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

Abstract

Cenozoic 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.

Crustal Scale Imaging of the Arabia‐Central Iran Collision Boundary Across the Zagros Suture Zone, West of Iran

“…Granitic plutons have exhumed to the surface and show mylonite fabrics (mylonite granite; Mohajjel et al, ). Thermal modeling of zircon, apatite (U‐TH)/He, and apatite fission‐track data on the Jurassic plutons and metasediments in the Sanandaj‐Sirjan zone indicated multiepisodic cooling from 180 to 220 °C, during the Cenozoic time (Barber et al, ). This suggests at least 7–9 km of exhumation and denudation of rocks bringing denser rocks (high velocity characteristics) of the middle/lower crust close to the surface.…”

Testing Models of Cenozoic Exhumation in the Western Greater Caucasus

“…This was first noted by Axen et al (2001) and Allen et al (2004) and estimated to begin at c. 5 ± 2 Ma. Subsequent studies are beginning to establish a longer, c. 12-4 Ma, interval of reorganization and/or increased exhumation, largely from observations in the Zagros (e.g., Barber et al, 2018;Gavillot et al, 2010;Mouthereau, 2011), Alborz (e.g., Guest et al, 2006;Rezaeian et al, 2012), and Talesh (Madanipour et al, 2017). The precise cause of this reorganization is unclear.…”

“…The precise cause of this reorganization is unclear. Models include final Arabia-Eurasia suturing (i.e., "hard collision"; Axen et al, 2001;Barber et al, 2018), which could include Greater Caucasus Basin closure, a switch from a free to constrained eastern margin of the collision zone (Allen et al, 2011), Neotethyan slab-break off (Agard et al, 2011;Keskin, 2003), or the initiation of Anatolian extrusion (Westaway, 1994). Given the size and complexity of the region and the diachronous nature of events, it is likely that a number of potentially interlinked processes will have been responsible.…”

Tectono-stratigraphic evolution of the intermontane Tarom Basin (NW sectors of the Arabia-Eurasia collision zone): insights into the vertical growth of the Iranian Plateau margin

“…This implies that plateau uplift must be younger than ~ 16.5 Ma. Flexural subsidence was triggered by mountain building processes along the plate suture zone as documented by early Miocene low-temperature thermochronology data from the Sanandaj-Sirjan Zone (Francois et al, 2014;Barber et al, 2018). Foreland basin initiation in the plateau interior coincided with the development of the endorheic Tarom Basin and hence with Middle Miocene topographic growth along the northern sectors of the Arabia-Eurasia collision zone (Ballato et al, 2011(Ballato et al, , 2013(Ballato et al, , 2015Rezaeian et al, 2012).…”