Carbon and nitrogen isotope, and mineral inclusion studies on the diamonds from the Pozanti-Karsanti chromitite, Turkey

The Pozanti-Karsanti ophiolite (PKO) is one of the largest oceanic remnants in the Tauride belt, Turkey. Micro-diamonds were recovered from the podiform chromitites, and these diamonds were investigated based on morphology, color, cathodoluminescence, nitrogen content, carbon and nitrogen isotopes, internal structure and inclusions. The diamonds recovered from the PKO are mainly mixed-habit diamonds with sectors of different brightness under the cathodoluminescence images. The total delta C-13 range of the PKO diamonds varies between - 18.8 and - 28.4aEuro degrees, with a principle delta C-13 mode at - 25aEuro degrees. Nitrogen contents of the diamonds range from 7 to 541 ppm with a mean value of 171 ppm, and the delta N-15 values range from - 19.1 to 16.6aEuro degrees, with a delta N-15 mode of - 9aEuro degrees. Stacking faults and partial dislocations are commonly observed in the Transmission Electron Microscopy foils whereas inclusions are rather rare. Combinations of (Ca0.81Mn0.19)SiO3, NiMnCo-alloy and nano-sized, quenched fluid phases were observed as inclusions in the PKO diamonds. We believe that the C-13-depleted carbon signature of the PKO diamonds derived from previously subducted crustal matter. These diamonds may have crystallized from C-saturated fluids in the asthenospheric mantle at depth below 250 km which were subsequently carried rapidly upward by asthenospheric melts.