Petrology of ultramafic to mafic cumulate rocks from the G?ksun(Kahramanmaras) ophiolite,southeast Turkey

The G?ksun(Kahramanmaras)ophiolite(GKO),cropping out in a tectonic window bounded by the Malatya metamorphic unit on both the north and south,is located in the EW-trending lower nappe zone of the southeast Anatolian orogenic belt(Turkey).It exhibits a complete oceanic lithospheric section and overlies the Middle Eocene Maden Group/Complex with a tectonic contact at its base.The ophiolitic rocks and the tectonically overlying Malatya metamorphic(continental)unit were intruded by I-type calc-alkaline Late Cretaceous granitoid(~81-84 Ma).The ultramafic to cumulates in the GKO are represented by wehrlite,plagioclase wehrlite,olivine gabbro and gabbro.The crystallization order for the cumulate rocks is as follows:olivine±chromian spinel→clinopyroxene→plagioclase.The major and trace element geochemistry as well as the mineral chemistry of the ultramafic to mafic cumulate rocks suggest that the primary magma generating the GKO is compositionally similar to that observed in the modern island-arc tholeiitic sequences.The mineral chemistry of the ultramafic to mafic cumulates indicates that they were derived from a mantle source that was previously depleted by earlier partial melting events.The highly magnesian olivine(Fo77-83),clinopyroxene(Mg#of 82-90)and the highly Ca-plagioclase(An81-89)exhibit a close similarity to those,which formed in a supra-subduction zone(SSZ)setting.The field and the geochemical evidence suggest that the GKO formed as part of a much larger sheet of oceanic lithosphere,which accreted to the base of the Tauride active continental margin,including the ispendere,K?mürhan and the Guleman ophiolites.The latter were contemporaneous and genetically/tectonically related within the same SSZ setting during the closure of the Neotethyan oceanic basin(Berit Ocean)between the Taurides to the north and the Bitlis-Pütürge massif to the south during the Late Cretaceous.

Ruby Occurrences in Turkey: Principle Characteristics

The G ksun Ophiolites in Do an ehir area (Malatya-Southern Turkey) contain corundum mineralizations with significant gem-quality (ruby). Modal mineralogical composition of ruby-bearing rocks consists of hornblende (65%-70 %), plagioclase (20%-25%), green garnet (4%-5 %), ruby (2%-3%), and opaque minerals (<1%). Although ruby shows varying colors in the groundmass, it is generally colorless and rarely very pale pink and has high relief. It has no cleavage but rotund fractures. It has highest interference colors and twinning in some poly-prismatic crystals under the microscope. Crystal sizes range from 2x10 mm up to 30x50 mm. The most remarkable properties are red to pink in color, low to medium transparency, medium to big crystal sizes, lamellar and deformation twinning, secondary liquid feathers, hollow tubes, mineral inclusions, asterism, high birefringence and refractive indices and specific gravity. Rubies show crimson red cathodoluminescence colors activated by Cr3+ in the crystal structure, which is confirmed by the Electron Probe Microanalyses (EPMA). Tectonic setting, geological environment, petrographical, mineralogical, geochemical and gemological characteristics of rubies suggest that the Do an ehir ruby mineralization can be classified into the amphibolite-hosted type of corundum deposits of Tanzania.