Whole rock and spinel compositions of serpentinized peridotites from the Divriği-Sivas region, eastern Turkey: Implications for their tectonic setting

Whole rock chemistry of Divriği wehrlites resembles serpentinized peridotites in Himalayas. They have high MgO (average 31.27 wt%) and low Al2O3 (average 0.56 wt%) concentrations and Mg/Si and Al/Si ratios imply that peridotites formed in a supra-subduction zone environment. The U-shaped REE patterns of serpentinized wehrlites are formed by partial melting, coupled with interaction between peridotite and hydrous melts in the mantle wedge. The spinels collected from serpentinized wehrlites show compositions ranging from chromite in the core to ferritchromite and Cr-magnetite at the rims and have high Cr2O3 (46.5-56.2 wt%) and very low TiO2 contents (<0.3 wt%). Cr# values (0.71-0.84) of studied spinels are consistent with those of selected spinels from Anatolian peridotites but their Mg# values (0.26-0.46) are significantly lower. Cr# values of Divriği spinels correspond to SSZ peridotites and indicate high-degree partial melting (>%35). Parental melt compositions computed (8.69-11.71 wt% for Al2O3 and 0.1 to 0.37 wt% for TiO2) from chromite-melt equilibrium conditions yield a boninitic affinity. Our data suggest that spinels from serpentinized wehrlites in the Divriği area are similar to peridotite xenoliths from the Kamchatka arc and West Bismarck.