Mineral records of the pyroxenites formed within harzburgites (Ulas, Sivas, Turkey): implications on petrogenesis and tectonic setting

In this article, the petrological processes of the clinopyroxenite dykes and host peridotites occurring in Ulas District (Sivas, mid-Anatolia, Turkey) are discussed. The new geochemical data from major minerals in the clinopyroxenite dykes and host harzburgites revealed differences to the supra-subduction zone (SSZ)-type pyroxenites and peridotites. In particular, the NiO content of olivines in the host harzburgites showed the signature of the mantle, whereas rare olivines of the clinopyroxenites had a NiO content and Fo number that were inferior to those of mantle peridotites. The high Mg-number of clinopyroxenes in the clinopyroxenites was likely associated with the partial remelting of the host harzburgites. Additionally, the rare earth element pattern of clinopyroxenes from the studied clinopyroxenites exhibited a similar pattern to those of the other SSZ or fore-arc clinopyroxenes. Additionally, the low Mg-number and relatively high Cr-number of spinels in the clinopyroxenites showed similarity to the subduction-related origin. Based on textural and geochemical evidence, the harzburgites were interpreted as depleted mantle rock, which was modified by melt-peridotite interactions. Consequently, the pyroxenites likely occurred as a crystallizing or cumulative zone of the SSZ-type melt and the minerals were gained from partial melting of the harzburgites through the interaction with such magma.