DIACHRONOUS INITIATION OF ARABIA COLLISION SINCE THE MIDDLE EOCENE IN EASTERN ANATOLIA: NEW INSIGHTS FROM A KINEMATIC RECONSTRUCTION OF THE ARABIA-EURASIA COLLISION ZONE

One of the most important, yet often overlooked consequences of continental collision is the lateral extrusion or ‘escape’ of continental material away from the collision zone, typically facilitated by lithosphere-scale strike-slip fault systems. Despite significant progress in understanding a world-class example of active tectonic escape in Anatolia (Turkey), the driving geodynamic mechanisms responsible for the transitions from subduction to collision and to tectonic escape remain poorly understood. Furthermore, the link between collision and escape in Anatolia is made more unclear because the timing of initial Arabia collision remains controversial, with most reliable estimates ranging between ~50 and 15 Ma.

We present a new GPlates-based kinematic reconstruction of the entire 2400 km-long Arabia-Eurasia collision zone that incorporates published minimum constraints on the magnitudes of crustal shortening and continental subduction, and on the pre-collisional geometry of the Arabia passive margin, that reconciles seemingly disparate estimates of collision inception into a single model for diachronous Arabia collision. Initial underthrusting or ‘soft collision’ of the thinned Arabian passive margin first occurred by ~45 Ma along the Bitlis suture and transmitted strain northward across central and eastern Anatolia to the earlier Izmir-Ankara-Erzincan suture. Collision inception was progressively younger along strike toward the southeast in the northwestern (~40–35 Ma), central (~35–27 Ma), and southeastern (~27–20 Ma) Zagros.

Regional-scale compilations of thermochronologic and geochronologic data reveal that initial Arabia collision was followed by similarly diachronous and widespread exhumation and magmatic quiescence across the collision zone since ~40 Ma, and incipient extension in western Anatolia and the Aegean since ~35 Ma. The arrival of relatively thick, unextended Arabian continental crust at the Bitlis suture marked a transition to mature or ‘hard’ collision by ~20–15 Ma that led to enhanced plate coupling/deceleration, slab rollback and trench retreat along the Hellenic and Cyprean subduction zones, and upper-plate extension across the Aegean that ultimately facilitated the westward escape of the Anatolian microplate by ~7–5 Ma.