Scientists have identified evidence of a previously unknown continental volcanic system that was active in what is now northwestern Iran between about 101 million and 97 million years ago. The discovery of the Azerbaijan continental magmatic arc reveals a previously obscured chapter in the region’s geological history and offers new clues about tectonic changes affecting the ancient Neo-Tethys Ocean.
Mountains preserve rare records of Earth’s distant past, including traces of vanished oceans, shifting continents and geological processes that operated over millions of years. These records can be difficult to interpret because later tectonic activity, erosion and sediment burial may obscure evidence of earlier events.
An international team led by Istanbul Technical University (ITU) identified the remains of an unrecognized ancient continental magmatic arc in the region that is now part of the Arabia-Eurasia collision zone. The researchers call this system the Azerbaijan continental magmatic arc.
The study, published in Earth Science Frontiers, indicates that the volcanic system was active during the Late Cretaceous, when the 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 the arc.
Reconstructing a lost volcanic system
To investigate this overlooked period in Earth’s history, the researchers analyzed volcanic and plutonic rocks collected from several locations in northwestern Iran. Much of the work focused on geological formations along the Sia-Chesme-Koi-Misho-Tabriz fault.
The team used zircon U-Pb geochronology to determine when the rocks formed, hafnium isotope analysis to investigate their origins, and whole-rock geochemistry to examine their chemical composition.
Together, the results showed signatures consistent with magmatic activity in a continental arc. 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 at the Chinese Academy of Sciences also contributed to the research, along with researchers from ETH Zurich in Switzerland, Karadeniz Technical University in Turkiye and Damgan University in Iran.
Adding a missing chapter to Iran’s geological history
Earlier reconstructions of Iran’s ancient magmatic activity 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 element to this history. It suggests that northwestern Iran experienced a separate episode of continental-arc activity during the Late Cretaceous, giving scientists a more detailed view of how the region developed.
The findings also point to a potentially important role for the Sia-Chesme-Koi-Misho-Tabriz fault. The researchers suggest that it may mark a major tectonic boundary linked to changes in the ancient Neo-Tethyan ocean system.
Those changes may have involved slab rollback, in which a descending tectonic plate retreats as it subducts into Earth’s interior, or the relocation of volcanic arcs. Such processes could help explain why this episode of magma formation lasted for a relatively short period.
Clues to the disappearance of ancient oceans
The discovery also illustrates how geological history can be hidden over vast periods of time. Ancient magmatic arcs do not always survive as continuous, easily recognizable rock layers. Tectonic forces can break them apart, erosion can remove exposed rocks, and sediment can bury the remaining fragments. Later volcanic activity can further complicate the geological record.
Identifying surviving fragments of these structures can help scientists reconstruct how tectonic plates subducted, how volcanic arcs shifted, how continental crust grew and how once-vast oceans eventually closed.
The Azerbaijan continental magmatic arc provides new evidence for the Late Cretaceous evolution of northwestern Iran and the wider Neo-Tethyan region. It may also help researchers refine geological models for areas shaped by repeated ocean closures and continental collisions.
The ancient Neo-Tethys Ocean 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 piece to the complex story of how Earth’s continents and oceans evolved over millions of years.
Source: www.sciencedaily.com
