Subduction‐Induced Back‐Arc Extension Versus Far‐Field Stretching: Contrasting Modes for Continental Marginal Break‐Up

Abstract

Abstract Continental break‐up is an ingredient of plate tectonics and the Wilson cycle. During the evolution of the Tethyan Realm since the Paleozoic, a series of ribbon‐like (micro‐)continents are split from the Gondwana and drifted northwards to the Eurasian continent. The initial opening of the Neo‐Tethys Ocean follows a typical continental marginal break‐up of Cimmeria from Gondwana, which is generally considered to be driven by subduction of the Paleo‐Tethyan plate. Yet, the competition between back‐arc extension and far‐field stretching is matter of a long‐standing debate. Therefore, the authors here present the results of systematic 2‐D numerical simulations. The results reveal four types of subduction‐induced continental marginal break‐ups: back‐arc extension, far‐field stretching, double break‐up, and subduction channel opening. A weak relic suture zone is a prerequisite for continental break‐up and an important factor controlling the mode selection. The back‐arc extension mode occurs for relatively short and shallow dipping highly viscous subducted slabs. The far‐field stretching mode, on the other hand, preferably occurs for spatially long and wide subducted slabs without mid‐ocean ridges. Combining the geological observations, numerical simulations and force balance analyses, the authors propose that the northward, single‐sided Paleo‐Tethys oceanic subduction beneath Laurasia, was most likely responsible for the far‐field break‐up of the Cimmerian terranes from Gondwana. This would have required both pre‐existing relic suture zones and the already subducted mid‐ocean ridge, which thus played an important role in the opening of the Neo‐Tethys Ocean.