Tectonic exhumation across the Talesh-Alborz Belt, Iran, and its implication to the Arabia-Eurasia convergence

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, and apatite fission track) 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 in the Talesh record late Neoproterozoic 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. Our inverse thermal modeling of apatite fission-track data suggests that the Talesh region shares a similar exhumation history with the Alborz that includes the Paleocene-early Eocene, Oligocene and Miocene events, but responds variably. When integrated with previous results, the combined data show a less exhumed zone in the Talesh and westernmost Alborz as a more rigid unit, and regionally enhanced exhumation by the Late Miocene. Late Miocene onset of deformation may relate to a re-organization of Arabia-Eurasia 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. • New thermochronology data for the Talesh reveal comparable exhumation events with the Alborz. • Low thermochronology ages suggest a less exhumed and more deformation-resistant Talesh than the Alborz. • The Cenozoic exhumation variation of the combined Talesh-Alborz Belt disappeared at the Miocene (~20 Ma). • The co-evolution of the Talesh-Alborz Belt may hint to the formation of the Iranian Plateau.