Scientists have identified evidence of a previously unknown volcanic system that formed about 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 tectonic forces that reshaped ancient oceans and continents.
Mountains preserve rare records of Earth’s distant past, including traces of vanished oceans, shifting continents and geological processes that transformed the planet over millions of years. These records can be difficult to interpret, however, because later tectonic activity, erosion and sedimentation may obscure evidence of older events.
Evidence of a lost volcanic system
An international team led by Istanbul Technical University (ITU) has identified the remains of a previously unrecognized ancient continental magmatic arc. The researchers named it the Azerbaijan continental magmatic arc. It formed during the Late Cretaceous in an area that is now part of the Arabia–Eurasia collision zone.
The research, published in Earth Science Frontiers, indicates that the volcanic system was active approximately 101 million to 97 million years ago, when the ancient Neo-Tethys Ocean was undergoing major geological changes. Tectonic deformation, erosion, burial beneath sedimentary basins and younger Eocene volcanism later obscured much of the evidence for its existence.
To reconstruct this overlooked period of Earth’s history, the researchers examined volcanic and plutonic rocks collected from multiple locations in northwestern Iran. Much of the work focused on geological formations along the Sia-Chesme-Koi-Misho-Tabriz fault.
The team used several techniques to determine when the rocks formed and where their original material came from. These included zircon U-Pb geochronology to establish their age, hafnium isotope analysis to investigate their origin, and whole-rock geochemistry to examine their chemical composition.
Taken together, the results revealed signatures consistent with magmatic activity in continental arcs. Such arcs form when one tectonic plate subducts beneath another, generating magma that can rise through the overlying continental crust.
Dr. Ali Mohammadi, the study’s lead author from Istanbul Technical University, said: “This study shows that the magmatic history of northwest Iran is more complex than previously recognized. By integrating geochronological, isotopic and geochemical evidence, we identified a Late Cretaceous continental arc that was obscured by subsequent tectonic deformation.”
Scientists from the Tibetan Plateau Research Institute and the Xinjiang Institute of Ecogeography of the Chinese Academy of Sciences also participated. Other institutions involved included ETH Zurich in Switzerland, Karadeniz Technical University in Turkiye and Damgan University in Iran.
A missing part of Iran’s geological history
Previous reconstructions of ancient magmatic activity in Iran have focused mainly on two major geological features: the Sananda-Sirjan magmatic arc and the Urmiyeh-Doctor magmatic arc.
The newly identified Azerbaijan continental magmatic arc adds another important element to this history. The discovery suggests that northwestern Iran experienced a separate episode of continental-arc activity during the Late Cretaceous, improving scientists’ understanding of how the region developed.
The findings also indicate that the Sia-Chesme-Koi-Misho-Tabriz fault may have played an important role. The researchers suggest that it could mark a major tectonic boundary linked to changes in the ancient Neo-Tethyan ocean system.
Those changes may have included slab rollback, in which a descending tectonic plate retreats as it subducts into Earth’s interior, or the movement of volcanic arcs to new locations. Such processes could help explain why this episode of magma formation lasted for a relatively short period.
Clues to the disappearance of ancient seas
The discovery also provides broader insight into how Earth’s geological history can be obscured over vast periods of time.
Ancient magmatic arcs do not always survive as continuous, easily recognizable formations. Tectonic forces can break their rocks apart, erosion can remove exposed material, and sedimentation can bury what remains. Later volcanic activity can further complicate the record, making older systems particularly difficult to identify.
By identifying fragments of these ancient structures, scientists can better reconstruct how tectonic plates subducted, how volcanic arcs moved, how continental crust grew and how once-vast oceans eventually closed.
The Azerbaijan continental magmatic arc provides new evidence for understanding the Late Cretaceous evolution of northwestern Iran and the wider Neo-Tethyan region. It may also help researchers refine geological models of areas shaped by repeated ocean closures and continental collisions.
The ancient Neo-Tethys Sea played a major role in the geological development of the Eastern Mediterranean, the Middle East and Western Asia. Its eventual disappearance helped shape the modern landscapes of these regions.
By identifying a volcanic system that had been largely erased from the geological record, the researchers have added a new element to the complex story of how Earth’s continents and oceans evolved over millions of years.
Source: www.sciencedaily.com