Precambrian zircons in chromitites of the Cretaceous Aladag ophiolite (Turkey) indicate deep crustal recycling in oceanic mantle

Crustal recycling into Earth's deep mantle has been inferred from both seismic tomography and geochemical observations. As a further line of evidence, we report on zircons having a wide range of ages that were recovered from the Aladag chromitites, providing direct evidence for crustal recycling. Mesozoic zircons represent the earliest stages of Neotethyan seafloor spreading magmatism, whereas Neoproterozoic and Mesoproterozoic-Archean zircons record recycled old crustal material entrained in the ophiolitic mantle melt sources. The incorporation of such old, crustal zircons into the Neotethyan mantle might have followed from previous subduction events, from lithospheric delamination, and/or from the dismantling of West Gondwana in the Permo-Triassic. Subduction-affiliated ophiolitic melts may have picked up these recycled zircons and integrated them into chromitites, which precipitated from peridotite-melt interactions in a mantle wedge beneath the Inner-Tauride (a Neotethyan seaway) seafloor spreading system. Common in ophiolitic chromitites within the Neotethyan realm, such unusually old zircons present unique archives for tracking crustal recycling and mantle processes during rift-drift, seafloor spreading and subduction zone evolution of the oceanic mantle. We conclude that ophiolitic mantle peridotite and chromitite may be an important archive for preserving the recycling history of crustal material back into Earth's deep mantle.