A plate tectonics oddity: Caterpillar-walk exhumation of subducted continental crust

Abstract

Since plate tectonics began on Earth, grandiose “subduction factories” have continually shaped the continents, accreting continental blocks and new crust at the convergent plate boundaries. An enigmatic product of subduction factories is the high-pressure to ultrahigh-pressure (HP-UHP) metamorphic crustal rocks, regurgitated to Earth’s surface, sometimes from depths as great as 200 km. The Aegean backarc domain comprises two continental blocks that underwent HP metamorphism during the subduction of the African plate. Here, we use thermomechanical numerical simulations to show that subduction of small continental-lithosphere blocks separated by oceanic domains induces variations in the slab buoyancy, giving rise to episodic rollback-exhumation cycles. The single, self-consistent numerical model successfully reproduces the major structural patterns and pressure-temperature-time paths of HP rocks across the Aegean. We suggest that the “caterpillar walk” of exhuming HP rock units, revealed by our simulations, is a fundamental mechanism behind HP exhumation globally.