Cenozoic Exhumation and Foreland Basin Evolution of the Zagros Orogen During the Arabia‐Eurasia Collision, Western Iran

Abstract

AbstractCenozoic exhumation patterns in the internal and external Zagros reveal a long‐term deformation record associated with geodynamic restructuring of Arabia‐Eurasia collisional zone from continental subduction to plate suturing, which can be evaluated from thermochronometric, provenance, and subsidence analyses. Thermal modeling of zircon and apatite (U‐Th)/He ages and apatite fission track data from the Sanandaj‐Sirjan Zone (SSZ) indicates exhumation and inferred uplift along the leading edge of Eurasia starting in the Late Eocene (~35 Ma), coeval with initial foreland flexural subsidence of Arabia. Together with deceleration in Arabia‐Eurasia convergence and diminished subduction‐related magmatism, these events signal the final Neotethys closure and onset of long‐term (15–20 Myr) Arabian continental subduction beneath Eurasia, facilitated by the attenuated architecture of the precollisional Arabian margin. From 35 to 20 Ma, crustal shortening was relatively subdued and restricted to areas along the Arabia‐Eurasia plate boundary and diffuse inversion structures within continental interiors. Acceleration in SSZ cooling/exhumation rates from 19 to 16 Ma was synchronous with rapid basin subsidence and clastic progradation in the Zagros foreland. These events were contemporaneous with 20‐ to 16‐Ma surge in calc‐alkaline magmatism in central Iran and may have been linked to reorganization/deflection of Arabian plate vectors during the main phase of Red Sea rifting at 19–18 Ma. Transition from continental subduction to Arabia‐Eurasia suturing by ~12 Ma forced a transfer of strain from the subduction zone to intraplate deformational structures. This was marked by rapid outward expansion of the Zagros orogen, involving a shift in exhumation from the SSZ to Zagros fold‐thrust belt and Iranian plate interior.