Dönmez, Cahit; Aral, Zehra Deveci; Saka, Samet; Günay, Kurtulus; Yildirim, Nail; Yildirim, Esra; Yagcioglu, Kiymet Deniz; Maqsud, Isoqov; Movlanov, Jakhongir; Dovronovich, Mamarozikov Usmonjon

The Central Asian Orogenic Belt's ophiolites lack a full ophiolitic succession and instead occur as irregular fragments and slices in tectonic melanges and accretionary complexes. The Teskuduk and Northern Nurata ophiolites in Uzbekistan comprise extensively serpentinized mantle rocks that contain minor podiform chromitites, situated in the western area of the southern Tien Shan belt. Chromites in this region are found in a very limited area, and this study aims to determine the geochemical properties and formation environments of chromites by conducting geochemical studies on a limited number of recently discovered chromitites. In this context, mineral chemistry and platinum group element (PGE) geochemistry analyses were carried out on chromites. For Teskuduk chromitites, the Cr2O3, Al2O3, and TiO2 contents range from 53.2 to 55.7wt%, 11.1 to 12.7wt%, and 0.14 to 0.20 wt%, respectively, whereas for Nurata chromitites, the corresponding values range from 36.2 to 37.2 wt%, 23.1 to 30.2 wt%, and 0.10 to 0.30 wt%. The Teskuduk and Nurata chromitites contain a total average of 370 ppb and 117 ppb PGEs, respectively. They are classified as unfractionated chromitites, with low Pd/Ir ratios (0.03-0.20). These chromitite samples have chondrite-normalized PGE patterns that are identical to Cr-rich mantle-derived chromitites found in subduction-related ophiolites. Collectively, these data suggest that the Teskuduk ophiolites formed in a forearc setting, whereas the Nurata ophiolites evolved in a back-arc setting within the same oceanic branch.

Uysal, Ibrahim; Dokuz, Abdurrahman; Kapsiotis, Argyrios; Saka, Samet; Karsli, Orhan; Kaliwoda, Melanie; Mueller, Dirk

The eastern Orhaneli ophiolite in NW Anatolia (Turkey) consists of voluminous dunite and minor harzburgite intruded by clinopyroxenite veins. Harzburgite contains spinel of low Cr# [100 x Cr/(Cr + Al) = 40-45] and diopside of low Al2O3 and TiO2 contents, whereas dunite contains spinel of higher Cr# (62-82) and diopside (blebs) (even more) depleted in Al2O3 and TiO2 (than harzburgite). The concentrations of Heavy Rare Earth Elements (HREE) in harzburgite are consistent with derivation of this type of peridotite from 19% dry melting of a fertile mantle protolith at a MOR regime. Dunites have lower concentrations of HREE than harzburgite implying that dunites were generated by higher degrees (> 30%) of (cumulative) melting of the same protolith. Furthermore, the characteristic U-shapes of the chondrite-normalized REE-patterns of dunites indicate the involvement of hydrous melt-peridotite interaction processes in their genesis. Nevertheless, a set of mosaic-in texture dunite samples contain olivine that has lower Fo# [100 x Mg/(Mg + Fe2+)] and NiO contents than olivine in harzburgite. These dunites are probably of cumulate origin as it is also indicated by their enrichment in Pt and Pd (<= 17.92 ppb). Micro-textural and Re-Os isotopic data support that clinopyroxenite intrusions do not have a pure magmatic origin and their formation was partly controlled by metasomatic processes. Overall data indicate that the eastern Orhaneli ultramafic rocks have a complex petrological history including various stages of partial melting, metasomatism and magmatism in an evolving from MOR to SSZ geotectonic setting.

Uysal, Ibrahim; Şen, A. Dündar; Ersoy, E. Yalçin; Dilek, Yildirim; Saka, Samet; Zaccarini, Federica; Escayola, Monica; Karsli, Orhan

We present the whole-rock and the mineral chemical data for upper mantle peridotites from the Harmanci{dotless}k region in NW Turkey and discuss their petrogenetic-tectonic origin. These peridotites are part of a Tethyan ophiolite belt occurring along the İzmir-Ankara-Ercincan suture zone in northern Turkey, and include depleted lherzolites and refractory harzburgites. The Al2O3 contents in orthopyroxene and clinopyroxene from the depleted lherzolite are high, and the Cr-number in the coexisting spinel is low falling within the abyssal field. However, the orthopyroxene and clinopyroxene in the harzburgites have lower Al2O3 contents for a given Cr-number of spinel, and plot within the lower end of the abyssal field. The whole-rock geochemical and the mineral chemistry data imply that the Harmanci{dotless}k peridotites formed by different degrees of partial melting (~%10-27) of the mantle. The depleted lherzolite samples have higher MREE and HREE abundances than the harzburgitic peridotites, showing convex-downward patterns. These peridotites represent up to ~16 % melting residue that formed during the initial seafloor spreading stage of the Northern Neotethys. On the other hand, the more refractory harzburgites represent residues after ~4-11 % hydrous partial melting of the previously depleted MOR mantle, which was metasomatized by slab-derived fluids during the early stages of subduction. The Harmanci{dotless}k peridotites, hence, represent the fragments of upper mantle rocks that formed during different stages of the tectonic evolution of the Tethyan oceanic lithosphere in Northern Neotethys. We infer that the multi-stage melting history of the Harmanci{dotless}k peridotites reflect the geochemically heterogeneous character of the Tethyan oceanic lithosphere currently exposed along the İzmir-Ankara-Erzincan suture zone.