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Iran is a remarkable geoscientific laboratory where the full range of processes that form and modify the continental crust can be studied. Iran's crustal nucleus formed as a magmatic arc above an S-dipping subduction zone on the northern margin of Gondwana 600–500 Ma. This nucleus rifted and drifted north to be accreted to SW Eurasia ∼250 Ma. A new, N-dipping subduction zone formed ∼100 Ma along ∼3,000 km of the SW Eurasian margin, including Iran's southern flank; this is when most of Iran's many ophiolites formed. Iran evolved as an extensional continental arc in Paleogene time (66–23 Ma) and began colliding with Arabia ∼25 Ma. Today, Iran is an example of a convergent plate margin in the early stages of continent-continent collision, with a waning magmatic arc behind (north of) a large and growing accretionary prism, the Zagros Fold-and-Thrust Belt. Iran's crustal evolution resulted in both significant economic resources and earthquake hazards. Iran is a natural laboratory for studying how convergent plate margins form, evolve, and behave during the early stages of continental collision. Iran formed in the past 600 million years, originating on the northern flank of Gondwana, rifting away, and accreting to SW Eurasia. Iran is actively deforming as a result of collision with the Arabian plate, but earthquakes do not outline the position of the subducting slab. The Cenozoic evolution of Iran preserves the main elements of a convergent plate margin, including foredeep (trench), accretionary prism, and magmatic arc. [ABSTRACT FROM AUTHOR]

Subduction initiation (SI) requires the sinking of one plate beneath another and this exerts extensional stress on the overlying plate. How broad a region is affected by SI-related extension is unclear because most of the clearest SI examples– such as Izu-Bonin-Mariana arc– are deep under the ocean. A major SI event is recorded in the Late Cretaceous forearc ophiolites of Iran, related to the subduction of Neotethyan oceanic lithosphere beneath Eurasia. This caused extreme extension of the Iranian plate, up to ~1000 km away from the proto-trench and generated a series of back-arc oceanic basins, sedimentary basins, and core complexes and exhumed high-P rocks. The Late Cretaceous Iran example shows that SI can cause strong extension over a much wider region of the overriding plate than heretofore imagined and offers an accessible natural laboratory for studying SI processes. This understanding also provides an attractive new explanation for the origin of the South Caspian Sea. • Subduction initiation (SI) is a mechanism for forming Neotethyan ophiolites. • Ophiolites of Iran show SI exerts extensional stress on the overlying plate. • SI-related extension can affect broad regions of the overriding plate. [ABSTRACT FROM AUTHOR]