The Paired Metamorphism during Subduction of the Neotethys Oceanic Crust: Evidence from the Central Segment of the Sanandaj-Sirjan Zone, Iran

In this study we synthesized the existing research to propose the presence of a paired metamorphic belt within the central segment of the Sanandaj-Sirjan Zone (SaSZ) in Iran, a region that evolved in association with the northward subduction of the Neotethys oceanic lithosphere beneath the Central Iran microplate during the Mesozoic. Below the trench and forearc setting, high-pressure/low-temperature (HP/LT) rocks, including eclogites and blueschists, formed within accretionary prisms and are nowadays exposed in the Shahrekord metamorphic complex (SMC). Concurrently, subduction-related magmatism in the inner arc regions elevated geothermal gradients, resulting in low-pressure/high-temperature (LP/HT) metamorphism and anatexis, which is particularly evident in the Aligudarz, Broujerd, Hamedan, and Ghorveh areas. The observed similarities between the SaSZ metamorphic terrains and other well-known paired metamorphic belts worldwide, such as their associations with subduction zones, the relatively short temporal intervals between metamorphic phases and igneous activity, the co-occurrence of LP/HT metamorphism and magmatism, and the presence of migmatites, support our interpretation. This study provides a framework for understanding the metamorphic and tectonic evolution of the SaSZ within the context of Mesozoic subduction processes.