Generation and exhumation of granitoid intrusions in the Penjween ophiolite complex, NW Zagros of the Kurdistan region of Iraq: Implications for the geodynamic evolution of the Arabian-Eurasian collision zone

: Sabah A. Ismail, Renas I. Koshnaw, Douglas E. Barber, Heider Al Humadi, Daniel F. Stockli

Publisher: ELSEVIER

: 2020

: Lithos

: LITHOS

: ARTN 105714

: 376

: 13

: 0024-4937

: 1872-6143

DOI: https://doi.org/10.1016/j.lithos.2020.105714

The Penjween ophiolite complex represents a remnant of the Neotethys oceanic crust that was preserved in the Zagros Suture Zone of NE Iraq. The complex is composed of dunite, harzburgite, and pyroxenite at the bottom, gabbro in the middle, and diorite at the top. Minor peraluminous granitiod intrusions of different types were identified in the complex. These granitoids are classified into trondhjemite and pegmatitic granite. Zircon grains from these intrusions show different ages and geochemistry, pointing at differences in their genesis and composition of the parentmelts. The trondhjemite has an age of similar to 90Ma giving the minimum age of the ultramafic section. This indicates that the mafic rocks were underlain by a source capable of yielding silica-saturated sodic granitoids. The pegmatitic granitewith high potassiumcontent, has a U-Pb zircon age of similar to 46Ma, suggesting derivation froma non-mafic sourcemelt at a younger age. The (U-Th)/(He-Pb) double dating on zircons from the trondhjemite and pegmatitic granite intrusions indicate a comparable exhumation age of similar to 23 Ma. These results suggest that two episodes of magmatism occurred prior to the final closure of the Neotethys. In the Late Cretaceous event, melting of amafic source formed trondhjemites, whereas in themiddle Eocene event, possiblymelting of the associated sedimentary rockswith the downgoing Neothethys oceanic slab formed pegmatitic granite. The similar exhumation time of the two genetically different granitoids suggests that the Penjween ophiolite complex was exhumed by the beginning of Miocene, potentially as a consequence of the Arabian-Eurasian plate collision.