Petrogenesis, age and origin of (ultra)mafic, magmatic and metamorphic rocks of the Makran Accretionary Wedge, Southern Makran Zone, SE Iran

• Applicant: Dr. Martin Jan Timmerman
• Subject Area: Palaeontology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 512327277

This project focuses on the origin, nature, age and geodynamic setting of (ultra)mafic, magmatic and metamorphic rocks in the centre of the southern Makran Zone (SMZ) in SE Iran, an active subduction zone overlain by one of the most extensive Cenozoic accretionary wedges on Earth. Several studies have been carried out but many aspects of its evolution remain poorly understood, such as subduction initiation, subsequent development, the timing and evolution of island arc magmatism, its contribution to the production of continental crust, arc collision and accretion, and the detachment and exhumation of (ultra)mafic or deep arc crust.A common process in subduction zones for especially young and thin ocean plates is the detachment of parts of the uppermost basaltic crust and their accretion to the base of the accretionary complex. Besides sediments scraped off the downgoing ocean plate along décollements, other material can be transferred and accreted to the overriding plate. This can occur at depth below arcs and involve (ultra)mafic arc root material and high-pressure metamorphic rocks (blueschists), or at shallower levels within and below the wedge and generally involving (very) low-grade metamorphic rocks, or rocks not metamorphosed at all. The sediments in the centre of the Iranian SMZ contains (very) large bodies of (layered) gabbros, pyroxenites and peridotites with smaller volumes of felsic to intermediate magmatic rocks, and amphibolites and blueschists. These are discontinuously exposed over a large, 200 by 40 km area situated at a distance of about 200 kilometres from the trench. As accretionary wedges are zones of high accretion rate, low heat flow and normally lack igneous activity, the occurrence of large bodies of magmatic and metamorphic rocks in the centre of the wedge needs to be explained. This study aims to establish the causes and timing of accretion and detachment processes within wedges, and to elucidate the evolution of the SMZ. Geochemistry, mineral composition and zircon dating will establish whether the rocks represent remnants of island arc material and/or ocean crust. Petrology and 40Ar/39Ar dating of blueschists will yield information about separation depths and exhumation rates of HP metamorphic rocks in an active subduction zone. The results will allow correlation with comparable rock types in the wider Himalayan subduction-collision zone. The Neotethys ocean did not yet close in SE Iran and by studying geological aspects of the SMZ, we can better study these processes such as subduction, accretion, collision, metamorphism, and exhumation that took place in other parts of the Alpine-Himalayan orogen. Importantly, large parts of the Makran wedge are exposed on land, allowing access to wedge structures and rocks, but also to crystalline rocks that are inaccessible in other active subduction systems. In fact, the SMZ may well be the only place on Earth for a land-based study of actively subducting oceanic crust.

• DFG Programme: Research Grants
• International Connection: Iran
• Cooperation Partner: Dr. Hadi Omrani
• Co-Investigator: Dr. Christina Günter