Geochemistry, geochronology and tectonic significance of the Guleman (Elazığ) ophiolite

The dismembered Guleman (Elazığ) ophiolite hosts one of the most important chromitite mineralizations in Turkey and consists of mantle tectonites, ultramafic-mafic cumulates, plagiogranite and basic volcanics from base to top. U-Pb age dating from zircons from the plagiogranite samples yielded the Late Cretaceous crystallization age of 92.0±3.7 Ma. Mantle tectonites of the Guleman ophiolite formed in a fore-arc geodynamic environment. Chrome spinels of the mantle tectonites are represented by medium to high Cr# [Cr/(Cr+Al)=0.43–0.76]. Olivines of harzburgites and dunites are rich in forsterite (Fo89-96) indicating a high degree of partial melting of mantle source depleted in a fore-arc environment. The primary magma composition of chrome spinels within the chromitites indicates the reaction between boninitic melts and depleted peridotites. Ultramafic cumulates begin with dunitic rocks including disseminated and banded chromitites at the base and are followed by verlite and clinopyroxenite intercalations. Olivine-gabbro, gabbronorite and gabbro constitute the top section of the cumulates. Crystallization order of mineral phases of the cumulate rocks is characterized by olivine (Fo81-84)±chrome spinel (Cr#0.61-0.49), clinopyroxene (Mg#75-96), plagioclase (An84-98) and orthopyroxene (Mg#69-85). The presence of clinopyroxenes and orthopyroxenes with relatively high magnesium and the lack of plagioclase as an early fractionation phase indicate crystal fractionation from a primary basaltic melt under medium to high-pressure conditions (<10 kb). The data from the cumulate rocks suggest a subduction-related environment. Major, trace and rare earth elements of the Caferi volcanic rocks also support the origination from a fore-arc environment. The results suggest that the oceanic lithosphere of the Guleman ophiolite formed in the Southern branch of the Neotethyan oceanic basin due to subduction initiation processes during the Late Cretaceous and it displays many similarities to other ophiolites in the Eastern Mediterranean region.