Scientists have uncovered evidence of a previously unknown volcanic system that formed roughly 100 million years ago in what is now northwestern Iran. The discovery reveals a missing chapter in the region's geological history and offers new clues about the powerful tectonic forces that shaped ancient oceans and continents. Mountain ranges contain valuable records of Earth's distant past, preserving traces of vanished oceans, shifting continents, and the geological processes that transformed the planet over millions of years.
However, these records are often difficult to interpret because later tectonic activity, erosion, and layers of buried sediment can conceal evidence of much older events. An international team led by Istanbul Technical University (ITU) has now identified remnants of an ancient continental magmatic arc that had previously gone unrecognized. Named the Azerbaijan Continental Magmatic Arc, the system formed during the Late Cretaceous period in a region that is now part of the Arabia-Eurasia collision zone.
The research, published in Geoscience Frontiers, indicates that the volcanic system was active approximately 101 to 97 million years ago, when the ancient Neo-Tethys Ocean was undergoing major geological changes. Over time, tectonic deformation, erosion, burial beneath sedimentary basins, and a younger episode of volcanic activity during the Eocene obscured much of the evidence of its existence. Ancient Rocks Reveal a Lost Volcanic System To reconstruct this overlooked chapter of Earth's history, the researchers examined volcanic and plutonic rocks collected from multiple locations across northwestern Iran.
Much of their investigation focused on formations along the Siah Cheshmeh-Khoy-Misho-Tabriz Fault. The team used several advanced techniques to determine when the rocks formed and where their original materials came from. These included zircon U-Pb geochronology to establish their ages, Hf isotope analyses to investigate their sources, and whole-rock geochemistry to examine their chemical composition.
Together, the results revealed signatures consistent with continental arc magmatism, a geological process that occurs when one tectonic plate sinks beneath another, generating magma that can rise through the overlying continental crust. Ali Mohammadi, the study's corresponding author 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." The international research effort also involved scientists 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.
A Missing Piece of Iran's Geological History Previous reconstructions of Iran's ancient magmatic activity have largely centered on two major geological features: the Sananda-Sirjan Magmatic Arc and the Urumieh-Dokhtar Magmatic Arc. The newly identified Azerbaijan Continental Magmatic Arc adds another important piece to that history. Its discovery suggests that northwestern Iran experienced a separate episode of continental arc activity during the Late Cretaceous, expanding scientists' understanding of how the region developed.
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