G3:Subduction-Induced Back-Arc Extension Versus Far-Field Stretching: Contrasting Modes for Continental Marginal Break-Up

发布时间:2021-09-15 放大 缩小

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.

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