Geochronology, petrogenesis and tectonic importance of Eocene I-type magmatism in the Eastern Pontides, NE Turkey

Abstract

Eastern Pontides are hosted to many granitoids with different composition, size and age ranges from Paleozoic to Cenozoic. Of these granitoids, especially those of the Cenozoic age are commonly observed in the southern part of the Eastern Pontides, and rarely in the northern part. This paper focuses on the Eocene aged Avliyana Granitoid, located south of the Eastern Pontides, intruding into Late Cretaceous and Eocene volcanic and sedimentary rocks. The Avliyana Granitoid is mainly diorite and tonalite and composed of plagioclase, quartz, orthoclase, hornblende, biotite, pyroxene, and Fe-Ti oxides. It shows granular, locally poikilitic and micrographic texture. The Avliyana Granitoid has I-type, medium to high-K calc-alkaline, and metaluminous character, and has a narrow SiO2 contents (57–64 wt.%). The rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile element (LILEs), and depleted in high field strength elements (HFSEs). Chondrite-normalized REE distributions are concave shaped (LaN/LuN = 5.87–11.92) and show negative Eu anomaly (Eu / Eu * = 0.55–0.81). Geochemical results show that plagioclase, pyroxene, hornblende, and Fe-Ti oxide fractionation are effective in the development of the rocks. The eNd(i) values of the rocks are between – 1.0 and – 0.1, 87Sr/86Sr(i) values are between 0.70531 and 0.70563, and the model ages (TDM) are between 0.79 and 0.93. U-Pb SHRIMP zircon ages of the Avliyana Granitoid rocks range from 45.60 ± 0.55 to 44.75 ± 0.36 Ma. In calculations made from zircon and apatite, the crystallization temperatures vary between 714 and 867 °C. The data revealed that the parental magma of the Avliyana Granitoid was derived from the enriched lithospheric mantle, and fractional crystallization and lesser assimilation played a role in the evolution of the rocks.