Early Cretaceous to Miocene Tectonic Evolution of the NW Cyclades Based on 40Ar/39Ar Multiple Single Crystal Dating of White Mica From Andros

The Aegean region marks the convergent boundary between the African and Eurasian plates, reflecting complex tectonic processes, including the closure of the Pindos ocean. The Pelagonian unit (PU) forms the core of mainland Greece and was part of the Eurasian continental margin, while the Pindos oceanic crust subducted beneath it. This crust underwent high-pressure metamorphism and is now represented in the Aegean region by the Cycladic Blueschist Unit (CBU). On Andros, the northernmost Cycladic island, the contact between the deeply subducted CBU and the supracrustal Hellenic nappe stack is exposed. The tectonic affinity of the Makrotantalon Unit (MU) and Upper Unit (UU), both overlying the CBU, and the timing of deformation along the shear zones separating them remain unclear. We used structural analysis and white mica single-grain 40Ar/39Ar dating to reinterpret the northern Andros structure. We propose that the MU and UU form a single unit equivalent to the PU. The MU- CBU contact is interpreted as the lateral equivalent of the UU-CBU contact, which was reactivated during the Oligocene-Miocene, forming the North Cycladic Detachment System. Our multiple single-grain 40Ar/39Ar dating approach is capable of resolving mixed ages from three distinct deformation events by dating individual crystals in a single sample. Early Cretaceous ages reflect deformation in the MU and UU caused by the Pelagonian-Rhodopia collision. Eocene exhumation of the CBU as an extrusion wedge through the subduction channel was followed by extensional exhumation along the North Cycladic Detachment System, leading to Oligocene-Miocene ages and brittle deformation.