Dynamic Mantle Support Beneath the Eastern Anatolian Plateau Since ~13 Ma Inferred from Zircon Hf Isotopes

The Eastern Anatolian Plateau is a broad, high-elevation (~2 km), low-relief collisional plateau in eastern Turkey that developed following the Arabia-Eurasia collision and the transition to a post-collisional tectonic setting. It occupies a central position between the Bitlis-Zagros suture to the south and the Eastern Pontides-Lesser Caucasus mountain ranges to the north and is associated with widespread Neogene volcanism. Since the Early-Middle Miocene, uplifted regions along the Bitlis segment of the Arabia-Eurasia convergence zone, including parts of the Eastern Anatolian Plateau, were drained toward the northern Eastern Mediterranean, delivering large volumes of sediment to the deep sea and forming thick flysch successions. These deposits archive the crustal inventory exposed at the time and provide a valuable record of the tectono-magmatic evolution of the convergence zone. Here, we present detrital zircon U-Pb-Hf data from Late Miocene sediments recovered from DSDP Sites 375/376 and ODP Site 968 in the northern Eastern Mediterranean to constrain the sequence of tectono-magmatic events associated with Arabia-Eurasia convergence, with particular emphasis on the timing of the establishment of a post-collisional regime. Detrital zircon U-Pb-Hf data record Upper Cretaceous and Eocene magmatic flare-ups related to Neotethys subduction, as well as a prominent Miocene magmatic flare-up with distinct age modes at ~17, ~11, and ~6 Ma associated with the transition to a post-collisional regime. Hf isotope compositions of Miocene detrital zircons reveal a systematic shift from highly variable, evolved signatures before ~13 Ma to predominantly juvenile signatures thereafter. This shift indicates an increasing contribution of mantle-derived sources to magmatism since the mid-Miocene, relative to earlier evolved or mixed mantle-crustal sources. We interpret this transition to indicate that Neotethys slab break-off or lithospheric mantle delamination beneath Eastern Anatolia had largely progressed toward completion by ~13 Ma, signaling the establishment of post-collisional tectonic conditions. Notably, this transition slightly predates the inferred onset of plateau uplift at ~11 Ma, suggesting that mantle reorganization beneath Eastern Anatolia preceded, and was not synchronous with, the surface expression of uplift.