U–Pb zircon ages of Late Cretaceous Nain–Dehshir ophiolites, central Iran

Abstract

Late Cretaceous Zagros ophiolites are part of the c . 3000 km long Late Cretaceous Ophiolite Belt of SW Asia including the Troodos (Cyprus), eastern Mediterranean (Turkey, Syria), Zagros (Iran) and Semail ophiolites (Oman). This ophiolite belt represents a magmatic forearc that formed when subduction of the Neotethys began along the SW margin of Eurasia. Geochronological data for Zagros ophiolites are limited to a few K–Ar and 40 Ar– 39 Ar ages. New thermal ionization mass spectrometry U–Pb zircon ages indicate that the Nain and Dehshir ophiolites of central Iran formed c . 101–103 Ma, with Nain (102.9 ± 0.3 Ma) being c . 1 Ma older than Dehshir (100.9 ± 0.2 Ma; 100.4 ± 0.1 Ma), and that these ophiolites were emplaced almost immediately after formation (Nain emplacement 101.2 ± 0.2 Ma; Dehshir emplacement 99.0 ± 1.1 Ma). These formation ages are significantly older than the 98–90 Ma U–Pb zircon ages of other Late Cretaceous ophiolites in this belt such as the Kizildag (Turkey), Semail (Oman) and Troodos ophiolites (Cyprus). If the subduction initiation model applies to this ophiolite belt, it suggests that subduction initiation began near the Zagros margin and propagated at c . 7 cm a −1 to the east (Semail) and c . 15 cm a −1 to the west (Troodos). Supplementary materials: Simplified geological maps of the Nain and Dehshir ophiolites, showing sample locations, are available at www.geolsoc.org.uk/SUP18554 .