Geologists from an international team led by Istanbul Technical University (ITU) have identified evidence of a previously unrecognized Late Cretaceous continental magmatic arc in northwestern Iran, named the Azerbaijan Continental Magmatic Arc.

This arc was active roughly 101- 97 million years ago during Neo-Tethyan subduction. It had been largely obscured by later tectonic overprinting, erosion, and basin burial.

The findings, published in Geoscience Frontiers (open access), come from integrating new zircon U- Pb geochronology, Lu- Hf isotopic data, and whole- rock geochemistry on volcanic and plutonic rocks from the Misho, Sufian, Moro, Amand, Vanyar, and Iskandar regions.

Key results

• Ages of ~101- 97 Ma for gabbros and granodiorites.
• εHf(t) values ranging from +9.8 to −7.2, indicating mixed mantle and crustal sources.
• Arc- like geochemical signatures (LREE enrichment and subduction- related anomalies).
• Magmatic evolution from juvenile tholeiitic to enriched shoshonitic compositions, linked to increasing crustal assimilation and slab rollback.
• Structural alignment along the Siah Cheshmeh- Khoy- Misho- Tabriz Fault (SKMT), interpreted as a possible concealed suture related to arc migration and back-arc basin development.

The system is distinct from the better- known Sanandaj- Sirjan and Urumieh- Dokhtar magmatic belts and was later overprinted by Eocene Urumieh- Dokhtar magmatism. Corresponding author Dr. Ali Mohammadi (ITU) noted that the magmatic history of northwestern Iran is more complex than previously recognized.

Authors include Ali Mohammadi, Hadi Shafaii Moghadam, Amaneh Kaveh- Firouz, Anna Lechmann, Fulong Cai, and Lin Ding (affiliations involving ITU, Damghan University, ETH Zurich, and others). Supplementary data (zircon images, geochemical tables, etc.) are available via Mendeley Data.

This discovery fills a gap in the tectonic evolution of the Arabia- Eurasia collision zone and highlights how continental arcs can be cryptically preserved despite later deformation. Note that separate recent work has addressed a broader “missing” Late Cretaceous arc in Iran (e.g., via detrital zircons in the Makran), proposing removal by subduction erosion or strike- slip displacement; the ITU- led study specifically documents preserved remnants in the northwest.

The discovery of the previously unrecognized Late Cretaceous Azerbaijan Continental Magmatic Arc in northwestern Iran is significant because it fills a major gap in the tectonic and magmatic history of the Arabia- Eurasia collision zone and revises models of Neo- Tethyan subduction.

Key aspects of its importance

Completes the magmatic record: Iran’s well-documented magmatic belts have long focused on the Jurassic- Cretaceous Sanandaj- Sirjan Magmatic Arc and the Cenozoic Urumieh- Dokhtar Magmatic Arc. This work shows that northwestern Iran also preserves remnants of a distinct, short- lived continental arc active ~101- 97 million years ago. It demonstrates that the region’s magmatic evolution was more complex and continuous than previously recognized.

Evidence of a “missing” or cryptic arc: The arc was largely obscured by later deformation, erosion, and burial. Identifying it through zircon U- Pb ages, Hf isotopes, and geochemistry highlights how continental arcs can leave only cryptic traces yet still record critical phases of subduction. This has broader implications for reconstructing ancient convergent margins worldwide where similar overprinting may hide important geological events.

Constraints on Neo- Tethyan subduction dynamics: The rocks record a transient flare-up during Neo-Tethys Ocean subduction beneath the Iranian margin. Magmatism evolved from juvenile tholeiitic (mantle-dominated) to enriched shoshonitic compositions, tracking increasing crustal assimilation and slab rollback. Structural links to the Siah Cheshmeh- Khoy- Misho- Tabriz Fault (SKMT) suggest this fault marks a concealed suture that accommodated arc migration and back- arc basin development.

Refines regional tectonic models: The findings link Late Cretaceous arc activity to later Eocene overprinting by the Urumieh- Dokhtar system. They improve understanding of crustal growth, arc migration, and the transition from subduction to collision in the Arabia- Eurasia zone- one of the world’s major active collision belts.

In short, the discovery provides direct geological evidence for a missing piece of Iran’s subduction history, improves reconstructions of Neo- Tethyan plate interactions, and underscores that even heavily overprinted regions can preserve critical records of Earth’s tectonic evolution when examined with modern geochronological and isotopic tools.

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

It is published under a Creative Commons license (open access).

Core findings (from the abstract and highlights)

The study documents a previously unrecognized Azerbaijan Continental Magmatic Arc in northwestern Iran that was active ~101- 97 million years ago. This Late Cretaceous continental arc is distinct from the better-known Sanandaj- Sirjan and Urumieh- Dokhtar belts. It was largely hidden by later tectonic overprinting, erosion, and burial, then partly overprinted by Eocene Urumieh- Dokhtar magmatism.

Key evidence comes from volcanic and plutonic rocks in the Misho, Sufian, Moro, Amand, Vanyar, and Iskandar regions:

• Zircon U-Pb ages of ~101- 97 Ma for gabbros and granodiorites.
• εHf(t) values ranging from +9.8 to -7.2 (mixed juvenile mantle and crustal sources).
• Arc- like geochemical signatures (LREE enrichment, subduction- related anomalies).
• Magmatic evolution from juvenile tholeiitic to enriched shoshonitic compositions, linked to crustal assimilation and slab rollback.
• Spatial association with the Siah Cheshmeh- Khoy- Misho- Tabriz Fault (SKMT), interpreted as a possible concealed suture that accommodated arc migration and back- arc basin development.

Significance (as stated in the paper)

The results fill a gap in the Neo-Tethyan subduction history of the Arabia- Eurasia collision zone. They demonstrate cryptic preservation of continental arcs and refine models of arc migration, crustal growth, and the transition between major magmatic belts in NW Iran.

Supplementary data (zircon CL images, geochemical tables, isotopic data, sample locations, etc.) are available with the paper.

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

Journal: Geoscience Frontiers, Volume 17, Issue 1, January 2026, Article 102205

DOI: 10.1016/j.gsf.2025.102205

Provided: Istanbul Technical University

Authors: Ali Mohammadi (corresponding), Hadi Shafaii Moghadam, Amaneh Kaveh-Firouz, Anna Lechmann, Fulong Cai, Lin Ding

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 ε_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.