Evolution of magma oxidation states and volatile components in the Cenozoic porphyry ore systems in the western Turkey, Tethyan domain : Constraints from the compositions of zircon and apatite

In the middle part of the Tethys metallogenic domain, the western section of Turkey concentrates porphyry-type deposits associated with three primary tectonic settings : subduction, collisiona-post-collision, and extension. Many studies have been performed on the petrogenesis and tectonic setting of porphyry deposits in the western section of Turkey. However, the current research is still in its infancy. Little systematic work has been done on the nature of the mineralized magma source, the content of ore elements-volatile elements , and the evolution of ore materials in porphyry deposits under different tectonic settings. It is crucial to understand the crustal thickness, the tectonic model, degree of crust-mantle interaction, and the evolution of ore materials during the formation of porphyry deposits during the subduction of the New Tethyan Ocean and the collisional-post-collisional-extension process of the Eurasian-Tauride-Anatolide plate since the Late Cretaceous in the middle section of Tethyan domain. In this study, zircon trace elements and apatite major elements were studied in five porphyry deposits from three metallogenic belts ( Tavpnli belt, Biga Peninsula metallogenic belt, and Afyon-Konya belt) in the western part of Turkey, to define zircon trace element characteristics, crystallizing temperature-oxygen fugacity conditions and volatile-component concentrations in the melts during the formation of porphyry deposits in different tectonic environments, and then to constrain the evolving processes of ore materials and to decipher the deep-crustal processes during the formation of porphyry systems during continental collision, subsequent post-collisional and extensional environments in the Tethyan domain. Zircon trace elements show that most igneous rocks from Cenozoic porphyry deposits in western Turkey show the features of high water content and high oxygen fugacity, with similar chondrite-normalized zircon REE patterns, and the mafic mineral enclaves present higher total rare-earth contents than the contemporaneous rocks; most zircons have Eu-N/Eu-N* from 0.4 to 0. 7, and zircon grains related to the porphyry Mo and porphyry Mo-Cu are more influenced by fractional crystallization plagioclase in the magma chamber; Ti-in-zircon thermometer estimates the crystallizing temperature of igneous rocks, ranging from 650 degrees C to 900 degrees C , with decreasing crystallization temperature from porphyry Au, to porphyritic Cu-Mo/Mo-Cu, then to porphyritic Mo deposits. The composition of zircon trace elements ( Yb/Gd and Hf/Y-Th/U) suggests the the features of trace elements in zircon are mainly controlled by fractional crystallization of hornblende +/- titanite +/- apatite; zircon oxygen fugacity Ce4+/Ce3+ ratio shows a decreasing ( porphyry Cu-Mo to porphyry Mo) and then increasing (porphyry Mo-Cu to porphyry Au) trend from Eocene to Miocene. Most of the Cenozoic porphyry deposits and their coeval magmatism in western Turkey exhibit " normal" volatile-element contents : EoceneOligocene porphyry Cu-Mo and Mo deposits have relatively high F and low Cl contents in the melt.In contrast, porphyry Mo-Cu and porphyry Au deposits formed in the Miocene extensional environments generally have high magmatic Cl contents. Magmatic sulphur content obtained from calculations of the apatite compositions in mafic mineral enclaves and mafic dykes contemporaneous with the causative magmatic rocks is greater than the sulphur content of the corresponding magma, and the sulphur content in apatite and the calculated melt sulphur content are not uniform in composition, indicating that the injection of mafic magma may have provided sulphur to the magma chamber; Among 16 similar to 12Ma volcanic rocks near the Kisladag porphyry gold deposit in the Afyon-Konya belt, dacite (12. 6Ma) close to the epoch of the Au mineralization has the highest magmatic sulphur content composition, reasonably resulting in the Au mineralization. Based on the regional dynamics analysis and crustal thickness estimates, we suggest that the kinetic mechanism triggering the formation of Cenozoic porphyry ore deposits in western Turkey.The Eocene-Oligocene porphyry deposits in the north were controlled by the collision and post-collisional subduction of the Neotethyan oceanic plate ( Vardar Ocean) , including slab-roll back and break-off process; the formation of Miocene porphyry deposits in the southern section was controlled by the crustal extension and thinning process under the tectonic setting of the subduction of the Aegean plate. The formation of Eocene-Oligocene porphyry deposits in the northern Taypnlr and Biga Peninsula porphyry belts near the Izmir-Ankara-Erzincan suture zone is related to the meltingassimilation-storage-homogenization process (MASH) , and the deep crustal hot zone process ( DCHZ) is related to the formation of porphyry ore deposits in the Miocene Afyon-Konya belt.