Geologists uncover evidence of a missing Late Cretaceous magmatic arc in northwestern Iran

Mountains preserve evidence of ancient oceans, moving continents and tectonic processes that have shaped Earth over millions of years. Later deformation, erosion and burial, however, can obscure important parts of this geological record. An international research team led by Istanbul Technical University (ITU) has identified evidence of a previously unrecognized Late Cretaceous continental magmatic arc in northwestern Iran.

The study was conducted in collaboration with researchers from the Institute of Tibetan Plateau Research and Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences; ETH Zurich, Switzerland; Karadeniz Technical University, Türkiye; and Damghan University, Iran.

The researchers refer to this system as the Azerbaijan Continental Magmatic Arc, providing new constraints on the tectonic evolution of the region that is now part of the Arabia–Eurasia collision zone.

Tracing a buried Cretaceous arc

Published in Geoscience Frontiers, the study indicates that the arc was active approximately 101–97 million years ago, during the evolution of the Neo-Tethys Ocean. Its geological record was subsequently obscured by tectonic deformation, erosion, basin burial and younger Eocene magmatism.

The researchers investigated volcanic and plutonic rocks from several localities in northwestern Iran, particularly along the Siah Cheshmeh–Khoy–Misho–Tabriz Fault. Using zircon U-Pb geochronology, Hf isotope analyses and whole-rock geochemistry, the team constrained the ages and sources of the rocks and identified characteristics consistent with subduction-related continental arc magmatism.

Dr. Ali Mohammadi, corresponding author of the study at Istanbul Technical University, explained, “This study shows that the magmatic history of northwestern Iran is more complex than previously recognized. By integrating geochronological, isotopic and geochemical evidence, we identified a Late Cretaceous continental arc that was subsequently obscured by later tectonic processes.”

A distinct chapter in Iran’s magmatism

The finding extends the conventional framework for Iran’s magmatic history, which has largely focused on the Sanandaj–Sirjan Magmatic Arc and Urumieh–Dokhtar Magmatic Arc. The study indicates that northwestern Iran also preserves remnants of a distinct Late Cretaceous magmatic system.

The authors further suggest that the Siah Cheshmeh–Khoy–Misho–Tabriz Fault may represent an important tectonic boundary associated with the reorganization of the Neo-Tethyan system. Changes in the subduction system, including possible slab rollback and arc migration, may have contributed to the development of this relatively short-lived magmatic episode.

Refining models of Neo-Tethyan ocean closure

More broadly, the discovery demonstrates how ancient magmatic arcs can become fragmented or obscured by later tectonic activity, erosion and sedimentation. Recognizing these remnants provides new information for reconstructing subduction, arc migration, continental growth and the closure of ancient oceans.

The study contributes to a better understanding of the Late Cretaceous evolution of northwestern Iran and the wider Neo-Tethyan realm, helping refine tectonic models for a region shaped by a long history of ocean closure and continental collision.

The findings also provide broader insights into the Neo-Tethyan Ocean system, whose closure played a major role in shaping the geology of the eastern Mediterranean, the Middle East and western Asia.

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