Geochronology and petrochemistry of Karabiga pluton in western Sakarya Zone (NW Turkey): Implications from new zircon U-Pb and biotite Ar/Ar ages, Sr-Nd isotope data and bulk-rock geochemistry

The closure of the Neo-Tethys Ocean and the following continental collision produced extensive Eocene-aged granitic plutons in the northern margin of Gondwana. This paper deals with the geochronology and petrogenesis of the Karabiga pluton in western Sakarya Zone. The pluton comprises K-feldspar, plagioclase, hornblende, biotite, quartz and accessory minerals (e.g., titanite, zircon, apatite, opaques), and secondary minerals such as chlorite, sericite, epidote, carbonate and clay minerals. Laser ablation inductively coupled plasma mass spectrometer zircon U-Pb dating yielded perfect ages of 48.27 ± 0.21 and 47.06 ± 0.32 Ma, indicating that the pluton were emplaced in the Early Eocene. Our results indicate that Ti-in-zircon temperature (ca. 900 °C), which is consistent with zircons grew in the continental crust, are higher than zircon saturation temperatures (740–884 °C). ⁴⁰Ar/³⁹Ar dating of biotites of the pluton yielded cooling ages between 47.34 ± 0.43 Ma and 46.30 ± 0.52 Ma. These dates are interpreted as the cooling age of the Karabiga pluton. The pluton is characterized by high SiO₂ (72.40–76.48 wt%), K₂O (5.12–6.44 wt%) and Na₂O (3.26–5.55 wt%) contents and exhibit enriched LREEs, K, Rb, Th, U, and Pb, and depleted Nb, Ta, P, and Ti contents. It belongs to shoshonite series, and displays peraluminous, I-type character. ⁸⁷Sr/⁸⁶S_(i) ratios of the pluton vary between 0.703296 and 0.706654, while those of ¹⁴³Nd/¹⁴⁴Nd_(i) lie between 0.512596 and 0.512629. In conclusion, Karabiga pluton could be originated from dehydration-melting of metagreywacke and metapelites in middle-upper crust due to slab breakoff/delamination and major, trace element contents, decreasing Al₂O₃, Fe₂O₃, MgO and TiO₂ with increasing SiO₂ as well as initial Sr-Nd homogenity show that fractional crystallization played a role in the evolution of the pluton.