Petrogenesis of Late Cretaceous A-type plutonic rocks from the Eastern Pontides Orogenic Belt (NE Turkey): constraints from zircon U-Pb geochronology, zircon Lu-Hf and whole-rock Sr-Nd-Pb-Hf isotopes

ABSTRACT

The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO₂ contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K₂O and Na₂O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (La_N/Lu_N = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (⁸⁷Sr/⁸⁶Sr)_i ratios and ɛNd_(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf_(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf_(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes.

KEYWORDS:

• A-type plutons
• zircon U-Pb ages
• zircon Lu-Hf isotopes
• Sr-Nd-Pb-Hf isotopes
• Late Cretaceous
• NE Turkey

Acknowledgments

The author would like to thank Frank Ramos for her assistance during lab work for radiogenic isotopes, Keewook Yi for his help with the dating analysis and for hosting the first author during lab works in KBSI (Ochang, Korea), and Youn-Joong Jeong for help with Lu-Hf isotopic analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2269447.

Additional information

Funding

This work was financially supported by the Scientific Research Projects Foundation of Gümüşhane University (Project number: 19.F5114.01.01).