Geochronology and petrogenesis of mafic and ultramafic rocks in the Tekirova ophiolites

The Antalya Complex, located in the southwestern part of the Isparta Angle, includes ophiolitic suites in the Tekirova and Gödene zones. Tekirova zone contains all ophiolitic units except volcanic units and Gödene zone contains serpentinised harzburgite, pyroxenite, gabbro, isolated diabase dikes cutting these rocks, volcanics and deep-sea sediments in ophiolitic mélange. The isolated dikes in the Tekirova zone are generally greyish in colour and have a fractured-cracked structure. Their thickness generally varies between 1-2 m. The isolated dikes in the Gödene Zone are lighter in colour than the isolated dikes in the Tekirova Zone; and their thicknesses are generally similar. It is observed that the isolated dikes in Gödene Zone are more altered than those in Tekirova Zone. The alteration types in the field are generally serpentinization and rodengitization. Petrographic analyses of the host rocks in the Tekirova and Gödene zones show that they have serpentinite and gabbro, while the isolated dikes are diabase in composition. Mineral chemistry studies on the minerals that form the host rocks and isolated dikes in the Tekirova and Gödene zones show that plagioclases are generally composed of labradorite, clinopyroxenes are diopside, orthopyroxenes are enstatite and amphiboles are magnesio-hornblende in compositions. The crystallization temperatures of isolated dikes in the Tekirova Zone are 626-750°C on average according to the titanium content in amphiboles. On the basis of 2 (two) pyroxene geothermobarometers in the gabbro (host rock) sample of the Gödene Zone, the average crystallization temperature was calculated as 876-941°C and the average crystallization pressure was defined as 4.6 kbar. According to the results of whole-rock geochemical analyses, isolated dikes in Tekirova Zone are generally gabbro, host rocks are gabbro and gabbroic diorite, isolated dikes and host rocks in Gödene Zone are gabbro in composition. In addition, all rocks in these zones show tholeiitic characteristics. In primitive mantle normalized multi-element trace element diagrams of the host rocks and isolated dikes show enrichment in LIL elements, slight depletion in HFS elements and parallelism with the MORB line in Tekirova and Gödene Zone. According to the condrite-normalized REE diagram, the isolated dikes in the Tekirova zone show depletion in light rare earth elements and a horizontal and near horizontal trend in heavy rare earth elements, while the isolated dikes in the Gödene Zone show depletion in LRE elements and a near horizontal distribution of HRE elements. In addition, all rocks plot within the field of fore-arc basalts. As a result of the petrogenetic investigations it was determined that the isolated dikes in the Tekirova and Gödene zones are enriched with supra-subduction zone components from the depleted mantle source, are associated with subduction, are in fore-arc basalts and have IAT composition. On the basis of radiogenic isotope (Strontium, Neodymium, Lead) analyses, isolated dikes in the Tekirova and Gödene zones are fall into the island arc volcanic area in the Sr-Nd element correlation diagrams and all rocks in the Tekirova and Gödene zones fall into the lower crust and close to the MORB and EM II area in the Pb element correlation diagrams. However, since there is no determining feature related to the continental crustal source, it can be stated that these rocks are derived from the MORB source and the sediments in the subducting slab enrich the mantle source region of the magma and cause an increase in radiogenic lead. According to the geochronological analyses, titanite U-Pb dating, the crystallization ages of the diabase dike samples in the Tekirova Zone were determined as 80.47 ± 4.77 and 89.40 ± 13.40 Ma; and based on these data, the age of the rocks was determined as Late Cretaceous. As a result of all the analyses, it can be stated that the isolated dikes and host rocks in the Tekirova and Gödene zones are derived from 10-20 % partial melting of N-MORB-derived spinel-bearing peridotites with slab roll-back system in the supra-subduction zone and formed in the fore-arc, arc-related environment.