The missing late Cretaceous magmatic arc in the Arabia-Eurasia collision zone (NW Iran): constraints from zircon geochronology, Hf isotopes, and geochemistry

Abstract

The Late Cretaceous magmatic evolution of northwestern (NW) Iran reveals a previously unrecognized continental arc system, the Azerbaijan Continental Magmatic Arc, herein termed the Azerbaijan Continental Magmatic Arc, which is largely obscured by subsequent tectonic overprinting, erosion, and basin burial. Integration of new zircon U-Pb ages, Lu-Hf isotopic data, and whole-rock geochemical compositions from volcanic and plutonic rocks in the Misho, Sufian, Moro, Amand, Vanyar, and Iskandar regions identifies a subduction-related arc system distinct from the Sanandaj-Sirjan and Urumieh-Dokhtar magmatic belts. The ∼ 101-97 Ma gabbros and granodiorites record e Hf ( t ) values from + 9.8 to − 7.2, reflecting variable mantle and crustal inputs. Arc-like trace-element patterns, including LREE enrichment and subduction-related anomalies, together with structural alignments along the Siah Cheshmeh-Khoy-Misho-Tabriz Fault (SKMT), indicate arc magmatism contemporaneous with transpressional deformation. The magmatic series evolved from juvenile tholeiitic to enriched shoshonitic compositions, tracking increasing crustal assimilation and slab rollback. This flare-up event represents a transient phase of Neo-Tethyan subduction, later overprinted by Eocene intrusions of the Urumieh-Dokhtar Magmatic Arc. Collectively, these results highlight the cryptic preservation of continental arcs and propose that the SKMT Fault marks a concealed suture accommodating Late Cretaceous arc migration and back-arc basin development in NW Iran.

Keywords

Arc magmatism / Zircon U-Pb age / Hf isotopes / Neo-Tethyan subduction / Iran

Data availability

Zircon cathodoluminescence images with corresponding U-Pb ages are shown in Supplementary Data Fig. S1. Th and U concentrations and Th/U ratios of zircon grains are illustrated in Supplementary Data Fig. S2. Na₂O + K₂O vs. SiO₂ classification diagrams for plutonic and volcanic rocks are shown in Supplementary Data Fig. S3. The sample type and locations for bulk rock geochemistry, zircon U-Pb age, and in-situ Lu-Hf analyses are provided in Supplementary Data Table S1. Whole rock major and trace elemen t data are provided in Supplementary Data Table S2. Zircon U-Pb isotopic data and calcu-lated ages are presented in Supplementary Data Tables S3. Zircon Lu-Hf isotopic data were reported in Supplementary Data Table S4, and zircon LA-ICP-MS U-(Th) Pb metadata were provided in Supplementary Data Table S5. Further inquiries can be directed to the corresponding author.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the State Key Laboratory of Tibetan Plateau Earth System, Resources and Environment, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China; the Swiss National Science Foundation, Switzerland; under Grants 2-77644-09 and 2-77979-14; and the Forschungsreserven/Burg J.-P. fund under Grant 2-78159-99. We sincerely thank Mohssen Moazzen for his invaluable assistance and logistical support during fieldwork in the Sufian and Amand areas. We are also grateful to Oscar Laurent and Marcel Guillong for their expert guidance in conducting the Laser Ablation ICP-MS and Hf isotope analyses, and to Lydia Zehnder for her support with the XRF analyses. Special thanks are extended to Remy Lüchinger and Naser Mosayebzadeh for their assistance in preparing the thin sections. Invaluable comments by Associate Editor Sanghoon Kwon and two anonymous reviewers considerably improved the paper. We thank M. Santosh for the efficient editorial handling of the manuscript.

Appendix A. Supplementary data

Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.gsf.2025.102205.

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