The mineralogical and petrological constraints of the Cretaceous Kermanshah ophiolitic complex in Nourabad and Dinavar regions in western Iran

As a part of the Kermanshah ophiolite in western Iran, the Cretaceous Nourabad-Dinavar ophiolitic complex is a remnant of the Neo-Tethys oceanic lithosphere and represents transitional mantle-crust and upper crust units in the Nourabad and Dinavar regions, respectively. All the units were affected by the two metamorphic regimes of static metamorphism and dynamic metamorphism. The whole-rock chemical data of the basic samples (i.e. gabbros, basalts, and dykes) show that they are related to the island-arc regime. The main reasons for this conclusion are as follows: their affinity with the calc-alkaline series, LREE enrichment, and subduction-related proxies such as the negative anomalies of Nb, Ta, Zr, and Hf and the positive anomaly of Th. On the other hand, the mineral chemistry analysis confirms that the studied ophiolitic complex is a MORB-type ophiolite emplaced in the supra-subduction zone. This is supported by mineralogical evidence including the compositional dependence of olivines (fo_90-91) on the spinel peridotite mantle facies, spinel minerals (Al-chromite and Mg/Cr-bearing hercynite), and Mg-rich orthopyroxenes (enstatite) in the harzburgites. The geochemical modeling implies that this complex evolved through the following successive magmatic steps: 1) the partial melting of a mixed NMORB-EMORB (50:50) source producing spinel harzburgite residues; 2) the fractional crystallization of the basic partial melts during their ascent to the surface and the formation of gabbro bodies; 3) the assimilation and fractional crystallization process as the NMORB components re-enter the chamber and produce basic pillow lavas, lava flows, and some fine-grained gabbro bodies (i.e. dykes). Accordingly, it can be interpreted that the emplacement history of the studied ophiolite succession has two stages: 1) an obduction stage in the Campanian; 2) an exhumation stage in the post-Cretaceous.