The Tozlu metaophiolite is composed predominantly of metagabbro, banded amphibolite, metadunite, and serpentinite, which are exposed in the Kazdağ Massif located in the northwestern part of Turkey. The geochemistry (major, trace, and rare earth elements) and petrography of the Tozlu metaophiolite in the Kazdağ Massif provided significant knowledge about protolith, petrogenesis, source characteristics and tectonic setting in northwest Turkey. Trace element geochemistry, Ti/Y (29.95–296.92 ppm) and Nb/Y (0.01–0.17 ppm) ratios suggest that metaophiolitic rocks were derived from a tholeiitic magma and igneous protolith of basaltic composition. The immobile trace element tectono-magmatic discrimination diagrams define a mid-ocean ridge basalt (MORB) to volcanic arc (IAT) affinity for the Tozlu metaophiolite. The metaophiolitic rocks demonstrate flat rare earth element (REE) patterns and enrichment of large ion lithophile elements (LILEs; i.e., Rb, Ba, Th), as well as depletion of high field strength elements (HFSEs; i.e., Nb, Th, Ti, Hf). N-MORB characteristics of the Tozlu metaophiolite on a multi-element diagram suggest that the protolith of metaophiolitic rocks generated in a subduction-related setting. The tholeiitic metaophiolitic rocks resulted from the metamorphism of an island arc-type basaltic protolith and display subduction zone components according to the Th/Yb and Ta/Yb ratios. The Tozlu metaophiolite with MORB/IAT affinity witness for supra-subduction zone originated in island arc/back-arc settings.