Diachronous initiation of Arabia–Eurasia collision from eastern Anatolia to the southeastern Zagros Mountains since middle Eocene time

The persistent debate over the timing of initial Arabia–Eurasia collision has eluded consensus for decades, with most estimates ranging widely from ~50 to 10 Ma along both the Anatolian and Zagros segments of the orogen. Here, we independently evaluate the timing and location of initial collision using a quantitative plate tectonic reconstruction that is the first to include the entire Arabian microcontinent and regions to the north in eastern Anatolia, northwestern Iran, and the Caucasus. The reconstruction combines new kinematic constraints from recent global plate models with a synthesis of available constraints on crustal shortening and continental and back-arc subduction to restore the pre-collisional geometries of the Arabian and Eurasian continental margins and to track their interaction through time. Our preferred model suggests that initial continental underthrusting, or soft collision, of the relatively thin Arabian passive margin with Eurasia occurred by ca. 42 Ma along the eastern Bitlis suture zone and began transmitting strain across central and eastern Anatolia, the Caucasus, and northwestern Iran. Collision inception then propagated westward into central Anatolia and southeastward into the northwestern Zagros Mountains by late Eocene time (ca. 40–35 Ma), the central Zagros by latest Eocene to early Oligocene time, (ca. 35–25 Ma), and finally the southeastern Zagros by latest Oligocene to middle Miocene time (ca. 25–15 Ma). The diachroneity of Arabia collision led to widespread upper-plate (Eurasian) contraction and a similarly time-transgressive magmatic lull that lagged behind the onset of collision by ~2–12 Myr. By incorporating the entire Arabian microcontinent and regions to the north, this new tectonic reconstruction highlights the diachronous nature of Arabia–Eurasia collision that occurred first along the Bitlis suture zone in eastern Anatolia during late middle Eocene time and became progressively younger to the southeast along strike of the Zagros suture zone.