Multi-stage Evolution of the Mehmetalan Ophiolite: Cr-Spinel Characteristics of Podiform Chromitites

Abstract

In this study, we aimed to report preliminary Cr-spinel chemistry results from the podiform chromitites of the Mehmetalan Ophiolite to shed light on their petrogenesis and tectonic settings. Mehmetalan ophiolite is ordinarily represented by peridotite (harzburgite, dunite, serpentinite), ultramaficmafic cumulates (layered-isotropic-pegmatitic gabbro, pyroxenite-dunite intercalation). The maficultramafic lithologies are locally cut by pyroxenite and isolated diabase dykes. In the chromites, lens-shaped massive, nodular and partially banded structures are seen, although alteration with Fe is not very common. However, the effects of dynamic metamorphism are observed as fractures on Cr-spinels. Chromitites of Mehmetalan Ophiolites can be divided into two groups according to the composition of their Cr#. Cr-spinel in the Group-1 (high-Al) chromitites have much lower Cr# values (0.49–0.52) than those in the Group-2 (high-Cr) chromitites (0.72–0.74). The spinel types of high-Al chromitites (Group-1) are spinel and magnesiochromite, whereas high-Cr chromitites (Group-2) with metallurgical character are magnesiochromite. Mineralogical and geochemical data obtained from Mehmetalan Ophiolite chromitites show that high-Al composition chromitites (Group-1) are associated with MORB-type melts formed from partial melting at a lower rate. In contrast, high-Cr chromitites (Group-2) are formed concerning boninitic composition melts formed by re-depleting the previously partially depleted mantle.