The Sr, Nd, Pb and Hf isotopes and crystallization conditions of the middle Eocene Dagdibi Pluton in the eastern Sakarya Zone, Turkey

Magmatic activity in the Sakarya Zone, an important segment of the Alpine orogenic belt, continues intermittently from the middle Carboniferous to Miocene. In this study, we provide geochronological and geochemical data from the Dagdibi Pluton in the eastern Sakarya Zone to present some inferences on the source region and petrogenesis of the middle Eocene magmatism. U-Pb zircon geochronology from two granodiorite samples gives middle Eocene ages of 44.75 +/- 0.92 and 45.01 +/- 0.59 Ma. The pluton is mainly composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe-Ti oxides and small amounts of biotite, and secondary chlorite and epidote. Parental magma of the intrusive rocks has a high-K calc-alkaline affinity with metaluminous character. The oxygen fugacity values vary between -18 and -17. The rocks show slightly radiogenic Sr-87/Sr-86((i)) (0.704845-0.705726) ratios and epsilon Nd-i values between -0.96 and +0.52. Pb-Pb isotope ratios are typical for those of the lower continental crust. epsilon Hf-(i) values of the zircons range from 0.14 to 10.26. The geochemical and isotopic features of the pluton point to a parental magma derived from a depleted mantle that was metasomatized by fluids during previous subduction events. The volumetric abundances of the rock types are decreased as the silica content increase, implying that the fractional crystallization is the most important process during the formation of the present compositional range of the pluton. Amphibole, plagioclase and Fe-Ti oxides are the fractionated phases while K-feldspar is largely accumulated. In the light of the data presented above, slab breakoff is regarded as the geodynamic process responsible for the formation of the Dagdibi Pluton in the middle Eocene.

Automated summary

In this study, geochronological and geochemical data from the Dagdibi Pluton in the Sakarya Zone were obtained to understand the source region and petrogenesis of the middle Eocene magmatism. The pluton has been dated to around 45 million years ago and is primarily composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe-Ti oxides, and small amounts of biotite. The geochemical and isotopic characteristics of the pluton suggest that it originated from a depleted mantle that was metasomatized by fluids during previous subduction events.