Temporal and spatial exhumation variations across the Talesh-Alborz Belt, Iran, reveal different responses to the Arabia-Eurasia collision

Abstract:

Accommodation of plate convergence during the Arabia-Eurasia collision is expressed in the exhumation record of the broad collision zone. In order to better constrain the spatial and temporal patterns of exhumation, this paper presents new geochronology (zircon U-Pb) and thermochronology (zircon and apatite (U-Th)/He) data for 18 samples from the Talesh Mountains of northwest Iran. The Talesh and the adjacent Alborz Mountains form the northern side of the Iranian Plateau, itself a first order feature of the collision zone. Zircon U-Pb ages record late Precambrian intrusion and metamorphism (~570 Ma), and a series of Jurassic, Cretaceous, and Oligocene intrusive events. Zircon U-Th/He ages are predominantly Mesozoic (150-90 Ma), whereas apatite (U-Th)/He ages are <20 Ma, peaking at ~7 Ma. When integrated with previous results, the combined data show more limited exhumation in the Talesh and northern Alborz than the southern Alborz, and a regional peak in exhumation in the Late Miocene (~7 Ma). We interpret the exhumation record to show that limited Cenozoic deformation and exhumation affected the Talesh and northern Alborz before the Late Miocene, at which time these areas were involved in significant deformation that persists to the present. Late Miocene onset of deformation may relate to a re-organization of plate convergence. The causes of this re-organization are debated, but could include elevation of the Iranian Plateau to a level at which it resisted further thickening, causing deformation to be accommodated in other regions.