New and compiled geochemical, isotopic and geochronological data allow us to propose a new explanation for Paleogene oceanic magmatic rocks along the Iran–Iraq border. These rocks are represented by a thick pile (>1000 m) of pillow lavas and pelagic sediments and underlying plutonic rocks. These are sometimes argued to represent a Paleogene ophiolite but there are no associated mantle rocks. Integrated zircon U–Pb ages, bulk rock major and trace element and radiogenic isotope data indicate that these rocks are more likely related to forearc rifting due to extreme extension during Late Paleogene time which also triggered high-flux magmatism in the Urumieh–Dokhtar Magmatic Belt and exhumation of core complexes in Iran. These observations are most consistent with formation of the Paleogene oceanic igneous rocks in a >220 km long forearc rift zone.

Supplementary material: Detailed analytical procedure and tables S1 to S6 are available at: https://doi.org/10.6084/m9.figshare.c.4972994

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