Petrological features of ophiolitic rocks observed in Harmancik - Orhaneli (Bursa) regions

Ultramafic to mafic rocks from the Late Cretaceous Harmancık and Orhaneli ophiolites, derived from the İzmir-Ankara-Erzincan (IAE) oceanic basin, crop out to the south of Bursa in NW Turkey. Harmancık (Bursa) region is characterized by mantle tectonites (Cpx-harzburgite, harzburgite and dunite) and associated isolated dikes intruding at different structural levels, whereas the Orhaneli area is represented mainly by ultramafic to mafic cumulated and mantle peridotites to a lesser extend. In the Harmancık region, there are intense podiform chromitite occurences and less banded chromitites, while in the Orhaneli region there are predominantly banded chromitites. Harmancık region peridotites, presenting abyssal to fore-arc character, were resulted from 10-20% partial melting residues with Cr# values of 0.38-0.68. Peridotites of the Orhaneli ophiolite, on the other hand present a fore-arc character and were resulted from 15-22% partial melting residues with Cr# values of 0.47-0.86. Chromitites are classified as podiform chromites. The Cr# values of the Harmancık region chromitites range from 0.66 to 0.82, while the Orhaneli region chromitites 0.76 to 0.92, suggesting that both chromitites formed by >30% partial melting processes. It was concluded that the chromitites in both regions were formed due to the interaction of the boninitic magma with the host rock (harzburgite).