Chromite, ultramafic and mafic rocks from Eldivan, YapraklA, Ayli Dag, Kure, Elekdag and KAzAlArmak in northern Turkey have been studied to determine their mineral and whole-rock geochemical, and Re-Os isotope geochemical characteristics. Most of the studied peridotites display depleted but commonly V-shaped chondrite-normalized rare-earth element (REE) patterns while some peridotites as well as pyroxenites from all areas exhibit light REE depleted patterns. Olivine (forsterite 82 to 92 mol%) and spinel (chromium number 13 to 63) in the studied peridotites exhibit a wide range of compositions. Compositions of spinels suggest that peridotites from Eldivan, Ayli Dag and Kure experienced relatively large degrees of partial melting (similar to 15 and 19 wt%), whereas those of the KAzAlArmak area most likely reflect lower melting degrees (similar to 4-6 wt%). Whole-rock and mineral chemical data indicate that the ultramafic rocks are similar to abyssal and supra-subduction zone peridotites. The ultramafic rocks of the investigated areas exhibit a wide range of Re-187/Os-188 (0.12 to 6.6) and measured Os-187/Os-188 (0.122-1.14), while the basaltic rocks from Kure, Eldivan and KAzAlArmak areas have high Re-187/Os-188 (128-562) and measured Os-187/Os-188 (0.724-1.943). On the other hand, chromite from Eldivan, Elekdag and KAzAlArmak show high Os contents (21.81-44.04 ppb) and low Re-187/Os-188 (0.015-0.818) and Os-187/Os-188 (0.122-0.133). Re-Os model ages (T-Chur) for all analyzed samples yielded scattered ages ranging from Jurassic to Proterozoic. Overall, geochemical data are interpreted to reflect different degrees of partial melting, melt - rock interactions and metasomatic effects that produced a heterogeneous mantle in a supra-subduction setting.