaceous zircon MDAs. Both slices have Late Cretaceous strata at the top of the section with cosmopolitan detrital zircon (DZ) signatures. 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. DZ provenance data and multi-dimensional scaling (MDS) comparisons demonstrate a tectono-metamorphic linkage between the Pelion rocks and the Cycladic Blueschist Unit (CBU), and between the southern Pelion Basement and the Cycladic Basement (CB). 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 CBU, are comprised of two separate, coherent upper-crustal slivers that were underplated and metamorphosed during Hellenic subduction beneath the Pelagonian margin. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: https://doi.org/10.6084/m9.figshare.c.7008123