Eocene tonalite–granodiorite from the Havza (Samsun) area, northern Turkey: adakite-like melts of lithospheric mantle and crust generated in a post-collisional setting

ABSTRACT

Eocene intermediate to felsic plutons of different sizes and compositions are widespread in the Eastern Pontides Orogenic Belt in northern Turkey. Of these, the Taşlık Tepe pluton in the Havza (Samsun) area is fine-to-medium-grained, with granular, porphyritic, and micrographic textures, and include mafic microgranular enclaves (MMEs). LA-ICP-MS U-Pb zircon dating yielded emplacement ages of 42.9 (± 1.4) and 40.5 (± 1.3) Ma for the host granodioritic pluton and the dioritic MMEs, respectively. Petrochemically, the host pluton has I-type, high-K calc-alkaline, and metaluminous-to-slightly peraluminous features (A/CNK = 0.95–1.06). The host pluton also shows geochemical features of adakite-like rocks with high SiO₂ (67–68 wt%) and Al₂O₃ (15.5–16.0 wt%) content and Ba/La (17–23), Sr/Y (40.7–61.6), and La_N/Yb_N (14.4–23.7) ratios and low Y (8.2–9.9 ppm) and Yb_N (3.1–4.4) contents. Whole-rock major and trace element variations suggest that fractional crystallisation played a significant role in the pluton evolution. The N-MORB normalised trace element patterns of the pluton are similar to those of MMEs with enrichment in large-ion lithophile elements, Th and Ce, and negative Nb and Ti anomalies. Chondrite-normalised rare earth element plots show moderate-to-highly enriched concave patterns (La_N/Lu_N = 14.2–21.6) with insignificant negative Eu anomalies (Eu_N/Eu* = 0.86–1.14), all of which imply hornblende fractionation during magmatic evolution. The pluton samples have ⁸⁷Sr/⁸⁶Sr ratios of 0.704767 to 0.704927, ¹⁴³Nd/¹⁴⁴Nd ratios of 0.512767–0.512774, εNd values of (+2.52) – (+2.65), and δ¹⁸O values of 7.9–9.7‰. The isotopic compositions of the host pluton and MMEs are similar to I-type granitoids derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. Combined with regional studies, these new data suggest that the parental magma of the studied adakite-like pluton was generated from the lithospheric mantle and then modified by fractional crystallisation and assimilation in a post-collisional setting.

Graphical abstract

KEYWORDS:

• Adakite-like pluton
• mafic enclaves
• U-Pb zircon dating
• Sr-Nd-Pb-O isotopes
• Eocene
• Turkey

Highlights

• U-Pb zircon dating, whole-rock geochemistry, Sr-Nd-Pb-O isotopic data of the adakite-like pluton were reported.

• The adakite-like pluton and their MMEs emplaced at ~ 43-41 Ma.

• The MMEs reveal incomplete magma mixing/mingling, representing small bodies of mafic parental magma.

• The parental magma of the pluton was derived from the lithospheric mantle and then modified by fractional crystallisation and assimilation.

Acknowledgments

The authors would like to thank Jessica Langlade for her assistance during lab work at IFERMER EPMA laboratories (Brest, France) and Bin Chen (Peking University, China) for performing U-Pb zircon dating. We thank editor in chief Robert J. Stern, and reviewers Simon Large, Greg Shellnutt, Hossein Azizi and an anonymous reviewer for their critical and constructive comments to improve our paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary materials

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Additional information

Funding

This work was financially supported by the Turkish Scientific Research Council (TÜBİTAK-ÇAYDAG project number: 113Y404).